上一篇已经完整的解析了Android View的事件分发机制，今天给大家代码viewGroup事件分发的源码解析~~凡是自定义ViewGroup实现各种滑动效果的，不可避免的会出现很多事件的冲突，对ViewGroup事件分发机制的了解，也有益于大家了解冲突产生的原因，以及对冲突进行处理~
1、案例
首先我们接着上一篇的代码，在代码中添加一个自定义的LinearLayout：
package com.example.zhy_event03;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.widget.LinearLayout;
public class MyLinearLayout extends LinearLayout
{
private static final String TAG = MyLinearLayout.class.getSimpleName();
public MyLinearLayout(Context context, AttributeSet attrs)
{
super(context, attrs);
}
@Override
public boolean dispatchTouchEvent(MotionEvent ev)
{
int action = ev.getAction();
switch (action)
{
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "dispatchTouchEvent ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG, "dispatchTouchEvent ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "dispatchTouchEvent ACTION_UP");
break;
default:
break;
}
return super.dispatchTouchEvent(ev);
}
@Override
public boolean onTouchEvent(MotionEvent event)
{
int action = event.getAction();
switch (action)
{
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "onTouchEvent ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG, "onTouchEvent ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "onTouchEvent ACTION_UP");
break;
default:
break;
}
return super.onTouchEvent(event);
}
@Override
public boolean onInterceptTouchEvent(MotionEvent ev)
{
int action = ev.getAction();
switch (action)
{
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "onInterceptTouchEvent ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG, "onInterceptTouchEvent ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "onInterceptTouchEvent ACTION_UP");
break;
default:
break;
}
return super.onInterceptTouchEvent(ev);
}
@Override
public void requestDisallowInterceptTouchEvent(boolean disallowIntercept)
{
Log.e(TAG, "requestDisallowInterceptTouchEvent ");
super.requestDisallowInterceptTouchEvent(disallowIntercept);
}
}
继承LinearLayout，然后复写了与事件分发机制有关的代码，添加上了日志的打印~
然后看我们的布局文件：
<com.example.zhy_event03.MyLinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".MainActivity" >
<com.example.zhy_event03.MyButton
android:id="@+id/id_btn"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="click me" />
</com.example.zhy_event03.MyLinearLayout>
MyLinearLayout中包含一个MyButton，MyButton都上篇博客中已经出现过，这里就不再贴代码了，不清楚可以去查看~
然后MainActivity就是直接加载布局，没有任何代码~~~
直接运行我们的代码，然后点击我们的Button，依然是有意的MOVE一下，不然不会触发MOVE事件，看一下日志的输出：
09-06 09:57:27.287: E/MyLinearLayout(959): dispatchTouchEvent ACTION_DOWN 09-06 09:57:27.287: E/MyLinearLayout(959): onInterceptTouchEvent ACTION_DOWN 09-06 09:57:27.287: E/MyButton(959): dispatchTouchEvent ACTION_DOWN 09-06 09:57:27.297: E/MyButton(959): onTouchEvent ACTION_DOWN 09-06 09:57:27.297: E/MyButton(959): onTouchEvent ACTION_MOVE 09-06 09:57:27.327: E/MyLinearLayout(959): dispatchTouchEvent ACTION_MOVE 09-06 09:57:27.327: E/MyLinearLayout(959): onInterceptTouchEvent ACTION_MOVE 09-06 09:57:27.337: E/MyButton(959): dispatchTouchEvent ACTION_MOVE 09-06 09:57:27.337: E/MyButton(959): onTouchEvent ACTION_MOVE 09-06 09:57:27.457: E/MyLinearLayout(959): dispatchTouchEvent ACTION_UP 09-06 09:57:27.457: E/MyLinearLayout(959): onInterceptTouchEvent ACTION_UP 09-06 09:57:27.457: E/MyButton(959): dispatchTouchEvent ACTION_UP 09-06 09:57:27.457: E/MyButton(959): onTouchEvent ACTION_UP
可以看到大体的事件流程为：
MyLinearLayout的dispatchTouchEvent -> MyLinearLayout的onInterceptTouchEvent -> MyButton的dispatchTouchEvent ->Mybutton的onTouchEvent
可以看出，在View上触发事件，最先捕获到事件的为View所在的ViewGroup，然后才会到View自身~
下面我们按照日志的输出，进入源码~
2、源码分析
ViewGroup - dispatchTouchEvent
1、ViewGroup - dispatchTouchEvent – ACTION_DOWN
首先是ViewGroup的dispatchTouchEvent方法：
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
if (!onFilterTouchEventForSecurity(ev)) {
return false;
}
final int action = ev.getAction();
final float xf = ev.getX();
final float yf = ev.getY();
final float scrolledXFloat = xf + mScrollX;
final float scrolledYFloat = yf + mScrollY;
final Rect frame = mTempRect;
boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (action == MotionEvent.ACTION_DOWN) {
if (mMotionTarget != null) {
// this is weird, we got a pen down, but we thought it was
// already down!
