剖析Android自带Widget-Music播放器

本文剖析Android自带widget-Music，其涉及到众多事件的处理，虽然麻烦，但可看出是如何和服务进行交互的。首先我们看下music程序中AndroidManifest.xml中有关widgets的定义。下面是xml/appwidget_info的内容，里面包含了这个widget程序的基本定义。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;}@Overridepublic 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 messageString 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 userviews.setViewVisibility(R.id.title, View.GONE);views.setTextViewText(R.id.artist, errorState);} else {// No error, so show normal titlesviews.setViewVisibility(R.id.title, View.VISIBLE);views.setTextViewText(R.id.title, titleName);views.setTextViewText(R.id.artist, artistName);}// Set correct drawable for pause statefinal 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 intentslinkButtons(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 eventsIntent 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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