docs/html/training/game-controllers/multiple-controllers.jd

page.title=Supporting Multiple Game Controllers
trainingnavtop=true

@jd:body

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<h2>This lesson teaches you to</h2>
<ol>
  <li><a href="#map">Map Players to Controller Device IDs</a></li>
  <li><a href="#detect">Process Multiple Controller Input</a></li>
</ol>

<h2>Try it out</h2>
<div class="download-box">
  <a href="http://developer.android.com/shareables/training/ControllerSample.zip"
class="button">Download the sample</a>
  <p class="filename">ControllerSample.zip</p>
</div>


</div>
</div>
<p>While most games are designed to support a single user per Android device,
it's also possible to support multiple users with game controllers that are
connected simultaneously on the same Android device.</p>
<p>This lesson covers some basic techniques for handling input in your single
device multiplayer game from multiple connected controllers. This includes
maintaining a mapping between player avatars and each controller device and
processing controller input events appropriately.
</p>

<h2 id="map">Map Players to Controller Device IDs</h2>
<p>When a game controller is connected to an Android device, the system
assigns it an integer device ID. You can obtain the device IDs for connected
game controllers by calling {@link android.view.InputDevice#getDeviceIds() InputDevice.getDeviceIds()}, as shown in <a href="controller-input.html#input">Verify a Game Controller is Connected</a>. You can then associate each
device ID with a player in your game, and process game actions for each player separately.
</p>
<p class="note"><strong>Note: </strong>On devices running Android 4.1 (API
level 16) and higher, you can obtain an input device’s descriptor using
{@link android.view.InputDevice#getDescriptor()}, which returns a unique
persistent string value for the input device. Unlike a device ID, the descriptor
value won't change even if the input device is disconnected, reconnected, or
reconfigured.
</p>
<p>The code snippet below shows how to use a {@link android.util.SparseArray}
to associate a player's avatar with a specific controller. In this example, the
{@code mShips} variable stores a collection of {@code Ship} objects. A new
player avatar is created in-game when a new controller is attached by a user,
and removed when its associated controller is removed.
</p>
<p>The {@code onInputDeviceAdded()} and {@code onInputDeviceRemoved()} callback
methods are part of the abstraction layer introduced in
<a href="{@docRoot}training/game-controllers/compatibility.html#status_callbacks}">
Supporting Controllers Across Android Versions</a>. By implementing these
listener callbacks, your game can identify the game controller's device ID when a
controller is added or removed. This detection is compatible with Android 2.3
(API level 9) and higher.
</p>

<pre>
private final SparseArray&lt;Ship&gt; mShips = new SparseArray&lt;Ship&gt;();

&#64;Override
public void onInputDeviceAdded(int deviceId) {
    getShipForID(deviceId);
}

&#64;Override
public void onInputDeviceRemoved(int deviceId) {
    removeShipForID(deviceId);
}

private Ship getShipForID(int shipID) {
    Ship currentShip = mShips.get(shipID);
    if ( null == currentShip ) {
        currentShip = new Ship();
        mShips.append(shipID, currentShip);
    }
    return currentShip;
}

private void removeShipForID(int shipID) {
    mShips.remove(shipID);
}
</pre>

<h2 id="detect">Process Multiple Controller Input</h2>
<p>Your game should execute the following loop to process
input from multiple controllers:
</p>
<ol>
<li>Detect whether an input event occurred.</li>
<li>Identify the input source and its device ID.</li>
<li>Based on the action indicated by the input event key code or axis value,
    update the player avatar associated with that device ID.</li>
<li>Render and update the user interface.</li>
</ol>
<p>{@link android.view.KeyEvent} and {@link android.view.MotionEvent} input
events have device IDs associated with them. Your game can take advantage of
this to determine which controller the input event came from, and update the
player avatar associated with that controller.
</p>
<p>The following code snippet shows how you might get a player avatar reference
corresponding to a game controller device ID, and update the game based on the
user's button press on that controller.
</p>
<pre>
&#64;Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if ((event.getSource() &amp; InputDevice.SOURCE_GAMEPAD)
                == InputDevice.SOURCE_GAMEPAD) {
        int deviceId = event.getDeviceId();
        if (deviceId != -1) {
            Ship currentShip = getShipForId(deviceId);
            // Based on which key was pressed, update the player avatar
            // (e.g. set the ship headings or fire lasers)
            ...
            return true;
        }
    }
    return super.onKeyDown(keyCode, event);
}
</pre>
<p class="note"><strong>Note: </strong>As a best practice, when a user's
game controller disconnects, you should pause the game and ask if the user
wants to reconnect.
</p>