invalidate()/postInvalidate()/postInvalidateOnAnimation()的区别

1、invalidate()

#View.java
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) {
           ...
           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);
               //ViewParent
               p.invalidateChild(this, damage);
           }
           ...
       }
   }

#ViewRootImpl.java
public void invalidateChild(View child, Rect dirty) {
       invalidateChildInParent(null, dirty);
   }

public ViewParent invalidateChildInParent(int[] location, Rect dirty) { 
       checkThread();
       ...
       invalidateRectOnScreen(dirty);
       return null;
   }


private void invalidateRectOnScreen(Rect dirty) {
       ...
       if (!mWillDrawSoon && (intersected || mIsAnimating)) {
           scheduleTraversals();
       }
   }

void scheduleTraversals() {
       if (!mTraversalScheduled) {
           mTraversalScheduled = true;
           mTraversalBarrier = mHandler.getLooper().getQueue().postSyncBarrier();
           mChoreographer.postCallback(Choreographer.CALLBACK_TRAVERSAL, mTraversalRunnable,null);
           if (!mUnbufferedInputDispatch) {
               scheduleConsumeBatchedInput();
           }
           notifyRendererOfFramePending();
           pokeDrawLockIfNeeded();
       }
   }

可以看到invalidate()的调用顺序为：

View.invalidate()->View.invalidateInternal()->ViewRootImpl.invalidateChild()->
ViewRoottImpl.invalidateChildInParent()->ViewRootImpl.invalidateRectOnScreen()->
ViewRootImpl.scheduleTraversals()

2、postInvalidate()

#View.java
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);
        }
    }
#ViewRootImpl.java
 public void dispatchInvalidateDelayed(View view, long delayMilliseconds) {
        Message msg = mHandler.obtainMessage(MSG_INVALIDATE, view);
        mHandler.sendMessageDelayed(msg, delayMilliseconds);
    }

 final class ViewRootHandler extends Handler {

 @Override
        public void handleMessage(Message msg) {
            switch (msg.what) {
                  case MSG_INVALIDATE:
                    ((View) msg.obj).invalidate();
                    break;
                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;
                ...
           }
...
}

可以看到postInvalidate()调用顺序为：

View.postInvalidate()->View.postInvalidateDelayed()->ViewRootImpl.dispatchInvalidateDelayed()->
handleMessage(MSG_INVALIDATE/MSG_INVALIDATE_RECT)->View.invalidate()

所以invalidate()和postinvalidate()的区别就是
postinvalidate()官方的注释：

• Cause an invalidate of the specified area to happen on a subsequent cycle through the event loop. Use this to invalidate the View from a non-UI thread.
  可以在非UI线程刷新UI。

3、postInvalidateOnAnimation()

#ViewCompat.java
public static void postInvalidateOnAnimation(@NonNull View view) {
        //SDK版本
        if (Build.VERSION.SDK_INT >= 16) {
            view.postInvalidateOnAnimation();
        } else {
            view.postInvalidate();
        }
    }

public void postInvalidateOnAnimation() {
        // 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.dispatchInvalidateOnAnimation(this);
        }
    }

public void dispatchInvalidateOnAnimation(View view) {
        mInvalidateOnAnimationRunnable.addView(view);
    }

final InvalidateOnAnimationRunnable mInvalidateOnAnimationRunnable =
            new InvalidateOnAnimationRunnable();
final class InvalidateOnAnimationRunnable implements Runnable {
        private boolean mPosted;
        private final ArrayList mViews = new ArrayList();
        private final ArrayList mViewRects =
                new ArrayList();
        private View[] mTempViews;
        private AttachInfo.InvalidateInfo[] mTempViewRects;

        public void addView(View view) {
            synchronized (this) {
                mViews.add(view);
                postIfNeededLocked();
            }
        }
        public void removeView(View view) {
            synchronized (this) {
                mViews.remove(view);
                ...
                if (mPosted && mViews.isEmpty() && mViewRects.isEmpty()) {
                  mChoreographer.removeCallbacks(Choreographer.CALLBACK_ANIMATION, this, null);
                    mPosted = false;
                }
            }
        }

        @Override
        public void run() {
            final int viewCount;
            final int viewRectCount;
            synchronized (this) {
            ...
            for (int i = 0; i < viewCount; i++) {
                mTempViews[i].invalidate();
                mTempViews[i] = null;
            }

            for (int i = 0; i < viewRectCount; i++) {
                final View.AttachInfo.InvalidateInfo info = mTempViewRects[i];
                info.target.invalidate(info.left, info.top, info.right, info.bottom);
                info.recycle();
            }
        }

        private void postIfNeededLocked() {
            if (!mPosted) {
                mChoreographer.postCallback(Choreographer.CALLBACK_ANIMATION, this, null);
                mPosted = true;
            }
        }
    }

postInvalidateOnAnimation()调用顺序为：

View.postInvalidateOnAnimation()->ViewRootImpl.dispatchInvalidateOnAnimation()->
InvalidateOnAnimationRunnable.postIfNeededLocked()->
Choreographer.CALLBACK_ANIMATION->View.invalidate()

总结

invalidate()会立即调用scheduleTraversals().
postinvalidate()会通过消息机制调用invalidate()最终调用scheduleTraversals().
postInvalidateOnAnimation()会通过Vsync机制插入到Choreographer的ANIMATION队列，下次屏幕刷新信号到来时调用invalidate()然后scheduleTraversals()。这个方法也可以在非UI线程调用。