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剖析Android自带Widget - Music播放器

发布者:android
发布日期:2011/4/12 21:00:28   更新日期:2011/4/12 21:00:28
阅读次数:4215
评分:4.80
介绍:剖析Android自带Widget - Music播放器
正文:

作者:Android开发网


   昨天的带指针时钟比较简单,今天我们继续android自带widget剖析,相对于alarmclock而言music程序稍微复杂些,主要是涉及到众多事件的处理,不过可以看出如何是和服务进行交互的。继续按照昨天的分析步骤和过程,首先我们看下music程序中AndroidManifest.xml中有关widgets的定义。

<receiver android:name="MediaAppWidgetProvider">
     <intent-filter>
          <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
     </intent-filter>
     <meta-data android:name="android.appwidget.provider" android:resource="@xml/appwidget_info" />
</receiver>

  下面是xml/appwidget_info的内容,里面包含了这个widget程序的基本定义。

<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android" 
  android:minWidth="294dip"   //最小宽度
  android:minHeight="72dip"  //最小高度
  android:updatePeriodMillis="0"  //更新频率
  android:initialLayout="@layout/album_appwidget">   //widget界面布局文件
</appwidget-provider>

整个设计还是十分清晰,这里我们就不再做过多的赘述。

  public class MediaAppWidgetProvider extends AppWidgetProvider {
       
    public static final String CMDAPPWIDGETUPDATE = "appwidgetupdate";
   
    static final ComponentName THIS_APPWIDGET =
        new ComponentName("com.android.music", "com.android.music.MediaAppWidgetProvider");
   
    private static MediaAppWidgetProvider sInstance;
   
    static synchronized MediaAppWidgetProvider getInstance() {
        if (sInstance == null) {
            sInstance = new MediaAppWidgetProvider();
        }
        return sInstance;
    }

    @Override
    public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
        defaultAppWidget(context, appWidgetIds);
       
        // 发送一个Intent广播给MediaPlaybackService以便立即更新

        Intent updateIntent = new Intent(MediaPlaybackService.SERVICECMD);
        updateIntent.putExtra(MediaPlaybackService.CMDNAME,MediaAppWidgetProvider.CMDAPPWIDGETUPDATE);
        updateIntent.putExtra(AppWidgetManager.EXTRA_APPWIDGET_IDS, appWidgetIds);
        updateIntent.addFlags(Intent.FLAG_RECEIVER_REGISTERED_ONLY);
        context.sendBroadcast(updateIntent);
    }
   
    /*
     * 初始化widget默认状态,如果服务没有运行,我们启动music的时候默认单击隐藏
     */
    private void defaultAppWidget(Context context, int[] appWidgetIds) {
        final Resources res = context.getResources();
        final RemoteViews views = new RemoteViews(context.getPackageName(), R.layout.album_appwidget);
       
        views.setViewVisibility(R.id.title, View.GONE);
        views.setTextViewText(R.id.artist, res.getText(R.string.emptyplaylist));

        linkButtons(context, views, false /* 没有播放*/);
        pushUpdate(context, appWidgetIds, views);
    }
   
    private void pushUpdate(Context context, int[] appWidgetIds, RemoteViews views) {
        // 更新指定的列表

        final AppWidgetManager gm = AppWidgetManager.getInstance(context);
        if (appWidgetIds != null) {
            gm.updateAppWidget(appWidgetIds, views);
        } else {
            gm.updateAppWidget(THIS_APPWIDGET, views);
        }
    }
   
    /**
     * Check against {@link AppWidgetManager} if there are any instances of this widget.
     */
    private boolean hasInstances(Context context) {
        AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context);
        int[] appWidgetIds = appWidgetManager.getAppWidgetIds(THIS_APPWIDGET);
        return (appWidgetIds.length > 0);
    }

