From dd05f1812ee86bc8c6176c9dbd30aae8fe0db8b8 Mon Sep 17 00:00:00 2001 From: Joe Malin Date: Wed, 19 Jan 2011 14:33:23 -0800 Subject: Doc Change: Topics for copy/paste/drag/drop Change-Id: I755216fe9d2afca87a9adaeb99840142ff34a685 --- docs/html/guide/guide_toc.cs | 49 +- docs/html/guide/topics/clipboard/copy-paste.jd | 1094 ++++++++++++++++++++ docs/html/guide/topics/ui/drag-drop.jd | 995 ++++++++++++++++++ .../images/ui/clipboard/copy_paste_framework.png | Bin 0 -> 37996 bytes 4 files changed, 2119 insertions(+), 19 deletions(-) create mode 100644 docs/html/guide/topics/clipboard/copy-paste.jd create mode 100644 docs/html/guide/topics/ui/drag-drop.jd create mode 100755 docs/html/images/ui/clipboard/copy_paste_framework.png diff --git a/docs/html/guide/guide_toc.cs b/docs/html/guide/guide_toc.cs index c52fd6acd73c..a2a2be9d7708 100644 --- a/docs/html/guide/guide_toc.cs +++ b/docs/html/guide/guide_toc.cs @@ -125,7 +125,12 @@ Creating Status Bar Notifications - + +
  • + + Dragging and Dropping + new! +
  • Applying Styles and Themes
    • @@ -248,6 +253,12 @@ +
  • + + Copying and Pasting + + new! +
  • Audio and Video
    • @@ -399,24 +410,24 @@
  • - Managing Virtual Devices - + Creating and Managing Virtual Devices +
    • @@ -425,7 +436,7 @@ Using Hardware Devices - +
  • @@ -440,7 +451,7 @@
  • - From the Command Line + On the Command Line
    • @@ -470,12 +481,12 @@ diff --git a/docs/html/guide/topics/clipboard/copy-paste.jd b/docs/html/guide/topics/clipboard/copy-paste.jd new file mode 100644 index 000000000000..9a50a351a2b0 --- /dev/null +++ b/docs/html/guide/topics/clipboard/copy-paste.jd @@ -0,0 +1,1094 @@ +page.title=Copying and Pasting +@jd:body +
    +
    +

    Quickview

    +
      +
    • + A clipboard-based framework for copying and pasting data. +
      • +
    • + Supports both simple and complex data, including text strings, complex data + structures, text and binary stream data, and application assets. +
      • +
    • + Copies and pastes simple text directly to and from the clipboard. +
      • +
    • + Copies and pastes complex data using a content provider. +
      • +
    • + Requires API 11. +
      • +
    +

    In this document

    +
      +
    1. + The Clipboard Framework +
      2. +
    2. + Clipboard Classes +
        +
      1. + ClipboardManager +
        2. +
      2. + + ClipData, ClipDescription, and ClipData.Item + +
        3. +
      3. + ClipData convenience methods +
        4. +
      4. + Coercing the clipboard data to text +
        5. +
      +
      3. +
    3. + Copying to the Clipboard +
      4. +
    4. + Pasting from the Clipboard +
        +
      1. + Pasting plain text +
        2. +
      2. + Pasting data from a content URI +
        3. +
      3. + Pasting an Intent +
        4. +
      +
      5. +
    5. + Using Content Providers to Copy Complex Data +
        +
      1. + Encoding an identifier on the URI +
        2. +
      2. + Copying data structures +
        3. +
      3. + Copying data streams +
        4. +
      +
      6. +
    6. + Designing Effective Copy/Paste Functionality +
      7. +
    +

    Key classes

    +
      +
    1. + {@link android.content.ClipboardManager ClipboardManager} +
      2. +
    2. + {@link android.content.ClipData ClipData} +
      3. +
    3. + {@link android.content.ClipData.Item ClipData.Item} +
      4. +
    4. + {@link android.content.ClipDescription ClipDescription} +
      5. +
    5. + {@link android.net.Uri Uri} +
      6. +
    6. + {@link android.content.ContentProvider} +
      7. +
    7. + {@link android.content.Intent Intent} +
      8. +
    +

    Related Samples

    +
      +
    1. + + Note Pad sample application +
      2. +
    +

    See also

    +
      +
    1. + Content Providers +
      2. +
    +
    +
    +

    + Android provides a powerful clipboard-based framework for copying and pasting. It + supports both simple and complex data types, including text strings, complex data + structures, text and binary stream data, and even application assets. Simple text data is stored + directly in the clipboard, while complex data is stored as a reference that the pasting + application resolves with a content provider. Copying and pasting works both within an + application and between applications that implement the framework. +

    + +

    + Since a part of the framework uses content providers, this topic assumes some + familiarity with the Android Content Provider API, which is described in the topic + Content Providers. +

    +

    The Clipboard Framework

    +

    + When you use the clipboard framework, you put data into a clip object, and then + put the clip object on the system-wide clipboard. The clip object can take one of three forms: +

    +
    +
    Text
    +
    + A text string. You put the string directly into the clip object, which you then put onto + the clipboard. To paste the string, you get the clip object from the clipboard and copy + the string to into your application's storage. +
    +
    URI
    +
    + A {@link android.net.Uri} object representing any form of URI. This is primarily for + copying complex data from a content provider. To copy data, you put a + {@link android.net.Uri} object into a clip object and put the clip object onto + the clipboard. To paste the data, you get the clip object, get the + {@link android.net.Uri} object, resolve it to a data source such as a content provider, + and copy the data from the source into your application's storage. +
    +
    Intent
    +
    + An {@link android.content.Intent}. This supports copying application shortcuts. To copy + data, you create an Intent, put it into a clip object, and put the clip object onto the + clipboard. To paste the data, you get the clip object and then copy the Intent object + into your application's memory area. +
    +
    +

    + The clipboard holds only one clip object at a time. When an application puts a clip object on + the clipboard, the previous clip object disappears. +

    +

    + If you want to allow users to paste data into your application, you don't have to handle all + types of data. You can examine the data on the clipboard before you give users the option to + paste it. Besides having a certain data form, the clip object also contains metadata that tells + you what MIME type or types are available. This metadata helps you decide if your application + can do something useful with the clipboard data. For example, if you have an application that + primarily handles text you may want to ignore clip objects that contain a URI or Intent. +

    +

    + You may also want to allow users to paste text regardless of the form of data on the + clipboard. To do this, you can force the clipboard data into a text representation, and then + paste this text. This is described in the section Coercing the + clipboard to text. +

    +

    Clipboard Classes

    +

    + This section describes the classes used by the clipboard framework. +

    +

    ClipboardManager

    +

    + In the Android system, the system clipboard is represented by the global + {@link android.content.ClipboardManager} class. You do not instantiate this + class directly; instead, you get a reference to it by invoking + {@link android.content.Context#getSystemService(String) getSystemService(CLIPBOARD_SERVICE)}. +

    +

    ClipData, ClipData.Item, and ClipDescription

    +

    + To add data to the clipboard, you create a {@link android.content.ClipData} object that + contains both a description of the data and the data itself. The clipboard holds only one + {@link android.content.ClipData} at a time. A {@link android.content.ClipData} contains a + {@link android.content.ClipDescription} object and one or more + {@link android.content.ClipData.Item} objects. +

    +

    + A {@link android.content.ClipDescription} object contains metadata about the clip. In + particular, it contains an array of available MIME types for the clip's data. When you put a + clip on the clipboard, this array is available to pasting applications, which can examine it to + see if they can handle any of available the MIME types. +

    +

    + A {@link android.content.ClipData.Item} object contains the text, URI, or Intent data: +

    +
    +
    Text
    +
    + A {@link java.lang.CharSequence}. +
    +
    URI
    +
    + A {@link android.net.Uri}. This usually contains a content provider URI, although any + URI is allowed. The application that provides the data puts the URI on the clipboard. + Applications that want to paste the data get the URI from the clipboard and use it to + access the content provider (or other data source) and retrieve the data. +
    +
    Intent
    +
    + An {@link android.content.Intent}. This data type allows you to copy an application shortcut + to the clipboard. Users can then paste the shortcut into their applications for later use. +
    +
    +

