[android 自定义控件]（3）事件传递的一些案例思考

怼烎@ 2022-02-28 08:33 176阅读 0赞

### 文章目录 ###

*  案例
 *   *  环境：
     *  案例1：无onTouch监听的默认情况
     *  案例2： onInterceptTouchEvent调用时机问题

上一篇： [\[android 自定义控件\]（2）事件传递][android _2]

# 案例 #

## 环境： ##

View类

package com.example.dispatcheventapp;
    
    import android.annotation.SuppressLint;
    import android.content.Context;
    import android.util.AttributeSet;
    import android.util.Log;
    import android.view.MotionEvent;
    import android.widget.Button;
    
    @SuppressLint("AppCompatCustomView")
    public class MyButton extends Button { 
        public  final  static  String MyButton_TAG="View";
    
        public MyButton(Context context) { 
            super(context);
        }
    
        public MyButton(Context context, AttributeSet attrs) { 
            super(context, attrs);
        }
    
        public MyButton(Context context, AttributeSet attrs, int defStyleAttr) { 
            super(context, attrs, defStyleAttr);
        }
    
        public MyButton(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) { 
            super(context, attrs, defStyleAttr, defStyleRes);
        }
    
        @Override
        public boolean dispatchTouchEvent(MotionEvent event) { 
            Log.e(MyButton_TAG,"ENTER dispatchTouchEvent");
            return super.dispatchTouchEvent(event);
        }
    
        @Override
        public boolean onTouchEvent(MotionEvent event) { 
            Log.e(MyButton_TAG,"ENTER onTouchEvent");
            return super.onTouchEvent(event);
        }
    }

ViewGoup类

package com.example.dispatcheventapp;
    
    import android.content.Context;
    import android.support.annotation.Nullable;
    import android.util.AttributeSet;
    import android.util.Log;
    import android.view.MotionEvent;
    import android.widget.LinearLayout;
    
    public class MyLayout extends LinearLayout { 
        public  final  static  String Mylayout_TAG="ViewGroup";
        public MyLayout(Context context) { 
            super(context);
        }
    
        public MyLayout(Context context, @Nullable AttributeSet attrs) { 
            super(context, attrs);
        }
    
        public MyLayout(Context context, @Nullable AttributeSet attrs, int defStyleAttr) { 
            super(context, attrs, defStyleAttr);
        }
    
        public MyLayout(Context context, AttributeSet attrs, int defStyleAttr, int defStyleRes) { 
            super(context, attrs, defStyleAttr, defStyleRes);
        }
        @Override
        public boolean dispatchTouchEvent(MotionEvent event) { 
            Log.e(Mylayout_TAG,"ENTER dispatchTouchEvent");
            return super.dispatchTouchEvent(event);
        }
    
        @Override
        public boolean onTouchEvent(MotionEvent event) { 
            Log.e(Mylayout_TAG,"ENTER onTouchEvent");
    
            return super.onTouchEvent(event);
        }
    }

Activity类

package com.example.dispatcheventapp;
    
    import android.app.Activity;
    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import android.util.Log;
    import android.view.MotionEvent;
    
    public class MainActivity extends Activity { 
        public  final  static  String Activity_TAG="Activity";
    
        @Override
        protected void onCreate(Bundle savedInstanceState) { 
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
        }
        @Override
        public boolean dispatchTouchEvent(MotionEvent event) { 
            Log.e(Activity_TAG,"ENTER dispatchTouchEvent");
    
            return super.dispatchTouchEvent(event);
        }
    
        @Override
        public boolean onTouchEvent(MotionEvent event) { 
            Log.e(Activity_TAG,"ENTER onTouchEvent");
    
            return super.onTouchEvent(event);
        }
    }

layout文件

<?xml version="1.0" encoding="utf-8"?>
    <com.example.dispatcheventapp.MyLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context=".MainActivity" android:id="@+id/my_layout">
        <com.example.dispatcheventapp.MyButton android:id="@+id/my_button" android:text="点我" android:layout_width="wrap_content" android:layout_height="wrap_content" />
    
