你需要了解下Android View的更新 requestLayout 与重绘 invalidate
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作者：guojun
链接：https://juejin.im/post/5c9c2c76f265da60c576fab1
声明：本文来自guojun投稿，转发等请联系原作者授权
在大家都了解过Android View的测量、布局、绘制机制后，我们来细化地分析一下关于View的重绘invalidate与更新requestLayout
现象
public class CustomEmptyView extends View { public CustomEmptyView(Context context) { super(context); } public CustomEmptyView(Context context, @Nullable AttributeSet attrs) { super(context, attrs); } public CustomEmptyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) { super(context, attrs, defStyleAttr); } @Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { super.onMeasure(widthMeasureSpec, heightMeasureSpec); Log.i("CustomEmptyView", "onMeasure"); } @Override protected void onLayout(boolean changed, int left, int top, int right, int bottom) { super.onLayout(changed, left, top, right, bottom); Log.i("CustomEmptyView", "onLayout"); } @Override protected void onDraw(Canvas canvas) { super.onDraw(canvas); Log.i("CustomEmptyView", "onDraw"); }}class CustomEmptyView extends View {
public CustomEmptyView(Context context) {
super(context);
}
public CustomEmptyView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
}
public CustomEmptyView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {
super(context, attrs, defStyleAttr);
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
Log.i("CustomEmptyView", "onMeasure");
}
@Override
protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
super.onLayout(changed, left, top, right, bottom);
Log.i("CustomEmptyView", "onLayout");
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
Log.i("CustomEmptyView", "onDraw");
}
}
从View的绘制机制可知，View从测量、布局、绘制的步骤中会对应执行该View#onMeasure()、View#onLayout()、View#onDraw()。那么我们今天讨论的View#invalidate()和View#requestLayout()呢？我们打印一下数据。
View#invalidate()的执行步骤是:
2019-03-26 17:32:34.739 8075-8075/com.example.myapplication I/CustomEmptyView: onDrawView#requestLayout()的执行步骤是:
2019-03-26 17:33:13.497 8075-8075/com.example.myapplication I/CustomEmptyView: onMeasure2019-03-26 17:33:13.501 8075-8075/com.example.myapplication I/CustomEmptyView: onLayout2019-03-26 17:33:13.503 8075-8075/com.example.myapplication I/CustomEmptyView: onDraw
2019-03-26 17:33:13.503 8075-8075/com.example.myapplication I/CustomEmptyView: onDraw
从打印数据来推测就是View#invalidate()只会执行View#onDraw()；而View#requestLayout()则会重新走View的绘制流程。接下来我们从源码的角度来分析一下。
下面的源码分析基于android-28
View#requestLayout()
我们分析一下View#requestLayout()。我们定位到对应的源码
/** * Call this when something has changed which has invalidated the * layout of this view. This will schedule a layout pass of the view * tree. This should not be called while the view hierarchy is currently in a layout * pass ({@link #isInLayout()}. If layout is happening, the request may be honored at the * end of the current layout pass (and then layout will run again) or after the current * frame is drawn and the next layout occurs. * * 当某内容发生更改，导致该视图的布局重绘时调用此函数。这将安排视图树的布局传递。 * 当视图层次结构当前处于布局Layout事件时，不会执行该函数. * 如果正在进行布局，可以在当前布局传递结束时(然后布局将再次运行)或在绘制当前帧并执行下一个布局之后执行请求。 * Subclasses which override this method should call the superclass method to * handle possible request-during-layout errors correctly.
