private void performLayout(WindowManager.LayoutParams lp, int desiredWindowWidth,
            int desiredWindowHeight) {
        // 先将当前是否有布局请求的flag设置为false
        mLayoutRequested = false;
       
        mScrollMayChange = true;
        // 将当前正在布局的flag设置为true
        mInLayout = true;
        // 获取decorView
        final View host = mView;
        if (DEBUG_ORIENTATION || DEBUG_LAYOUT) {
            Log.v(TAG, "Laying out " + host + " to (" +
                    host.getMeasuredWidth() + ", " + host.getMeasuredHeight() + ")");
        }

        Trace.traceBegin(Trace.TRACE_TAG_VIEW, "layout");
        try {
        	// 对decorView进行布局
            host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());
			// 将当前正在布局的flag设置为false
            mInLayout = false;
            // 获取当前请求布局的View的个数
            int numViewsRequestingLayout = mLayoutRequesters.size();
            if (numViewsRequestingLayout > 0) {
                // requestLayout() was called during layout.
                // If no layout-request flags are set on the requesting views, there is no problem.
                // If some requests are still pending, then we need to clear those flags and do
                // a full request/measure/layout pass to handle this situation.
                // 获取需要进行布局的View
                ArrayList<View> validLayoutRequesters = getValidLayoutRequesters(mLayoutRequesters,
                        false);
                if (validLayoutRequesters != null) {
                    // Set this flag to indicate that any further requests are happening during
                    // the second pass, which may result in posting those requests to the next
                    // frame instead
                    // 设置正在处理布局请求的flag为true
                    mHandlingLayoutInLayoutRequest = true;

                    // Process fresh layout requests, then measure and layout
                    // 获取需要进行布局的View的个数
                    int numValidRequests = validLayoutRequesters.size();
                    for (int i = 0; i < numValidRequests; ++i) {
                        final View view = validLayoutRequesters.get(i);
                        Log.w("View", "requestLayout() improperly called by " + view +
                                " during layout: running second layout pass");
                        view.requestLayout();
                    }
                    measureHierarchy(host, lp, mView.getContext().getResources(),
                            desiredWindowWidth, desiredWindowHeight);
                    mInLayout = true;
                    host.layout(0, 0, host.getMeasuredWidth(), host.getMeasuredHeight());

                    mHandlingLayoutInLayoutRequest = false;

                    // Check the valid requests again, this time without checking/clearing the
                    // layout flags, since requests happening during the second pass get noop'd
                    validLayoutRequesters = getValidLayoutRequesters(mLayoutRequesters, true);
                    if (validLayoutRequesters != null) {
                        final ArrayList<View> finalRequesters = validLayoutRequesters;
                        // Post second-pass requests to the next frame
                        getRunQueue().post(new Runnable() {
                            @Override
                            public void run() {
                                int numValidRequests = finalRequesters.size();
                                for (int i = 0; i < numValidRequests; ++i) {
                                    final View view = finalRequesters.get(i);
                                    Log.w("View", "requestLayout() improperly called by " + view +
                                            " during second layout pass: posting in next frame");
                                    view.requestLayout();
                                }
                            }
                        });
                    }
                }

            }
        } finally {
            Trace.traceEnd(Trace.TRACE_TAG_VIEW);
        }
        mInLayout = false;
        
    }

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

/**
   * Set the activity content from a layout resource.  The resource will be
   * inflated, adding all top-level views to the activity.
   *
   * @param layoutResID Resource ID to be inflated.
   *
   * @see #setContentView(android.view.View)
   * @see #setContentView(android.view.View, android.view.ViewGroup.LayoutParams)
   */
  public void setContentView(@LayoutRes int layoutResID) {
      getWindow().setContentView(layoutResID);
      initWindowDecorActionBar();
  }

// Window 类下的setContentView()
public abstract void setContentView(View view);

private float mWidth, mHeight;

   /**
    * 在View大小发生变化是会被调用.可以在此函数进行View的大小,位置以及其他相关值的计算
    *
    * @param w    当前View的宽度
    * @param h    当前View的高度
    * @param oldw View改变前的宽度
    * @param oldh View改变前的高度
    */
   @Override
   protected void onSizeChanged(int w, int h, int oldw, int oldh) {
       float xpad = (float)(getPaddingLeft()+getPaddingRight());
       float ypad = (float)(getPaddingTop()+getPaddingBottom());

       mWidth = w-xpad;
       mHeight = h-ypad;

   }