Android 的事件分发（2019-03-07）

2019-03-07 本文已影响0人 Guow110

事件分发机制

举个例子：

ViewGroup1----->ViewGroup----->View

默认的时候：(View可点击)

点击事件会由外向内传递,每一个动作都会发生事件的传递

//-----------------Down---------------------------
E/ViewGroup1: dispatchTouchEvent: viewgroup1----
E/ViewGroup1: onInterceptTouchEvent: viewgroup1----
E/ViewGroup: dispatchTouchEvent: viewgroup----
E/ViewGroup: onInterceptTouchEvent: viewgroup----
E/Button1: dispatchTouchEvent: button1----
E/Button1: onTouchEvent: button1----
E/Button1: onTouchEventDown: button1----
//===================Up========================
E/ViewGroup1: dispatchTouchEvent: viewgroup1----
E/ViewGroup1: onInterceptTouchEvent: viewgroup1----
E/ViewGroup: dispatchTouchEvent: viewgroup----
E/ViewGroup: onInterceptTouchEvent: viewgroup----
E/Button1: dispatchTouchEvent: button1----
E/Button1: onTouchEvent: button1----
E/Button1: onTouchEventUp: button1----

默认的时候：(View不可点击)

当点击事件分发到最底层的时候，并且最底层的子View没有消费时间的能力时，此时会将Down事件交由它的父布局进行处理，如果父布局处理不了，逐级上传，一直到Activity

E/ViewGroup1: dispatchTouchEvent: viewgroup1----
E/ViewGroup1: onInterceptTouchEvent: viewgroup1----
E/ViewGroup: dispatchTouchEvent: viewgroup----
E/ViewGroup: onInterceptTouchEvent: viewgroup----
E/Button1: dispatchTouchEvent: button1----
E/Button1: onTouchEvent: button1----
E/Button1: onTouchEventDown: button1----
E/ViewGroup: onTouchEvent: viewgroup----
E/ViewGroup: onTouchEventDown: viewgroup----
E/ViewGroup1: onTouchEvent: viewgroup1----
E/ViewGroup1: onTouchEventDown: viewgroup1----

View的父布局拦截事件（onInterceptTouchEvent ------> true）

当点击事件在ViewGroup处进行拦截的时候，Down事件将不会再传递到他的子View,同时，他回交由自己的onTouchEvent方法进行事件的处理，如果没有处理能力，则将时间逐级上传，直到Activity

E/ViewGroup1: dispatchTouchEvent: viewgroup1----
E/ViewGroup1: onInterceptTouchEvent: viewgroup1----
E/ViewGroup: dispatchTouchEvent: viewgroup----
E/ViewGroup: onInterceptTouchEvent: viewgroup----
E/ViewGroup: onTouchEvent: viewgroup----
E/ViewGroup: onTouchEventDown: viewgroup----
E/ViewGroup1: onTouchEvent: viewgroup1----
E/ViewGroup1: onTouchEventDown: viewgroup1----

View的父布局拦截事件（onInterceptTouchEvent ------> true ,onTouchEvent----->true）

onTouchEvent----->true:表示事件可以在此方法内消费掉，所以ViewGroup不会再将Down事件交由它的上级进行处理。

//=======================Down=======================
E/ViewGroup1: dispatchTouchEvent: viewgroup1----
E/ViewGroup1: onInterceptTouchEvent: viewgroup1----
E/ViewGroup: dispatchTouchEvent: viewgroup----
E/ViewGroup: onInterceptTouchEvent: viewgroup----
E/ViewGroup: onTouchEvent: viewgroup----
E/ViewGroup: onTouchEventDown: viewgroup----
//======================Up======================
E/ViewGroup1: dispatchTouchEvent: viewgroup1----
E/ViewGroup1: onInterceptTouchEvent: viewgroup1----
E/ViewGroup: dispatchTouchEvent: viewgroup----
E/ViewGroup: onTouchEvent: viewgroup----
E/ViewGroup: onTouchEventUp: viewgroup----

最外层的ViewGroup1拦截事件（onInterceptTouchEvent ------> true）

事件将到此为止，交给自己的onTouchEvent进行处理，不能处理的话则交由上级。

可以在布局里设置clickable="true"，或者是onTouchEvent返回true

//====================clickable="false"============================
E/ViewGroup1: dispatchTouchEvent: viewgroup1----
E/ViewGroup1: onInterceptTouchEvent: viewgroup1----
E/ViewGroup1: onTouchEvent: viewgroup1----
E/ViewGroup1: onTouchEventDown: viewgroup1----
//=========================clickable="true"===============================
E/ViewGroup1: dispatchTouchEvent: viewgroup1----
E/ViewGroup1: onInterceptTouchEvent: viewgroup1----
E/ViewGroup1: onTouchEvent: viewgroup1----
E/ViewGroup1: onTouchEventDown: viewgroup1----
E/ViewGroup1: dispatchTouchEvent: viewgroup1----
E/ViewGroup1: onTouchEvent: viewgroup1----
E/ViewGroup1: onTouchEventMove: viewgroup1----
E/ViewGroup1: dispatchTouchEvent: viewgroup1----
E/ViewGroup1: onTouchEvent: viewgroup1----
E/ViewGroup1: onTouchEventUp: viewviewgroup1----

