流程圖

（大體流程矛市，從Activity接受啟動開始）

源碼分析

基于API 23

Window創(chuàng)建

ActivityThread.handleLaunchActivity

ActivityThread.performLaunchActivity

ActivityThread處理并執(zhí)行Activity啟動

//ActivityThread
private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
    ...
    //獲取WindowManagerService的Binder引用(proxy端)拗秘。
    WindowManagerGlobal.initialize();

    //執(zhí)行Activity的onCreate,onStart,onResotreInstanceState方法
    Activity a = performLaunchActivity(r, customIntent);
    if (a != null) {
        ...
        //執(zhí)行Activity的onResume方法.
        handleResumeActivity(r.token, false, r.isForward,
                !r.activity.mFinished && !r.startsNotResumed, r.lastProcessedSeq, reason);

        ...
    } 

}


private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {

   //通過類加載器創(chuàng)建Activity
   Activity activity = mInstrumentation.newActivity(cl, component.getClassName(), r.intent);

   ...      

   //通過LoadedApk的makeApplication方法來創(chuàng)建Application對象
   Application app = r.packageInfo.makeApplication(false, mInstrumentation);


   if (activity != null) {
       ...
       // 執(zhí)行 attach 方法
       activity.attach(appContext, this, getInstrumentation(), r.token,
               r.ident, app, r.intent, r.activityInfo, title, r.parent,
               r.embeddedID, r.lastNonConfigurationInstances, config,
               r.referrer, r.voiceInteractor, window);
       ...

       //onCreate
       mInstrumentation.callActivityOnCreate(activity, r.state);

       //onStart
       activity.performStart();

   }
   return activity;
}

Activity.attach

• 構(gòu)造PhoneWindow （Window唯一具體實現(xiàn)）
• 設(shè)置自身為Window的Callback秒紧，從而Activity能作為callback接受window的key和touch事件
• 初始化且設(shè)置WindowManager交排，每個Activity對應(yīng)一個WindowManager盛撑，通過WM與WMS進行通信

final void attach(...) {
    //綁定上下文
    attachBaseContext(context);
    
    //創(chuàng)建Window,PhoneWindow是Window的唯一具體實現(xiàn)類
    mWindow = new PhoneWindow(this, window);//此處的window==null植阴，但不影響
    mWindow.setWindowControllerCallback(this);
    // 設(shè)置 Window.Callback
    mWindow.setCallback(this);
    ...
    //設(shè)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());
    }
    //創(chuàng)建完后通過getWindowManager就可以得到WindowManager實例
    mWindowManager = mWindow.getWindowManager();//其實它是WindowManagerImpl

}

Window添加View過程

前面在handleLauncherActivity完成了PhoneWindow的創(chuàng)建過程涧卵，下面我們繼續(xù)查看Activity執(zhí)行生命周期handleResumeActivity方法勤家，查看Activity對應(yīng)View被加載到PhoneWindow容器過程

ActivityThread.handleResumeActivity

• 獲取ActivityClientRecord，將對應(yīng)DecorView設(shè)置為不可見柳恐，因為當(dāng)前View還未繪制
• 通過Window對應(yīng)的WindowManager執(zhí)行addView（decor伐脖，l）操作
• View繪制完成后，會將decorView設(shè)置可見乐设，展示該Activity對應(yīng)內(nèi)容讼庇，最后onResume完成

final void handleResumeActivity(IBinder token,
            boolean clearHide, boolean isForward, boolean reallyResume, int seq, String reason) {

   //把activity數(shù)據(jù)記錄更新到ActivityClientRecord
   ActivityClientRecord r = performResumeActivity(token, clearHide);

   if (r != null) {

       if (r.window == null && !a.mFinished && willBeVisible) {
           r.window = r.activity.getWindow();
           View decor = r.window.getDecorView();
           decor.setVisibility(View.INVISIBLE);//不可見
           ViewManager wm = a.getWindowManager();
           WindowManager.LayoutParams l = r.window.getAttributes();
           a.mDecor = decor;
           l.type = WindowManager.LayoutParams.TYPE_BASE_APPLICATION;

           ...
           if (a.mVisibleFromClient && !a.mWindowAdded) {
               a.mWindowAdded = true;
               wm.addView(decor, l);// 把decor添加到窗口上
           }

       } 
           //屏幕參數(shù)發(fā)生了改變
           performConfigurationChanged(r.activity, r.tmpConfig);

           WindowManager.LayoutParams l = r.window.getAttributes();

               if (r.activity.mVisibleFromClient) {
                   ViewManager wm = a.getWindowManager();
                   View decor = r.window.getDecorView();
                   wm.updateViewLayout(decor, l);//更新窗口狀態(tài)
               }


           ...
           if (r.activity.mVisibleFromClient) {
               //已經(jīng)成功添加到窗口上了（繪制和事件接收），設(shè)置為可見
               r.activity.makeVisible();
           }