*/ @CallSuper 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(); // 该方法不在布局事件期间中执行 if (viewRoot != null && viewRoot.isInLayout()) { if (!viewRoot.requestLayoutDuringLayout(this)) { return; } } mAttachInfo.mViewRequestingLayout = this; } // PFLAG_FORCE_LAYOUT会在执行View的measure()和layout()方法时判断,这个是以前的文章看到的。 // 但是在当前源码的View.class和ViewRootImpl.class，全局搜索PFLAG_FORCE_LAYOUT,并没有直接的判断，导致View#requestLayout()不执行测量和布局方法 mPrivateFlags |= PFLAG_FORCE_LAYOUT; mPrivateFlags |= PFLAG_INVALIDATED; // isLayoutRequested()对应是mLayoutRequested字段，该字段在默认为false if (mParent != null && !mParent.isLayoutRequested()) { // 执行父容器的requestLayout()方法 mParent.requestLayout(); } if (mAttachInfo != null && mAttachInfo.mViewRequestingLayout == this) { mAttachInfo.mViewRequestingLayout = null; } }
@CallSuper
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();
// 该方法不在布局事件期间中执行
if (viewRoot != null && viewRoot.isInLayout()) {
if (!viewRoot.requestLayoutDuringLayout(this)) {
return;
}
}
mAttachInfo.mViewRequestingLayout = this;
}
// PFLAG_FORCE_LAYOUT会在执行View的measure()和layout()方法时判断,这个是以前的文章看到的。
// 但是在当前源码的View.class和ViewRootImpl.class，全局搜索PFLAG_FORCE_LAYOUT,并没有直接的判断，导致View#requestLayout()不执行测量和布局方法
mPrivateFlags |= PFLAG_FORCE_LAYOUT;
mPrivateFlags |= PFLAG_INVALIDATED;
// isLayoutRequested()对应是mLayoutRequested字段，该字段在默认为false
if (mParent != null && !mParent.isLayoutRequested()) {
// 执行父容器的requestLayout()方法
mParent.requestLayout();
}
if (mAttachInfo != null && mAttachInfo.mViewRequestingLayout == this) {
mAttachInfo.mViewRequestingLayout = null;
}
}
当我们点击ViewGroup#requestLayout(),发现它是一个空实现，我们可知ViewParent是interface类，我们通过之前的View的分析，可以去ViewRootImpl类看看ViewGroup#requestLayout()的实现方法。
@Override public void requestLayout() { // mHandlingLayoutInLayoutRequest这个参数，通过全局变量定位，在performLayout()开始时为true,结束时为false，与之前说的，不在布局期间执行相对应 if (!mHandlingLayoutInLayoutRequest) { // 检查是否UI线程 checkThread(); // 这里将mLayoutRequested设为true mLayoutRequested = true; scheduleTraversals(); } } void scheduleTraversals() { if (!mTraversalScheduled) { mTraversalScheduled = true; mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier(); mChoreographer.postCallback( Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null); if (!mUnbufferedInputDispatch) { scheduleConsumeBatchedInput(); } notifyRendererOfFramePending(); pokeDrawLockIfNeeded(); } }
public void requestLayout() {
// mHandlingLayoutInLayoutRequest这个参数，通过全局变量定位，在performLayout()开始时为true,结束时为false，与之前说的，不在布局期间执行相对应
if (!mHandlingLayoutInLayoutRequest) {
// 检查是否UI线程
checkThread();
// 这里将mLayoutRequested设为true
mLayoutRequested = true;
scheduleTraversals();
}
}
void scheduleTraversals() {
if (!mTraversalScheduled) {
mTraversalScheduled = true;
mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
if (!mUnbufferedInputDispatch) {
scheduleConsumeBatchedInput();
}
notifyRendererOfFramePending();
pokeDrawLockIfNeeded();
}
}
看到scheduleTraversals()，我相信大家都觉得快触摸到真相，但是发现点击该方法里的实现，并不能找到我们想要的，此时我们想一下之前的打印数据，View#requestLayout()会重新执行View的绘制步骤，View的绘制步骤最核心是ViewRootImpl#performTraverals，按照这个思路我们继续寻找。
从上面的源码中，我们看到mChoreographer这个对象，我们曾经在分析滑动流程度的时候，提及过Choreographer编舞者这个对象，我们最后从mChoreographer这个对象中的mTraversalRunnable参数找到线索。
final class TraversalRunnable implements Runnable { @Override public void run() { doTraversal(); } } final TraversalRunnable mTraversalRunnable = new TraversalRunnable(); void doTraversal() { if (mTraversalScheduled) { mTraversalScheduled = false; mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier); if (mProfile) { Debug.startMethodTracing("ViewAncestor"); } performTraversals(); if (mProfile) { Debug.stopMethodTracing(); mProfile = false; } } } class TraversalRunnable implements Runnable {
