一、View的dispatchTouchEvent和onTouchEvent
探讨Android事件传递机制前，明确android的两大基础控件类型:View和ViewGroup。View即普通的控件，没有子布局的，如Button、TextView. ViewGroup继承自View，表示可以有子控件，如Linearlayout、Listview这些。而事件即MotionEvent，最重要的有3个:
(1)MotionEvent.ACTION_DOWN 按下View，是所有事件的开始
(2)MotionEvent.ACTION_MOVE 滑动事件
(3)MotionEvent.ACTION_UP 与down对应，表示抬起
另外，明确事件传递机制的最终目的都是为了触发执行View的点击监听和触摸监听:
******.setOnClickListener(new View.OnClickListener() { @Override public void onClick(View v) { // TODO Auto-generated method stub Log.i(tag, "testLinelayout---onClick..."); } });
*******.setOnTouchListener(new View.OnTouchListener() { @Override public boolean onTouch(View v, MotionEvent event) { // TODO Auto-generated method stub return false; } });
我们简称为onClick监听和onTouch监听，一般程序会注册这两个监听。从上面可以看到，onTouch监听里默认return false。不要小看了这个return false，后面可以看到它有大用。
对于View来说，事件传递机制有两个函数：dispatchTouchEvent负责分发事件，在dispatch***里又会调用onTouchEvent表示执行事件，或者说消费事件，结合源码分析其流程。事件传递的入口是View的dispatchTouchEvent()函数:
/** * Pass the touch screen motion event down to the target view, or this * view if it is the target. * * @param event The motion event to be dispatched. * @return True if the event was handled by the view, false otherwise. */ public boolean dispatchTouchEvent(MotionEvent event) { if (mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onTouchEvent(event, 0); } if (onFilterTouchEventForSecurity(event)) { //noinspection SimplifiableIfStatement ListenerInfo li = mListenerInfo; if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED && li.mOnTouchListener.onTouch(this, event)) { return true; } if (onTouchEvent(event)) { return true; } } if (mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onUnhandledEvent(event, 0); } return false; } 找到这个判断:
if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED && li.mOnTouchListener.onTouch(this, event)) { return true; }
他会执行View的OnTouchListener.onTouch这个函数，也就是上面说的onTouch监听。里面有三个判断，如果三个都为1，就会执行return true，不往下走了。而默认的onTouch监听返回false，只要一个是false，就不会返回true。接着往下看，程序执行onTouchEvent：
if (onTouchEvent(event)) { return true; } onTouchEvent的源码比较多，贴最重要的:
if (!mHasPerformedLongPress) { // This is a tap, so remove the longpress check removeLongPressCallback(); // Only perform take click actions if we were in the pressed state if (!focusTaken) { // 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(); } } } 可以看到有个performClick(),它的源码里有这么一句 li.mOnClickListener.onClick(this);
public boolean performClick() { sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED); ListenerInfo li = mListenerInfo; if (li != null && li.mOnClickListener != null) { playSoundEffect(SoundEffectConstants.CLICK); li.mOnClickListener.onClick(this); return true; } return false; } 终于对上了，它执行了我们注册的onClick监听。当然执行前会经过一系列判断，是否注册了监听等。 总结:
1、事件入口是dispatchTouchEvent(),它会先执行注册的onTouch监听,如果一切顺利的话，接着执行onTouchEvent，在onTouchEvent里会执行onClick监听。
2、无论是dispatchTouchEvent还是onTouchEvent，如果返回true表示这个事件已经被消费、处理了，不再往下传了。在dispathTouchEvent的源码里可以看到，如果onTouchEvent返回了true，那么它也返回true。如果dispatch***在执行onTouch监听的时候，onTouch返回了true，那么它也返回true，这个事件提前被onTouch消费掉了。就不再执行onTouchEvent了，更别说onClick监听了。
3、我们通常在onTouch监听了设置图片一旦被触摸就改变它的背景、透明度之类的，这个onTouch表示事件的时机。而在onClick监听了去具体干某些事。
二、ViewGroup的dispatchTouchEvent、onInterceptTouchEvent、onTouchEvent
再来看ViewGroup，在复写ViewGroup时可以发现它的onTouchEvent在在View里的，表示这两个方法是一样的。但dispatchTouchEvent是在ViewGroup里的，表示和View的dispatchTouchEvent不一样，多了一个onInterceptTouchEvent函数，表示拦截的意思。 打个很形象的比喻，这玩意就像个秘书、谋士。为啥View没有呢，因为它级别不够，一个Button里面是不可能有子View的。但LinearLayout(继承ViewGroup)就有孩子(子布局)，这个onInterceptTouchEvent就会判断事件要不要通知它的孩子呢。它的源码如下：
public boolean dispatchTouchEvent(MotionEvent ev) { if (mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onTouchEvent(ev, 1); } boolean handled = false; if (onFilterTouchEventForSecurity(ev)) { final int action = ev.getAction(); final int actionMasked = action & MotionEvent.ACTION_MASK; // Handle an initial down. 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(); } // Check for interception. final boolean intercepted; if (actionMasked == MotionEvent.ACTION_DOWN || mFirstTouchTarget != null) { final boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0; if (!disallowIntercept) { intercepted = onInterceptTouchEvent(ev); ev.setAction(action); // restore action in case it was changed } else { intercepted = false; } } else { // There are no touch targets and this action is not an initial down // so this view group continues to intercept touches. intercepted = true; } // Check for cancelation. final boolean canceled = resetCancelNextUpFlag(this) || actionMasked == MotionEvent.ACTION_CANCEL; // Update list of touch targets for pointer down, if needed. final boolean split = (mGroupFlags & FLAG_SPLIT_MOTION_EVENTS) != 0; TouchTarget newTouchTarget = null; boolean alreadyDispatchedToNewTouchTarget = false; if (!canceled && !intercepted) { if (actionMasked == MotionEvent.ACTION_DOWN || (split && actionMasked == MotionEvent.ACTION_POINTER_DOWN) || actionMasked == MotionEvent.ACTION_HOVER_MOVE) { final int actionIndex = ev.getActionIndex(); // always 0 for down final int idBitsToAssign = split ? 