转载请标明出处:http://blog.csdn.net/lmj623565791/article/details/39102591,本文出自【张鸿洋的博客】
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~
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); } }
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>
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
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~
ViewGroup - dispatchTouchEvent
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,如果在,47行,执行child.dispatchTouchEvent(ev),就进入了View的dispatchTouchEvent代码中了,如果不了解请参考: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,如果代码中不做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,如果在,则把事件分发下去。
按照日志,接下来到达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
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,如果没有拦截,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,如果没有拦截,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,如果没有拦截,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;
上面的总结都是基于:如果没有拦截;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: //如果你觉得需要拦截 return true ; case MotionEvent.ACTION_MOVE: //如果你觉得需要拦截 return true ; case MotionEvent.ACTION_UP: //如果你觉得需要拦截 return true ; } return false; }
原因很简单,当onInterceptTouchEvent(ev) return true的时候,会把mMotionTarget 置为null ;
如果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); }
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; }
注:如果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~~~
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 ;
如果你仔细看了,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; }
但是如果返回false,那么mMotionTarget 依然是null
mMotionTarget 为null会咋样呢?
其实ViewGroup也是View的子类,如果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); }
2、那么什么时候子View.dispatchTouchEvent(ev)返回的为true
如果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 ; }
关于代码流程上面已经总结过了~
1、如果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,如果是,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~~
原文地址:http://blog.csdn.net/lmj623565791/article/details/39102591