@Override
public void run() {
doTraversal();
}
}
final TraversalRunnable mTraversalRunnable = new TraversalRunnable();
void doTraversal() {
if (mTraversalScheduled) {
mTraversalScheduled = false;
mHandler.getLooper().getQueue().removeSyncBarrier(mTraversalBarrier);
if (mProfile) {
Debug.startMethodTracing("ViewAncestor");
}
performTraversals();
if (mProfile) {
Debug.stopMethodTracing();
mProfile = false;
}
}
}
最终我们发现mTraversalRunnable这个是一个Runnable对象，在scheduleTraversals()中传入mTraversalRunnable，就会执行doTraversal()，在doTraversal()中我们也如愿地找到我们想要的核心方法ViewRootImpl#performTraverals().当调用ViewRootImpl#performTraverals就重新开始该控件的测量、布局、绘制步骤。符合了我们一开始的打印数据。
View#invalidate()
接着我们看一下View#invalidate的源码。
/** * Invalidate the whole view. If the view is visible, * 重绘整个View，如果View是可视的。 * {@link #onDraw(android.graphics.Canvas)} will be called at some point in * the future. * * This must be called from a UI thread. To call from a non-UI thread, call * {@link #postInvalidate()}. * 这个方法必须被使用在UI线程，用在非UI线程的方法为postInvalidate() */ public void invalidate() { invalidate(true); } /** * This is where the invalidate() work actually happens. A full invalidate() * causes the drawing cache to be invalidated, but this function can be * called with invalidateCache set to false to skip that invalidation step * for cases that do not need it (for example, a component that remains at * the same dimensions with the same content). * 这就是invalidate()方法工作发生的地方，一个完整的invalidate()方法会引起绘制 * 缓存失效，但是这个函数能设置参数invalidateCache为false来跳过重绘步骤，由于 * 该方法不被需要，例如一个组件保持相同的尺寸和相同的内容 * * @param invalidateCache Whether the drawing cache for this view should be * invalidated as well. This is usually true for a full * invalidate, but may be set to false if the View's contents or * dimensions have not changed. * 这绘制缓存是否应被重绘.一个完整的重绘通常为true，但是可能设置为false,如果View的内容和尺寸没有被改变。 * * @hide */ 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) { // 暂不见赋值，从下面的方法中，得出他是一个被舍弃的方法，可以跳过 if (mGhostView != null) { mGhostView.invalidate(true); return; } // 跳过重绘。从方法描述可知，该方法判断该View不被重绘，当它处于不可见和没有处于动画中 if (skipInvalidate()) { return; } // 这里大量的参数对比，应该就是上面所说的判断坐标位置有没发生变化，如果发生了变化就标识为需要重绘 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; } mPrivateFlags |= PFLAG_DIRTY; // 如果需要全部重绘，invalidate()未传参调用时默认为true if (invalidateCache) { // 记住这个PFLAG_INVALIDATED标志位 mPrivateFlags |= PFLAG_INVALIDATED; mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID; } // Propagate the damage rectangle to the parent view. // 从下面参数mParent可知，应该是将需要重绘这个事件通知给父容器 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); // 这个就是重点，我们去看一下父容器的invalidateChild()方法 p.invalidateChild(this, damage); } // Damage the entire projection receiver, if necessary. if (mBackground != null && mBackground.isProjected()) { final View receiver = getProjectionReceiver(); if (receiver != null) { receiver.damageInParent(); } } } }
public void invalidate() {
invalidate(true);
}
/**
* This is where the invalidate() work actually happens. A full invalidate()
* causes the drawing cache to be invalidated, but this function can be
* called with invalidateCache set to false to skip that invalidation step
* for cases that do not need it (for example, a component that remains at
* the same dimensions with the same content).