    + You can add more than one {@link android.content.ClipData.Item} object to a clip. This allows + users to copy and paste multiple selections as a single clip. For example, if you have a list + widget that allows the user to select more than one item at a time, you can copy all the items + to the clipboard at once. To do this, you create a separate + {@link android.content.ClipData.Item} for each list item, and then you add the + {@link android.content.ClipData.Item} objects to the {@link android.content.ClipData} object. +

    +

    ClipData convenience methods

    +

    + The {@link android.content.ClipData} class provides static convenience methods for creating + a {@link android.content.ClipData} object with a single {@link android.content.ClipData.Item} + object and a simple {@link android.content.ClipDescription} object: +

    +
    +
    +{@link android.content.ClipData#newPlainText(CharSequence,CharSequence) newPlainText(label, text)} +
    +
    + Returns a {@link android.content.ClipData} object whose single + {@link android.content.ClipData.Item} object contains a text string. The + {@link android.content.ClipDescription} object's label is set to label. + The single MIME type in {@link android.content.ClipDescription} is + {@link android.content.ClipDescription#MIMETYPE_TEXT_PLAIN}. +

    + Use +{@link android.content.ClipData#newPlainText(CharSequence,CharSequence) newPlainText()} + to create a clip from a text string. +

    +
    +{@link android.content.ClipData#newUri(ContentResolver, CharSequence, Uri) newUri(resolver, label, URI)} +
    +
    + Returns a {@link android.content.ClipData} object whose single + {@link android.content.ClipData.Item} object contains a URI. The + {@link android.content.ClipDescription} object's label is set to label. + If the URI is a content URI ({@link android.net.Uri#getScheme() Uri.getScheme()} returns + content:), the method uses the {@link android.content.ContentResolver} object + provided in resolver to retrieve the available MIME types from the + content provider and store them in {@link android.content.ClipDescription}. For a URI that + is not a content: URI, the method sets the MIME type to + {@link android.content.ClipDescription#MIMETYPE_TEXT_URILIST}. +

    + Use +{@link android.content.ClipData#newUri(ContentResolver, CharSequence, Uri) newUri()} + to create a clip from a URI, particularly a content: URI. +

    +
    +
    + {@link android.content.ClipData#newIntent(CharSequence, Intent) newIntent(label, intent)} +
    +
    + Returns a {@link android.content.ClipData} object whose single + {@link android.content.ClipData.Item} object contains an {@link android.content.Intent}. + The {@link android.content.ClipDescription} object's label is set to label. + The MIME type is set to {@link android.content.ClipDescription#MIMETYPE_TEXT_INTENT}. +

    + Use +{@link android.content.ClipData#newIntent(CharSequence, Intent) newIntent()} + to create a clip from an Intent object. +

    +
    +

    Coercing the clipboard data to text

    +

    + Even if your application only handles text, you can copy non-text data from the + clipboard by converting it with the method + {@link android.content.ClipData.Item#coerceToText(Context) ClipData.Item.coerceToText()}. +

    +

    + This method converts the data in {@link android.content.ClipData.Item} to text and + returns a {@link java.lang.CharSequence}. The value that + {@link android.content.ClipData.Item#coerceToText(Context) ClipData.Item.coerceToText()} + returns is based on the form of data in {@link android.content.ClipData.Item}: +

    +
    +
    Text
    +
    + If {@link android.content.ClipData.Item} is text + ({@link android.content.ClipData.Item#getText()} is not null), + {@link android.content.ClipData.Item#coerceToText(Context) coerceToText()} returns the + text. +
    +
    URI
    +
    + If {@link android.content.ClipData.Item} is a URI + ({@link android.content.ClipData.Item#getUri()} is not null), + {@link android.content.ClipData.Item#coerceToText(Context) coerceToText()} tries to use + it as a content URI: +
      +
    • + If the URI is a content URI and the provider can return a text stream, + {@link android.content.ClipData.Item#coerceToText(Context) coerceToText()} returns + a text stream. +
      • +
    • + If the URI is a content URI but the provider does not offer a text stream, + {@link android.content.ClipData.Item#coerceToText(Context) coerceToText()} returns + a representation of the URI. The representation is the same as that returned by + {@link android.net.Uri#toString() Uri.toString()}. +
      • +
    • + If the URI is not a content URI, + {@link android.content.ClipData.Item#coerceToText(Context) coerceToText()} returns + a representation of the URI. The representation is the same as that returned by + {@link android.net.Uri#toString() Uri.toString()}. +
      • +
    +
    +
    Intent
    +
    + If {@link android.content.ClipData.Item} is an Intent + ({@link android.content.ClipData.Item#getIntent()} is not null), + {@link android.content.ClipData.Item#coerceToText(Context) coerceToText()} converts it to + an Intent URI and returns it. The representation is the same as that returned by + {@link android.content.Intent#toUri(int) Intent.toUri(URI_INTENT_SCHEME)}. +
    +
    +

    + The clipboard framework is summarized in Figure 1. To copy data, an application puts a + {@link android.content.ClipData} object on the {@link android.content.ClipboardManager} global + clipboard. The {@link android.content.ClipData} contains one or more + {@link android.content.ClipData.Item} objects and one + {@link android.content.ClipDescription} object. To paste data, an application gets the + {@link android.content.ClipData}, gets its MIME type from the + {@link android.content.ClipDescription}, and gets the data either from + the {@link android.content.ClipData.Item} or from the content provider referred to by + {@link android.content.ClipData.Item}. +

    + + A block diagram of the copy and paste framework +

    + Figure 1. The Android clipboard framework +

    +

    Copying to the Clipboard

    +

    + As described previously, to copy data to the clipboard you get a handle to the global + {@link android.content.ClipboardManager} object, create a {@link android.content.ClipData} + object, add a {@link android.content.ClipDescription} and one or more + {@link android.content.ClipData.Item} objects to it, and add the finished + {@link android.content.ClipData} object to the {@link android.content.ClipboardManager} object. + This is described in detail in the following procedure: +

    +
      +
    1. + If you are copying data using a content URI, set up a content + provider. +

      + The + Note Pad sample application is an example of using a content provider for + copying and pasting. The + + NotePadProvider class implements the content provider. The + + NotePad class defines a contract between the provider and other applications, + including the supported MIME types. +

      +
      2. +
    2. + Get the system clipboard: +
      +
+...
+
+// if the user selects copy
+case R.id.menu_copy:
+
+// Gets a handle to the clipboard service.
+ClipboardManager clipboard = (ClipboardManager)
+        getSystemService(Context.CLIPBOARD_SERVICE);
+
      +
      3. +
    3. +

      + Copy the data to a new {@link android.content.ClipData} object: +

      +
        +
      • +

        For text

        +
        +// Creates a new text clip to put on the clipboard
+ClipData clip = ClipData.newPlainText("simple text","Hello, World!");
+
        +
        • +
      • +

        For a URI

        +

        + This snippet constructs a URI by encoding a record ID onto the content URI + for the provider. This technique is covered in more detail + in the section Encoding an identifier on the URI: +

        +
        +// Creates a Uri based on a base Uri and a record ID based on the contact's last name
+// Declares the base URI string
+private static final String CONTACTS = "content://com.example.contacts";
+
+// Declares a path string for URIs that you use to copy data
+private static final String COPY_PATH = "/copy";
+
+// Declares the Uri to paste to the clipboard
+Uri copyUri = Uri.parse(CONTACTS + COPY_PATH + "/" + lastName);
+
+...
+
+// Creates a new URI clip object. The system uses the anonymous getContentResolver() object to
+// get MIME types from provider. The clip object's label is "URI", and its data is
+// the Uri previously created.
+ClipData clip = ClipData.newUri(getContentResolver(),"URI",copyUri);
+
        +
        • +
      • +

        For an Intent

        +

        + This snippet constructs an Intent for an application + and then puts it in the clip object: +

