Android View控件的事件派发

Posted 2022-11-30 dsliang12

转载请标明出处：
http://blog.csdn.net/zq2114522/article/details/52081697；
本文出自:【梁大盛的博客】

android View控件的事件派发

引:一直想写View,GroupView控件的事件派发流程.终于现在一口气都写出来.一鼓作气!当然考虑了很久应该用怎么样的方式写这些流程性的东西,应该用什么用的语言来描述.后来想就按照聊天的方式把!尽量把整个派发过程都写下来,并且实现一个简单的山寨派发流程.有点只见树不见山的感觉.但是觉得自己写一次view的事件派发胜过再多的理论!

派发流程

---

首先我们来看看view的事件派发.

关键函数
public boolean dispatchTouchEvent(MotionEvent event);
public boolean onTouchEvent(MotionEvent event);

看看一个简单的”演示代码-1”.
继承view并且在dispatchTouchEvent和onTouchEvent添加打印信息.

MainActivity.java

package com.dsliang.eventdispatch;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity 

    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    

EventDispatchView.java

package com.dsliang.eventdispatch;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

/**
 * Created by dsliang on 16-7-31.
 */
public class EventDispatchView extends View 

    public static String Tag = EventDispatchView.class.getSimpleName();

    public EventDispatchView(Context context) 
        super(context);
    

    public EventDispatchView(Context context, AttributeSet attrs) 
        super(context, attrs);
    

    public EventDispatchView(Context context, AttributeSet attrs, int defStyleAttr) 
        super(context, attrs, defStyleAttr);
    

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) 

        boolean result;
        Log.d(Tag, "dispatchTouchEvent: " + event.getAction());

        result = super.dispatchTouchEvent(event);

        Log.d(Tag, "dispatchTouchEvent result: " + result);

        return result;
    

    @Override
    public boolean onTouchEvent(MotionEvent event) 

        boolean result;

        Log.d(Tag, "onTouchEvent: " + event.getAction());

        result = super.onTouchEvent(event);

        Log.d(Tag, "onTouchEvent result: " + result);


        return result;
    

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical">

    <com.dsliang.eventdispatch.EventDispatchView
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:background="@android:color/darker_gray" />

</LinearLayout>

其实在上面的”演示代码-1”里面我们其实什么事情都没处理.看看在模拟器上运行的效果是怎么样把.

结论:当我们点击红色区域的时候.先后打印出dispatchTouchEvent,onTouchEvent.在这里我们可以知道分发过程必定是先调用dispatchTouchEvent函数然后再调用onTouchEvent函数.

如果你的代码这样写,那么对于我这篇文章你就没必要继续看下去了.事实上我的代码不应该这样写!

一切起于零

---

然后看看接下来的”演示代码-2”.我们仅仅修改文件EventDispatchView.java文件.

EventDispatchView.java

package com.dsliang.eventdispatch;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

/**
 * Created by dsliang on 16-7-31.
 */
public class EventDispatchView extends View 

    public static String Tag = EventDispatchView.class.getSimpleName();

    public EventDispatchView(Context context) 
        super(context);
    

    public EventDispatchView(Context context, AttributeSet attrs) 
        super(context, attrs);
    

    public EventDispatchView(Context context, AttributeSet attrs, int defStyleAttr) 
        super(context, attrs, defStyleAttr);
    

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) 

        boolean result;
        Log.d(Tag, "dispatchTouchEvent: " + event.getAction());

//        result = super.dispatchTouchEvent(event);
        result = false;

        Log.d(Tag, "dispatchTouchEvent result: " + result);

        return result;
    

    @Override
    public boolean onTouchEvent(MotionEvent event) 

        boolean result;

        Log.d(Tag, "onTouchEvent: " + event.getAction());

//        result = super.onTouchEvent(event);
        result = false;

        Log.d(Tag, "onTouchEvent result: " + result);


        return result;
    

我们在dispatchTouchEvent函数里面返回false并且调用父类的dispatchTouchEvent方法.对onTouchEvent函数我们也进行同样的修改.(对于此时,两个函数的返回值是true/false对目前)

结论:很明显能看到onTouchEvent函数并没有调用.那么就是说明其实在父类的dispatchTouchEvent里面一定是调用了onTouchEvent函数.

小试牛刀

---

这个道理你懂了以后我们要达到父类的相同效果,我们现在就针对dispatchTouchEvent进行一番修改.

现在我们也是只修改EventDispatchView.java文件.