* 这就是invalidate()方法工作发生的地方，一个完整的invalidate()方法会引起绘制
* 缓存失效，但是这个函数能设置参数invalidateCache为false来跳过重绘步骤，由于
* 该方法不被需要，例如一个组件保持相同的尺寸和相同的内容
*
* @param invalidateCache Whether the drawing cache for this view should be
* invalidated as well. This is usually true for a full
* invalidate, but may be set to false if the View's contents or
* dimensions have not changed.
* 这绘制缓存是否应被重绘.一个完整的重绘通常为true，但是可能设置为false,如果View的内容和尺寸没有被改变。
*
* @hide
*/
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) {
// 暂不见赋值，从下面的方法中，得出他是一个被舍弃的方法，可以跳过
if (mGhostView != null) {
mGhostView.invalidate(true);
return;
}
// 跳过重绘。从方法描述可知，该方法判断该View不被重绘，当它处于不可见和没有处于动画中
if (skipInvalidate()) {
return;
}
// 这里大量的参数对比，应该就是上面所说的判断坐标位置有没发生变化，如果发生了变化就标识为需要重绘
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;
}
mPrivateFlags |= PFLAG_DIRTY;
// 如果需要全部重绘，invalidate()未传参调用时默认为true
if (invalidateCache) {
// 记住这个PFLAG_INVALIDATED标志位
mPrivateFlags |= PFLAG_INVALIDATED;
mPrivateFlags &= ~PFLAG_DRAWING_CACHE_VALID;
}
// Propagate the damage rectangle to the parent view.
// 从下面参数mParent可知，应该是将需要重绘这个事件通知给父容器
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);
// 这个就是重点，我们去看一下父容器的invalidateChild()方法
p.invalidateChild(this, damage);
}
// Damage the entire projection receiver, if necessary.
if (mBackground != null && mBackground.isProjected()) {
final View receiver = getProjectionReceiver();
if (receiver != null) {
receiver.damageInParent();
}
}
}
}
从上面的分析可知，经过invalidate()的重载方法，最终会调用invalidateInternal()，在这个方法里头，要判断是否需要重绘，如果需要重绘，就对该View进行标识，然后将该View的Rect信息传递给父容器的invalidateChild().
与之前的View#requestLayout()相似，最终同样是执行ViewRootImpl#invalidateChild()，然后我继续分析ViewRootImpl#invalidateChild()的实现。
@Override public void invalidateChild(View child, Rect dirty) { invalidateChildInParent(null, dirty); } // 由于没有注释，我们从方法名去分析源码,重载至这个最终的方法，意思为在父容器中重绘子控件 @Override public ViewParent invalidateChildInParent(int[] location, Rect dirty) { // 检查线程，里面判断为，该方法需要执行在UI线程，验证了之前View#invalidate()的描述 checkThread(); if (DEBUG_DRAW) Log.v(mTag, "Invalidate child: " + dirty); // 从上一步可知，dirty是不为空的 if (dirty == null) { invalidate(); return null; } else if (dirty.isEmpty() && !mIsAnimating) { return null; } // 这里应该是一些坐标位置的设置赋值 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); } } // 从方法的命名，这里应该是我们需要的方法，重绘 invalidateRectOnScreen(dirty); return null; } private void invalidateRectOnScreen(Rect dirty) { 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)) { // 上面的设置和调整，最终调用scheduleTraversals() scheduleTraversals(); } } void scheduleTraversals() { if (!mTraversalScheduled) { mTraversalScheduled = true; mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier(); mChoreographer.postCallback( Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null); if (!mUnbufferedInputDispatch) { scheduleConsumeBatchedInput(); } notifyRendererOfFramePending(); pokeDrawLockIfNeeded(); } }
public void invalidateChild(View child, Rect dirty) {
invalidateChildInParent(null, dirty);
}
// 由于没有注释，我们从方法名去分析源码,重载至这个最终的方法，意思为在父容器中重绘子控件
@Override
public ViewParent invalidateChildInParent(int[] location, Rect dirty) {
// 检查线程，里面判断为，该方法需要执行在UI线程，验证了之前View#invalidate()的描述
checkThread();
if (DEBUG_DRAW) Log.v(mTag, "Invalidate child: " + dirty);
