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本文背景:前些天用到了之前写的自定义图片文字复合控件，在给他设置监听时遇到了麻烦。虽然最后解决了问题，但发现在不重写LinearLayout的onInterceptTouchEvent时，子ImageView、子TextView、父Linearlayout三者不同的属性配置(android:clickable android:focuseable)会造成自定义控件onClick监听失败、或成功。复写了父Linearlayout 的onInterceptTouchEvent时，监听不受子图片、子文字的属性影响。为知其所以然，深入研究android的事件传递机制，记录于此。
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。
下面通过代码来说明,自定义一个TestButton继承自Button，重写它的dispath***和onTouchEvent方法，为了简单只关注down和up事件。
package org.yanzi.ui;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.Button;
public class TestButton extends Button {
private final static String tag = "yan";
public TestButton(Context context, AttributeSet attrs) {
super(context, attrs);
// TODO Auto-generated constructor stub
}
@Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub
switch(event.getAction()){
case MotionEvent.ACTION_DOWN:
Log.i(tag, "TestButton-onTouchEvent-ACTION_DOWN...");
break;
case MotionEvent.ACTION_UP:
Log.i(tag, "TestButton-onTouchEvent-ACTION_UP...");
break;
default:break;
}
return super.onTouchEvent(event);
}
@Override
public boolean dispatchTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub
switch(event.getAction()){
case MotionEvent.ACTION_DOWN:
Log.i(tag, "TestButton-dispatchTouchEvent-ACTION_DOWN...");
break;
case MotionEvent.ACTION_UP:
Log.i(tag, "TestButton-dispatchTouchEvent-ACTION_UP...");
break;
default:break;
}
return super.dispatchTouchEvent(event);
}
}
在Activity里注册两个监听:
testBtn.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
// TODO Auto-generated method stub
Log.i(tag, "testBtn---onClick...");
}
});
testBtn.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
// TODO Auto-generated method stub
switch(event.getAction()){
case MotionEvent.ACTION_DOWN:
Log.i(tag, "testBtn-onTouch-ACTION_DOWN...");
break;
case MotionEvent.ACTION_UP:
Log.i(tag, "testBtn-onTouch-ACTION_UP...");
break;
default:break;
}
return false;
}
});
同时复写Activity的dispatch方法和onTouchEvent方法：
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
// TODO Auto-generated method stub
switch(ev.getAction()){
case MotionEvent.ACTION_DOWN:
Log.i(tag, "MainActivity-dispatchTouchEvent-ACTION_DOWN...");
break;
case MotionEvent.ACTION_UP:
Log.i(tag, "MainActivity-dispatchTouchEvent-ACTION_UP...");
break;
default:break;
}
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
// TODO Auto-generated method stub
switch(event.getAction()){
case MotionEvent.ACTION_DOWN:
Log.i(tag, "MainActivity-onTouchEvent-ACTION_DOWN...");
break;
case MotionEvent.ACTION_UP:
Log.i(tag, "MainActivity-onTouchEvent-ACTION_UP...");
break;
default:break;
}
return super.onTouchEvent(event);
}
最终一次点击，打印信息如下:
Line 33: 01-08 14:59:45.847 I/yan ( 4613): MainActivity-dispatchTouchEvent-ACTION_DOWN... Line 35: 01-08 14:59:45.849 I/yan ( 4613): TestButton-dispatchTouchEvent-ACTION_DOWN... Line 37: 01-08 14:59:45.849 I/yan ( 4613): testBtn-onTouch-ACTION_DOWN... Line 39: 01-08 14:59:45.849 I/yan ( 4613): TestButton-onTouchEvent-ACTION_DOWN... Line 41: 01-08 14:59:45.939 I/yan ( 4613): MainActivity-dispatchTouchEvent-ACTION_UP... Line 43: 01-08 14:59:45.941 I/yan ( 4613): TestButton-dispatchTouchEvent-ACTION_UP... Line 45: 01-08 14:59:45.944 I/yan ( 4613): testBtn-onTouch-ACTION_UP... Line 47: 01-08 14:59:45.946 I/yan ( 4613): TestButton-onTouchEvent-ACTION_UP... Line 49: 01-08 14:59:45.974 I/yan ( 4613): testBtn---onClick...
事件先由Activity的dispatchTouchEvent进行分发，然后TestButton的dispatchTouchEvent进行分发，接着执行onTouch监听，然后执行onTouchEvent。第二次UP动作的时候，在onTouchEvent里又执行了onClick监听。
如果我们想这个TestButton只能执行onTouch监听不能执行onClick监听，方法有很多。在onTouch监听里默认返回false改为true，如下:
testBtn.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View v, MotionEvent event) {
// TODO Auto-generated method stub
switch(event.getAction()){
case MotionEvent.ACTION_DOWN:
Log.i(tag, "testBtn-onTouch-ACTION_DOWN...");
break;
case MotionEvent.ACTION_UP:
Log.i(tag, "testBtn-onTouch-ACTION_UP...");
break;
default:break;
}
return true;
}
});
事件流程为:
Line 75: 01-08 15:05:51.627 I/yan ( 5262): MainActivity-dispatchTouchEvent-ACTION_DOWN... Line 77: 01-08 15:05:51.628 I/yan ( 5262): TestButton-dispatchTouchEvent-ACTION_DOWN... Line 79: 01-08 15:05:51.629 I/yan ( 5262): testBtn-onTouch-ACTION_DOWN... Line 81: 01-08 15:05:51.689 I/yan ( 5262): MainActivity-dispatchTouchEvent-ACTION_UP... Line 83: 01-08 15:05:51.691 I/yan ( 5262): TestButton-dispatchTouchEvent-ACTION_UP... Line 85: 01-08 15:05:51.695 I/yan ( 5262): testBtn-onTouch-ACTION_UP...
可以看到压根就没执行onTouchEvent。因为onTouch返回了true，已提前将这个事件消费了，就不往下传了，dispatch流程提前终止。
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。链接 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 = 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 |