// XXX: We should probably send an ACTION_UP to the current
// target.
mMotionTarget = null;
}
// If we're disallowing intercept or if we're allowing and we didn't
// intercept
if (disallowIntercept || !onInterceptTouchEvent(ev)) {
// reset this event's action (just to protect ourselves)
ev.setAction(MotionEvent.ACTION_DOWN);
// We know we want to dispatch the event down, find a child
// who can handle it, start with the front-most child.
final int scrolledXInt = (int) scrolledXFloat;
final int scrolledYInt = (int) scrolledYFloat;
final View[] children = mChildren;
final int count = mChildrenCount;
for (int i = count - 1; i >= 0; i--) {
final View child = children[i];
if ((child.mViewFlags & VISIBILITY_MASK) == VISIBLE
|| child.getAnimation() != null) {
child.getHitRect(frame);
if (frame.contains(scrolledXInt, scrolledYInt)) {
// offset the event to the view's coordinate system
final float xc = scrolledXFloat - child.mLeft;
final float yc = scrolledYFloat - child.mTop;
ev.setLocation(xc, yc);
child.mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
if (child.dispatchTouchEvent(ev)) {
// Event handled, we have a target now.
mMotionTarget = child;
return true;
}
// The event didn't get handled, try the next view.
// Don't reset the event's location, it's not
// necessary here.
}
}
}
}
} ....//other code omitted
代码比较长，决定分段贴出，首先贴出的是ACTION_DOWN事件相关的代码。
16行：进入ACTION_DOWN的处理
17-23行：将mMotionTarget置为null
26行：进行判断：if(disallowIntercept || !onInterceptTouchEvent(ev))
两种可能会进入IF代码段
1、当前不允许拦截，即disallowIntercept =true，
2、当前允许拦截但是不拦截，即disallowIntercept =false,但是onInterceptTouchEvent(ev)返回false ;
注：disallowIntercept 可以通过viewGroup.requestDisallowInterceptTouchEvent(boolean);进行设置，后面会详细说；而onInterceptTouchEvent(ev)可以进行复写。
36-57行：开始遍历所有的子View
41行：进行判断当前的x,y坐标是否落在子View身上，假如在，47行，执行child.dispatchTouchEvent(ev)，就进入了View的dispatchTouchEvent代码中了，假如不了解请参考：Android View的事件分发机制，当child.dispatchTouchEvent(ev)返回true，则为mMotionTarget=child;然后return true;
ViewGroup的ACTION_DOWN分析结束，总结一下：
ViewGroup实现捕获到DOWN事件，假如代码中不做TOUCH事件拦截，则开始查找当前x,y是否在某个子View的区域内，假如在，则把事件分发下去。
按照日志，接下来到达ACTION_MOVE
2、ViewGroup - dispatchTouchEvent – ACTION_MOVE
首先我们源码进行删减，只留下MOVE相关的代码：
@Override
public boolean dispatchTouchEvent(MotionEvent ev) {
final int action = ev.getAction();
final float xf = ev.getX();
final float yf = ev.getY();
final float scrolledXFloat = xf + mScrollX;
final float scrolledYFloat = yf + mScrollY;
final Rect frame = mTempRect;
boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
//...ACTION_DOWN
//...ACTIN_UP or ACTION_CANCEL
// The event wasn't an ACTION_DOWN, dispatch it to our target if
// we have one.
final View target = mMotionTarget;
// if have a target, see if we're allowed to and want to intercept its
// events
if (!disallowIntercept && onInterceptTouchEvent(ev)) {
//....