// 从上一步可知，dirty是不为空的
if (dirty == null) {
invalidate();
return null;
} else if (dirty.isEmpty() && !mIsAnimating) {
return null;
}
// 这里应该是一些坐标位置的设置赋值
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);
}
}
// 从方法的命名，这里应该是我们需要的方法，重绘
invalidateRectOnScreen(dirty);
return null;
}
private void invalidateRectOnScreen(Rect dirty) {
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)) {
// 上面的设置和调整，最终调用scheduleTraversals()
scheduleTraversals();
}
}
void scheduleTraversals() {
if (!mTraversalScheduled) {
mTraversalScheduled = true;
mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
mChoreographer.postCallback(
Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable, null);
if (!mUnbufferedInputDispatch) {
scheduleConsumeBatchedInput();
}
notifyRendererOfFramePending();
pokeDrawLockIfNeeded();
}
}
看到这里，我们马上联想起之前分析的View#requestLayout(),同样是scheduleTraversals(),但是从打印数据可知，View#invalidate()是不会执行测量与布局的，但是目前来看它们最终调用的方法可是一致的。
我们可以留意一下之前的ViewRootImpl#requestLayout()方法中，主动将一个全局变量mLayoutRequested设置为true;那么大胆猜测这个对象肯定会影响到performMeasure()与performLayout()，我们翻一下ViewRootImpl#performTraversals()
private void performTraversals() { ··· boolean layoutRequested = mLayoutRequested && (!mStopped || mReportNextDraw); ··· boolean windowShouldResize = layoutRequested && windowSizeMayChange && ((mWidth != host.getMeasuredWidth() || mHeight != host.getMeasuredHeight()) || (lp.width == ViewGroup.LayoutParams.WRAP_CONTENT && frame.width() < desiredWindowWidth && frame.width() != mWidth) || (lp.height == ViewGroup.LayoutParams.WRAP_CONTENT && frame.height() < desiredWindowHeight && frame.height() != mHeight)); ··· if (mFirst || windowShouldResize || insetsChanged || viewVisibilityChanged || params != null || mForceNextWindowRelayout) { ··· performMeasure(childWidthMeasureSpec, childHeightMeasureSpec); ··· } ··· final boolean didLayout = layoutRequested && (!mStopped || mReportNextDraw); boolean triggerGlobalLayoutListener = didLayout || mAttachInfo.mRecomputeGlobalAttributes; if (didLayout) { performLayout(lp, mWidth, mHeight); } ··· }
···
boolean layoutRequested = mLayoutRequested && (!mStopped || mReportNextDraw);
···
boolean windowShouldResize = layoutRequested && windowSizeMayChange
&& ((mWidth != host.getMeasuredWidth() || mHeight != host.getMeasuredHeight())
|| (lp.width == ViewGroup.LayoutParams.WRAP_CONTENT &&
frame.width() < desiredWindowWidth && frame.width() != mWidth)
|| (lp.height == ViewGroup.LayoutParams.WRAP_CONTENT &&
frame.height() < desiredWindowHeight && frame.height() != mHeight));
···
if (mFirst || windowShouldResize || insetsChanged || viewVisibilityChanged || params != null || mForceNextWindowRelayout) {
···
performMeasure(childWidthMeasureSpec, childHeightMeasureSpec);
···
}
···
final boolean didLayout = layoutRequested && (!mStopped || mReportNextDraw);
boolean triggerGlobalLayoutListener = didLayout
|| mAttachInfo.mRecomputeGlobalAttributes;
if (didLayout) {
performLayout(lp, mWidth, mHeight);
}
···
}
对于复杂的ViewRootImpl#performTraversals(),我们抽取一些关键的代码，的确可以验证mLayoutRequested对象是会影响测量和布局对应的方法的，因此可以验证我们一开始的打印数据，View#invalidate()是不会执行测量和布局的。
View#postInvalidate()
