Activity的啟動最終會通過ActivityThread#performLaunchActivity()來完成。
ActivityThread#performLaunchActivity()
PRivate Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) { //... //通過類加載器創建Activity實例 java.lang.ClassLoader cl = r.packageInfo.getClassLoader(); activity = mInstrumentation.newActivity( cl, component.getClassName(), r.intent); //... application app = r.packageInfo.makeApplication(false, mInstrumentation); Context appContext = createBaseContextForActivity(r, activity); CharSequence title = r.activityInfo.loadLabel(appContext.getPackageManager()); Configuration config = new Configuration(mCompatConfiguration); //關聯運行過程中所依賴的一系列上下文環境變量 activity.attach(appContext, this, getInstrumentation(), r.token, r.ident, app, r.intent, r.activityInfo, title, r.parent, r.embeddedID, r.lastNonConfigurationInstances, config, r.voiceInteractor); mActivities.put(r.token, r); return activity;}在attach方法里，系統會創建Activity所屬的Window對象并為其設置回調接口。
Activity#attach()
final void attach(Context context, ActivityThread aThread, Instrumentation instr, IBinder token, int ident, Application application, Intent intent, ActivityInfo info, CharSequence title, Activity parent, String id, NonConfigurationInstances lastNonConfigurationInstances, Configuration config, IVoiceInteractor voiceInteractor) { attachBaseContext(context); mFragments.attachActivity(this, mContainer, null); //創建Window對象 mWindow = PolicyManager.makeNewWindow(this); //設置回調 比如我們熟悉的onAttachedToWindow、onDetachedFromWindow、dispatchTouchEvent //[重要] 當Window接收到外界的狀態改變時就會調用Activity實現的回調 mWindow.setCallback(this); mWindow.setOnWindowDismissedCallback(this); //賦值 if (info.softInputMode != WindowManager.LayoutParams.SOFT_INPUT_STATE_UNSPECIFIED) { mWindow.setSoftInputMode(info.softInputMode); } if (info.uiOptions != 0) { mWindow.setUiOptions(info.uiOptions); } mUiThread = Thread.currentThread(); mMainThread = aThread; mInstrumentation = instr; mToken = token; mIdent = ident; mApplication = application; mIntent = intent; mComponent = intent.getComponent(); mActivityInfo = info; mTitle = title; mParent = parent; mEmbeddedID = id; mLastNonConfigurationInstances = lastNonConfigurationInstances; //... //設置WindowManager mWindow.setWindowManager( (WindowManager)context.getSystemService(Context.WINDOW_SERVICE), mToken, mComponent.flattenToString(), (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0); if (mParent != null) { mWindow.setContainer(mParent.getWindow()); } mWindowManager = mWindow.getWindowManager(); mCurrentConfig = config;}再來看 PolicyManager.makeNewWindow(this)，PilicyManager的真正實現類是Policy類。 位于source/frameworks/base/policy/src/com/android/internal/policy/impl/Policy.java
public Window makeNewWindow(Context context) { return new PhoneWindow(context);}可以發現Window的實現類確實是PhoneWindow。
Window初始完畢后，再來看Activity的視圖是如何依附在Window上的。Activity的視圖通過setContent方法提供。
public void setContentView(int layoutResID) { getWindow().setContentView(layoutResID); initWindowDecorActionBar();}可以發現，Activity的setContentView將具體實現交由Window處理。
phoneWindow#setContentView()
@Overridepublic void setContentView(int layoutResID) { // Note: FEATURE_CONTENT_TRANSITIONS may be set in the process of installing the window // decor, when theme attributes and the like are crystalized. Do not check the feature // before this happens. //1.創建DecorView (如果沒有創建的話) if (mContentParent == null) { installDecor(); } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) { mContentParent.removeAllViews(); } if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) { final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID, getContext()); transitionTo(newScene); //2.將View添加到DecorView的mContentParent中 mLayoutInflater.inflate(layoutResID, mContentParent); } //3.回調Activity的onContentChanged()通知Activity視圖已經發生改變 final Callback cb = getCallback(); if (cb != null && !isDestroyed()) { cb.onContentChanged(); }}經過setContentView方法，DecorView已經被創建并初始化完畢，Activity的布局文件也已經成功添加到DecorView的mContentParent中，但這個時候DecorView還沒有被WindowManager添加到Window中。 (在添加之前)