}
// finally offset the event to the target's coordinate system and
// dispatch the event.
final float xc = scrolledXFloat - (float) target.mLeft;
final float yc = scrolledYFloat - (float) target.mTop;
ev.setLocation(xc, yc);
return target.dispatchTouchEvent(ev);
}
18行：把ACTION_DOWN时赋值的mMotionTarget，付给target ;
23行：if (!disallowIntercept && onInterceptTouchEvent(ev)) 当前允许拦截且拦截了，才进入IF体，当然了默认是不会拦截的~这里执行了onInterceptTouchEvent(ev)
28-30行：把坐标系统转化为子View的坐标系统
32行：直接return target.dispatchTouchEvent(ev);
可以看到，正常流程下，ACTION_MOVE在检测完是否拦截以后，直接调用了子View.dispatchTouchEvent，事件分发下去；
最后就是ACTION_UP了
3、ViewGroup - dispatchTouchEvent – ACTION_UP
public boolean dispatchTouchEvent(MotionEvent ev) {
if (!onFilterTouchEventForSecurity(ev)) {
return false;
}
final int action = ev.getAction();
final float xf = ev.getX();
final float yf = ev.getY();
final float scrolledXFloat = xf + mScrollX;
final float scrolledYFloat = yf + mScrollY;
final Rect frame = mTempRect;
boolean disallowIntercept = (mGroupFlags & FLAG_DISALLOW_INTERCEPT) != 0;
if (action == MotionEvent.ACTION_DOWN) {...}
boolean isUpOrCancel = (action == MotionEvent.ACTION_UP) ||
(action == MotionEvent.ACTION_CANCEL);
if (isUpOrCancel) {
mGroupFlags &= ~FLAG_DISALLOW_INTERCEPT;
}
final View target = mMotionTarget;
if(target ==null ){...}
if (!disallowIntercept && onInterceptTouchEvent(ev)) {...}
if (isUpOrCancel) {
mMotionTarget = null;
}
// finally offset the event to the target's coordinate system and
// dispatch the event.
final float xc = scrolledXFloat - (float) target.mLeft;
final float yc = scrolledYFloat - (float) target.mTop;
ev.setLocation(xc, yc);
return target.dispatchTouchEvent(ev);
}
17行：判断当前是否是ACTION_UP
21，28行：分别重置拦截标志位以及将DOWN赋值的mMotionTarget置为null，都UP了，当然置为null，下一次DOWN还会再赋值的~
最后，修改坐标系统，然后调用target.dispatchTouchEvent(ev);
正常情况下，即我们上例整个代码的流程我们已经走完了：
1、ACTION_DOWN中，ViewGroup捕获到事件，然后判断是否拦截，假如没有拦截，则找到包含当前x,y坐标的子View，赋值给mMotionTarget，然后调用 mMotionTarget.dispatchTouchEvent
2、ACTION_MOVE中，ViewGroup捕获到事件，然后判断是否拦截，假如没有拦截，则直接调用mMotionTarget.dispatchTouchEvent(ev)
3、ACTION_UP中，ViewGroup捕获到事件，然后判断是否拦截，假如没有拦截，则直接调用mMotionTarget.dispatchTouchEvent(ev)
当然了在分发之前都会修改下坐标系统，把当前的x，y分别减去child.left 和 child.top ，然后传给child;
3、关于拦截
1、如何拦截
上面的总结都是基于：假如没有拦截；那么如何拦截呢？
复写ViewGroup的onInterceptTouchEvent方法：
@Override
public boolean onInterceptTouchEvent(MotionEvent ev)
{
int action = ev.getAction();
switch (action)
{
case MotionEvent.ACTION_DOWN:
//假如你觉得需要拦截
return true ;
case MotionEvent.ACTION_MOVE:
//假如你觉得需要拦截
return true ;
case MotionEvent.ACTION_UP:
//假如你觉得需要拦截
return true ;
}
return false;
}
默认是不拦截的，即返回false；假如你需要拦截，只要return true就行了，这要该事件就不会往子View传递了，并且假如你在DOWN retrun true ，则DOWN,MOVE,UP子View都不会捕获事件；假如你在MOVE return true , 则子View在MOVE和UP都不会捕获事件。
原因很简单，当onInterceptTouchEvent(ev) return true的时候，会把mMotionTarget 置为null ;
2、如何不被拦截
假如ViewGroup的onInterceptTouchEvent(ev) 当ACTION_MOVE时return true ，即拦截了子View的MOVE以及UP事件；
此时子View希望依然能够响应MOVE和UP时该咋办呢？
Android给我们提供了一个方法：requestDisallowInterceptTouchEvent(boolean) 用于设置是否允许拦截，我们在子View的dispatchTouchEvent中直接这么写：
@Override
public boolean dispatchTouchEvent(MotionEvent event)
{
getParent().requestDisallowInterceptTouchEvent(true);
int action = event.getAction();
switch (action)
{
case MotionEvent.ACTION_DOWN:
Log.e(TAG, "dispatchTouchEvent ACTION_DOWN");
break;
case MotionEvent.ACTION_MOVE:
Log.e(TAG, "dispatchTouchEvent ACTION_MOVE");
break;
case MotionEvent.ACTION_UP:
Log.e(TAG, "dispatchTouchEvent ACTION_UP");
break;
default:
break;
}
return super.dispatchTouchEvent(event);
}
getParent().requestDisallowInterceptTouchEvent(true); 这样即使ViewGroup在MOVE的时候return true，子View依然可以捕获到MOVE以及UP事件。
从源码也可以解释：
ViewGroup MOVE和UP拦截的源码是这样的：
if (!disallowIntercept && onInterceptTouchEvent(ev)) {
final float xc = scrolledXFloat - (float) target.mLeft;
final float yc = scrolledYFloat - (float) target.mTop;
mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
ev.setAction(MotionEvent.ACTION_CANCEL);
ev.setLocation(xc, yc);
if (!target.dispatchTouchEvent(ev)) {
// target didn't handle ACTION_CANCEL. not much we can do
// but they should have.
