private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
         //創(chuàng)建一個Activity，并調(diào)用生命周期onCreate方法
         Activity a = performLaunchActivity(r, customIntent);
          if (a != null) {
             //如果Activity成功創(chuàng)建，則會調(diào)用生命周期onResume方法。
             handleResumeActivity(r.token, false, r.isForward,
                      !r.activity.mFinished && !r.startsNotResumed);
          }
  }

private Activity performLaunchActivity(ActivityClientRecord r, Intent customIntent) {
          Activity activity = null;
                try {
                    // Instrumentation mInstrumentation;
                    //拿到類加載器，最后會通過反射的方式創(chuàng)建Activity對象
                    //(Activity) cl.loadClass(className).newInstance();
                    java.lang.ClassLoader cl = r.packageInfo.getClassLoader();
                    activity = mInstrumentation.newActivity(
                            cl, component.getClassName(), r.intent);
                } catch (Exception e) {
                    if (!mInstrumentation.onException(activity, e)) {
                        throw new RuntimeException(
                            "Unable to instantiate activity " + component
                            + ": " + e.toString(), e);
                    }
                }
                if(activity!=null){
                //調(diào)用Activity.attach，
                 activity.attach(appContext, this, getInstrumentation(), r.token,
                                        r.ident, app, r.intent, r.activityInfo, title, r.parent,
                                        r.embeddedID, r.lastNonConfigurationInstances, config,
                                        r.voiceInteractor);
                }
                //通過這個方法調(diào)用了Activity的onCreate方法
                if (r.isPersistable()) {
                    mInstrumentation.callActivityOnCreate(activity, r.state, r.persistentState);
                    // activity.performCreate(icicle, persistentState);
                    // onCreate(icicle, persistentState);
                } else {
                    mInstrumentation.callActivityOnCreate(activity, r.state);
                    //activity.performCreate(icicle);
                    // onCreate(icicle);
                }
          return activity;
}

 final void attach(...){
     //初始化了window的子類 初始化了PhoneWindow，PhoneWindow中有一個Decoview對象
     mWindow = new PhoneWindow(this, window, activityConfigCallback);
     mWindow.setWindowManager(
                    (WindowManager)context.getSystemService(Context.WINDOW_SERVICE),
                    mToken, mComponent.flattenToString(),
                    (info.flags & ActivityInfo.FLAG_HARDWARE_ACCELERATED) != 0);
     //mWindowManager 是WindowManagerImpl的實(shí)例。
     mWindowManager = mWindow.getWindowManager();
 }

//getWindow拿到的是PhoneWindow
   public void setContentView(@LayoutRes int layoutResID) {
        getWindow().setContentView(layoutResID);
   }
 @Override
 public void setContentView(int layoutResID) {
    if (mContentParent == null) {
          //初始化Decorview和mContentParent
          installDecor();
      }
    //加載并解析傳進(jìn)來的布局文件，并add到mContentParent上。
    //這個操作比較耗時，因?yàn)橐獜膞ml文件中解析，然后再通過反射的方式生成Java中的View對象。
    //所以在recyclerView和listView中要對這一步進(jìn)行緩存優(yōu)化，
    mLayoutInflater.inflate(layoutResID, mContentParent);
 }

//mDecorView是PhoneWindow的一個成員變量
private DecorView mDecor;
private void installDecor() {
     //創(chuàng)建mDecor
     if (mDecor == null) {
         mDecor = generateDecor(-1);
		  //new DecorView(context, featureId, this, getAttributes());
     }
    //創(chuàng)建mContentParent,將創(chuàng)建的DecorView作為參數(shù)傳遞
     if (mContentParent == null) {
         mContentParent = generateLayout(mDecor);
     }
}

 protected ViewGroup generateLayout(DecorView decor) {
        int layoutResource;
        //這個布局文件就在android.jar--res--layout目錄下。
        layoutResource = R.layout.screen_simple;
        mDecor.onResourcesLoaded(mLayoutInflater, layoutResource);
       // int ID_ANDROID_CONTENT = com.android.internal.R.id.content;
       //這個R.id.content就是定義在screen_simple中的一個FrameLayout
       //  android:id="@android:id/content"
        ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
        ....
        return contentParent;
  }
   //將布局R.layout.screen_simple 加載成view，并添加到DecorView中
  void onResourcesLoaded(LayoutInflater inflater, int layoutResource) {
        ......
         final View root = inflater.inflate(layoutResource, null);
        ......
        // Put it below the color views.
         addView(root, 0, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
  }

