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Android View的刷新机制

时间:2024-3-2 19:43     作者:韩俊     分类: Android


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

标签: android

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