Android-View 的刷新机制

http://www.oschina.net/question/163910_27566

Android-View 的刷新机制

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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：

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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

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private void addViewInner(View child, int index, LayoutParams params, boolean preventRequestLayout) {          .....          // tell our children          if (preventRequestLayout) {              child.assignParent( this );          } else {              child.mParent = this ;          }         ..... }   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

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void dispatchAttachedToWindow(AttachInfo info, int visibility) {      mAttachInfo = info;         ..... }

ViewGroup.java

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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

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private void addViewInner(View child, int index, LayoutParams params, boolean preventRequestLayout) {         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。

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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

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public void invalidateChild(View child, Rect dirty) {         scheduleTraversals();    }

原文链接：http://blog.youkuaiyun.com/dragondog/article/details/6454551