从View#invalidate()的注释描述可知，View#invalidate()需要执行在UI线程中，如果在非UI线程需要使用View#postInvalidate()，我们简单地分析一下源码。
public void postInvalidate() { postInvalidateDelayed(0); } public void postInvalidate(int left, int top, int right, int bottom) { postInvalidateDelayed(0, left, top, right, bottom); } public void postInvalidateDelayed(long delayMilliseconds, int left, int top, int right, int bottom) { // 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) { final AttachInfo.InvalidateInfo info = AttachInfo.InvalidateInfo.obtain(); info.target = this; info.left = left; info.top = top; info.right = right; info.bottom = bottom; attachInfo.mViewRootImpl.dispatchInvalidateRectDelayed(info, delayMilliseconds); } }
postInvalidateDelayed(0);
}
public void postInvalidate(int left, int top, int right, int bottom) {
postInvalidateDelayed(0, left, top, right, bottom);
}
public void postInvalidateDelayed(long delayMilliseconds, int left, int top,
int right, int bottom) {
// 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) {
final AttachInfo.InvalidateInfo info = AttachInfo.InvalidateInfo.obtain();
info.target = this;
info.left = left;
info.top = top;
info.right = right;
info.bottom = bottom;
attachInfo.mViewRootImpl.dispatchInvalidateRectDelayed(info, delayMilliseconds);
}
}
ViewRootImpl#dispatchInvalidateRectDelayed()
public void dispatchInvalidateRectDelayed(AttachInfo.InvalidateInfo info, long delayMilliseconds) { final Message msg = mHandler.obtainMessage(MSG_INVALIDATE_RECT, info); mHandler.sendMessageDelayed(msg, delayMilliseconds); } @Override public void handleMessage(Message msg) { switch (msg.what) { case MSG_INVALIDATE_RECT: final View.AttachInfo.InvalidateInfo info = (View.AttachInfo.InvalidateInfo) msg.obj; info.target.invalidate(info.left, info.top, info.right, info.bottom); info.recycle(); break; ··· } }
final Message msg = mHandler.obtainMessage(MSG_INVALIDATE_RECT, info);
mHandler.sendMessageDelayed(msg, delayMilliseconds);
}
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
case MSG_INVALIDATE_RECT:
final View.AttachInfo.InvalidateInfo info = (View.AttachInfo.InvalidateInfo) msg.obj;
info.target.invalidate(info.left, info.top, info.right, info.bottom);
info.recycle();
break;
···
}
}
从源码可知，View#postInvalidate()会发送一个MSG_INVALIDATE_RECT的Handler消息，在接收消息后，同样是执行View#invalidate()方法。
疑问：requestLayout不执行performDraw()?
在翻阅资料的时候，很多地方都会描述到View#requestLayout不执行performDraw()，但是自己的打印结果是会显示执行performDraw()的。我们带着问题翻一下源码。直接定位到ViewRootImpl#performTraversals的performDraw()
private void performTraversals() { ··· // dispatchOnPreDraw()返回注释是：如果当前绘制应该被取消和重新调度，则为True，否则为false。 // final boolean isViewVisible = viewVisibility == View.VISIBLE; 只要是显示的View，cancelDraw为true boolean cancelDraw = mAttachInfo.mTreeObserver.dispatchOnPreDraw() || !isViewVisible; // cancelDraw通过dispatchOnPreDraw()的注释解析和isViewVisible，得出cancelDraw应该为false // newSurface默认为false，在测量判断逻辑中，在判断是否新的Surface会设置为true，这里应该是false // 因为会执行performDraw() if (!cancelDraw && !newSurface) { if (mPendingTransitions != null && mPendingTransitions.size() > 0) { for (int i = 0; i < mPendingTransitions.size(); ++i) { mPendingTransitions.get(i).startChangingAnimations(); } mPendingTransitions.clear(); } performDraw(); } }
