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Android View刷新机制实例分析

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0714

这篇文章主要介绍了Android View刷新机制,结合实例形式较为详细的分析了Android的View刷新机制功能、原理与具体使用技巧,需要的朋友可以参考下

本文实例讲述了Android View刷新机制。分享给大家供大家参考，具体如下：

一、总体说明

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。

二、代码分析

1).ViewGroup的addView方法，理解参数的意义和传递

invalidate调用父类View的方法
addViewInner方法主要做的事情是

view的dispatchAttachedToWindow(AttachInfo info, int visibility)方法

1).View的invalidate方法，这是一个从下第向上回溯的过程，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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void invalidate(boolean invalidateCache) {
    if (ViewDebug.TRACE_HIERARCHY) {
      ViewDebug.trace(this, ViewDebug.HierarchyTraceType.INVALIDATE);
    }
    if (skipInvalidate()) {
      return;
    }
    if ((mPrivateFlags & (DRAWN | HAS_BOUNDS)) == (DRAWN | HAS_BOUNDS) ||
        (invalidateCache && (mPrivateFlags & DRAWING_CACHE_VALID) == DRAWING_CACHE_VALID) ||
        (mPrivateFlags & INVALIDATED) != INVALIDATED || isOpaque() != mLastIsOpaque) {
      mLastIsOpaque = isOpaque();
      mPrivateFlags &= ~DRAWN;
      mPrivateFlags |= DIRTY;
      if (invalidateCache) {
        mPrivateFlags |= INVALIDATED;
        mPrivateFlags &= ~DRAWING_CACHE_VALID;
      }
      final AttachInfo ai = mAttachInfo;
      final ViewParent p = mParent;
      //noinspection PointlessBooleanExpression,ConstantConditions
      if (!HardwareRenderer.RENDER_DIRTY_REGIONS) {
        if (p != null && ai != null && ai.mHardwareAccelerated) {
          // fast-track for GL-enabled applications; just invalidate the whole hierarchy
          // with a null dirty rect, which tells the ViewAncestor to redraw everything
          p.invalidateChild(this, null);
          return;
        }
      }
      if (p != null && ai != null) {
        final Rect r = ai.mTmpInvalRect;
        r.set(0, 0, mRight - mLeft, mBottom - mTop);
        // Don't call invalidate -- we don't want to internally scroll
        // our own bounds
        p.invalidateChild(this, r);//调用子类的方法完成
      }
    }
  }

2)ViewGrop的invalidateChild方法

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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) {
}

由ViewRoot对象的performTraversals()方法调用draw()方法发起绘制该View树，值得注意的是每次发起绘图时，并不会重新绘制每个View树的视图，而只会重新绘制那些“需要重绘”的视图，View类内部变量包含了一个标志位DRAWN，当该视图需要重绘时，就会为该View添加该标志位。

调用流程 ：

mView.draw()开始绘制，draw()方法实现的功能如下：

1 、绘制该View的背景
2 、为显示渐变框做一些准备操作(见5，大多数情况下，不需要改渐变框)
3、调用onDraw()方法绘制视图本身   (每个View都需要重载该方法，ViewGroup不需要实现该方法)
4、调用dispatchDraw ()方法绘制子视图(如果该View类型不为ViewGroup，即不包含子视图，不需要重载该
方法)值得说明的是，ViewGroup类已经为我们重写了dispatchDraw ()的功能实现，应用程序一般不需要重写该
方法，但可以重载父类函数实现具体的功能。

4.1 dispatchDraw()方法内部会遍历每个子视图，调用drawChild()去重新回调每个子视图的draw()方法(注意，这个 地方“需要重绘”的视图才会调用draw()方法)。值得说明的是，ViewGroup类已经为我们重写了dispatch

Draw()的功能实现，应用程序一般不需要重写该方法，但可以重载父类函数实现具体的功能。

希望本文所述对大家Android程序设计有所帮助。