EventDispatchView.java

package com.dsliang.eventdispatch;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

/**
 * Created by dsliang on 16-7-31.
 */
public class EventDispatchView extends View 

    public static String Tag = EventDispatchView.class.getSimpleName();

    public EventDispatchView(Context context) 
        super(context);
    

    public EventDispatchView(Context context, AttributeSet attrs) 
        super(context, attrs);
    

    public EventDispatchView(Context context, AttributeSet attrs, int defStyleAttr) 
        super(context, attrs, defStyleAttr);
    

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) 

        boolean result;
        Log.d(Tag, "dispatchTouchEvent: " + event.getAction());

//        result = super.dispatchTouchEvent(event);
        result = doOnDispatchTouchEvent(event);


        Log.d(Tag, "dispatchTouchEvent result: " + result);

        return result;
    

    private boolean doOnDispatchTouchEvent(MotionEvent event) 
        return onTouchEvent(event);
    

    @Override
    public boolean onTouchEvent(MotionEvent event) 

        boolean result;

        Log.d(Tag, "onTouchEvent: " + event.getAction());

//        result = super.onTouchEvent(event);
        result = false;

        Log.d(Tag, "onTouchEvent result: " + result);


        return result;
    

添加doOnDispatchTouchEvent函数,在dispatchTouchEvent调用doOnDispatchTouchEvent函数,doOnDispatchTouchEvent函数调用onTouchEvent函数.这样修改效果基本就和父类有一样的行为了.

从上面的效果图也可以看出的确现在这样修改以后和"演示代码-1"行为上看起来好像已经是一致了.

但是现在我又注意到一个问题!event.getAction函数返回是0?进去MotionEvent类看看0代表什么.其实0就是ACTION_DOWN.原来是按钮按下事件.但是也是不科学吧?稍稍有android事件的常事我们都会意识到.点击过程至少会有三个事件会触发.分别是按下,移动,抬起.怎么说再不赖也得有抬起事件把?

来到这里,首先抛出一个结论.如果dispatchTouchEvent在按下事件返回false说明此控件并没有消耗此次事件.那么系统(在view的角度触发你可以认为是系统,但是准确来说应该是你的包含你空间的布局容器)会认为你对接下来的一系列事件(移动,抬起)都不感兴趣.简单说就是在收到按下事件的时候返回false,接下来的移动,抬起事件都不会传递到次控件.(这个结论在下一篇”Android GroupView控件的事件派发”会具体阐述说明)

稍稍做润色

---

嗯嗯,那么稍稍把onTouchEvent的会返回值修改一下.这个就是我们的”演示代码-3”了.同样也是只修改EventDispatchView.java文件.

EventDispatchView.java

package com.dsliang.eventdispatch;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

/**
 * Created by dsliang on 16-7-31.
 */
public class EventDispatchView extends View 

    public static String Tag = EventDispatchView.class.getSimpleName();

    public EventDispatchView(Context context) 
        super(context);
    

    public EventDispatchView(Context context, AttributeSet attrs) 
        super(context, attrs);
    

    public EventDispatchView(Context context, AttributeSet attrs, int defStyleAttr) 
        super(context, attrs, defStyleAttr);
    

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) 

        boolean result;
        Log.d(Tag, "dispatchTouchEvent: " + event.getAction());

//        result = super.dispatchTouchEvent(event);
        result = doOnDispatchTouchEvent(event);


        Log.d(Tag, "dispatchTouchEvent result: " + result);

        return result;
    

    private boolean doOnDispatchTouchEvent(MotionEvent event) 
        return onTouchEvent(event);
    

    @Override
    public boolean onTouchEvent(MotionEvent event) 

        boolean result;

        Log.d(Tag, "onTouchEvent: " + event.getAction());

//        result = super.onTouchEvent(event);
        result = true;

        Log.d(Tag, "onTouchEvent result: " + result);


        return result;
    

现在这样可以看的按下,移动,抬起都派发给我们的EventDispatchView控件了!

现在我们先来一个小总结.
1,dispatchTouchEvent函数会调用onTouchEvent函数
2,只有在按下到来的时候dispatchTouchEvent返回true才会接收到移动,抬起事件.

初试锋芒

---

看起来这一节应该是结束的节奏了吧?图样图森破了!
你是忘了在使用控件的时候,可以设置点击事件和接听滑动事件么?
接下来看看”演示代码-4”.为了突出点击事件,滑动事件.dispatchTouchEvent和onTouchEvent只调用父类的方法.另外给EventDispatchView设置点击事件和滑动事件的监听函数.

MainActivity.java

package com.dsliang.eventdispatch;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

public class MainActivity extends Activity 

    public static String Tag = MainActivity.class.getSimpleName();

    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        View view = findViewById(R.id.viewEventDispatchView);

        view.setOnClickListener(new View.OnClickListener() 
            @Override
            public void onClick(View view) 
                Log.d(Tag, "onClick");
            
        );

        view.setOnTouchListener(new View.OnTouchListener() 
            @Override
            public boolean onTouch(View view, MotionEvent motionEvent) 
                Log.d(Tag, "onTouch");
                return true;
            
        );
    

EventDispatchView.java

package com.dsliang.eventdispatch;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

/**
 * Created by dsliang on 16-7-31.
 */
public class EventDispatchView extends View 

    public static String Tag = EventDispatchView.class.getSimpleName();

    public EventDispatchView(Context context) 
        super(context);
    

    public EventDispatchView(Context context, AttributeSet attrs) 
        super(context, attrs);
    

    public EventDispatchView(Context context, AttributeSet attrs, int defStyleAttr) 
        super(context, attrs, defStyleAttr);
    