        +
        +// Creates the Intent
+Intent appIntent = new Intent(this, com.example.demo.myapplication.class);
+
+...
+
+// Creates a clip object with the Intent in it. Its label is "Intent" and its data is
+// the Intent object created previously
+ClipData clip = ClipData.newIntent("Intent",appIntent);
+
        +
        • +
      +
      4. +
    4. + Put the new clip object on the clipboard: +
      +// Set the clipboard's primary clip.
+clipboard.setPrimaryClip(clip);
+
      +
      5. +
    +

    Pasting from the Clipboard

    +

    + As described previously, you paste data from the clipboard by getting the global clipboard + object, getting the clip object, looking at its data, and if possible copying the data from + the clip object to your own storage. This section describes in detail how to do this for + the three forms of clipboard data. +

    +

    Pasting plain text

    +

    + To paste plain text, first get the global clipboard and verify that it can return plain text. + Then get the clip object and copy its text to your own storage using + {@link android.content.ClipData.Item#getText()}, as described in the following procedure: +

    +
      +
    1. + Get the global {@link android.content.ClipboardManager} object using + {@link android.content.Context#getSystemService(String) getSystemService(CLIPBOARD_SERVICE)}. Also + declare a global variable to contain the pasted text: +
      +ClipboardManager clipboard = (ClipboardManager) getSystemService(Context.CLIPBOARD_SERVICE);
+
+String pasteData = "";
+
+
      +
      2. +
    2. + Next, determine if you should enable or disable the "paste" option in the + current Activity. You should verify that the clipboard contains a clip and that you + can handle the type of data represented by the clip: +
      +// Gets the ID of the "paste" menu item
+MenuItem mPasteItem = menu.findItem(R.id.menu_paste);
+
+// If the clipboard doesn't contain data, disable the paste menu item.
+// If it does contain data, decide if you can handle the data.
+if (!(clipboard.hasPrimaryClip())) {
+
+    mPasteItem.setEnabled(false);
+
+    } else if (!(clipboard.getPrimaryClipDescription().hasMimeType(MIMETYPE_TEXT_PLAIN))) {
+
+        // This disables the paste menu item, since the clipboard has data but it is not plain text
+        mPasteItem.setEnabled(false);
+    } else {
+
+        // This enables the paste menu item, since the clipboard contains plain text.
+        mPasteItem.setEnabled(true);
+    }
+}
+
      +
      3. +
    3. + Copy the data from the clipboard. This point in the program is only reachable if the + "paste" menu item is enabled, so you can assume that the clipboard contains + plain text. You do not yet know if it contains a text string or a URI that points to plain + text. The following snippet tests this, but it only shows the code for handling plain text: +
      +// Responds to the user selecting "paste"
+case R.id.menu_paste:
+
+// Examines the item on the clipboard. If getText() does not return null, the clip item contains the
+// text. Assumes that this application can only handle one item at a time.
+ ClipData.Item item = clipboard.getPrimaryClip().getItemAt(0);
+
+// Gets the clipboard as text.
+pasteData = item.getText();
+
+// If the string contains data, then the paste operation is done
+if (pasteData != null) {
+    return;
+
+// The clipboard does not contain text. If it contains a URI, attempts to get data from it
+} else {
+    Uri pasteUri = item.getUri();
+
+    // If the URI contains something, try to get text from it
+    if (pasteUri != null) {
+
+        // calls a routine to resolve the URI and get data from it. This routine is not
+        // presented here.
+        pasteData = resolveUri(Uri);
+        return;
+    } else {
+
+    // Something is wrong. The MIME type was plain text, but the clipboard does not contain either
+    // text or a Uri. Report an error.
+    Log.e("Clipboard contains an invalid data type");
+    return;
+    }
+}
+
      +
      4. +
    +

    Pasting data from a content URI

    +

    + If the {@link android.content.ClipData.Item} object contains a content URI and you + have determined that you can handle one of its MIME types, create a + {@link android.content.ContentResolver} and then call the appropriate content provider + method to retrieve the data. +

    +

    + The following procedure describes how to get data from a content provider based on a + content URI on the clipboard. It checks that a MIME type that the application can use + is available from the provider: +

    +
      +
    1. + Declare a global variable to contain the MIME type: +
      +// Declares a MIME type constant to match against the MIME types offered by the provider
+public static final String MIME_TYPE_CONTACT = "vnd.android.cursor.item/vnd.example.contact"
+
      +
      2. +
    2. + Get the global clipboard. Also get a content resolver so you can access the content + provider: +
      +// Gets a handle to the Clipboard Manager
+ClipboardManager clipboard = (ClipboardManager) getSystemService(Context.CLIPBOARD_SERVICE);
+
+// Gets a content resolver instance
+ContentResolver cr = getContentResolver();
+
      +
      3. +
    3. + Get the primary clip from the clipboard, and get its contents as a URI: +
      +// Gets the clipboard data from the clipboard
+ClipData clip = clipboard.getPrimaryClip();
+
+if (clip != null) {
+
+    // Gets the first item from the clipboard data
+    ClipData.Item item = clip.getItemAt(0);
+
+    // Tries to get the item's contents as a URI
+    Uri pasteUri = item.getUri();
+
      +
      4. +
    4. + Test to see if the URI is a content URI by calling + {@link android.content.ContentResolver#getType(Uri) getType(Uri)}. This method returns + null if Uri does not point to a valid content provider: +
      +    // If the clipboard contains a URI reference
+    if (pasteUri != null) {
+
+        // Is this a content URI?
+        String uriMimeType = cr.getType(pasteUri);
+
      +
      5. +
    5. + Test to see if the content provider supports a MIME type that the current application + understands. If it does, call + {@link android.content.ContentResolver#query(Uri, String[], String, String[], String) + ContentResolver.query()} to get the data. The return value is a + {@link android.database.Cursor}: +
      +        // If the return value is not null, the Uri is a content Uri
+        if (uriMimeType != null) {
+
+            // Does the content provider offer a MIME type that the current application can use?
+            if (uriMimeType.equals(MIME_TYPE_CONTACT)) {
+
+                // Get the data from the content provider.
+                Cursor pasteCursor = cr.query(uri, null, null, null, null);
+
+                // If the Cursor contains data, move to the first record
+                if (pasteCursor != null) {
+                    if (pasteCursor.moveToFirst()) {
+
+                    // get the data from the Cursor here. The code will vary according to the
+                    // format of the data model.
+                    }
+                }
+
+                // close the Cursor
+                pasteCursor.close();
+             }
+         }
+     }
+}
+
      +
      6. +
    +

    Pasting an Intent

    +

    + To paste an Intent, first get the global clipboard. Examine the + {@link android.content.ClipData.Item} object to see if it contains an Intent. Then call + {@link android.content.ClipData.Item#getIntent()} to copy the Intent to your own storage. + The following snippet demonstrates this: +

    +
    +// Gets a handle to the Clipboard Manager
+ClipboardManager clipboard = (ClipboardManager) getSystemService(Context.CLIPBOARD_SERVICE);
+
+// Checks to see if the clip item contains an Intent, by testing to see if getIntent() returns null
+Intent pasteIntent = clipboard.getPrimaryClip().getItemAt(0).getIntent();
+
+if (pasteIntent != null) {
+
+    // handle the Intent
+
+} else {
+
+    // ignore the clipboard, or issue an error if your application was expecting an Intent to be
+    // on the clipboard
+}
+
    +

    Using Content Providers to Copy Complex Data

    +

    + Content providers support copying complex data such as database records or file streams. + To copy the data, you put a content URI on the clipboard. Pasting applications then get this + URI from the clipboard and use it to retrieve database data or file stream descriptors. +

    +

    + Since the pasting application only has the content URI for your data, it needs to know which + piece of data to retrieve. You can provide this information by encoding an identifier for the + data on the URI itself, or you can provide a unique URI that will return the data you want to + copy. Which technique you choose depends on the organization of your data. +

    +

    + The following sections describe how to set up URIs, how to provide complex data, and how to + provide file streams. The descriptions assume that you are familiar with the general principles + of content provider design. +

    +

    Encoding an identifier on the URI

    +

    + A useful technique for copying data to the clipboard with a URI is to encode an identifier for + the data on the URI itself. Your content provider can then get the identifier from the URI and + use it to retrieve the data. The pasting application doesn't have to know that the identifier + exists; all it has to do is get your "reference" (the URI plus the identifier) from + the clipboard, give it your content provider, and get back the data. +