1 << ev.getPointerId(actionIndex) : TouchTarget.ALL_POINTER_IDS; // Clean up earlier touch targets for this pointer id in case they // have become out of sync. removePointersFromTouchTargets(idBitsToAssign); final int childrenCount = mChildrenCount; if (childrenCount != 0) { // Find a child that can receive the event. // Scan children from front to back. final View[] children = mChildren; final float x = ev.getX(actionIndex); final float y = ev.getY(actionIndex); final boolean customOrder = isChildrenDrawingOrderEnabled(); for (int i = childrenCount - 1; i >= 0; i--) { final int childIndex = customOrder ? getChildDrawingOrder(childrenCount, i) : i; final View child = children[childIndex]; if (!canViewReceivePointerEvents(child) || !isTransformedTouchPointInView(x, y, child, null)) { continue; } newTouchTarget = getTouchTarget(child); if (newTouchTarget != null) { // Child is already receiving touch within its bounds. // Give it the new pointer in addition to the ones it is handling. newTouchTarget.pointerIdBits |= idBitsToAssign; break; } resetCancelNextUpFlag(child); if (dispatchTransformedTouchEvent(ev, false, child, idBitsToAssign)) { // Child wants to receive touch within its bounds. mLastTouchDownTime = ev.getDownTime(); mLastTouchDownIndex = childIndex; mLastTouchDownX = ev.getX(); mLastTouchDownY = ev.getY(); newTouchTarget = addTouchTarget(child, idBitsToAssign); alreadyDispatchedToNewTouchTarget = true; break; } } } if (newTouchTarget == null && mFirstTouchTarget != null) { // Did not find a child to receive the event. // Assign the pointer to the least recently added target. newTouchTarget = mFirstTouchTarget; while (newTouchTarget.next != null) { newTouchTarget = newTouchTarget.next; } newTouchTarget.pointerIdBits |= idBitsToAssign; } } } // Dispatch to touch targets. 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. TouchTarget predecessor = null; TouchTarget target = mFirstTouchTarget; while (target != null) { final TouchTarget next = target.next; if (alreadyDispatchedToNewTouchTarget && target == newTouchTarget) { handled = true; } else { final boolean cancelChild = resetCancelNextUpFlag(target.child) || intercepted; if (dispatchTransformedTouchEvent(ev, cancelChild, target.child, target.pointerIdBits)) { handled = true; } if (cancelChild) { if (predecessor == null) { mFirstTouchTarget = next; } else { predecessor.next = next; } target.recycle(); target = next; continue; } } predecessor = target; target = next; } } // Update list of touch targets for pointer up or cancel, if needed. if (canceled || actionMasked == MotionEvent.ACTION_UP || actionMasked == MotionEvent.ACTION_HOVER_MOVE) { resetTouchState(); } else if (split && actionMasked == MotionEvent.ACTION_POINTER_UP) { final int actionIndex = ev.getActionIndex(); final int idBitsToRemove = 1 << ev.getPointerId(actionIndex); removePointersFromTouchTargets(idBitsToRemove); } } if (!handled && mInputEventConsistencyVerifier != null) { mInputEventConsistencyVerifier.onUnhandledEvent(ev, 1); } return handled; } 可以看到标红的有两句(intercepted = onInterceptTouchEvent(ev); if (!canceled && !intercepted) )，它会先调用 intercepted = onInterceptTouchEvent(ev);然后通过if判断。
public boolean onInterceptTouchEvent(MotionEvent ev) { return false; } 它就一句话，默认false。也就是说这个谋士默认的意见是，永远不拦截！！！！只要有孩子，就交给孩子们处理吧。
最后的结论:
1、如果是自定义复合控件，如图片+文字，我再Activity里给你注册了onClick监听，期望点击它执行。那么最简单的方法就是将图片+文字的父布局，也即让其容器ViewGroup的秘书将事件拦下，这样父亲就可以执行onClick了。这时候的父亲就像一个独立的孩子一样了(View)，无官一身轻，再也不用管它的孩子了,可以正常onClick onTouch.
2、如果希望一个View只onTouch而不onClick，在onTouch里return true就ok了。
3、dispatch是为了onTouch监听，onTouchEvent是为了onClick监听。
4、自定义布局时，一般情况下：
@Override public boolean onTouchEvent(MotionEvent event) {return super.onTouchEvent(event);}
@Override public boolean dispatchTouchEvent(MotionEvent event) {return super.dispatchTouchEvent(event);
我们可以复写，但是最后的super.***是万万不能少滴。如果少了，表示连dispatch*** onTouchEvent压根就不调用了，事件就此打住。
转载：http://blog.csdn.net/yanzi1225627/article/details/22592831