Android系统启动，SystemServer创建AppWidgetService，并调用AppWidgetServiceImpl.onStart()方法，初始化相关管理器，注册四个广播接收器:
第一、注册有关软件包安装、删除、改变的广播，以便我们可以更新provider列表。;
// Register for broadcasts about package install, etc., so we can
// update the provider list.
IntentFilter packageFilter = new IntentFilter();
packageFilter.addAction(Intent.ACTION_PACKAGE_ADDED);
packageFilter.addAction(Intent.ACTION_PACKAGE_CHANGED);
packageFilter.addAction(Intent.ACTION_PACKAGE_REMOVED);
packageFilter.addDataScheme("package");
mContext.registerReceiverAsUser(mBroadcastReceiver, UserHandle.ALL,
packageFilter, null, null);
第二、当锁定状态发生变化时会播放一些事件:
IntentFilter offModeFilter = new IntentFilter();
offModeFilter.addAction(Intent.ACTION_MANAGED_PROFILE_AVAILABLE);
offModeFilter.addAction(Intent.ACTION_MANAGED_PROFILE_UNAVAILABLE);
mContext.registerReceiverAsUser(mBroadcastReceiver, UserHandle.ALL,
offModeFilter, null, null);
第三、暂停或解除暂停应用广播;
IntentFilter offModeFilter = new IntentFilter();
offModeFilter.addAction(Intent.ACTION_MANAGED_PROFILE_AVAILABLE);
offModeFilter.addAction(Intent.ACTION_MANAGED_PROFILE_UNAVAILABLE);
mContext.registerReceiverAsUser(mBroadcastReceiver, UserHandle.ALL,
offModeFilter, null, null);
第四、注册sdcard的安装与卸载的广播。
// Register for events related to sdcard installation.
IntentFilter sdFilter = new IntentFilter();
sdFilter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_AVAILABLE);
sdFilter.addAction(Intent.ACTION_EXTERNAL_APPLICATIONS_UNAVAILABLE);
mContext.registerReceiverAsUser(mBroadcastReceiver, UserHandle.ALL,
sdFilter, null, null);
Launcher启动onCreate()方法初始化mAppWidgetManager, mAppWidgetHost对象，AppWidgetHost是launcher承载AppWidgetView的宿主
mAppWidgetHost.startListening，通过
public void onCreate() {
...
// 13 //得到AppWidget管理实例 ： AppWidgetManager , AppWidgetHost , AppWidgetHostView三个类的关系
mAppWidgetManager = AppWidgetManagerCompat.getInstance(this);
mAppWidgetHost = new LauncherAppWidgetHost(this);
// Host启动监听,监听LauncherProvider中的数据改变
mAppWidgetHost.startListening();
...
}
1、初始化AppWidgetHostd对象，创建用于回调的Callbacks服务类IAppWidgetHost.Stub, 绑定服务bindService，得到IAppWidgetService对象，进行launcher和AppWidgetService之间的调用
public AppWidgetHost(Context context, int hostId, InteractionHandler handler, Looper looper) {
mContextOpPackageName = context.getOpPackageName();
mHostId = hostId;
mInteractionHandler = handler;
mHandler = new UpdateHandler(looper);
mCallbacks = new Callbacks(mHandler);
mDisplayMetrics = context.getResources().getDisplayMetrics();
bindService(context);
}
2、在startListening 方法中 ，通过IAppWidgetService.startListening 方法解析Launcher中的AppWidget信息保存到系统服务成员变量中， 3、当添加AppWidget时，首页返回到Launcher中的onActivityResult中，在handleActivityResult中
addAppWidgetImpl(
appWidgetId, requestArgs, null,
requestArgs.getWidgetHandler(),
ON_ACTIVITY_RESULT_ANIMATION_DELAY);
创建添加小部件意图，之后返回到onActivityForResult,调用completeAddAppWidget，通过IAppWidgetService.getAppWidgetInfo,获取AppWidgetProviderInfo,保存到本地数据库中addItemToDatabase()，
@Thunk void completeAddAppWidget(int appWidgetId, ItemInfo itemInfo,
1070 AppWidgetHostView hostView, LauncherAppWidgetProviderInfo appWidgetInfo) {
1071
1072 if (appWidgetInfo == null) {
1073 appWidgetInfo = mAppWidgetManager.getLauncherAppWidgetInfo(appWidgetId);
1074 }
1075
1076 LauncherAppWidgetInfo launcherInfo;
1077 launcherInfo = new LauncherAppWidgetInfo(appWidgetId, appWidgetInfo.provider);
1078 launcherInfo.spanX = itemInfo.spanX;
1079 launcherInfo.spanY = itemInfo.spanY;
1080 launcherInfo.minSpanX = itemInfo.minSpanX;
1081 launcherInfo.minSpanY = itemInfo.minSpanY;
1082 launcherInfo.user = appWidgetInfo.getProfile();
1083
1084 getModelWriter().addItemToDatabase(launcherInfo,
1085 itemInfo.container, itemInfo.screenId, itemInfo.cellX, itemInfo.cellY);
1086
1087 if (hostView == null) {
1088 // Perform actual inflation because we're live
1089 hostView = mAppWidgetHost.createView(this, appWidgetId, appWidgetInfo);
1090 }
1091 hostView.setVisibility(View.VISIBLE);
1092 prepareAppWidget(hostView, launcherInfo);
1093 mWorkspace.addInScreen(hostView, launcherInfo);
1094 }
1095
1096 private void prepareAppWidget(AppWidgetHostView hostView, LauncherAppWidgetInfo item) {
1097 hostView.setTag(item);
// 计算AppWidget的显示大小位置
1098 item.onBindAppWidget(this, hostView);
1099 hostView.setFocusable(true);
1100 hostView.setOnFocusChangeListener(mFocusHandler);
1101 }
并创建AppWidgetHostView 对象，mAppWidgetHost.createView，返回RemoteView对象，IAppWidgetService。getAppWidgetViews（）
public final AppWidgetHostView createView(Context context, int appWidgetId,
AppWidgetProviderInfo appWidget) {
if (sService == null) {
return null;
}
AppWidgetHostView view = onCreateView(context, appWidgetId, appWidget);
view.setInteractionHandler(mInteractionHandler);
view.setAppWidget(appWidgetId, appWidget);
synchronized (mViews) {
mViews.put(appWidgetId, view);
}
RemoteViews views;
try {
views = sService.getAppWidgetViews(mContextOpPackageName, appWidgetId);
} catch (RemoteException e) {
throw new RuntimeException("system server dead?", e);
}
view.updateAppWidget(views);
return view;
}
调用AppWidgetHostView.updateAppWidget(views);更新View到launcher界面上mWorkspace.addInScreen(hostView, launcherInfo);
当AppWidgetProvider获得更新的广播，并执行onUpdate()，onUpdate()中创建了RemoteViews并通过AppWidgetManager.updateAppWidget()更新到AppWidgetService之后，AppWidgetService会通过注册的IAppWidgetHost的回调，执行AppWidgetHost的更新。
