Android View的刷新.jpg
postInvalidate
今天刚好用到了view的postInvalidate方法，只是知道它可以在非UI线程实现view的重绘，这里简单梳理一下view刷新的流程。
public void postInvalidate(int left, int top, int right, int bottom) {
postInvalidateDelayed(0, left, top, right, bottom);
}
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);
}
}
可以看到postInvalidate实际上是通过ViewRootImpl.dispatchInvalidateDelayed方法实现的，并且把当前view对象this传递给dispatchInvalidateDelayed方法。
public void dispatchInvalidateDelayed(View view, long delayMilliseconds) {
Message msg = mHandler.obtainMessage(MSG_INVALIDATE, view);
mHandler.sendMessageDelayed(msg, delayMilliseconds);
}
这里通过handler消息处理，我们接着看一下handler方法。
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MSG_INVALIDATE:
((View) msg.obj).invalidate();
break;
//......
实际上还是通过View.invalidate方法实现界面刷新，这里是view对象就是之前传递过来的this。
invalidate
接着看下invalidate方法，这里把当前view的尺寸和状态传递给invalidateInternal方法。
public void invalidate() {
invalidate(true);
}
@UnsupportedAppUsage
public 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;
}
if (skipInvalidate()) {
return;
}
// Reset content capture caches
mCachedContentCaptureSession = null;
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;
}
mPrivateFlags |= PFLAG_DIRTY;
if (invalidateCache) {
mPrivateFlags |= PFLAG_INVALIDATED;
mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
}
// Propagate the damage rectangle to the parent view.
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);
p.invalidateChild(this, damage);//1
}
// Damage the entire projection receiver, if necessary.
if (mBackground != null && mBackground.isProjected()) {
final View receiver = getProjectionReceiver();
if (receiver != null) {
receiver.damageInParent();
}
}
}
}
这里重点可以看下注释1处，调用父view的invalidateChild方法对自己进行刷新。但是ViewParent只是一个接口，实现类是ViewGroup。invalidateChild的代码较多，这里重点看下注释1处，通过一个do while循环去不断查找view的父view。
注释2处，通过invalidateChildInParent方法获取父view。
public final void invalidateChild(View child, final Rect dirty) {
final AttachInfo attachInfo = mAttachInfo;
//......
ViewParent parent = this;
//......
do {
View view = null;
if (parent instanceof View) {
view = (View) parent;//1
}
//......
parent = parent.invalidateChildInParent(location, dirty);//2
//......
} while (parent != null);
}
}
通过前面的文章我们知道一个activity顶层的view是DecorView，所以这个循环最后获取到的是DecorView实例，因为DecorView的mParent对象是ViewRootImpl，所以最后是跑到ViewRootImpl.invalidateChildInParent方法，
public ViewParent invalidateChildInParent(int[] location, Rect dirty) {
checkThread();
if (DEBUG_DRAW) Log.v(mTag, "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);
}
}
invalidateRectOnScreen(dirty);//1
return null;
}
注释1处调用了invalidateRectOnScreen方法。
private void invalidateRectOnScreen(Rect dirty) {
final Rect localDirty = mDirty;
// 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();//1
}
}
接着注释1处调用scheduleTraversals方法。
void scheduleTraversals() {
if (!mTraversalScheduled) {
mTraversalScheduled = true;
mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);//1
if (!mUnbufferedInputDispatch) {
scheduleConsumeBatchedInput();
}
notifyRendererOfFramePending();
pokeDrawLockIfNeeded();
}
}
注释1处的mTraversalRunnable是一个TraversalRunnable对象，在它的run方法中会调用doTraversal方法。
void doTraversal() {
if (mTraversalScheduled) {
mTraversalScheduled = false;
mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);
if (mProfile) {
Debug.startMethodTracing("ViewAncestor");
}
performTraversals();
if (mProfile) {
Debug.stopMethodTracing();
mProfile = false;
}
}
}
然后在这里调用了performTraversals方法，里面通过performMeasure()、performLayout()、performDraw（）调用了mView.measure() mView.layout 、mView.draw等方法。最后view的draw方法会调用我们在自定义view中重写的onDraw。
参考：
https://blog.csdn.net/u010019468/article/details/72792558
http://onlylemi.github.io/blog/android-invalidate-postInvalidate/
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