ViewGroup和View以及TouchDelegate的触摸事件源码简析
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参考：
浅尝安卓事件分发机制
http://blog.csdn.net/zhaizu/article/details/50489398深入Android开发之--理解View#onTouchEvent
https://my.oschina.net/banxi/blog/187267?p=1
Android 触摸消息处理
http://blog.csdn.net/siobhan/article/details/8257334
public boolean dispatchTouchEvent(MotionEvent ev) { ...... final int action = ev.getAction(); final int actionMasked = action & MotionEvent.ACTION_MASK; //down事件来时，清理之前的各种状态 if (actionMasked == MotionEvent.ACTION_DOWN) { // Throw away all previous state when starting a new touch gesture. // The framework may have dropped the up or cancel event for the previous gesture // due to an app switch, ANR, or some other state change. cancelAndClearTouchTargets(ev); resetTouchState(); } //ViewGroup节点是否要处理本次触摸事件，down事件或者mFirstTouchTarget不为空，则要检查子节点是否不允许父节点打断时间流程 final boolean intercepted; if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) { final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; //子节点未设置不允许父节点打断流程，则调用onInterceptTouchEvent询问父节点是否要自己处理该事件 if (!disallowIntercept) { intercepted = onInterceptTouchEvent(ev); ev.setAction(action); // restore action in case it was changed } else { intercepted = false; } } else { //当前不是down事件，并且在之前的down事件中，没有子节点来处理事件，所以move和up都由当前viewgroup来处理 intercepted = true; } //当前ViewGroup不处理该事件，且为down事件，则尝试找一个子节点处理 if (!canceled && !intercepted) { if (actionMasked == MotionEvent.ACTION_DOWN) { final int childrenCount = mChildrenCount; if (newTouchTarget == null && childrenCount != 0) { //找到一个触摸位置在该chile里的节点 final View[] children = mChildren; for (int i = childrenCount - 1; i >= 0; i--) { final View child = children[i]; if(dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)){ mFirstTouchTarget = target; alreadyDispatchedToNewTouchTarget ＝ true; } } } } } //找不到处理该消息的子节点，则由当前节点处理 if (mFirstTouchTarget == null) { // No touch targets so treat this as an ordinary view. handled = dispatchTransformedTouchEvent(ev, canceled, null, TouchTarget.ALL_POINTER_IDS); } else { // Dispatch to touch targets, excluding the new touch target if we already // dispatched to it. Cancel touch targets if necessary. //由mFirstTouchTarget继续处理剩余事件 TouchTarget predecessor = null; TouchTarget target = mFirstTouchTarget; if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) { handled = true; } else { if (dispatchTransformedTouchEvent(ev, cancelChild, target.child, target.pointerIdBits)) { handled = true; } } } return handled;}public boolean onInterceptTouchEvent(MotionEvent ev) { //默认都为false return false;}//如果child为空，则由当前的ViewGroup调用它作为View的dispatchTouchEvent，否则调用child的dispatchTouchEventprivate boolean dispatchTransformedTouchEvent(MotionEvent event, boolean cancel, View child, int desiredPointerIdBits) { final boolean handled; final MotionEvent transformedEvent = MotionEvent.obtain(event); // Perform any necessary transformations and dispatch. if (child == null) { handled = super.dispatchTouchEvent(transformedEvent); } else { //坐标变换到child的空间 final float offsetX = mScrollX - child.mLeft; final float offsetY = mScrollY - child.mTop; transformedEvent.offsetLocation(offsetX, offsetY); handled = child.dispatchTouchEvent(transformedEvent); } // Done. transformedEvent.recycle(); return handled;}//是否可见，并且是否没有在播放动画private static boolean canViewReceivePointerEvents(@NonNull View child) { return (child.mViewFlags & VISIBILITY_MASK) == VISIBLE || child.getAnimation() != null;}protected boolean isTransformedTouchPointInView(float x, float y, View child, PointF outLocalPoint) { final float[] point = getTempPoint(); point[0] = x; point[1] = y; transformPointToViewLocal(point, child); final boolean isInView = child.pointInView(point[0], point[1]); if (isInView && outLocalPoint != null) { outLocalPoint.set(point[0], point[1]); } return isInView;}public void transformPointToViewLocal(float[] point, View child) { point[0] += mScrollX - child.mLeft; point[1] += mScrollY - child.mTop; if (!child.hasIdentityMatrix()) { child.getInverseMatrix().mapPoints(point); }}//View的dispatchTouchEvent的主要作用就是调用mOnTouchListener的onTouch和onTouchEventpublic boolean dispatchTouchEvent(MotionEvent event) { boolean result = false; final int actionMasked = event.getActionMasked(); ListenerInfo li = mListenerInfo; if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED && li.mOnTouchListener.onTouch(this, event)) { result = true; } if (!result && onTouchEvent(event)) { result = true; } return result;}//view自身处理事件，将点击事件的回调通过post来执行，保证了先看到UI的变化，再执行逻辑public boolean onTouchEvent(MotionEvent event) { final float x = event.getX(); final float y = event.getY(); final int