Android View 源码解析(一) - setContentView

  // This is the view in which the window contents are placed. It is either
  // mDecor itself, or a child of mDecor where the contents go.
  private ViewGroup mContentParent;

  @Override
  public 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.
      if (mContentParent == null) {
          //第一次调用
          //下面会详细分析
          installDecor();
      } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
          //移除该mContentParent下的所有View
          //又因为这个的存在  我们可以多次使用setContentView()
          mContentParent.removeAllViews();
      }
      //判断是否使用了Activity的过度动画
      if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
        //设置动画场景
          final Scene newScene = Scene.getSceneForLayout(mContentParent, layoutResID,
                  getContext());
          transitionTo(newScene);
      } else {
          //将资源文件通过LayoutInflater对象装换为View树
          //在PhoneWindow的构造函数中 mLayoutInflater = LayoutInflater.from(context);
          mLayoutInflater.inflate(layoutResID, mContentParent);
      }

      //View中
      /**
       * Ask that a new dispatch of {@link #onApplyWindowInsets(WindowInsets)} be performed.
       */
      // public void requestApplyInsets() {
      //     requestFitSystemWindows();
      // }
      mContentParent.requestApplyInsets();
      final Callback cb = getCallback();
      if (cb != null && !isDestroyed()) {
          cb.onContentChanged();
      }
  }

  @Override
  public void setContentView(View view) {
      setContentView(view, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
  }

  @Override
  public void setContentView(View view, ViewGroup.LayoutParams params) {
      if (mContentParent == null) {
          installDecor();
      } else if (!hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
          mContentParent.removeAllViews();
      }

      if (hasFeature(FEATURE_CONTENT_TRANSITIONS)) {
          view.setLayoutParams(params);
          final Scene newScene = new Scene(mContentParent, view);
          transitionTo(newScene);
      } else {
        //已经为View 直接使用View的addView方法追加到当前mContentParent中
          mContentParent.addView(view, params);
      }
      mContentParent.requestApplyInsets();
      final Callback cb = getCallback();
      //调用CallBack接口的onContentChange来通知Activity组件视图发生了变化
      if (cb != null && !isDestroyed()) {
          cb.onContentChanged();
      }
  }

  //截取部分主要分析代码
  private void installDecor() {
      if (mDecor == null) {
          //如果mDecor为空则创建一个DecorView实例
          // protected DecorView generateDecor() {
          //   return new DecorView(getContext(), -1);
          // }
          mDecor = generateDecor();  
          mDecor.setDescendantFocusability(ViewGroup.FOCUS_AFTER_DESCENDANTS);
          mDecor.setIsRootNamespace(true);
          if (!mInvalidatePanelMenuPosted && mInvalidatePanelMenuFeatures != 0) {
              mDecor.postOnAnimation(mInvalidatePanelMenuRunnable);
          }
      }
      if (mContentParent == null) {
          //根据窗口的风格修饰 选择对应的修饰布局文件 将id为content的FrameLayout赋值于mContentParent
          mContentParent = generateLayout(mDecor);
          ...
        }
  }

  protected ViewGroup generateLayout(DecorView decor) {
       // Apply data from current theme.
       //根据当前style修饰相应样式

       TypedArray a = getWindowStyle();

       ...
       //一堆if判断

       // 增加窗口修饰

       int layoutResource;
       int features = getLocalFeatures();

       ...
       //根据features选择不同的窗帘修饰布局文件得到
       //把选中的窗口修饰布局文件添加到DecorView中, 指定contentParent的值
       View in = mLayoutInflater.inflate(layoutResource, null);
       decor.addView(in, new ViewGroup.LayoutParams(MATCH_PARENT, MATCH_PARENT));
       mContentRoot = (ViewGroup) in;

       ViewGroup contentParent = (ViewGroup)findViewById(ID_ANDROID_CONTENT);
       if (contentParent == null) {
           throw new RuntimeException("Window couldn't find content container view");
       }

       ...
       return contentParent;
   }

  public boolean requestFeature(int featureId) {
      if (mContentParent != null) {
          throw new AndroidRuntimeException("requestFeature() must be called before adding content");
      }
      ...
  }

  /**
   * Return the current Callback interface for this window.
   */
  public final Callback getCallback() {
      return mCallback;
  }

  /**
   * Set the Callback interface for this window, used to intercept key
   * events and other dynamic operations in the window.
   *
   * @param callback The desired Callback interface.
   */
  public void setCallback(Callback callback) {
      mCallback = callback;
  }

  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, String referrer, IVoiceInteractor voiceInteractor) {
        ...
        mWindow.setCallback(this);
        ...
  }

  public void onContentChanged() {
  }

  final void handleResumeActivity(IBinder token,
             boolean clearHide, boolean isForward, boolean reallyResume) {
               ...
             if (!r.activity.mFinished && willBeVisible
                     && r.activity.mDecor != null && !r.hideForNow) {
                 ...
                 if (r.activity.mVisibleFromClient) {
                     r.activity.makeVisible();
                     //这里这里 通过调用Activity的makeVisible方法来显示我们通过setContentView创建的mDecor
                 }
                 ...
             }
         } else {
           ...
         }
     }

  //Activity的makeVisible方法
  void makeVisible() {
       if (!mWindowAdded) {
           ViewManager wm = getWindowManager();
           wm.addView(mDecor, getWindow().getAttributes());
           mWindowAdded = true;
       }
       mDecor.setVisibility(View.VISIBLE);
   }