}
// clear the target
mMotionTarget = null;
// Don't dispatch this event to our own view, because we already
// saw it when intercepting; we just want to give the following
// event to the normal onTouchEvent().
return true;
}
当我们把disallowIntercept设置为true时，!disallowIntercept直接为false，于是拦截的方法体就被跳过了~
注：假如ViewGroup在onInterceptTouchEvent(ev) ACTION_DOWN里面直接return true了，那么子View是木有办法的捕获事件的~~~
4、假如没有找到合适的子View
我们的实例，直接点击ViewGroup内的按钮，当然直接很顺利的走完整个流程；
但是有两种特殊情况
1、ACTION_DOWN的时候，子View.dispatchTouchEvent(ev)返回的为false ;
假如你仔细看了，你会注意到ViewGroup的dispatchTouchEvent(ev)的ACTION_DOWN代码是这样的
if (child.dispatchTouchEvent(ev)) {
// Event handled, we have a target now.
mMotionTarget = child;
return true;
}
只有在child.dispatchTouchEvent(ev)返回true了，才会认为找到了能够处理当前事件的View，即mMotionTarget = child;
但是假如返回false,那么mMotionTarget 依然是null
mMotionTarget 为null会咋样呢？
其实ViewGroup也是View的子类，假如没有找到能够处理该事件的子View，或者干脆就没有子View；
那么，它作为一个View，就相当于View的事件转发了~~直接super.dispatchTouchEvent(ev);
源码是这样的：
final View target = mMotionTarget;
if (target == null) {
// We don't have a target, this means we're handling the
// event as a regular view.
ev.setLocation(xf, yf);
if ((mPrivateFlags & CANCEL_NEXT_UP_EVENT) != 0) {
ev.setAction(MotionEvent.ACTION_CANCEL);
mPrivateFlags &= ~CANCEL_NEXT_UP_EVENT;
}
return super.dispatchTouchEvent(ev);
}
我们没有一个能够处理该事件的目标元素，意味着我们需要自己处理~~~就相当于传统的View~
2、那么什么时候子View.dispatchTouchEvent(ev)返回的为true
假如你仔细看了上篇博客，你会发现只要子View支持点击或者长按事件一定返回true~~
源码是这样的：
if (((viewFlags & CLICKABLE) == CLICKABLE ||
(viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE)) {
return true ;
5、总结
关于代码流程上面已经总结过了~
1、假如ViewGroup找到了能够处理该事件的View，则直接交给子View处理，自己的onTouchEvent不会被触发；
2、可以通过复写onInterceptTouchEvent(ev)方法，拦截子View的事件（即return true），把事件交给自己处理，则会执行自己对应的onTouchEvent方法
3、子View可以通过调用getParent().requestDisallowInterceptTouchEvent(true); 阻止ViewGroup对其MOVE或者UP事件进行拦截；
好了，那么实际应用中能解决哪些问题呢？
比如你需要写一个类似SlidingMenu的左侧隐藏menu，主Activity上有个Button、ListView或者任何可以响应点击的View，你在当前View上死命的滑动，菜单栏也出不来；因为MOVE事件被子View处理了~ 你需要这么做：在ViewGroup的dispatchTouchEvent中判断用户是不是想显示菜单，假如是，则在onInterceptTouchEvent(ev)拦截子View的事件；自己进行处理，这样自己的onTouchEvent就可以顺利展现出菜单栏了。