    </com.example.dispatcheventapp.MyLayout>

## 案例1：无onTouch监听的默认情况 ##

**点一下按钮的结果：**

03-25 10:53:33.629 7153-7153/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 10:53:33.629 7153-7153/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 10:53:33.629 7153-7153/com.example.dispatcheventapp E/View: ENTER dispatchTouchEvent
    03-25 10:53:33.629 7153-7153/com.example.dispatcheventapp E/View: ENTER onTouchEvent
    03-25 10:53:33.639 7153-7153/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 10:53:33.639 7153-7153/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 10:53:33.649 7153-7153/com.example.dispatcheventapp E/View: ENTER dispatchTouchEvent
    03-25 10:53:33.649 7153-7153/com.example.dispatcheventapp E/View: ENTER onTouchEvent
    03-25 10:53:33.679 7153-7153/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 10:53:33.679 7153-7153/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 10:53:33.679 7153-7153/com.example.dispatcheventapp E/View: ENTER dispatchTouchEvent
    03-25 10:53:33.679 7153-7153/com.example.dispatcheventapp E/View: ENTER onTouchEvent

**分析：**  
点按钮，down事件被View接受，然后因为没有onTouch监听，所以调用onTouchEvent的函数，被onTouchEvent函数处理之后，onTouchEvent返回true，View的dispatchTouchEvent返回true，ViewGroup的dispatchTouchEvent返回true，Activity的dispatchTouchEvent返回true，之后的move和up事件同理。

**点一下非按钮的结果：**

03-25 11:00:37.029 7153-7153/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 11:00:37.029 7153-7153/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 11:00:37.029 7153-7153/com.example.dispatcheventapp E/ViewGroup: ENTER onTouchEvent
    03-25 11:00:37.029 7153-7153/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent
    03-25 11:00:37.049 7153-7153/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 11:00:37.049 7153-7153/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent
    03-25 11:00:37.059 7153-7153/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 11:00:37.059 7153-7153/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent

**分析：**  
因为没有View能处理down事件，所以down事件时，ViewGoup的dispatchTouchEvent函数中，mFirstTouchTarget会被初始化为null，所以事件会被传递到ViewGroup的onTouchEvent（和View的onTouchEvent一样）中，又因为viewGroup都是disclickable的所以不能处理事件返回false，ViewGoup的dispatchTouchEven 返回false,，viewGroup的上级ViewGroup也返回false…最后Activity的dispatchTouchEvent中调用onTouchEvent来处理事件，最后也返回false。这样整个ViewGroup链条中每一个ViewGroup的mFirstTouchTarget都是null。之后的move和up往下传时，第一个会被传入根View（DecorView）中，因为mFirstTouchTarget被初始化为null，所以直接调用根View的onTouchEvent函数来处理，返回false。这样这些事件会之前返回给Activity的onTouchEvent来处理。

**思考1：** 我只想让我自定义的ViewGroup来处理事件，怎么弄？

首先我们要弄清楚为什么会发生这样的问题。通过上面的分析我们知道

1.  没有View能处理down事件（这个没办法解决）
2.  ViewGroup时disclickable的所以onTouchEvent只能返回false
3.  我们的布局和系统生成布局组成了一条ViewGroup链条（最少三层），因为上层的ViewGroup的dispatchEvent返回fasle，导致底层的ViewGroup的mFirstTouchTarget被初始化为null，这样整个链条上的ViewGroup就都是mFirstTouchTarget=null，所以下一次的move和up事件就指挥传递到根View的onTouchEvent中，上面的ViewGroup就没机会接收到这些事件了。（机制问题，无法解决）