viewFlags = mViewFlags; final int action = event.getAction(); if ((viewFlags & ENABLED_MASK) == DISABLED) { if (action == MotionEvent.ACTION_UP && (mPrivateFlags & PFLAG_PRESSED) != 0) { setPressed(false); } // A disabled view that is clickable still consumes the touch // events, it just doesn't respond to them. //disabled的View如果可点击，依然会吞噬事件 return (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE); } //如果有view设置了代理，则由代理view处理事件 if (mTouchDelegate != null) { if (mTouchDelegate.onTouchEvent(event)) { return true; } } if (((viewFlags & CLICKABLE) == CLICKABLE || (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) || (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) { switch (action) { case MotionEvent.ACTION_UP: boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0; if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) { // Use a Runnable and post this rather than calling // performClick directly. This lets other visual state // of the view update before click actions start. if (mPerformClick == null) { mPerformClick = new PerformClick(); } if (!post(mPerformClick)) { performClick(); } removeTapCallback(); } mIgnoreNextUpEvent = false; break; case MotionEvent.ACTION_DOWN: mHasPerformedLongPress = false; setPressed(true, x, y); checkForLongClick(0, x, y); break; case MotionEvent.ACTION_CANCEL: setPressed(false); ...... break; case MotionEvent.ACTION_MOVE: drawableHotspotChanged(x, y); // Be lenient about moving outside of buttons //是否移出了View之外 if (!pointInView(x, y, mTouchSlop)) { // Outside button removeTapCallback(); if ((mPrivateFlags & PFLAG_PRESSED) != 0) { // Remove any future long press/tap checks removeLongPressCallback(); setPressed(false); } } break; } return true; } return false;}public boolean pointInView(float localX, float localY, float slop) { return localX >= -slop && localY >= -slop && localX < ((mRight - mLeft) + slop) && localY < ((mBottom - mTop) + slop);}private final class PerformClick implements Runnable { @Override public void run() { performClick(); }}public boolean performClick() { final boolean result; final ListenerInfo li = mListenerInfo; if (li != null && li.mOnClickListener != null) { playSoundEffect(SoundEffectConstants.CLICK); li.mOnClickListener.onClick(this); result = true; } else { result = false; } return result;}//TouchDelegate类可以让一个view的点击区域变大，以方便点击//具体用法是，在当前view的父节点中设置TouchDelegate，传入当前view以及rect//rect的求法是view.getHitRect(rect)，表示view在父节点中的范围，再根据需要手动扩大rectpublic class TouchDelegate { //需要点击区域变大的那个view private View mDelegateView; //变大后的点击区域 private Rect mBounds; //在mBounds区域的基础上又考虑了slop private Rect mSlopBounds; /** * True if the delegate had been targeted on a down event (intersected mBounds). */ //down事件是否在mSlopBounds区域内，表示可以传递给mDelegateView private boolean mDelegateTargeted; private int mSlop; //bounds一般为delegateView.getHitRect(bounds)在扩大一部分，delegateView为最终接收点击事件的view，一般为当前节点的子节点 public TouchDelegate(Rect bounds, View delegateView) { mBounds = bounds; mSlop = ViewConfiguration.get(delegateView.getContext()).getScaledTouchSlop(); mSlopBounds = new Rect(bounds); mSlopBounds.inset(-mSlop, -mSlop); mDelegateView = delegateView; } //event为当前节点收到的事件，判断其是否在mBounds范围内，已决定是否传递给子节点delegateView public boolean onTouchEvent(MotionEvent event) { int x = (int)event.getX(); int y = (int)event.getY(); boolean sendToDelegate = false; boolean hit = true; boolean handled = false; switch (event.getAction()) { case MotionEvent.ACTION_DOWN: Rect bounds = mBounds; //点击位置在mBounds范围内，准备传递给子节点 if (bounds.contains(x, y)) { mDelegateTargeted = true; sendToDelegate = true; } break; case MotionEvent.ACTION_UP: case MotionEvent.ACTION_MOVE: sendToDelegate = mDelegateTargeted; if (sendToDelegate) { Rect slopBounds = mSlopBounds; if (!slopBounds.contains(x, y)) { hit = false; } } break; case MotionEvent.ACTION_CANCEL: sendToDelegate = mDelegateTargeted; mDelegateTargeted = false; break; } if (sendToDelegate) { final View delegateView = mDelegateView; if (hit) { // Offset event coordinates to be inside the target view //如果判定为在mBounds或mSlopBounds范围内，则设置点击位置为delegateView的中心 event.setLocation(delegateView.getWidth() / 2, delegateView.getHeight() / 2); } else { // Offset event coordinates to be outside the target view (in case it does // something like tracking pressed state) //未在范围内，则设定为一个负值 int slop = mSlop; event.setLocation(-(slop * 2), -(slop * 2)); } handled = delegateView.dispatchTouchEvent(event); } return handled; }}参考：
Android TouchDelegate http://blog.csdn.net/a220315410/article/details/9141265
http://blog.csdn.net/tongcpp/article/details/23450975
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