    +

    + You usually encode an identifier onto a content URI by concatenating it to the end of the URI. + For example, suppose you define your provider URI as the following string: +

    +
    +"content://com.example.contacts"
+
    +

    + If you want to encode a name onto this URI, you would use the following snippet: +

    +
    +String uriString = "content://com.example.contacts" + "/" + "Smith"
+
+// uriString now contains content://com.example.contacts/Smith.
+
+// Generates a uri object from the string representation
+Uri copyUri = Uri.parse(uriString);
+
    +

    + If you are already using a content provider, you may want to add a new URI path that indicates + the URI is for copying. For example, suppose you already have the following URI paths: +

    +
    +"content://com.example.contacts"/people
+"content://com.example.contacts"/people/detail
+"content://com.example.contacts"/people/images
+
    +

    + You could add another path that is specific to copy URIs: +

    +
    +"content://com.example.contacts/copying"
+
    +

    + You could then detect a "copy" URI by pattern-matching and handle it with code that + is specific for copying and pasting. +

    +

    + You normally use the encoding technique if you're already using a content provider, internal + database, or internal table to organize your data. In these cases, you have multiple pieces of + data you want to copy, and presumably a unique identifier for each piece. In response to a + query from the pasting application, you can look up the data by its identifier and return it. +

    +

    + If you don't have multiple pieces of data, then you probably don't need to encode an identifier. + You can simply use a URI that is unique to your provider. In response to a query, your provider + would return the data it currently contains. +

    +

    + Getting a single record by ID is used in the + Note Pad sample application to + open a note from the notes list. The sample uses the _id field from an SQL + database, but you can have any numeric or character identifier you want. +

    +

    Copying data structures

    +

    + You set up a content provider for copying and pasting complex data as a subclass of the + {@link android.content.ContentProvider} component. You should also encode the URI you put on + the clipboard so that it points to the exact record you want to provide. In addition, you + have to consider the existing state of your application: +

    + +

    +In the content provider, you will want to override at least the following methods: +

    +
    +
    +{@link android.content.ContentResolver#query(Uri, String[], String, String[], String) query()} +
    +
    + Pasting applications will assume that they can get your data by using this method with + the URI you put on the clipboard. To support copying, you should have this method + detect URIs that contain a special "copy" path. Your application can then + create a "copy" URI to put on the clipboard, containing the copy path and + a pointer to the exact record you want to copy. +
    +
    + {@link android.content.ContentProvider#getType(Uri) getType()} +
    +
    + This method should return the MIME type or types for the data you intend to copy. The method + {@link android.content.ClipData#newUri(ContentResolver, CharSequence, Uri) newUri()} calls + {@link android.content.ContentProvider#getType(Uri) getType()} in order to put the MIME + types into the new {@link android.content.ClipData} object. +

    + MIME types for complex data are described in the topic + Content Providers. +

    +
    +
    +

    + Notice that you don't have to have any of the other content provider methods such as + {@link android.content.ContentProvider#insert(Uri, ContentValues) insert()} or + {@link android.content.ContentProvider#update(Uri, ContentValues, String, String[]) update()}. + A pasting application only needs to get your supported MIME types and copy data from your + provider. If you already have these methods, they won't interfere with copy operations. +

    +

    + The following snippets demonsrate how to set up your application to copy complex data: +

    +
      +
    1. +

      + In the global constants for your application, + declare a base URI string and a path that identifies URI strings you are + using to copy data. Also declare a MIME type for the copied data: +

      +
      +// Declares the base URI string
+private static final String CONTACTS = "content://com.example.contacts";
+
+// Declares a path string for URIs that you use to copy data
+private static final String COPY_PATH = "/copy";
+
+// Declares a MIME type for the copied data
+public static final String MIME_TYPE_CONTACT = "vnd.android.cursor.item/vnd.example.contact"
+
      +
      2. +
    2. + In the Activity from which users copy data, + set up the code to copy data to the clipboard. In response to a copy request, put + the URI on the clipboard: +
      +public class MyCopyActivity extends Activity {
+
+    ...
+
+// The user has selected a name and is requesting a copy.
+case R.id.menu_copy:
+
+    // Appends the last name to the base URI
+    // The name is stored in "lastName"
+    uriString = CONTACTS + COPY_PATH + "/" + lastName;
+
+    // Parses the string into a URI
+    Uri copyUri = Uri.parse(uriString);
+
+    // Gets a handle to the clipboard service.
+    ClipboardManager clipboard = (ClipboardManager)
+        getSystemService(Context.CLIPBOARD_SERVICE);
+
+    ClipData clip = ClipData.newUri(getContentResolver(), "URI", copyUri);
+
+    // Set the clipboard's primary clip.
+    clipboard.setPrimaryClip(clip);
+
      +
      3. + +
    3. +

      + In the global scope of your content provider, create a URI matcher and add a URI + pattern that will match URIs you put on the clipboard: +

      +
      +public class MyCopyProvider extends ContentProvider {
+
+    ...
+
+// A Uri Match object that simplifies matching content URIs to patterns.
+private static final UriMatcher sURIMatcher = new UriMatcher(UriMatcher.NO_MATCH);
+
+// An integer to use in switching based on the incoming URI pattern
+private static final int GET_SINGLE_CONTACT = 0;
+
+...
+
+// Adds a matcher for the content URI. It matches
+// "content://com.example.contacts/copy/*"
+sUriMatcher.addURI(CONTACTS, "names/*", GET_SINGLE_CONTACT);
+
      +
      4. +
    4. +

      + Set up the + {@link android.content.ContentProvider#query(Uri, String[], String, String[], String) query()} + method. This method can handle different URI patterns, depending on how you code it, but + only the pattern for the clipboard copying operation is shown: +

      +
      +// Sets up your provider's query() method.
+public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs,
+    String sortOrder) {
+
+    ...
+
+    // Switch based on the incoming content URI
+    switch (sUriMatcher.match(uri)) {
+
+    case GET_SINGLE_CONTACT:
+
+        // query and return the contact for the requested name. Here you would decode
+        // the incoming URI, query the data model based on the last name, and return the result
+        // as a Cursor.
+
+    ...
+
+}
+
      +
      5. +
    5. +

      + Set up the {@link android.content.ContentProvider#getType(Uri) getType()} method to + return an appropriate MIME type for copied data: +

      +
      +// Sets up your provider's getType() method.
+public String getType(Uri uri) {
+
+    ...
+
+    switch (sUriMatcher.match(uri)) {
+
+    case GET_SINGLE_CONTACT:
+
+            return (MIME_TYPE_CONTACT);
+
      +
      6. +
    +

    + The section Pasting data from a content URI + describes how to get a content URI from the clipboard and use it to get and paste data. +

    +

    Copying data streams

    +

    + You can copy and paste large amounts of text and binary data as streams. The data can have + forms such as the following: +

    + +

    + A content provider for data streams provides access to its data with a file descriptor object + such as {@link android.content.res.AssetFileDescriptor} instead of a + {@link android.database.Cursor} object. The pasting application reads the data stream using + this file descriptor. +

    +

    + To set up your application to copy a data stream with a provider, follow these steps: +

    +
      +
    1. + Set up a content URI for the data stream you are putting on the clipboard. Options + for doing this include the following: +
        +
      • + Encode an identifier for the data stream onto the URI, + as described in the section + Encoding an identifier on the URI, and then maintain a + table in your provider that contains identifiers and the corresponding stream name. +
        • +
      • + Encode the stream name directly on the URI. +
        • +
      • + Use a unique URI that always returns the current stream from the provider. If you + use this option, you have to remember to update your provider to point to a + different stream whenever you copy the stream to the clipboard via the URI. +
        • +
      +
      2. +
    2. + Provide a MIME type for each type of data stream you plan to offer. Pasting applications + need this information to determine if they can paste the data on the clipboard. +
      3. +
    3. + Implement one of the {@link android.content.ContentProvider} methods that returns + a file descriptor for a stream. If you encode identifiers on the content URI, use this + method to determine which stream to open. +
      4. +
    4. + To copy the data stream to the clipboard, construct the content URI and place it + on the clipboard. +
      5. +
    +

