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android 事件处理机制是对用户触摸屏幕产生的Motion Event事件的传递响应处理机制。
Motion Event事件类型很多，包括单触点及多触点的各种情况，可以参考这篇文章Android MotionEvent详解
本文不对源码做详细分析，源码分析可参考:
Andriod 从源码的角度详解View,ViewGroup的Touch事件的分发机制
处理机制涉及activity,viewGroup,view三类对象。
viewGroup,view可以处理触摸事件是显而易见的，但activity是界面的载体不是界面，那么activity为什么可以处理呢？看一下acitvity的源码：
public class Activity extends ContextThemeWrapper
implements LayoutInflater.Factory2,
Window.Callback,KeyEvent.Callback,
OnCreateContextMenuListener,
ComponentCallbacks2,
window.OnWindowDismissedCallback,
WindowControllerCallback{}可以看到，activity实现了Window.Callback接口，顾名思义，Window是可以处理触摸事件的。实际上Activity在onCreate时调用attach方法，在attach方法中会创建window对象。window对象创建时并没有创建 DocerView 对象。用户在Activity中调用setContentView,然后调用window的setContentView，这时会检查DecorView是否存在，如果不存在则创建DecorView对象，然后把用户自己的 View 添加到 DecorView 中。这样，activity就和window建立了联系。
事件处理流程按照先后顺序是acivity<->viewGroup<->view。
涉及三个处理方法：dispatchTouchEvent（事件处理流程）,onTouchEvent（处理Touch事件）,onInterceptTouchEvent（拦截Touch事件）。
dispatchTouchEvent就像我们算法常用的递归回溯调用一样，一层一层推动流程。
首先，Activity进行处理，它就直接交由上层的viewGroup。ViewGroup如果不消耗，就交给它的下一层ViewGroup处理，如果仍旧不消耗就一层层直到指定的View。View进行处理，就是调用它的onTouchEvent，如果不做处理，就把这件事扔回上一层，像递归一样一层层往上走，直到有人处理。
如果有一层ViewGroup不想向下传递事件而是直接拦截，就通过onInterceptTouchEvent方法设置拦截。
需要注意的是
action动作包含Action_Down开始的一系列行为，如果Acition_Down事件在本层被消耗了，后续的动作不再做判断，直接在此处消耗，直到新的action系列开始。但如果Action_Down时未被消耗，以后的动作仍需要每次做判断，是否处理。
activity,view包含如下两个方法:
public boolean dispatchTouchEvent(MotionEvent ev)
public boolean onTouchEvent(MotionEvent ev)ViewGroup包含所有三个方法：
public boolean dispatchTouchEvent(MotionEvent ev)
public boolean onInterceptTouchEvent(MotionEvent ev)
public boolean onTouchEvent(MotionEvent ev)处理关系简图：
onTouch ，OnClick执行顺序的问题
这个其实参考View的onTouchEvent源码就清楚了
public boolean dispatchTouchEvent(MotionEvent event) {
// If the event should be handled by accessibility focus first.
if (event.isTargetAccessibilityFocus()) {
// We don't have focus or no virtual descendant has it, do not handle the event.
if (!isAccessibilityFocusedViewOrHost()) {
return false;
}
// We have focus and got the event, then use normal event dispatch.
event.setTargetAccessibilityFocus(false);
}
boolean result = false;
if (mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onTouchEvent(event, 0);
}
final int actionMasked = event.getActionMasked();
if (actionMasked == MotionEvent.ACTION_DOWN) {
// Defensive cleanup for new gesture
stopNestedScroll();
}
if (onFilterTouchEventForSecurity(event)) {
if ((mViewFlags & ENABLED_MASK) == ENABLED && handleScrollBarDragging(event)) {
result = true;
}
//noinspection SimplifiableIfStatement
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;
}
}
if (!result && mInputEventConsistencyVerifier != null) {
mInputEventConsistencyVerifier.onUnhandledEvent(event, 0);
}
// Clean up after nested scrolls if this is the end of a gesture;
// also cancel it if we tried an ACTION_DOWN but we didn't want the rest
// of the gesture.
if (actionMasked == MotionEvent.ACTION_UP ||
actionMasked == MotionEvent.ACTION_CANCEL ||
(actionMasked == MotionEvent.ACTION_DOWN && !result)) {
stopNestedScroll();
}
return result;
}代码比较长，我们提出相关的那部分：
if (li != null && li.mOnTouchListener != null
&& (mViewFlags & ENABLED_MASK) == ENABLED
&& li.mOnTouchListener.onTouch(this, event)) {
result = true;
}
if (!result && onTouchEvent(event)) {
result = true;
}可以看到，第一个if语句，先判断执行onTouchListener的onTouch方法，如果都返回true，代码就不再执行下一个if 语句。那onClick在在哪呢？在第二个if语句里的onTouchEvent里。
代码比较长，只要关注performClick方法的调用就行了。
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.
return (((viewFlags & CLICKABLE) == CLICKABLE
|| (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)
|| (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE);
}
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) {
// take focus if we don't have it already and we should in
// touch mode.
boolean focusTaken = false;
if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {
focusTaken = requestFocus();
}
if (prepressed) {
// The button is being released before we actually
// showed it as pressed. Make it show the pressed
// state now (before scheduling the click) to ensure
// the user sees it.
setPressed(true, x, y);
}
if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {
// 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();
}
}
}
if (mUnsetPressedState == null) {
mUnsetPressedState = new UnsetPressedState();
}
if (prepressed) {
postDelayed(mUnsetPressedState,
ViewConfiguration.getPressedStateDuration());
} else if (!post(mUnsetPressedState)) {
// If the post failed, unpress right now
mUnsetPressedState.run();
}
removeTapCallback();
}
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_DOWN:
mHasPerformedLongPress = false;
if (performButtonActionOnTouchDown(event)) {
break;
}
// Walk up the hierarchy to determine if we're inside a scrolling container.
boolean isInScrollingContainer = isInScrollingContainer();
// For views inside a scrolling container, delay the pressed feedback for
// a short period in case this is a scroll.
if (isInScrollingContainer) {
mPrivateFlags |= PFLAG_PREPRESSED;
if (mPendingCheckForTap == null) {
mPendingCheckForTap = new CheckForTap();
}
mPendingCheckForTap.x = event.getX();
mPendingCheckForTap.y = event.getY();
postDelayed(mPendingCheckForTap, ViewConfiguration.getTapTimeout());
} else {
// Not inside a scrolling container, so show the feedback right away
setPressed(true, x, y);
checkForLongClick(0, x, y);
}
break;
case MotionEvent.ACTION_CANCEL:
setPressed(false);
removeTapCallback();
removeLongPressCallback();
mInContextButtonPress = false;
mHasPerformedLongPress = false;
mIgnoreNextUpEvent = false;
break;
case MotionEvent.ACTION_MOVE:
drawableHotspotChanged(x, y);
// Be lenient about moving outside of buttons
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 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;
}
sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
return result;
}
结论
事件处理机制网上的帖子很多，讲得也很清楚，只是自己写一下，会理解更好一点。