摘要：
怀着沉痛的心情发表这篇博客，不知道是不是我在CSDN上发表的最后一篇。这两天打算研究framework层和Linux的一些东西，顺便总结11月份和12月份的一些知识！！
怀着沉痛的心情发表这篇博客，不知道是不是我在CSDN上发表的最后一篇。这两天打算研究framework层和Linux的一些东西，顺便总结11月份和12月份的一些知识！！
// 本来以为AppWidget是通过AIDL和MediaPlaybackService通信了，后来看了看不是
// 如果一些基础的看不懂的话可以看看我上一篇
public class MediaAppWidgetProvider extends AppWidgetProvider {
static final String TAG = "MusicAppWidgetProvider";
public static final String CMDAPPWIDGETUPDATE = "appwidgetupdate";
private static MediaAppWidgetProvider sInstance;
// 单例模式，当你点击一个播放时所有的AppWidget都播放
static synchronized MediaAppWidgetProvider getInstance() {
if (sInstance == null) {
sInstance = new MediaAppWidgetProvider();
}
return sInstance;
}
// 每次在创建AppWiget的时候或者到了更新频率的时候执行此函数
@Override
public void onUpdate(Context context, AppWidgetManager appWidgetManager, int[] appWidgetIds) {
// 设置AppWidget的一些默认设置，并且传递一些相关参数
defaultAppWidget(context, appWidgetIds);
// Send broadcast intent to any running MediaPlaybackService so it can
// wrap around with an immediate update.
// 发送广播消息通知正在运行的MediaPlaybackService以响应AppWidget
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);
// 发送广播
context.sendBroadcast(updateIntent);
}
/**
* Initialize given widgets to default state, where we launch Music on default click
* and hide actions if service not running.
*/
// 初始化widget的默认状态,在onUpdate()里就开始执行
private void defaultAppWidget(Context context, int[] appWidgetIds) {
final Resources res = context.getResources();
// 获得AppWidget上的布局视图，然后通过views获得控件id
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.widget_initial_text));
// 开始创建Widget的时候默认是不播放音乐的
linkButtons(context, views, false /* not playing */);
pushUpdate(context, appWidgetIds, views);
}
// 刷新Widget的状态
private void pushUpdate(Context context, int[] appWidgetIds, RemoteViews views) {
// Update specific list of appWidgetIds if given, otherwise default to all
final AppWidgetManager gm = AppWidgetManager.getInstance(context);
if (appWidgetIds != null) {
gm.updateAppWidget(appWidgetIds, views);
} else {
gm.updateAppWidget(new ComponentName(context, this.getClass()), views);
}
}
/**
* Check against {@link AppWidgetManager} if there are any instances of this widget.
*/
// 通过AppWidgetManager检查是否有存在AppWidget
private boolean hasInstances(Context context) {
AppWidgetManager appWidgetManager = AppWidgetManager.getInstance(context);
int[] appWidgetIds = appWidgetManager.getAppWidgetIds(
new ComponentName(context, this.getClass()));
return (appWidgetIds.length > 0);
}
/**
* Handle a change notification coming over from {@link MediaPlaybackService}
*/
// 这个函数是在MediaPlaybackService中调用,作用是检查播放状态是否发生变化
void notifyChange(MediaPlaybackService service, String what) {
if (hasInstances(service)) {
if (MediaPlaybackService.META_CHANGED.equals(what) ||
MediaPlaybackService.PLAYSTATE_CHANGED.equals(what)) {
// 如果状态有改变，那么更新AppWidget的状态
performUpdate(service, null);
}
}
}
/**
* Update all active widget instances by pushing changes
*/
// 更新所有AppWidget的状态
void performUpdate(MediaPlaybackService service, int[] appWidgetIds) {
// 获取所有的相关资源
final Resources res = service.getResources();
// RemoteViews用于获取AppWidget的相关控件Id，及更新相关控件
final RemoteViews views = new RemoteViews(service.getPackageName(), R.layout.album_appwidget);
// 通过MediaPlaybackService获取歌曲相关信息，歌曲名，歌手名，SD卡的状态
CharSequence titleName = service.getTrackName();
CharSequence artistName = service.getArtistName();
CharSequence errorState = null;
// Format title string with track number, or show SD card message
// 获取扩展介质(一般指SD卡)状态以更新变量 errorState
// 各种状态可以查看string中值自己确定
String status = Environment.getExternalStorageState();
if (status.equals(Environment.MEDIA_SHARED) ||
status.equals(Environment.MEDIA_UNMOUNTED)) {
if (android.os.Environment.isExternalStorageRemovable()) {
errorState = res.getText(R.string.sdcard_busy_title);
} else {
errorState = res.getText(R.string.sdcard_busy_title_nosdcard);
}
} else if (status.equals(Environment.MEDIA_REMOVED)) {
if (android.os.Environment.isExternalStorageRemovable()) {
errorState = res.getText(R.string.sdcard_missing_title);
} else {
errorState = res.getText(R.string.sdcard_missing_title_nosdcard);
}
} else if (titleName == null) {
errorState = res.getText(R.string.emptyplaylist);
}
if (errorState != null) {
// Show error state to user
// 如果SD卡状态不符，歌曲名的TextView隐藏，在艺术家TextView中显示errorState
views.setViewVisibility(R.id.title, View.GONE);
views.setTextViewText(R.id.artist, errorState);
} else {
// No error, so show normal titles
// 正常显示
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
// 判断歌曲是否在播放，如果在播放是播放按钮显示为暂停，反之
final boolean playing = service.isPlaying();
if (playing) {
views.setImageViewResource(R.id.control_play, R.drawable.ic_appwidget_music_pause);
} else {
views.setImageViewResource(R.id.control_play, R.drawable.ic_appwidget_music_play);
}
// Link actions buttons to intents
// 根据Widget的布局事件，发送相应的Intent
linkButtons(service, views, playing);
// 更新所有AppWidget的状态
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;
// 关于PendingIntent的相关说明请看我上一篇说明
PendingIntent pendingIntent;
// 获取MediaPlaybackService的组件名称
final ComponentName serviceName = new ComponentName(context, MediaPlaybackService.class);
if (playerActive) {
// 如果正在播放，则启动播放器Activity 即MediaPlaybackActivity
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 {
// 如果没有在播放则启动音乐浏览Activity 即MusicBrowserActivity
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);
// 获取动作，播放下一首歌曲
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);
}
}