    + To paste a data stream, an application gets the clip from the clipboard, gets the URI, and + uses it in a call to a {@link android.content.ContentResolver} file descriptor method that + opens the stream. The {@link android.content.ContentResolver} method calls the corresponding + {@link android.content.ContentProvider} method, passing it the content URI. Your provider + returns the file descriptor to {@link android.content.ContentResolver} method. The pasting + application then has the responsibility to read the data from the stream. +

    +

    + The following list shows the most important file descriptor methods for a content provider. + Each of these has a corresponding {@link android.content.ContentResolver} method with the + string "Descriptor" appended to the method name; for example, the + {@link android.content.ContentResolver} analog of + {@link android.content.ContentProvider#openAssetFile(Uri, String) openAssetFile()} is +{@link android.content.ContentResolver#openAssetFileDescriptor(Uri, String) openAssetFileDescriptor()}: +

    +
    +
    +{@link android.content.ContentProvider#openTypedAssetFile(Uri,String,Bundle) openTypedAssetFile()} +
    +
    + This method should return an asset file descriptor, but only if the provided MIME type is + supported by the provider. The caller (the application doing the pasting) provides a MIME + type pattern. The content provider (of the application that has copied a URI to the + clipboard) returns an {@link android.content.res.AssetFileDescriptor} file handle if it + can provide that MIME type, or throws an exception if it can not. +

    + This method handles subsections of files. You can use it to read assets that the + content provider has copied to the clipboard. +

    +
    +
    + {@link android.content.ContentProvider#openAssetFile(Uri, String) openAssetFile()} +
    +
    + This method is a more general form of +{@link android.content.ContentProvider#openTypedAssetFile(Uri,String,Bundle) openTypedAssetFile()}. + It does not filter for allowed MIME types, but it can read subsections of files. +
    +
    + {@link android.content.ContentProvider#openFile(Uri, String) openFile()} +
    +
    + This is a more general form of + {@link android.content.ContentProvider#openAssetFile(Uri, String) openAssetFile()}. It can't + read subsections of files. +
    +
    +

    + You can optionally use the +{@link android.content.ContentProvider#openPipeHelper(Uri, String, Bundle, T, ContentProvider.PipeDataWriter) openPipeHelper()} + method with your file descriptor method. This allows the pasting application to read the + stream data in a background thread using a pipe. To use this method, you need to implement the + {@link android.content.ContentProvider.PipeDataWriter} interface. An example of doing this is + given in the Note Pad sample + application, in the openTypedAssetFile() method of + NotePadProvider.java. +

    +

    Designing Effective Copy/Paste Functionality

    +

    + To design effective copy and paste functionality for your application, remember these + points: +

    + diff --git a/docs/html/guide/topics/ui/drag-drop.jd b/docs/html/guide/topics/ui/drag-drop.jd new file mode 100644 index 000000000000..588b05b328db --- /dev/null +++ b/docs/html/guide/topics/ui/drag-drop.jd @@ -0,0 +1,995 @@ +page.title=Dragging and Dropping +@jd:body +
    +
    +

    Quickview

    +
      +
    • + Allow users to move data within your Activity layout using graphical gestures. +
      • +
    • + Supports operations besides data movement. +
      • +
    • + Only works within a single application. +
      • +
    • + Requires API 11. +
      • +
    +

    In this document

    +
      +
    1. + Overview +
        +
      1. + The drag/drop process +
        2. +
      2. + The drag event listener and callback method +
        3. +
      3. + Drag events +
        4. +
      4. + + The drag shadow +
        5. +
      +
      2. +
    2. + Designing a Drag and Drop Operation +
        +
      1. + Starting a drag +
        2. +
      2. + Responding to a drag start +
        3. +
      3. + Handling events during the drag +
        4. +
      4. + Responding to a drop +
        5. +
      5. + Responding to a drag end +
        6. +
      6. + Responding to drag events: an example +
        7. +
      +
      3. +
    +

    Key classes

    +
      +
    1. + {@link android.view.View View} +
      2. +
    2. + {@link android.view.View.OnLongClickListener OnLongClickListener} +
      3. +
    3. + {@link android.view.View.OnDragListener OnDragListener} +
      4. +
    4. + {@link android.view.DragEvent DragEvent} +
      5. +
    5. + {@link android.view.View.DragShadowBuilder DragShadowBuilder} +
      6. +
    6. + {@link android.content.ClipData ClipData} +
      7. +
    7. + {@link android.content.ClipDescription ClipDescription} +
      8. +
    +

    Related Samples

    +
      +
    1. + + Honeycomb-Gallery sample application. +
      2. +
    2. + +DragAndDropDemo.java and + +DraggableDot.java in Api Demos. +
      3. +
    +

    See also

    +
      +
    1. + Content Providers +
      2. +
    2. + Handling UI Events +
      3. +
    +
    +
    +

    + With the Android drag/drop framework, you can allow your users to move data + from one View to another View in the current layout using a graphical drag and drop gesture. + The framework includes a drag event class, drag listeners, and helper methods and classes. +

    +

    + Although the framework is primarily designed for data movement, you can use + it for other UI actions. For example, you could create an app that mixes colors when the user + drags a color icon over another icon. The rest of this topic, however, describes the + framework in terms of data movement. +

    +

    Overview

    +

    + A drag and drop operation starts when the user makes some gesture that you recognize as a + signal to start dragging data. In response, your application tells the system that the drag is + starting. The system calls back to your application to get a representation of the data + being dragged. As the user's finger moves this representation (a "drag shadow") + over the current layout, the system sends drag events to the drag event listener objects and + drag event callback methods associated with the {@link android.view.View} objects in the layout. + Once the user releases the drag shadow, the system ends the drag operation. +

    +

    + You create a drag event listener object ("listeners") from a class that implements + {@link android.view.View.OnDragListener}. You set the drag event listener object for a View + with the View object's + {@link android.view.View#setOnDragListener(View.OnDragListener) setOnDragListener()} method. + Each View object also has a {@link android.view.View#onDragEvent(DragEvent) onDragEvent()} + callback method. Both of these are described in more detail in the section + The drag event listener and callback method. +

    +

    + Note: For the sake of simplicity, the following sections refer to the routine + that receives drag events as the "drag event listener", even though it may actually + be a callback method. +

    +

    + When you start a drag, you include both the data you are moving and metadata describing this + data as part of the call to the system. During the drag, the system sends drag events to the + drag event listeners or callback methods of each View in the layout. The listeners or callback + methods can use the metadata to decide if they want to accept the data when it is dropped. + If the user drops the data over a View object, and that View object's listener or callback + method has previously told the system that it wants to accept the drop, then the system sends + the data to the listener or callback method in a drag event. +

    +

    + Your application tells the system to start a drag by calling the + {@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()} + method. This tells the system to start sending drag events. The method also sends the data that + you are dragging. +

    +

    + You can call + {@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()} + for any attached View in the current layout. The system only uses the View object to get access + to global settings in your layout. +

    +

    + Once your application calls + {@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()}, + the rest of the process uses events that the system sends to the View objects in your current + layout. +

    +

    The drag/drop process

    +

    + There are basically four steps or states in the drag and drop process: +

    +
    +
    + Started +
    +
    + In response to the user's gesture to begin a drag, your application calls + {@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()} + to tell the system to start a drag. The arguments + {@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()} + provide the data to be dragged, metadata for this data, and a callback for drawing the + drag shadow. +

    + The system first responds by calling back to your application to get a drag shadow. It + then displays the drag shadow on the device. +

    +

    + Next, the system sends a drag event with action type + {@link android.view.DragEvent#ACTION_DRAG_STARTED} to the drag event listeners for + all the View objects in the current layout. To continue to receive drag events, + including a possible drop event, a drag event listener must return true. + This registers the listener with the system. Only registered listeners continue to + receive drag events. At this point, listeners can also change the appearance of their + View object to show that the listener can accept a drop event. +

    +

    + If the drag event listener returns false, then it will not receive drag + events for the current operation until the system sends a drag event with action type + {@link android.view.DragEvent#ACTION_DRAG_ENDED}. By sending false, the + listener tells the system that it is not interested in the drag operation and + does not want to accept the dragged data. +

