src/com/android/photos/GalleryActivity.java

/*
 * Copyright (C) 2013 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.photos;

import android.app.ActionBar;
import android.app.ActionBar.Tab;
import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentTransaction;
import android.content.Intent;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;

import com.android.camera.CameraActivity;
import com.android.gallery3d.R;

public class GalleryActivity extends Activity {

    private final String FTAG_PHOTOSET = "PhotoSet";
    private final String FTAG_ALBUMSET = "AlbumSet";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        setupActionBar();
    }

    private void setupActionBar() {
        ActionBar ab = getActionBar();
        ab.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        ab.setDisplayShowHomeEnabled(false);
        ab.setDisplayShowTitleEnabled(false);
        Tab tab = ab.newTab();
        tab.setText(R.string.tab_photos);
        tab.setTabListener(new TabListener<PhotoSetFragment>(this,
                FTAG_PHOTOSET, PhotoSetFragment.class));
        ab.addTab(tab, true);
        tab = ab.newTab();
        tab.setText(R.string.tab_albums);
        tab.setTabListener(new TabListener<AlbumSetFragment>(this,
                FTAG_ALBUMSET, AlbumSetFragment.class));
        ab.addTab(tab);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        getMenuInflater().inflate(R.menu.gallery, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        switch (item.getItemId()) {
        case R.id.menu_camera:
            Intent intent = new Intent(this, CameraActivity.class);
            intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
            startActivity(intent);
            return true;
        default:
            return super.onOptionsItemSelected(item);
        }
    }

    private static class TabListener<T extends Fragment> implements ActionBar.TabListener {
        private Fragment mFragment;
        private final Activity mActivity;
        private final String mTag;
        private final Class<T> mClass;

        /** Constructor used each time a new tab is created.
          * @param activity  The host Activity, used to instantiate the fragment
          * @param tag  The identifier tag for the fragment
          * @param clz  The fragment's Class, used to instantiate the fragment
          */
        public TabListener(Activity activity, String tag, Class<T> clz) {
            mActivity = activity;
            mTag = tag;
            mClass = clz;
        }

        /* The following are each of the ActionBar.TabListener callbacks */

        @Override
        public void onTabSelected(Tab tab, FragmentTransaction ft) {
            // Check if the fragment is already initialized
            if (mFragment == null) {
                // If not, instantiate and add it to the activity
                mFragment = Fragment.instantiate(mActivity, mClass.getName());
                ft.add(android.R.id.content, mFragment, mTag);
            } else {
                // If it exists, simply attach it in order to show it
                ft.attach(mFragment);
            }
        }

        @Override
        public void onTabUnselected(Tab tab, FragmentTransaction ft) {
            if (mFragment != null) {
                // Detach the fragment, because another one is being attached
                ft.detach(mFragment);
            }
        }

        @Override
        public void onTabReselected(Tab tab, FragmentTransaction ft) {
            // User selected the already selected tab. Usually do nothing.
        }
    }
}