上面1和3时无法解决的，但是通过2我们就可以实现这样的目标了

//修改mylayout的代码，让他返回true，这样整个VewiGroup链条中前面的ViewGroup中mFirstTouchTarget！=null，事件也就会被传递下来
    @Override
        public boolean onTouchEvent(MotionEvent event) { 
            Log.e(Mylayout_TAG,"ENTER onTouchEvent");
    
             super.onTouchEvent(event);
            return true;
        }

**结果：**

03-25 11:56:19.059 16517-16517/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 11:56:19.069 16517-16517/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 11:56:19.069 16517-16517/com.example.dispatcheventapp E/ViewGroup: ENTER onTouchEvent
    03-25 11:56:19.079 16517-16517/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 11:56:19.079 16517-16517/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 11:56:19.079 16517-16517/com.example.dispatcheventapp E/ViewGroup: ENTER onTouchEvent
    03-25 11:56:19.089 16517-16517/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 11:56:19.089 16517-16517/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 11:56:19.099 16517-16517/com.example.dispatcheventapp E/ViewGroup: ENTER onTouchEvent

## 案例2： onInterceptTouchEvent调用时机问题 ##

通过之前的代码分析我们知道，onInterceptTouchEvent只有 ViewGroup中才有的方法，可以控制事件的拦截。默认是返回false，运行结果就和上面的代码一样。现在我们来看看返回true的结果

//在mylayout类中加入下面的代码
    @Override
        public boolean onInterceptTouchEvent(MotionEvent ev) { 
            return true;
        }

**点击按钮：**

03-25 12:26:39.639 21782-21782/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 12:26:39.639 21782-21782/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 12:26:39.639 21782-21782/com.example.dispatcheventapp E/ViewGroup: ENTER onTouchEvent
    03-25 12:26:39.639 21782-21782/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent
    03-25 12:26:39.649 21782-21782/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 12:26:39.649 21782-21782/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent
    03-25 12:26:39.679 21782-21782/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 12:26:39.679 21782-21782/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent

**分析：**  
因为onInterceptTouchEvent返回true，所以当dow事件传递到ViewGroup的dispatchTouchEvent中时，intercepted为true，所以之后就跳过寻找View的过程，mFirstTouchTarget也就时null，这样就会调用ViewGroup的onTouchEvent来处理事件。因为ViewGroup是disclickable的所以，返回False。这样整个ViewGroup链条中mFirstTouchTarget就都是null。所以剩下的事件就只能是Activity来处理。你会发现这和案例一中的点击非按钮区域是一样的。这也说明了android 提供的拦截机制还是很好的

**点击非按钮：**

03-25 12:30:13.059 21782-21782/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 12:30:13.069 21782-21782/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 12:30:13.069 21782-21782/com.example.dispatcheventapp E/ViewGroup: ENTER onTouchEvent
    03-25 12:30:13.069 21782-21782/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent
    03-25 12:30:13.079 21782-21782/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 12:30:13.079 21782-21782/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent
    03-25 12:30:13.099 21782-21782/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 12:30:13.099 21782-21782/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent

和上面一样，不分析了。

**思考1：** 如果我move和up拦截，down不拦截会怎么样？

//修改mylayout中的diamagnetic
    @Override
        public boolean onInterceptTouchEvent(MotionEvent ev) { 
                Log.e(Mylayout_TAG,"ENTER onInterceptTouchEvent");
    
            if(ev.getAction()==MotionEvent.ACTION_DOWN)
                return false;
            return true;
        }