···
// dispatchOnPreDraw()返回注释是：如果当前绘制应该被取消和重新调度，则为True，否则为false。
// final boolean isViewVisible = viewVisibility == View.VISIBLE; 只要是显示的View，cancelDraw为true
boolean cancelDraw = mAttachInfo.mTreeObserver.dispatchOnPreDraw() || !isViewVisible;
// cancelDraw通过dispatchOnPreDraw()的注释解析和isViewVisible，得出cancelDraw应该为false
// newSurface默认为false，在测量判断逻辑中，在判断是否新的Surface会设置为true，这里应该是false
// 因为会执行performDraw()
if (!cancelDraw && !newSurface) {
if (mPendingTransitions != null && mPendingTransitions.size() > 0) {
for (int i = 0; i < mPendingTransitions.size(); ++i) {
mPendingTransitions.get(i).startChangingAnimations();
}
mPendingTransitions.clear();
}
performDraw();
}
}
ViewRootImpl#performDraw()
private void performDraw() { // Display.STATE_OFF表示显示状态:显示关闭。 // mReportNextDraw对象默认false，可在ViewRootImpl#reportNextDraw()中设置为true，但是第一个判断已经为false，不影响判断 if (mAttachInfo.mDisplayState == Display.STATE_OFF && !mReportNextDraw) { return; } else if (mView == null) {// 必然不为null return; } final boolean fullRedrawNeeded = mFullRedrawNeeded || mReportNextDraw; mFullRedrawNeeded = false; mIsDrawing = true; Trace.traceBegin(Trace.TRACE_TAG_VIEW, "draw"); boolean usingAsyncReport = false; if (mReportNextDraw && mAttachInfo.mThreadedRenderer != null && mAttachInfo.mThreadedRenderer.isEnabled()) { usingAsyncReport = true; mAttachInfo.mThreadedRenderer.setFrameCompleteCallback((long frameNr) -> { // TODO: Use the frame number pendingDrawFinished(); }); } try { // 最重点是这句，draw()方法的执行,能影响这段代码的执行，只有上面的两个return逻辑。 boolean canUseAsync = draw(fullRedrawNeeded); if (usingAsyncReport && !canUseAsync) { mAttachInfo.mThreadedRenderer.setFrameCompleteCallback(null); usingAsyncReport = false; } } finally { mIsDrawing = false; Trace.traceEnd(Trace.TRACE_TAG_VIEW); } ··· }
// Display.STATE_OFF表示显示状态:显示关闭。
// mReportNextDraw对象默认false，可在ViewRootImpl#reportNextDraw()中设置为true，但是第一个判断已经为false，不影响判断
if (mAttachInfo.mDisplayState == Display.STATE_OFF && !mReportNextDraw) {
return;
} else if (mView == null) {// 必然不为null
return;
}
final boolean fullRedrawNeeded = mFullRedrawNeeded || mReportNextDraw;
mFullRedrawNeeded = false;
mIsDrawing = true;
Trace.traceBegin(Trace.TRACE_TAG_VIEW, "draw");
boolean usingAsyncReport = false;
if (mReportNextDraw && mAttachInfo.mThreadedRenderer != null
&& mAttachInfo.mThreadedRenderer.isEnabled()) {
usingAsyncReport = true;
mAttachInfo.mThreadedRenderer.setFrameCompleteCallback((long frameNr) -> {
// TODO: Use the frame number
pendingDrawFinished();
});
}
try {
// 最重点是这句，draw()方法的执行,能影响这段代码的执行，只有上面的两个return逻辑。
boolean canUseAsync = draw(fullRedrawNeeded);
if (usingAsyncReport && !canUseAsync) {
mAttachInfo.mThreadedRenderer.setFrameCompleteCallback(null);
usingAsyncReport = false;
}
} finally {
mIsDrawing = false;
Trace.traceEnd(Trace.TRACE_TAG_VIEW);
}
···
}
从上面的判断可以推断到draw()是会被执行，与网上得出结论不一致，暂时没得出什么原因，如有分析错误和不足的地方，希望指定一下。
总结
步骤图
View 绘制步骤是 performMeasure()、performLayout()、performDraw()，我们经过对 invalidate 和 requestLayout的源码分析，可以得出。
invalidate()方法只会执行performDraw()方法；而requestLayout()方法会执行performMeasure()、performLayout()、performDraw()。在对应的应用场景，如果只是View的显示内容发生变化且不改变View的大小和位置，则使用invalidate()，如果大小、位置、内容都发生改变则调用requestLayout()。
支持，「在看」