       //通知ActivityManagerService伤提，Activity完成Resumed
        ActivityManagerNative.getDefault().activityResumed(token);
   } 

}

WindowManagerImply.addView

WindowManagerGlobal.addView

• WindowManagerImpl的全局變量通過單例模式初始化了WindowManagerGlobal巫俺，（一個進程一個WMG對象）
• Window管理類添加View過程，創(chuàng)建ViewRootImpl肿男，將View處理操作交給ViewRootImpl實現(xiàn)

// WindowManagerImply
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
    applyDefaultToken(params);
    mGlobal.addView(view, params, mDisplay, mParentWindow);
}

// WindowManagerGlobal
public void addView(View view, ViewGroup.LayoutParams params,
           Display display, Window parentWindow) {
     
    synchronized (mLock) { 
        ...
        // 創(chuàng)建ViewRootImpl介汹，并將View與之綁定
        root = new ViewRootImpl(view.getContext(), display);
        
        view.setLayoutParams(wparams);
        
        mViews.add(view); // 將當(dāng)前view添加到mView集合中
        mRoots.add(root); // 將當(dāng)前root添加mRoots集合中
        mParams.add(wparams); // 將當(dāng)前window的params添加到mParams集合中
    }
    
    // setView 完成View的繪制流程却嗡，并添加到window上 
    root.setView(view, wparams, panelParentView);
   
}

ViewRootImpl.setView

• ViewRootImpl構(gòu)建過程中，會通過WindowManagerGlobal的getWindowSession（static方法）獲取IWindowSession即WindowSession
• 執(zhí)行requestLayout方法完成View的繪制流程
• 通過WindowSession與WindowManagerService通信嘹承，將View和InputChannel添加到WMS窗价，從而展示View并可以接受輸入事件

public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {

      ...
      int res
      requestLayout();//執(zhí)行 View的繪制流程

      if ((mWindowAttributes.inputFeatures
              & WindowManager.LayoutParams.INPUT_FEATURE_NO_INPUT_CHANNEL) == 0) {
          // 創(chuàng)建InputChannel
          mInputChannel = new InputChannel();
      }

      try {

          //通過WindowSession進行IPC調(diào)用，將View添加到Window上
          //mWindow即W類叹卷，用來接收WmS信息
          //同時通過InputChannel接收觸摸事件回調(diào)
          res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                  getHostVisibility(), mDisplay.getDisplayId(),
                  mAttachInfo.mContentInsets, mAttachInfo.mStableInsets,
                  mAttachInfo.mOutsets, mInputChannel);
      }

      ...

      //處理觸摸事件回調(diào)
      mInputEventReceiver = new WindowInputEventReceiver(mInputChannel,
                  Looper.myLooper());

}

WindowSession.addToDisplay

• Session執(zhí)行addToDisplay方法撼港，通過調(diào)用成員變量WMS進行addWindow操作

public int addToDisplay(...) {
   return mService.addWindow(this, window, seq, attrs, viewVisibility, displayId,
           outContentInsets, outStableInsets, outOutsets, outInputChannel);

}

WindowManagerService.addWindow

• 創(chuàng)建WindowState，保存Window狀態(tài)
• 調(diào)整LayoutParams參數(shù)骤竹、設(shè)置input帝牡、設(shè)置window zOrder
• 執(zhí)行WindowState的attach（創(chuàng)建Surface過程，詳情見下一篇）

public int addWindow(Session session, IWindow client, int seq,
       WindowManager.LayoutParams attrs, int viewVisibility, int displayId,
       Rect outContentInsets, Rect outStableInsets, Rect outOutsets,InputChannel outInputChannel) {
   
    ... // 一堆check邏輯

    WindowToken token = mTokenMap.get(attrs.token);
    //創(chuàng)建 WindowState
    WindowState win = new WindowState(this, session, client, token,
          attachedWindow, appOp[0], seq, attrs, viewVisibility, displayContent);
    ...

    //調(diào)整 WindowManager 的 LayoutParams 參數(shù)
    mPolicy.adjustWindowParamsLw(win.mAttrs);
    res = mPolicy.prepareAddWindowLw(win, attrs);
    addWindowToListInOrderLocked(win, true);

    // 設(shè)置 input
    mInputManager.registerInputChannel(win.mInputChannel, win.mInputWindowHandle);

    // 創(chuàng)建 Surface 與 SurfaceFlinger 通信蒙揣，
    win.attach();
    mWindowMap.put(client.asBinder(), win);
        
    if (win.canReceiveKeys()) {
    //當(dāng)該窗口能接收按鍵事件靶溜，則更新聚焦窗口
    focusChanged = updateFocusedWindowLocked(UPDATE_FOCUS_WILL_ASSIGN_LAYERS,
          false /*updateInputWindows*/);
    }
    assignLayersLocked(displayContent.getWindowList());

    ...

}

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參考
Android Window 機制探索