//R.layout.screen_simple
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:fitsSystemWindows="true"
     android:orientation="vertical">
     <ViewStub android:id="@+id/action_mode_bar_stub"
               android:inflatedId="@+id/action_mode_bar"
               android:layout="@layout/action_mode_bar"
               android:layout_width="match_parent"
               android:layout_height="wrap_content"
               android:theme="?attr/actionBarTheme" />
     <FrameLayout
          android:id="@android:id/content"
          android:layout_width="match_parent"
          android:layout_height="match_parent"
          android:foregroundInsidePadding="false"
          android:foregroundGravity="fill_horizontal|top"
          android:foreground="?android:attr/windowContentOverlay" />
 </LinearLayout>

  //加載并解析傳進(jìn)來的布局文件，并add到mContentParent上。
    mLayoutInflater.inflate(layoutResID, mContentParent);
  public View inflate(@LayoutRes int resource, @Nullable ViewGroup root) {
         return inflate(resource, root, root != null);
   }
   public View inflate(@LayoutRes int resource, @Nullable ViewGroup root, boolean attachToRoot) {
       final Resources res = getContext().getResources();
        //通過 Resource 得到了一個XML解析器。
       final XmlResourceParser parser = res.getLayout(resource);
       try {
           //解析我們自定義的layout，并添加到mParentContent上。
           //將xml中定義的ViewGroup和View解析成Java對象。
           //這塊代碼會單獨(dú)寫文章講解
           return inflate(parser, root, attachToRoot);
       } finally {
           parser.close();
       }
   }

   private void handleLaunchActivity(ActivityClientRecord r, Intent customIntent) {
           //創(chuàng)建一個Activity，并調(diào)用生命周期onCreate方法
           Activity a = performLaunchActivity(r, customIntent);
            if (a != null) {
               //如果Activity成功創(chuàng)建，則會調(diào)用生命周期onResume方法。
               handleResumeActivity(r.token, false, r.isForward,
                        !r.activity.mFinished && !r.startsNotResumed);
            }
   }
  final void handleResumeActivity(IBinder token,
               boolean clearHide, boolean isForward, boolean reallyResume) {
    //執(zhí)行Activity onResume生命周期方法
   ActivityClientRecord r = performResumeActivity(token, clearHide);
    if(r!=null){
                final Activity a = r.activity;
                //通過上面代碼我們知道 window 是PhoneWindow
                r.window = r.activity.getWindow();
                //拿到DecorView
                View decor = r.window.getDecorView();
                //wm 是 WindowManagerImpl
                ViewManager wm = a.getWindowManager();
                   if (a.mVisibleFromClient) {
                         a.mWindowAdded = true;
                         //關(guān)鍵代碼，將decorView 添加到wm中
                         wm.addView(decor, l);
                   }
           }
 }
 public final ActivityClientRecord performResumeActivity(IBinder token,
             boolean clearHide) {
        //執(zhí)行Activity onStart onResume方法
        ActivityClientRecord r = mActivities.get(token);
        r.activity.performResume();
     return r;
}

//Activity中 onStart onResume 生命周期方法
 final void performResume(boolean followedByPause, String reason) {
         performRestart(true /* start */, reason);
         mInstrumentation.callActivityOnResume(this);
 }
  final void performRestart(boolean start, String reason) {
     if (start) {
         performStart(reason);
      }
  }
public void callActivityOnResume(Activity activity) {
     activity.mResumed = true;
     activity.onResume();
}