    +
    +
    + Continuing +
    +
    + The user continues the drag. As the drag shadow intersects the bounding box of a View + object, the system sends one or more drag events to the View object's drag event + listener (if it is registered to receive events). The listener may choose to + alter its View object's appearance in response to the event. For example, if the event + indicates that the drag shadow has entered the bounding box of the View + (action type {@link android.view.DragEvent#ACTION_DRAG_ENTERED}), the listener + can react by highlighting its View. +
    +
    + Dropped +
    +
    + The user releases the drag shadow within the bounding box of a View that can accept the + data. The system sends the View object's listener a drag event with action type + {@link android.view.DragEvent#ACTION_DROP}. The drag event contains the data that was + passed to the system in the call to + {@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()} + that started the operation. The listener is expected to return boolean true to + the system if code for accepting the drop succeeds. +

    + Note that this step only occurs if the user drops the drag shadow within the bounding + box of a View whose listener is registered to receive drag events. If the user releases + the drag shadow in any other situation, no {@link android.view.DragEvent#ACTION_DROP} + drag event is sent. +

    +
    +
    + Ended +
    +
    + After the user releases the drag shadow, and after the system sends out (if necessary) + a drag event with action type {@link android.view.DragEvent#ACTION_DROP}, the system sends + out a drag event with action type {@link android.view.DragEvent#ACTION_DRAG_ENDED} to + indicate that the drag operation is over. This is done regardless of where the user released + the drag shadow. The event is sent to every listener that is registered to receive drag + events, even if the listener received the {@link android.view.DragEvent#ACTION_DROP} event. +
    +
    +

    + Each of these four steps is described in more detail in the section + Designing a Drag and Drop Operation. +

    +

    The drag event listener and callback method

    +

    + A View receives drag events with either a drag event listener that implements + {@link android.view.View.OnDragListener} or with its + {@link android.view.View#onDragEvent(DragEvent)} callback method. + When the system calls the method or listener, it passes to them + a {@link android.view.DragEvent} object. +

    +

    + You will probably want to use the listener in most cases. When you design UIs, you usually + don't subclass View classes, but using the callback method forces you to do this in order to + override the method. In comparison, you can implement one listener class and then use it with + several different View objects. You can also implement it as an anonymous inline class. To + set the listener for a View object, call +{@link android.view.View#setOnDragListener(android.view.View.OnDragListener) setOnDragListener()}. +

    +

    + You can have both a listener and a callback method for View object. If this occurs, + the system first calls the listener. The system doesn't call the callback method unless the + listener returns false. +

    +

    + The combination of the {@link android.view.View#onDragEvent(DragEvent)} method and + {@link android.view.View.OnDragListener} is analogous to the combination + of the {@link android.view.View#onTouchEvent(MotionEvent) onTouchEvent()} and + {@link android.view.View.OnTouchListener} used with touch events. +

    +

    Drag events

    +

    + The system sends out a drag event in the form of a {@link android.view.DragEvent} object. The + object contains an action type that tells the listener what is happening in the drag/drop + process. The object contains other data, depending on the action type. +

    +

    + To get the action type, a listener calls {@link android.view.DragEvent#getAction()}. There + are six possible values, defined by constants in the {@link android.view.DragEvent} class. These + are listed in table 1. +

    +

    + The {@link android.view.DragEvent} object also contains the data that your application provided + to the system in the call to + {@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()}. + Some of the data is valid only for certain action types. The data that is valid for each action + type is summarized in table 2. It is also described in detail with + the event for which it is valid in the section + Designing a Drag and Drop Operation. +

    +

    + Table 1. DragEvent action types +

    + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
    getAction() valueMeaning
    {@link android.view.DragEvent#ACTION_DRAG_STARTED} + A View object's drag event listener receives this event action type just after the + application calls +{@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()} and + gets a drag shadow. +
    {@link android.view.DragEvent#ACTION_DRAG_ENTERED} + A View object's drag event listener receives this event action type when the drag shadow + has just entered the bounding box of the View. This is the first event action type the + listener receives when the drag shadow enters the bounding box. If the listener wants to + continue receiving drag events for this operation, it must return boolean + true to the system. +
    {@link android.view.DragEvent#ACTION_DRAG_LOCATION} + A View object's drag event listener receives this event action type after it receives a + {@link android.view.DragEvent#ACTION_DRAG_ENTERED} event while the drag shadow is + still within the bounding box of the View. +
    {@link android.view.DragEvent#ACTION_DRAG_EXITED} + A View object's drag event listener receives this event action type after it receives a + {@link android.view.DragEvent#ACTION_DRAG_ENTERED} and at least one + {@link android.view.DragEvent#ACTION_DRAG_LOCATION} event, and after the user has moved + the drag shadow outside the bounding box of the View. +
    {@link android.view.DragEvent#ACTION_DROP} + A View object's drag event listener receives this event action type when the user + releases the drag shadow over the View object. This action type is only sent to a View + object's listener if the listener returned boolean true in response to the + {@link android.view.DragEvent#ACTION_DRAG_STARTED} drag event. This action type is not + sent if the user releases the drag shadow on a View whose listener is not registered, + or if the user releases the drag shadow on anything that is not part of the current + layout. +

    + The listener is expected to return boolean true if it successfully + processes the drop. Otherwise, it should return false. +

    +
    {@link android.view.DragEvent#ACTION_DRAG_ENDED} + A View object's drag event listener receives this event action type + when the system is ending the drag operation. This action type is not necessarily + preceded by an {@link android.view.DragEvent#ACTION_DROP} event. If the system sent + a {@link android.view.DragEvent#ACTION_DROP}, receiving the + {@link android.view.DragEvent#ACTION_DRAG_ENDED} action type does not imply that the + drop operation succeeded. The listener must call + {@link android.view.DragEvent#getResult()} to get the value that was + returned in response to {@link android.view.DragEvent#ACTION_DROP}. If an + {@link android.view.DragEvent#ACTION_DROP} event was not sent, then + {@link android.view.DragEvent#getResult()} returns false. +
    +

    + Table 2. Valid DragEvent data by action type

    + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + + +
    {@link android.view.DragEvent#getAction()} value{@link android.view.DragEvent#getClipDescription()} value{@link android.view.DragEvent#getLocalState()} value{@link android.view.DragEvent#getX()} value{@link android.view.DragEvent#getY()} value{@link android.view.DragEvent#getClipData()} value{@link android.view.DragEvent#getResult()} value
    {@link android.view.DragEvent#ACTION_DRAG_STARTED}XXX   
    {@link android.view.DragEvent#ACTION_DRAG_ENTERED}XXXX  
    {@link android.view.DragEvent#ACTION_DRAG_LOCATION}XXXX  
    {@link android.view.DragEvent#ACTION_DRAG_EXITED}XX    
    {@link android.view.DragEvent#ACTION_DROP}XXXXX 
    {@link android.view.DragEvent#ACTION_DRAG_ENDED}XX   X
    +

    + The {@link android.view.DragEvent#getAction()}, + {@link android.view.DragEvent#describeContents()}, + {@link android.view.DragEvent#writeToParcel(Parcel,int) writeToParcel()}, and + {@link android.view.DragEvent#toString()} methods always return valid data. +

    +

    + If a method does not contain valid data for a particular action type, it returns either + null or 0, depending on its result type. +

    +

    + The drag shadow +

    +

    + During a drag and drop operation, the system displays a image that the user drags. + For data movement, this image represents the data being dragged. For other operations, the + image represents some aspect of the drag operation. +

    +

    + The image is called a drag shadow. You create it with methods you declare for a + {@link android.view.View.DragShadowBuilder} object, and then pass it to the system when you + start a drag using + {@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()}. + As part of its response to + {@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()}, + the system invokes the callback methods you've defined in + {@link android.view.View.DragShadowBuilder} to obtain a drag shadow. +