    /**
     * Handle a change notification coming over from {@link MediaPlaybackService}
     */
    void notifyChange(MediaPlaybackService service, String what) {
        if (hasInstances(service)) {
            if (MediaPlaybackService.PLAYBACK_COMPLETE.equals(what) ||
                    MediaPlaybackService.META_CHANGED.equals(what) ||
                    MediaPlaybackService.PLAYSTATE_CHANGED.equals(what)) {
                performUpdate(service, null);
            }
        }
    }
   
    /**
     * Update all active widget instances by pushing changes
     */
    void performUpdate(MediaPlaybackService service, int[] appWidgetIds) {
        final Resources res = service.getResources();
        final RemoteViews views = new RemoteViews(service.getPackageName(), R.layout.album_appwidget);
       
        final int track = service.getQueuePosition() + 1;
        CharSequence titleName = service.getTrackName();
        CharSequence artistName = service.getArtistName();
        CharSequence errorState = null;
       
        // Format title string with track number, or show SD card message
        String status = Environment.getExternalStorageState();
        if (status.equals(Environment.MEDIA_SHARED) ||
                status.equals(Environment.MEDIA_UNMOUNTED)) {
            errorState = res.getText(R.string.sdcard_busy_title);
        } else if (status.equals(Environment.MEDIA_REMOVED)) {
            errorState = res.getText(R.string.sdcard_missing_title);
        } else if (titleName == null) {
            errorState = res.getText(R.string.emptyplaylist);
        }
       
        if (errorState != null) {
            // Show error state to user
            views.setViewVisibility(R.id.title, View.GONE);
            views.setTextViewText(R.id.artist, errorState);
           
        } else {
            // No error, so show normal titles
            views.setViewVisibility(R.id.title, View.VISIBLE);
            views.setTextViewText(R.id.title, titleName);
            views.setTextViewText(R.id.artist, artistName);
        }
       
        // Set correct drawable for pause state
        final boolean playing = service.isPlaying();
        if (playing) {
            views.setImageViewResource(R.id.control_play, R.drawable.appwidget_pause);
        } else {
            views.setImageViewResource(R.id.control_play, R.drawable.appwidget_play);
        }

        // Link actions buttons to intents
        linkButtons(service, views, playing);
       
        pushUpdate(service, appWidgetIds, views);
    }

    /**
     * Link up various button actions using {@link PendingIntents}.
     *
     * @param playerActive True if player is active in background, which means
     *            widget click will launch {@link MediaPlaybackActivity},
     *            otherwise we launch {@link MusicBrowserActivity}.
     */
    private void linkButtons(Context context, RemoteViews views, boolean playerActive) {
        // Connect up various buttons and touch events
        Intent intent;
        PendingIntent pendingIntent;
       
        final ComponentName serviceName = new ComponentName(context, MediaPlaybackService.class);
       
        if (playerActive) {
            intent = new Intent(context, MediaPlaybackActivity.class);
            pendingIntent = PendingIntent.getActivity(context,
                    0 /* no requestCode */, intent, 0 /* no flags */);
            views.setOnClickPendingIntent(R.id.album_appwidget, pendingIntent);
        } else {
            intent = new Intent(context, MusicBrowserActivity.class);
            pendingIntent = PendingIntent.getActivity(context,
                    0 /* no requestCode */, intent, 0 /* no flags */);
            views.setOnClickPendingIntent(R.id.album_appwidget, pendingIntent);
        }
       
        intent = new Intent(MediaPlaybackService.TOGGLEPAUSE_ACTION);
        intent.setComponent(serviceName);
        pendingIntent = PendingIntent.getService(context,
                0 /* no requestCode */, intent, 0 /* no flags */);
        views.setOnClickPendingIntent(R.id.control_play, pendingIntent);
       
        intent = new Intent(MediaPlaybackService.NEXT_ACTION);
        intent.setComponent(serviceName);
        pendingIntent = PendingIntent.getService(context,
                0 /* no requestCode */, intent, 0 /* no flags */);
        views.setOnClickPendingIntent(R.id.control_next, pendingIntent);
    }
}


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