在分析android事件分发机制前，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。今天我们先来了解view的事件分发机制。
先看下代码，非常简单，只有一个button，分别给它注册了onclick和ontouch的点击事件。
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btn.setonclicklistener(new view.onclicklistener() {
@override
public void onclick(view v) {
log.i("tag", "this is button onclick event");
}
});
btn.setontouchlistener(new view.ontouchlistener() {
@override
public boolean ontouch(view v, motionevent event) {
log.i("tag", "this is button ontouch action" + event.getaction());
return false;
}
});
运行一下项目，结果如下：
i/tag: this is button ontouch action0
i/tag: this is button ontouch action2
i/tag: this is button ontouch action2
i/tag: this is button ontouch action1
i/tag: this is button onclick event
可以看到，ontouch是有先于onclick执行的，因此事件的传递顺序是先ontouch，在到onclick。具体为什么这样，下面会通过源码来说明。这时，我们可能注意到了，ontouch的方法是有返回值，这里是返回false，我们将它改为true再运行一次，结果如下：
i/tag: this is button ontouch action0
i/tag: this is button ontouch action2
i/tag: this is button ontouch action2
i/tag: this is button ontouch action2
i/tag: this is button ontouch action1
对比两次结果，我们发现onclick方法不再执行，为什么会这样，下面我将通过源码给大家一步步理清这个思路。
查看源码时，首先要知道所有view类型控件事件入口都是dispatchtouchevent()，所以我们直接进入到view这个类里面的dispatchtouchevent（）方法看一下。
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)) {
//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;
}
从源码第25行处可以看到，montouchlistener.ontouch()的方法首先被执行，如果li != null && li.montouchlistener != null&& (mviewflags & enabled_mask) == enabled&& li.montouchlistener.ontouch(this, event)都为真的话，result赋值为true，否则就执行ontouchevent(event)方法。
从上面可以看到要符合条件有四个，
1、listenerinfo li，它是view中的一个静态类，里面定义view的事件的监听等等，所以有涉及到view的事件，listenerinfo都会被实例化，因此li不为null
2、montouchilistener是在setontouchlistener方法里面赋值的，只要touch事件被注册，montouchilistener一定不会null
3、 (mviewflags & enabled_mask) == enabled，是判断当前点击的控件是否是enable的，button默认为enable，这个条件也恒定为true，
4、重点来了，li.montouchlistener.ontouch(this, event)就是回调控件ontouch方法，当这个条件也为true时，result=true,ontouchevent（event）将不会被执行。如果ontouch返回false，就会再执行ontouchevent(event)方法。
我们接着再进入到ontouchevent方法查看源码。
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);
}
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;
}
从源码的21行我们可以看出，该控件可点击就会进入到switch判断中，当我们触发了手指离开的实际，则会进入到motionevent.action_up这个case当中。我们接着往下看，在源码的50行，调用到了mperformclick()方法，我们继续进入到这个方法的源码看看。
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;
}
现在我们可以看到，只要listenerinfo和monclicklistener不为null就会调用onclick这个方法，之前说过，只要有监听事件，listenerinfo就不为null，带monclicklistener又是在哪里赋值呢？我们再继续看下它的源码。
public void setonclicklistener(@nullable onclicklistener l) {
if (!isclickable()) {
setclickable(true);
}
getlistenerinfo().monclicklistener = l;
}
看到这里一切就清楚了，当我们调用setonclicklistener方法来给按钮注册一个点击事件时，就会给monclicklistener赋值。整个分发事件的顺序是ontouch()-->ontouchevent(event)-->performclick()-->onclick()。
现在我们可以解决之前的问题。
1、ontouch方法是优先于onclick，所以是执行了ontouch，再执行onclick。
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dispatchtouchevent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。
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持移动技术网。
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