    +

    + The {@link android.view.View.DragShadowBuilder} class has two constructors: +

    +
    +
    {@link android.view.View.DragShadowBuilder#View.DragShadowBuilder(View)}
    +
    + This constructor accepts any of your application's + {@link android.view.View} objects. The constructor stores the View object + in the {@link android.view.View.DragShadowBuilder} object, so during + the callback you can access it as you construct your drag shadow. + It doesn't have to be associated with the View (if any) that the user + selected to start the drag operation. +

    + If you use this constructor, you don't have to extend + {@link android.view.View.DragShadowBuilder} or override its methods. By default, + you will get a drag shadow that has the same appearance as the View you pass as an + argument, centered under the location where the user is touching the screen. +

    +
    +
    {@link android.view.View.DragShadowBuilder#View.DragShadowBuilder()}
    +
    + If you use this constructor, no View object is available in the + {@link android.view.View.DragShadowBuilder} object (the field is set to null). + If you use this constructor, and you don't extend + {@link android.view.View.DragShadowBuilder} or override its methods, + you will get an invisible drag shadow. + The system does not give an error. +
    +
    +

    + The {@link android.view.View.DragShadowBuilder} class has two methods: +

    +
    +
    +{@link android.view.View.DragShadowBuilder#onProvideShadowMetrics(Point,Point) onProvideShadowMetrics()} +
    +
    + The system calls this method immediately after you call +{@link android.view.View#startDrag(ClipData,View.DragShadowBuilder,Object,int) startDrag()}. Use it + to send to the system the dimensions and touch point of the drag shadow. The method has two + arguments: +
    +
    dimensions
    +
    + A {@link android.graphics.Point} object. The drag shadow width goes in + {@link android.graphics.Point#x} and its height goes in + {@link android.graphics.Point#y}. +
    +
    touch_point
    +
    + A {@link android.graphics.Point} object. The touch point is the location within the + drag shadow that should be under the user's finger during the drag. Its X + position goes in {@link android.graphics.Point#x} and its Y position goes in + {@link android.graphics.Point#y} +
    +
    +
    +
    + {@link android.view.View.DragShadowBuilder#onDrawShadow(Canvas) onDrawShadow()} +
    +
    + Immediately after the call to +{@link android.view.View.DragShadowBuilder#onProvideShadowMetrics(Point,Point) onProvideShadowMetrics()} + the system calls + {@link android.view.View.DragShadowBuilder#onDrawShadow(Canvas) onDrawShadow()} to get the + drag shadow itself. The method has a single argument, a {@link android.graphics.Canvas} + object that the system constructs from the parameters you provide in +{@link android.view.View.DragShadowBuilder#onProvideShadowMetrics(Point,Point) onProvideShadowMetrics()} + Use it to draw the drag shadow in the provided {@link android.graphics.Canvas} object. +
    +
    +

    + To improve performance, you should keep the size of the drag shadow small. For a single item, + you may want to use a icon. For a multiple selection, you may want to use icons in a stack + rather than full images spread out over the screen. +

    +

    Designing a Drag and Drop Operation

    +

    + This section shows step-by-step how to start a drag, how to respond to events during + the drag, how respond to a drop event, and how to end the drag and drop operation. +

    +

    Starting a drag

    +

    + The user starts a drag with a drag gesture, usually a long press, on a View object. + In response, you should do the following: +

    +
      +
    1. + As necessary, create a {@link android.content.ClipData} and + {@link android.content.ClipData.Item} for the data being moved. As part of the + ClipData object, supply metadata that is stored in a {@link android.content.ClipDescription} + object within the ClipData. For a drag and drop operation that does not represent data + movement, you may want to use null instead of an actual object. +

      + For example, this code snippet shows how to respond to a long press on a ImageView + by creating a ClipData object that contains the tag or label of an + ImageView. Following this snippet, the next snippet shows how to override the methods in + {@link android.view.View.DragShadowBuilder}: +

      +
      +// Create a string for the ImageView label
+private static final String IMAGEVIEW_TAG = "icon bitmap"
+
+// Creates a new ImageView
+ImageView imageView = new ImageView(this);
+
+// Sets the bitmap for the ImageView from an icon bit map (defined elsewhere)
+imageView.setImageBitmap(mIconBitmap);
+
+// Sets the tag
+imageView.setTag(IMAGEVIEW_TAG);
+
+    ...
+
+// Sets a long click listener for the ImageView using an anonymous listener object that
+// implements the OnLongClickListener interface
+imageView.setOnLongClickListener(new View.OnLongClickListener() {
+
+    // Defines the one method for the interface, which is called when the View is long-clicked
+    public boolean onLongClick(View v) {
+
+    // Create a new ClipData.
+    // This is done in two steps to provide clarity. The convenience method
+    // ClipData.newPlainText() can create a plain text ClipData in one step.
+
+    // Create a new ClipData.Item from the ImageView object's tag
+    ClipData.Item item = new ClipData.Item(v.getTag());
+
+    // Create a new ClipData using the tag as a label, the plain text MIME type, and
+    // the already-created item. This will create a new ClipDescription object within the
+    // ClipData, and set its MIME type entry to "text/plain"
+    ClipData dragData = new ClipData(v.getTag(),ClipData.MIMETYPE_TEXT_PLAIN,item);
+
+    // Instantiates the drag shadow builder.
+    View.DrawShadowBuilder myShadow = new MyDragShadowBuilder(imageView);
+
+    // Starts the drag
+
+            v.startDrag(dragData,  // the data to be dragged
+                        myShadow,  // the drag shadow builder
+                        null,      // no need to use local data
+                        0          // flags (not currently used, set to 0)
+            );
+
+    }
+}
+
      +
      2. +
    2. + The following code snippet defines {@code myDragShadowBuilder} + It creates a drag shadow for dragging a TextView as a small gray rectangle: +
      +    private static class MyDragShadowBuilder extends View.DragShadowBuilder {
+
+    // The drag shadow image, defined as a drawable thing
+    private static Drawable shadow;
+
+        // Defines the constructor for myDragShadowBuilder
+        public MyDragShadowBuilder(View v) {
+
+            // Stores the View parameter passed to myDragShadowBuilder.
+            super(v);
+
+            // Creates a draggable image that will fill the Canvas provided by the system.
+            shadow = new ColorDrawable(Color.LTGRAY);
+        }
+
+        // Defines a callback that sends the drag shadow dimensions and touch point back to the
+        // system.
+        @Override
+        public void onProvideShadowMetrics (Point size, Point touch)
+            // Defines local variables
+            private int width, height;
+
+            // Sets the width of the shadow to half the width of the original View
+            width = getView().getWidth() / 2;
+
+            // Sets the height of the shadow to half the height of the original View
+            height = getView().getHeight() / 2;
+
+            // The drag shadow is a ColorDrawable. This sets its dimensions to be the same as the
+            // Canvas that the system will provide. As a result, the drag shadow will fill the
+            // Canvas.
+            shadow.setBounds(0, 0, width, height);
+
+            // Sets the size parameter's width and height values. These get back to the system
+            // through the size parameter.
+            size.set(width, height);
+
+            // Sets the touch point's position to be in the middle of the drag shadow
+            touch.set(width / 2, height / 2);
+        }
+
+        // Defines a callback that draws the drag shadow in a Canvas that the system constructs
+        // from the dimensions passed in onProvideShadowMetrics().
+        @Override
+        public void onDrawShadow(Canvas canvas) {
+
+            // Draws the ColorDrawable in the Canvas passed in from the system.
+            shadow.draw(canvas);
+        }
+    }
+
      +

      + Note: Remember that you don't have to extend + {@link android.view.View.DragShadowBuilder}. The constructor + {@link android.view.View.DragShadowBuilder#View.DragShadowBuilder(View)} creates a + default drag shadow that's the same size as the View argument passed to it, with the + touch point centered in the drag shadow. +

      +
      3. +
    +

    Responding to a drag start

    +

    + During the drag operation, the system dispatches drag events to the drag event listeners + of the View objects in the current layout. The listeners should react + by calling {@link android.view.DragEvent#getAction()} to get the action type. + At the start of a drag, this methods returns {@link android.view.DragEvent#ACTION_DRAG_STARTED}. +

    +

    + In response to an event with the action type {@link android.view.DragEvent#ACTION_DRAG_STARTED}, + a listener should do the following: +