//WindowManagerImpl.java addView 方法
//WindowManagerGlobal 是一個單例模式，在ActivityThread 主進(jìn)程中 只有一個實(shí)例。
 private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();
    @Override
    public void addView(View view, ViewGroup.LayoutParams params) {
        mGlobal.addView(view, params, mDisplay, mParentWindow);
 }
WindowManagerGlobal.java
private final ArrayList<View> mViews = new ArrayList<View>();
private final ArrayList<ViewRootImpl> mRoots = new ArrayList<ViewRootImpl>();
private final ArrayList<WindowManager.LayoutParams> mParams = new ArrayList<WindowManager.LayoutParams>();
public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
       final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;
         ViewRootImpl root;
            ........
              root = new ViewRootImpl(view.getContext(), display);
            .........
           view.setLayoutParams(wparams);
         //將decorView ViewRootImpl 存到集合中
         mViews.add(view);
         mRoots.add(root);
         mParams.add(wparams);
         root.setView(view, wparams, panelParentView);
}

ViewRootImpl.java
  public ViewRootImpl(Context context, Display display) {
        mWindowSession = WindowManagerGlobal.getWindowSession();
        mThread = Thread.currentThread();
  }
 public void setView(View view, WindowManager.LayoutParams attrs, View panelParentView) {
      // Schedule the first layout -before- adding to the windowmanager,
        //to make sure we do the relayout before receiving
        // any other events from the system.
       //在添加到windowmanager之前進(jìn)行布局，確保在收到系統(tǒng)的event之前進(jìn)行relayout
       // 出發(fā)布局的繪制流程，measure，layout，view 的繪制流程，就是從這來的。
       //這個方法保證了，在添加的屏幕前已經(jīng)完成了測量、繪制。
        requestLayout();
        try {
            //通過binder和WindowManagerService進(jìn)行通信，將view添加到屏幕上。
            // mWindow = new W(this);
            // static class W extends IWindow.Stub {}
            //添加到屏幕的邏輯，稍后寫文章詳細(xì)分析。
             res = mWindowSession.addToDisplay(mWindow, mSeq, mWindowAttributes,
                                        getHostVisibility(), mDisplay.getDisplayId(),
                                        mAttachInfo.mContentInsets, mInputChannel);
        }catch (RemoteException e) {
            throw new RuntimeException("Adding window failed", e);
        }
 }

 public void requestLayout() {
     if (!mHandlingLayoutInLayoutRequest) {
         checkThread();
         mLayoutRequested = true;
         scheduleTraversals();
     }
 }

//mThread是在ViewRootImp初始初始化是所在的線程。
//在requestLayout時，會獲取當(dāng)前請求布局的線程。
//如果兩個線程不一致就會拋異常，只有原始創(chuàng)建的線程，可以修改views
  void checkThread() {
         if (mThread != Thread.currentThread()) {
             throw new CalledFromWrongThreadException(
                     "Only the original thread that created a view hierarchy can touch its views.");
         }
     }

 //開始遍歷
 void scheduleTraversals() {
   if (!mTraversalScheduled) {
     mTraversalScheduled = true;
        //發(fā)送一個同步消息，在handler機(jī)制分析中提過一下，同步屏障。關(guān)于這個知識點(diǎn)還會做詳細(xì)的分析。
            mTraversalBarrier = mHandler.getLooper().postSyncBarrier();
            //mChoreographer 編舞者類。
            //通過編舞者，執(zhí)行 runnable中 doTraversal 方法
            mChoreographer.postCallback(
                 Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
   }
 }

final class TraversalRunnable implements Runnable {
           @Override
           public void run() {
               doTraversal();
           }
    }
void doTraversal() {
        if (mTraversalScheduled) {
            mTraversalScheduled = false;
            mHandler.getLooper().removeSyncBarrier(mTraversalBarrier);
            performTraversals();
        }
  }

 private void performTraversals() {
       //mView DecorView
       final View host = mView;
      // Ask host how big it wants to be
       performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
        if (didLayout) {
          performLayout(lp, desiredWindowWidth, desiredWindowHeight);
       }
      performDraw();
}

 private void performMeasure(int childWidthMeasureSpec, int childHeightMeasureSpec) {
         mView.measure(childWidthMeasureSpec, childHeightMeasureSpec);
  }
   private void performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth,
              int desiredWindowHeight) {
        final View host = mView;
         host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());
  }
   private void performDraw() {
       draw(fullRedrawNeeded);
       //
  }