**点击按钮结果：**

03-25 12:47:17.739 24598-24598/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 12:47:17.739 24598-24598/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 12:47:17.739 24598-24598/com.example.dispatcheventapp E/ViewGroup: ENTER onInterceptTouchEvent
    03-25 12:47:17.739 24598-24598/com.example.dispatcheventapp E/View: ENTER dispatchTouchEvent
    03-25 12:47:17.739 24598-24598/com.example.dispatcheventapp E/View: ENTER onTouchEvent
    03-25 12:47:17.759 24598-24598/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 12:47:17.759 24598-24598/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 12:47:17.759 24598-24598/com.example.dispatcheventapp E/ViewGroup: ENTER onInterceptTouchEvent
    03-25 12:47:17.759 24598-24598/com.example.dispatcheventapp E/View: ENTER dispatchTouchEvent
    03-25 12:47:17.759 24598-24598/com.example.dispatcheventapp E/View: ENTER onTouchEvent
    03-25 12:47:17.769 24598-24598/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 12:47:17.779 24598-24598/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 12:47:17.779 24598-24598/com.example.dispatcheventapp E/ViewGroup: ENTER onTouchEvent
    03-25 12:47:17.779 24598-24598/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent
    03-25 12:47:17.789 24598-24598/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 12:47:17.789 24598-24598/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 12:47:17.789 24598-24598/com.example.dispatcheventapp E/ViewGroup: ENTER onTouchEvent
    03-25 12:47:17.789 24598-24598/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent

**分析：**  
down时调用onInterceptTouchEvent，不拦截。所以mFirstTouchTarget被初始化，View的onTouchEvent处理事件，返回true。所以ViewGroup的dispatchTouchEvent返回true。Activity的dispatchTouchEvent不调用onTouchEvent且返回true。通过down事件的初始化，viewGroup链条中的mFirstTouchTarget都被初始化为！=null。

接着move 传递到ViewGroup的dispatchTouchEvent中，因为mFirstTouchTarget！=null所以调用onInterceptTouchEvent函数，这是返回false，拦截。所以传递消息之前cancelChild 会被设置成True，这样所有的View都会收到cancel消息。因为View是Clickable的所以就算是cancel,onTouchEvent也是True，但是ViewGroup会清空mFirstTouchTarget，让其=null。此时我们自定义的ViewGroup的mFirstTouchTarget被清空了，但是整个链条中的其他ViewGroup的mFirstTouchTarget还是存在的。

当后面的move或up事件再一次传递到我们自定义的ViewGroup的dispatchTouchEvent中时。mFirstTouchTarget==null，所以不会调用onInterceptTouchEvent 方法，直接使intercepted=true。之后因为mFirstTouchTarget==null,所以使用ViewGroup的onTouchEvent处理处理事件返回false.这样整个链条中的ViewGroup的dispatchTouchEvent都返回false。就会进入Activity的onTouchEvent中。

**点击非按钮：**

03-25 13:08:07.489 24598-24598/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 13:08:07.489 24598-24598/com.example.dispatcheventapp E/ViewGroup: ENTER dispatchTouchEvent
    03-25 13:08:07.489 24598-24598/com.example.dispatcheventapp E/ViewGroup: ENTER onInterceptTouchEvent
    03-25 13:08:07.489 24598-24598/com.example.dispatcheventapp E/ViewGroup: ENTER onTouchEvent
    03-25 13:08:07.489 24598-24598/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent
    03-25 13:08:07.509 24598-24598/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 13:08:07.509 24598-24598/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent
    03-25 13:08:07.509 24598-24598/com.example.dispatcheventapp E/Activity: ENTER dispatchTouchEvent
    03-25 13:08:07.509 24598-24598/com.example.dispatcheventapp E/Activity: ENTER onTouchEvent

没有View能处理事件，就会和案例1一样结果。

**思考2：** 如果我down拦截，move和up不拦截又会怎么样？

能看到这说明你对事件传递已经有一个很深刻的认识了。上面的思考通过大脑也应该能想出来。我们来试试

down我们一旦拦截了，ViewGroup的mFirstTouchTarget就会等于null。这样的华以后压根就不会再调用onInterceptTouchEvent方法了。就算你设置了不拦截，结果还会是拦截。所以down事件会被ViewGroup的onTouchEvent处理，且返回false。这样整个VIewGroup的mFirstTouchTarget都会等于null。最后消息也都会由Activity来消化。

[android _2]: https://blog.csdn.net/god_wen/article/details/63253970