Dialog的Window創建過程和Activity類似
Dialog#構造方法
Dialog(Context context, int theme, boolean createContextThemeWrapper) { //... mContext = context; mWindowManager = (WindowManager)context.getSystemService(Context.WINDOW_SERVICE); //創建Window對象 Window w = PolicyManager.makeNewWindow(mContext); mWindow = w; w.setCallback(this); w.setOnWindowDismissedCallback(this); w.setWindowManager(mWindowManager, null, null); w.setGravity(Gravity.CENTER); mListenersHandler = new ListenersHandler(this);}再來看Dialog#setContentView()
public void setContentView(int layoutResID) { mWindow.setContentView(layoutResID);}同樣是交由Window處理。
當Dialog dismiss時，會通過WindowManager來移除DecorView
@Overridepublic void dismiss() { if (Looper.myLooper() == mHandler.getLooper()) { dismissDialog(); } else { mHandler.post(mDismissAction); }}void dismissDialog() { //... //移除DecorView mWindowManager.removeViewImmediate(mDecor); //...}普通Dialog需要使用Activity的Content 因為Window需要應用token，而應用token一般只有Activity才擁有。 系統Window比較特殊，它可以不需要token。
Toast屬于系統Window Toast內部有兩類ipC過程
Toast訪問NotifationManagerServiceNotificationManagerService回調Toast的TN接口Toast提供了show和cancel分別用于顯示和隱藏Toast [都是IPC過程]
public void show() { if (mNextView == null) { throw new RuntimeException("setView must have been called"); } INotificationManager service = getService(); String pkg = mContext.getOpPackageName(); TN tn = mTN; tn.mNextView = mNextView; try { service.enqueueToast(pkg, tn, mDuration); } catch (RemoteException e) { // Empty }} public void cancel() { mTN.hide(); try { getService().cancelToast(mContext.getPackageName(), mTN); } catch (RemoteException e) { // Empty }}主要來看enqueueToast()
//參數一:當前應用的包名//參數二:遠程回調//參數三:Toast的時長//enqueueToast首先將Toast封裝為ToastRecord對象并將其添加到一個名為mToastQueue的隊列中service.enqueueToast(pkg, tn, mDuration);當ToastRecord被添加到mToastQueue中后，Inotifacationmanager就會通過showNextToastLacked方法來顯示當前的Toast。
NotificationManagerService#showNextToastLocked()
void showNextToastLocked() { //獲取下一個ToastRecord ToastRecord record = mToastQueue.get(0); while (record != null) { if (DBG) Slog.d(TAG, "Show pkg=" + record.pkg + " callback=" + record.callback); try { //record.callback就是Toast.java類中的TN (Binder) 對象 record.callback.show(); //發送延遲消息來移除toast //scheduleTimeoutLocked -> mHandler.sendMessageDelayed -> cancelToastLocked -> record.callback.hide(); scheduleTimeoutLocked(record); return; } catch (RemoteException e) { Slog.w(TAG, "Object died trying to show notification " + record.callback + " in package " + record.pkg); // remove it from the list and let the process die int index = mToastQueue.indexOf(record); if (index >= 0) { mToastQueue.remove(index); } keepProcessAliveLocked(record.pid); if (mToastQueue.size() > 0) { record = mToastQueue.get(0); } else { record = null; } } }}可以發現，Toast的顯示和移除都是通過Toast的TN類(Binder對象)來完成的。
Toast內部類TN
private static class TN extends ITransientNotification.Stub { final Runnable mShow = new Runnable() { @Override public void run() { handleShow(); } }; final Runnable mHide = new Runnable() { @Override public void run() { handleHide(); // Don't do this in handleHide() because it is also invoked by handleShow() mNextView = null; } }; @Override public void show() { if (localLOGV) Log.v(TAG, "SHOW: " + this); mHandler.post(mShow); } @Override public void hide() { if (localLOGV) Log.v(TAG, "HIDE: " + this); mHandler.post(mHide); } //...}真正的顯示
public void handleShow() { //... mWM = (WindowManager)context.getSystemService //... if (mView.getParent() != null) { mWM.removeView(mView); } mWM.addView(mView, mParams); //... }}真正的隱藏
public void handleHide() { if (mView != null) { if (mView.getParent() != null) { mWM.removeView(mView); } mView = null; }}PhoneWindow偽代碼
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