requestLayout、invalidate与postInvalidate分析
requestLayout
http://www.jianshu.com/p/687010ccad66
当一个VIEW的布局属性发生了变化的时候，可以调用该方法，让父VIEW调用onmeasure 和onlayout重新定位该view的位置，需要在UI线程调用。
布局属性包括view的位置、大小、形状等。
view.requestLayout();
View#requestLayout方法：
public void requestLayout() {
if (mMeasureCache != null) mMeasureCache.clear();
if (mAttachInfo != null && mAttachInfo.mViewRequestingLayout == null) {
// Only trigger request-during-layout logic if this is the view requesting it,
// not the views in its parent hierarchy
ViewRootImpl viewRoot = getViewRootImpl();
if (viewRoot != null && viewRoot.isInLayout()) {
if (!viewRoot.requestLayoutDuringLayout(this)) {
return;
}
}
mAttachInfo.mViewRequestingLayout = this;
}
mPrivateFlags |= PFLAG_FORCE_LAYOUT;
mPrivateFlags |= PFLAG_INVALIDATED;
if (mParent != null && !mParent.isLayoutRequested()) {
mParent.requestLayout();
}
if (mAttachInfo != null && mAttachInfo.mViewRequestingLayout == this) {
mAttachInfo.mViewRequestingLayout = null;
}
}
这段代码的逻辑：
- 首先就是判断当前的view树是否在layout布局中，如果在的话，则直接返回了；如果不再，则把当前的view对象赋值给
mViewRequestingLayout； - 接着就是为view增加标记位，就是为了标记当前的view是需要进行重新布局的；
- 接着就是调用父view的
requestLayout方法（当然之前会判断下父view是否已经在布局中） - 而父容器又会调用它的父容器的requestLayout方法，即requestLayout事件层层向上传递，直到DecorView，即根View，而根View又会传递给ViewRootImpl，也即是说子View的requestLayout事件，最终会被ViewRootImpl接收并得到处理。
纵观这个向上传递的流程，其实是采用了责任链模式，即不断向上传递该事件，直到找到能处理该事件的上级，在这里，只有ViewRootImpl能够处理requestLayout事件。
ViewRootImpl#requestLayout方法：
@Override
public void requestLayout() {
if (!mHandlingLayoutInLayoutRequest) {
checkThread();
mLayoutRequested = true;
scheduleTraversals();
}
}
- 首先是主线程的检查，必须是在主线程调用
- 调用了scheduleTraversals方法，这个方法是一个异步方法
scheduleTraversals()
在scheduleTraversals中会调用Choregrapher.postCallback，将它post出去，而postSyncBarrier方法禁止了后续的消息处理，一旦post出去了同步的Barrier之后，所有的非异步调用的消息就会被停止分发。
void scheduleTraversals() {
if (!mTraversalScheduled) {
mTraversalScheduled = true;
mTraversalBarrier = mHandler.getLooper().postSyncBarrier();
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
scheduleConsumeBatchedInput();
}
}
doTraversal是在一个Runnable的run方法中执行的：
final class TraversalRunnable implements Runnable {
@Override
public void run() {
doTraversal();
}
}
final TraversalRunnable mTraversalRunnable = new TraversalRunnable();
而PerformTraversals函数，是在doTraversal方法中被调用的。
void doTraversal() {
if (mTraversalScheduled) {
mTraversalScheduled = false;
mHandler.getLooper().removeSyncBarrier(mTraversalBarrier);
if (mProfile) {
Debug.startMethodTracing("ViewAncestor");
}
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "performTraversals");
try {
performTraversals();
} finally {
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
if (mProfile) {
Debug.stopMethodTracing();
mProfile = false;
}
}
}
走到PerformTraversals()后，后面的流程就是measure、layout、draw了。
小结：子View调用requestLayout方法，会标记当前View及父容器，同时逐层向上提交，直到ViewRootImpl处理该事件，ViewRootImpl会调用三大流程，从measure开始，对于每一个含有标记位的view及其子View都会进行测量、布局、绘制。
invalidate
强制使view重绘，需要在UI线程调用。
该方法的调用会引起View树的重绘，常用于内部调用(比如 setVisiblity())或者需要刷新界面的时候,需要在主线程(即UI线程)中调用该方法。
public void invalidate() {
invalidate(true);
}
void invalidate(boolean invalidateCache) {
invalidateInternal(0, 0, mRight - mLeft, mBottom - mTop, invalidateCache, true);
}
void invalidateInternal(int l, int t, int r, int b, boolean invalidateCache,
boolean fullInvalidate) {
if (mGhostView != null) {
mGhostView.invalidate(true);
return;
}
//这里判断该子View是否可见或者是否处于动画中
if (skipInvalidate()) {
return;
}
//根据View的标记位来判断该子View是否需要重绘，假如View没有任何变化，那么就不需要重绘
if ((mPrivateFlags & (PFLAG_DRAWN | PFLAG_HAS_BOUNDS)) == (PFLAG_DRAWN | PFLAG_HAS_BOUNDS)
|| (invalidateCache && (mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == PFLAG_DRAWING_CACHE_VALID)
|| (mPrivateFlags & PFLAG_INVALIDATED) != PFLAG_INVALIDATED
|| (fullInvalidate && isOpaque() != mLastIsOpaque)) {
if (fullInvalidate) {
mLastIsOpaque = isOpaque();
mPrivateFlags &= ~PFLAG_DRAWN;
}
//设置PFLAG_DIRTY标记位
mPrivateFlags |= PFLAG_DIRTY;
if (invalidateCache) {
mPrivateFlags |= PFLAG_INVALIDATED;
mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
}
// Propagate the damage rectangle to the parent view.