当ViewGroup和View都有消费事件的能力时，情况和第一种其实是一样的，因为时间能够不被拦截，一直传递，所以在View的时候，已经把他消费掉了，就没有了。
当ViewGroup1的dispatchTouchEvent------>false时：
```
E/ViewGroup1: dispatchTouchEvent: viewgroup1----
```

当ViewGroup的dispatchTouchEvent------>false时：

表示事件不在分发下去，Down事件交由它的父布局进行处理，父布局处理不了，则再往上递交，一直到Activity

//---------0表示的是Down事件-----1表示Up事件
E/ViewGroup1: dispatchTouchEvent: viewgroup1----0
E/ViewGroup1: onInterceptTouchEvent: viewgroup1----0
E/ViewGroup: dispatchTouchEvent: viewgroup----0
//-----------ViewGroup1的onTouchEvent返回false时
E/ViewGroup1: onTouchEvent: viewgroup1----0
E/ViewGroup1: onTouchEventDown: viewgroup1----0
//-----------ViewGroup1的onTouchEvent返回true时
E/ViewGroup1: onTouchEvent: viewgroup1----0
E/ViewGroup1: onTouchEventDown: viewgroup1----0
E/ViewGroup1: dispatchTouchEvent: viewgroup1----1
E/ViewGroup1: onTouchEvent: viewgroup1----1
E/ViewGroup1: onTouchEventUp: viewviewgroup1----1

View.setOnClickListener/View.setOnTouchListener-----false

onTouch方法要优先于onClick方法执行

E/ViewGroup1: dispatchTouchEvent: viewgroup1----0
E/ViewGroup1: onInterceptTouchEvent: viewgroup1----0
E/ViewGroup: dispatchTouchEvent: viewgroup----
E/ViewGroup: onInterceptTouchEvent: viewgroup----
E/Button1: dispatchTouchEvent: button1----
E/MainActivity: onTouch: button1
E/Button1: onTouchEvent: button1----
E/Button1: onTouchEventDown: button1----
E/ViewGroup1: dispatchTouchEvent: viewgroup1----1
E/ViewGroup1: onInterceptTouchEvent: viewgroup1----1
E/ViewGroup: dispatchTouchEvent: viewgroup----
E/ViewGroup: onInterceptTouchEvent: viewgroup----
E/Button1: dispatchTouchEvent: button1----
E/MainActivity: onTouch: button1
E/Button1: onTouchEvent: button1----
E/Button1: onTouchEventUp: button1----
E/MainActivity: onClick: button1

View.setOnClickListener/View.setOnTouchListener-----true

E/ViewGroup1: dispatchTouchEvent: viewgroup1----0
E/ViewGroup1: onInterceptTouchEvent: viewgroup1----0
E/ViewGroup: dispatchTouchEvent: viewgroup----
E/ViewGroup: onInterceptTouchEvent: viewgroup----
E/Button1: dispatchTouchEvent: button1----
E/MainActivity: onTouch: button1
E/ViewGroup1: dispatchTouchEvent: viewgroup1----1
E/ViewGroup1: onInterceptTouchEvent: viewgroup1----1
E/ViewGroup: dispatchTouchEvent: viewgroup----
E/ViewGroup: onInterceptTouchEvent: viewgroup----
E/Button1: dispatchTouchEvent: button1----
E/MainActivity: onTouch: button1

说说原理：

一段伪代码开路

public boolean dispatchTouchEvent(MotionEvent ev) {
        boolean consume = false;//事件是否被消费
        if (onInterceptTouchEvent(ev)){//调用onInterceptTouchEvent判断是否拦截事件
            consume = onTouchEvent(ev);//如果拦截则调用自身的onTouchEvent方法
        }else{
            consume = child.dispatchTouchEvent(ev);//不拦截调用子View的dispatchTouchEvent方法
        }
        return consume;//返回值表示事件是否被消费，true事件终止，false调用父View的onTouchEvent方法
    }
//来自于：https://www.jianshu.com/p/238d1b753e64

特别强调

子View可以通过requestDisallowInterceptTouchEvent方法干预父View的事件分发过程（ACTION_DOWN事件除外）
对于View（注意！ViewGroup也是View）而言，如果设置了onTouchListener，那么OnTouchListener方法中的onTouch方法会被回调。onTouch方法返回true，则onTouchEvent方法不会被调用（onClick事件是在onTouchEvent中调用）所以三者优先级是onTouch->onTouchEvent->onClick
View 的onTouchEvent 方法默认都会消费掉事件（返回true），除非它是不可点击的（clickable和longClickable同时为false），View的longClickable默认为false，clickable需要区分情况，如Button的clickable默认为true，而TextView的clickable默认为false。

Android 的事件分发（2019-03-07）

事件分发机制

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