Android View的刷新机制

在Android的布局体系中，父View负责刷新、布局显示子View；而当子View需要刷新时，则是通知父View来完成。这种处理逻辑在View的代码中明确的表现出来：

 public void invalidate() {

     final ViewParent p = mParent;

     final AttachInfo ai = mAttachInfo;

     if (p != null && ai != null) {

         final Rect r = ai.mTmpInvalRect;

  

         // 设置刷新区域为自己的尺寸

         r.set(0, 0, mRight - mLeft, mBottom - mTop);

         p.invalidateChild(this, r);

     }

 }

 

子View调用invalidate时，首先找到自己父View(View的成员变量mParent记录自己的父View)，然后将AttachInfo中保存的信息告诉父View刷新自己。

View的父子关系的建立分为两种情况：

1) View加入ViewGroup中

 private void addViewInner(View child, int index, LayoutParams params, booleanpreventRequestLayout) {

  

         .....

  

             // tell our children

         if (preventRequestLayout) {

             child.assignParent(this);

         } else {

             child.mParent = this;

         }

  

        .....

  

 }

 

2)DecorView注册给WindowManagerImpl时，产生一个ViewRoot作为其父View。

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

  

     .....

  

     view.assignParent(this);

  

     ....

  

 }

 

AttachInfo是在View第一次attach到Window时，ViewRoot传给自己的子View的。这个AttachInfo之后，会顺着布局体系一直传递到最底层的View。

View.java

 void dispatchAttachedToWindow(AttachInfo info, int visibility) {

     mAttachInfo = info;

  

     .....

 }

 

ViewGroup.java

 void dispatchAttachedToWindow(AttachInfo info, int visibility) {

     super.dispatchAttachedToWindow(info, visibility);

  

     for (int i = 0; i < count; i++) {

         children[i].dispatchAttachedToWindow(info, visibility);

     }

 }

 

并且在新的View被加入ViewGroup时，也会将该AttachInfo传给加入的View

ViewGroup.java

 private void addViewInner(View child, int index, LayoutParams params, booleanpreventRequestLayout) {

  

     child.dispatchAttachedToWindow(mAttachInfo, (mViewFlags&VISIBILITY_MASK));

  

 }

 

到这里明白了mParent与AttachInfo代表的意义，可以继续刷新过程的分析。

在invalidate中，调用父View的invalidateChild，这是一个从第向上回溯的过程，每一层的父View都将自己的显示区域与传入的刷新Rect做交集。

 public final void invalidateChild(View child, final Rect dirty) {

     ViewParent parent = this;

  

     final AttachInfo attachInfo = mAttachInfo;

     if (attachInfo != null) {

         final int[] location = attachInfo.mInvalidateChildLocation;

  

         // 需要刷新的子View的位置

         location[CHILD_LEFT_INDEX] = child.mLeft;

         location[CHILD_TOP_INDEX] = child.mTop;

  

         // If the child is drawing an animation, we want to copy this flag onto

         // ourselves and the parent to make sure the invalidate request goes through

         final boolean drawAnimation = (child.mPrivateFlags & DRAW_ANIMATION) == DRAW_ANIMATION;

  

         // Check whether the child that requests the invalidate is fully opaque

         final boolean isOpaque = child.isOpaque() && !drawAnimation && child.getAnimation() != null;

  

         // Mark the child as dirty, using the appropriate flag

         // Make sure we do not set both flags at the same time

         final int opaqueFlag = isOpaque ? DIRTY_OPAQUE : DIRTY;

  

         do {

             View view = null;

             if (parent instanceof View) {

                 view = (View) parent;

             }

  

             if (drawAnimation) {

                 if (view != null) {

                         view.mPrivateFlags |= DRAW_ANIMATION;

                 } else if (parent instanceof ViewRoot) {

                         ((ViewRoot) parent).mIsAnimating = true;

                 }

             }

  

                 // If the parent is dirty opaque or not dirty, mark it dirty with the opaque

                 // flag coming from the child that initiated the invalidate

             if (view != null && (view.mPrivateFlags & DIRTY_MASK) != DIRTY) {

                 view.mPrivateFlags = (view.mPrivateFlags & ~DIRTY_MASK) | opaqueFlag;

             }

  

             parent = parent.invalidateChildInParent(location, dirty);

         } while (parent != null);

     }

 }

  

  

  

 public ViewParent invalidateChildInParent(final int[] location, final Rect dirty) {

     if ((mPrivateFlags & DRAWN) == DRAWN) {

         if ((mGroupFlags & (FLAG_OPTIMIZE_INVALIDATE | FLAG_ANIMATION_DONE)) !=

                         FLAG_OPTIMIZE_INVALIDATE) {

  

             // 根据父View的位置，偏移刷新区域

             dirty.offset(location[CHILD_LEFT_INDEX] - mScrollX, location[CHILD_TOP_INDEX] - mScrollY);

  

             final int left = mLeft;

             final int top = mTop;

  

             //计算实际可刷新区域

             if (dirty.intersect(0, 0, mRight - left, mBottom - top) ||

                         (mPrivateFlags & DRAW_ANIMATION) == DRAW_ANIMATION) {

                 mPrivateFlags &= ~DRAWING_CACHE_VALID;

  

                 location[CHILD_LEFT_INDEX] = left;

                 location[CHILD_TOP_INDEX] = top;

                 return mParent;

             }

         } else {

             mPrivateFlags &= ~DRAWN & ~DRAWING_CACHE_VALID;

  

             location[CHILD_LEFT_INDEX] = mLeft;

             location[CHILD_TOP_INDEX] = mTop;

  

            dirty.set(0, 0, mRight - location[CHILD_LEFT_INDEX],

                         mBottom - location[CHILD_TOP_INDEX]);

  

                 return mParent;

             }

         }

  

         return null;

 }

 

这个向上回溯的过程直到ViewRoot那里结束，由ViewRoot对这个最终的刷新区域做刷新。

ViewRoot.java

 public void invalidateChild(View child, Rect dirty) {

  

     scheduleTraversals();

  

 }
原文出至：http://www.android100.org/html/201204/14/948.html