//把需要重绘的区域传递给父容器
final AttachInfo ai = mAttachInfo;
final ViewParent p = mParent;
if (p != null && ai != null && l < r && t < b) {
final Rect damage = ai.mTmpInvalRect;
damage.set(l, t, r, b);
//调用父容器的方法，向上传递事件
p.invalidateChild(this, damage);
}
...
}
}
ViewGroup#invalidateChild方法：
/**
* Don't call or override this method. It is used for the implementation of
* the view hierarchy.
*/
public final void invalidateChild(View child, final Rect dirty) {
//设置 parent 等于自身
ViewParent parent = this;
final AttachInfo attachInfo = mAttachInfo;
if (attachInfo != null) {
// 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 & PFLAG_DRAW_ANIMATION)
== PFLAG_DRAW_ANIMATION;
// Check whether the child that requests the invalidate is fully opaque
// Views being animated or transformed are not considered opaque because we may
// be invalidating their old position and need the parent to paint behind them.
Matrix childMatrix = child.getMatrix();
final boolean isOpaque = child.isOpaque() && !drawAnimation &&
child.getAnimation() == null && childMatrix.isIdentity();
// Mark the child as dirty, using the appropriate flag
// Make sure we do not set both flags at the same time
int opaqueFlag = isOpaque ? PFLAG_DIRTY_OPAQUE : PFLAG_DIRTY;
if (child.mLayerType != LAYER_TYPE_NONE) {
mPrivateFlags |= PFLAG_INVALIDATED;
mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
}
//储存子View的mLeft和mTop值
final int[] location = attachInfo.mInvalidateChildLocation;
location[CHILD_LEFT_INDEX] = child.mLeft;
location[CHILD_TOP_INDEX] = child.mTop;
...
do {
View view = null;
if (parent instanceof View) {
view = (View) parent;
}
if (drawAnimation) {
if (view != null) {
view.mPrivateFlags |= PFLAG_DRAW_ANIMATION;
} else if (parent instanceof ViewRootImpl) {
((ViewRootImpl) 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) {
if ((view.mViewFlags & FADING_EDGE_MASK) != 0 &&
view.getSolidColor() == 0) {
opaqueFlag = PFLAG_DIRTY;
}
if ((view.mPrivateFlags & PFLAG_DIRTY_MASK) != PFLAG_DIRTY) {
//对当前View的标记位进行设置
view.mPrivateFlags = (view.mPrivateFlags & ~PFLAG_DIRTY_MASK) | opaqueFlag;
}
}
//调用ViewGrup的invalidateChildInParent，如果已经达到最顶层view,则调用ViewRootImpl
//的invalidateChildInParent。
parent = parent.invalidateChildInParent(location, dirty);
if (view != null) {
// Account for transform on current parent
Matrix m = view.getMatrix();
if (!m.isIdentity()) {
RectF boundingRect = attachInfo.mTmpTransformRect;
boundingRect.set(dirty);
m.mapRect(boundingRect);
dirty.set((int) (boundingRect.left - 0.5f),
(int) (boundingRect.top - 0.5f),
(int) (boundingRect.right + 0.5f),
(int) (boundingRect.bottom + 0.5f));
}
}
} while (parent != null);
}
}
，在该方法内部，先设置当前视图的标记位，接着有一个do...while...循环，该循环的作用主要是不断向上回溯父容器，求得父容器和子View需要重绘的区域的并集(dirty)。当父容器不是ViewRootImpl的时候，调用的是ViewGroup的invalidateChildInParent方法。
ViewGroup#invalidateChildInParent方法：
public ViewParent invalidateChildInParent(final int[] location, final Rect dirty) {
if ((mPrivateFlags & PFLAG_DRAWN) == PFLAG_DRAWN ||
(mPrivateFlags & PFLAG_DRAWING_CACHE_VALID) == PFLAG_DRAWING_CACHE_VALID) {
if ((mGroupFlags & (FLAG_OPTIMIZE_INVALIDATE | FLAG_ANIMATION_DONE)) !=
FLAG_OPTIMIZE_INVALIDATE) {
//将dirty中的坐标转化为父容器中的坐标，考虑mScrollX和mScrollY的影响
dirty.offset(location[CHILD_LEFT_INDEX] - mScrollX,
location[CHILD_TOP_INDEX] - mScrollY);
if ((mGroupFlags & FLAG_CLIP_CHILDREN) == 0) {
//求并集，结果是把子视图的dirty区域转化为父容器的dirty区域
dirty.union(0, 0, mRight - mLeft, mBottom - mTop);
}
final int left = mLeft;
final int top = mTop;
if ((mGroupFlags & FLAG_CLIP_CHILDREN) == FLAG_CLIP_CHILDREN) {
if (!dirty.intersect(0, 0, mRight - left, mBottom - top)) {
dirty.setEmpty();
}
}
mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
//记录当前视图的mLeft和mTop值，在下一次循环中会把当前值再向父容器的坐标转化
location[CHILD_LEFT_INDEX] = left;
location[CHILD_TOP_INDEX] = top;
if (mLayerType != LAYER_TYPE_NONE) {
mPrivateFlags |= PFLAG_INVALIDATED;
}
//返回当前视图的父容器
return mParent;
}
...
