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;
}

@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);
}
}