    +
      +
    1. + Call {@link android.view.DragEvent#getClipDescription()} to get the + {@link android.content.ClipDescription}. Use the MIME type methods in + {@link android.content.ClipDescription} to see if the listener can accept the data being + dragged. +

      + If the drag and drop operation does not represent data movement, this may not be + necessary. +

      +
      2. +
    2. + If the listener can accept a drop, it should return true. This tells + the system to continue to send drag events to the listener. + If it can't accept a drop, it should return false, and the system + will stop sending drag events until it sends out + {@link android.view.DragEvent#ACTION_DRAG_ENDED}. +
      3. +
    +

    + Note that for an {@link android.view.DragEvent#ACTION_DRAG_STARTED} event, these + the following {@link android.view.DragEvent} methods are not valid: + {@link android.view.DragEvent#getClipData()}, {@link android.view.DragEvent#getX()}, + {@link android.view.DragEvent#getY()}, and {@link android.view.DragEvent#getResult()}. +

    +

    Handling events during the drag

    +

    + During the drag, listeners that returned true in response to + the {@link android.view.DragEvent#ACTION_DRAG_STARTED} drag event continue to receive drag + events. The types of drag events a listener receives during the drag depend on the location of + the drag shadow and the visibility of the listener's View. +

    +

    + During the drag, listeners primarily use drag events to decide if they should change the + appearance of their View. +

    +

    + During the drag, {@link android.view.DragEvent#getAction()} returns one of three + values: +

    + +

    + The listener does not need to react to any of these action types. If the listener returns a + value to the system, it is ignored. Here are some guidelines for responding to each of + these action types: +

    + +

    Responding to a drop

    +

    + When the user releases the drag shadow on a View in the application, and that View previously + reported that it could accept the content being dragged, the system dispatches a drag event + to that View with the action type {@link android.view.DragEvent#ACTION_DROP}. The listener + should do the following: +

    +
      +
    1. + Call {@link android.view.DragEvent#getClipData()} to get the + {@link android.content.ClipData} object that was originally supplied in the call + to +{@link android.view.View#startDrag(ClipData, View.DragShadowBuilder, Object, int) startDrag()} + and store it. If the drag and drop operation does not represent data movement, + this may not be necessary. +
      2. +
    2. + Return boolean true to indicate that the drop was processed successfully, or + boolean false if it was not. The returned value becomes the value returned by + {@link android.view.DragEvent#getResult()} for an + {@link android.view.DragEvent#ACTION_DRAG_ENDED} event. +

      + Note that if the system does not send out an {@link android.view.DragEvent#ACTION_DROP} + event, the value of {@link android.view.DragEvent#getResult()} for an + {@link android.view.DragEvent#ACTION_DRAG_ENDED} event is false. +

      +
      3. +
    +

    + For an {@link android.view.DragEvent#ACTION_DROP} event, + {@link android.view.DragEvent#getX()} and {@link android.view.DragEvent#getY()} + return the X and Y position of the drag point at the moment of the drop, using the coordinate + system of the View that received the drop. +

    +

    + The system does allow the user to release the drag shadow on a View whose listener is not + receiving drag events. It will also allow the user to release the drag shadow + on empty regions of the application's UI, or on areas outside of your application. + In all of these cases, the system does not send an event with action type + {@link android.view.DragEvent#ACTION_DROP}, although it does send out an + {@link android.view.DragEvent#ACTION_DRAG_ENDED} event. +

    +

    Responding to a drag end

    +

    + Immediately after the user releases the drag shadow, the system sends a + drag event to all of the drag event listeners in your application, with an action type of + {@link android.view.DragEvent#ACTION_DRAG_ENDED}. This indicates that the drag operation is + over. +

    +

    + Each listener should do the following: +

    +
      +
    1. + If listener changed its View object's appearance during the operation, it should reset the + View to its default appearance. This is a visual indication to the user that the operation + is over. +
      2. +
    2. + The listener can optionally call {@link android.view.DragEvent#getResult()} to find out more + about the operation. If a listener returned true in response to an event of + action type {@link android.view.DragEvent#ACTION_DROP}, then + {@link android.view.DragEvent#getResult()} will return boolean true. In all + other cases, {@link android.view.DragEvent#getResult()} returns boolean false, + including any case in which the system did not send out a + {@link android.view.DragEvent#ACTION_DROP} event. +
      3. +
    3. + The listener should return boolean true to the system. +
      4. +
    +

    +

    +

    Responding to drag events: an example

    +

    + All drag events are initially received by your drag event method or listener. The following + code snippet is a simple example of reacting to drag events in a listener: +

    +
    +// Creates a new drag event listener
+mDragListen = new myDragEventListener();
+
+View imageView = new ImageView(this);
+
+// Sets the drag event listener for the View
+imageView.setOnDragListener(mDragListen);
+
+...
+
+protected class myDragEventListener implements View.OnDragEventListener {
+
+    // This is the method that the system calls when it dispatches a drag event to the
+    // listener.
+    public boolean onDrag(View v, DragEvent event) {
+
+        // Defines a variable to store the action type for the incoming event
+        final int action = event.getAction();
+
+        // Handles each of the expected events
+        switch(action) {
+
+            case DragEvent.ACTION_DRAG_STARTED:
+
+                // Determines if this View can accept the dragged data
+                if (event.getClipDescription().hasMimeType(ClipDescription.MIMETYPE_TEXT_PLAIN)) {
+
+                    // As an example of what your application might do,
+                    // applies a blue color tint to the View to indicate that it can accept
+                    // data.
+                    v.setColorFilter(Color.BLUE);
+
+                    // Invalidate the view to force a redraw in the new tint
+                    v.invalidate();
+
+                    // returns true to indicate that the View can accept the dragged data.
+                    return(true);
+
+                    } else {
+
+                    // Returns false. During the current drag and drop operation, this View will
+                    // not receive events again until ACTION_DRAG_ENDED is sent.
+                    return(false);
+
+                    }
+                break;
+
+            case DragEvent.ACTION_DRAG_ENTERED: {
+
+                // Applies a green tint to the View. Return true; the return value is ignored.
+
+                v.setColorFilter(Color.GREEN);
+
+                // Invalidate the view to force a redraw in the new tint
+                v.invalidate();
+
+                return(true);
+
+                break;
+
+                case DragEvent.ACTION_DRAG_LOCATION:
+
+                // Ignore the event
+                    return(true);
+
+                break;
+
+                case DragEvent.ACTION_DRAG_EXITED:
+
+                    // Re-sets the color tint to blue. Returns true; the return value is ignored.
+                    v.setColorFilter(Color.BLUE);
+
+                    // Invalidate the view to force a redraw in the new tint
+                    v.invalidate();
+
+                    return(true);
+
+                break;
+
+                case DragEvent.ACTION_DROP:
+
+                    // Gets the item containing the dragged data
+                    ClipData.Item item = event.getClipData().getItemAt(0);
+
+                    // Gets the text data from the item.
+                    dragData = item.getText();
+
+                    // Displays a message containing the dragged data.
+                    Toast.makeText(this, "Dragged data is " + dragData, Toast.LENGTH_LONG);
+
+                    // Turns off any color tints
+                    v.clearColorFilter();
+
+                    // Invalidates the view to force a redraw
+                    v.invalidate();
+
+                    // Returns true. DragEvent.getResult() will return true.
+                    return(true);
+
+                break;
+
+                case DragEvent.ACTION_DRAG_ENDED:
+
+                    // Turns off any color tinting
+                    v.clearColorFilter();
+
+                    // Invalidates the view to force a redraw
+                    v.invalidate();
+
+                    // Does a getResult(), and displays what happened.
+                    if (event.getResult()) {
+                        Toast.makeText(this, "The drop was handled.", Toast.LENGTH_LONG);
+
+                    } else {
+                        Toast.makeText(this, "The drop didn't work.", Toast.LENGTH_LONG);
+
+                    };
+
+                    // returns true; the value is ignored.
+                    return(true);
+
+                break;
+
+                // An unknown action type was received.
+                default:
+                    Log.e("DragDrop Example","Unknown action type received by OnDragListener.");
+
+                break;
+        };
+    };
+};
+
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