}
return null;
}
这个方法做的工作主要有：调用offset方法，把当前dirty区域的坐标转化为父容器中的坐标，接着调用union方法，把子dirty区域与父容器的区域求并集，换句话说，dirty区域变成父容器区域。最后返回当前视图的父容器，以便进行下一次循环。
最后还是到了ViewRootImpl。ViewRootImpl#invalidateChildInParent方法：
@Override
public ViewParent invalidateChildInParent(int[] location, Rect dirty) {
checkThread();
if (DEBUG_DRAW) Log.v(TAG, "Invalidate child: " + dirty);
if (dirty == null) {
invalidate();
return null;
} else if (dirty.isEmpty() && !mIsAnimating) {
return null;
}
if (mCurScrollY != 0 || mTranslator != null) {
mTempRect.set(dirty);
dirty = mTempRect;
if (mCurScrollY != 0) {
dirty.offset(0, -mCurScrollY);
}
if (mTranslator != null) {
mTranslator.translateRectInAppWindowToScreen(dirty);
}
if (mAttachInfo.mScalingRequired) {
dirty.inset(-1, -1);
}
}
final Rect localDirty = mDirty;
if (!localDirty.isEmpty() && !localDirty.contains(dirty)) {
mAttachInfo.mSetIgnoreDirtyState = true;
mAttachInfo.mIgnoreDirtyState = true;
}
// Add the new dirty rect to the current one
localDirty.union(dirty.left, dirty.top, dirty.right, dirty.bottom);
// Intersect with the bounds of the window to skip
// updates that lie outside of the visible region
final float appScale = mAttachInfo.mApplicationScale;
final boolean intersected = localDirty.intersect(0, 0,
(int) (mWidth * appScale + 0.5f), (int) (mHeight * appScale + 0.5f));
if (!intersected) {
localDirty.setEmpty();
}
if (!mWillDrawSoon && (intersected || mIsAnimating)) {
scheduleTraversals();
}
return null;
}
ViewRootImpl的处理逻辑和ViewGroup基本类似，就是将dirty区域转换成ViewRootImpl上的区域。
最后调用了scheduleTraversals方法，触发View的工作流程，由于没有添加measure和layout的标记位，因此measure、layout流程不会执行，而是直接从draw流程开始。
总结：当子View调用了invalidate方法后，会为该View添加一个标记位，同时不断向父容器请求刷新，父容器通过计算得出自身需要重绘的区域，直到传递到ViewRootImpl中，最终触发performTraversals方法，进行开始View树重绘流程(只绘制需要重绘的视图)。
postInvalidate
由于invalidate必须是在主线程上执行，postInvalidate的出现就是为了在非主线程上重绘。
public void postInvalidate() {
postInvalidateDelayed(0);
}
public void postInvalidateDelayed(long delayMilliseconds) {
// We try only with the AttachInfo because there's no point in invalidating
// if we are not attached to our window
final AttachInfo attachInfo = mAttachInfo;
if (attachInfo != null) {
attachInfo.mViewRootImpl.dispatchInvalidateDelayed(this, delayMilliseconds);
}
}
只有attachInfo不为null的时候才会继续执行，即只有确保视图被添加到窗口的时候才会通知view树重绘，因为这是一个异步方法，如果在视图还未被添加到窗口就通知重绘的话会出现错误，所以这样要做一下判断。
ViewRootImpl#dispatchInvalidateDelayed方法：
public void dispatchInvalidateDelayed(View view, long delayMilliseconds) {
Message msg = mHandler.obtainMessage(MSG_INVALIDATE, view);
mHandler.sendMessageDelayed(msg, delayMilliseconds);
}
final ViewRootHandler mHandler = new ViewRootHandler();
final class ViewRootHandler extends Handler {
@Override
public String getMessageName(Message message) {
....
}
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MSG_INVALIDATE:
((View) msg.obj).invalidate();
break;
...
}
}
}
最后还是调用invalidte()方法去绘制view。
整体的总结：