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) 

        boolean result;
        Log.d(Tag, "dispatchTouchEvent: " + event.getAction());

        result = super.dispatchTouchEvent(event);
//        result = doOnDispatchTouchEvent(event);


        Log.d(Tag, "dispatchTouchEvent result: " + result);

        return result;
    

    private boolean doOnDispatchTouchEvent(MotionEvent event) 
        return onTouchEvent(event);
    

    @Override
    public boolean onTouchEvent(MotionEvent event) 

        boolean result;

        Log.d(Tag, "onTouchEvent: " + event.getAction());

        result = super.onTouchEvent(event);
//        result = true;

        Log.d(Tag, "onTouchEvent result: " + result);


        return result;
    

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical">

    <com.dsliang.eventdispatch.EventDispatchView
        android:id="@+id/viewEventDispatchView"
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:background="@android:color/darker_gray" />

</LinearLayout>

这里有两个地方需要注意:
1,onTouch函数返回false.onTouch函数的返回值会对派发事件有什么影响?
2,dispatchTouchEvent函数和onTouchEvent函数均使用父类方法的返回值作为返回值.意味着我们只能获取到按下事件.(并没有消耗按下事件)

仔细看看,当我们设置了点击事件监听函数之后super.onTouchEvent(event)居然返回true了!不科学呀,明显很之前的有矛盾把?

先给出结论:设置了点击事件回调函数后会改变super.onTouchEvent函数的默认行为.

    /**
     * Register a callback to be invoked when this view is clicked. If this view is not
     * clickable, it becomes clickable.
     *
     * @param l The callback that will run
     *
     * @see #setClickable(boolean)
     */
    public void setOnClickListener(@Nullable OnClickListener l) 
        if (!isClickable()) 
            setClickable(true);
        
        getListenerInfo().mOnClickListener = l;
    

...

    /**
     * Enables or disables click events for this view. When a view
     * is clickable it will change its state to "pressed" on every click.
     * Subclasses should set the view clickable to visually react to
     * user's clicks.
     *
     * @param clickable true to make the view clickable, false otherwise
     *
     * @see #isClickable()
     * @attr ref android.R.styleable#View_clickable
     */
    public void setClickable(boolean clickable) 
        setFlags(clickable ? CLICKABLE : 0, CLICKABLE);
    

...

设置点击回调函数以后,setClickable函数将CLICKABLE置1了.(flags的CLICKABLE位).

public boolean onTouchEvent(MotionEvent event) 

       ...

        /*
        当设置了点击事件回调函数,次条件成立.然后无论是
        ACTION_UP,ACTION_DOWN,ACTION_CANCEL,ACTION_MOVE都返回true
        */
        if (((viewFlags & CLICKABLE) == CLICKABLE ||
                (viewFlags & LONG_CLICKABLE) == LONG_CLICKABLE) ||
                (viewFlags & CONTEXT_CLICKABLE) == CONTEXT_CLICKABLE) 
            switch (action) 
                case MotionEvent.ACTION_UP:

                    ...

                    break;

                case MotionEvent.ACTION_DOWN:

                   ...

                    break;

                case MotionEvent.ACTION_CANCEL:

                   ...

                    break;

                case MotionEvent.ACTION_MOVE:

                    ...

                    break;
            

            return true;
        

        return false;
    


...

    public boolean dispatchTouchEvent(MotionEvent event) 

        ...

        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;
            
        

        ...

    

...

事实上只有设置了点击回调函数/长按回调函数均会返回ture.所以也解释了为什么设置回调函数后super.onTouchEvent返回值变成true了.

仔细的同学可能发现了onClick回调函数是在ACTION_UP事件里面调用.这很符合我们使用习惯!哪一个软件不是松开手才调用按钮事件呢?具体情况是performClick函数负责调用onClick函数.

当然有更仔细的同学发现另一个问题了!super.dispatchTouchEvent在调用onTouchEvent函数之前会调用onTouch函数并且根据onTouch函数的返回值判断是否返回!!!这意味了什么?意味着如果你同时设置了onClick函数onTouch的情况下,如果onTouch返回false.那么一切都正常你不会发现什么很玄的东西.但是一旦你讲onTouch返回true.那么问题就会来了.onClick函数没有如愿的调用.就下下面展示的图片一样.

专属山寨版

---

到这里我们摸透view派发事件的默认行为了,那么我们模仿来写一个属于我们理解的派发过程把!

“演示代码-5”

MainActivity.java

package com.dsliang.eventdispatch;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

public class MainActivity extends Activity 

    public static String Tag = MainActivity.class.getSimpleName();

    @Override
    protected void onCreate(Bundle savedInstanceState) 
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        View view = findViewById(R.id.viewEventDispatchView);

        view.setOnClickListener(new View.OnClickListener() 
            @Override
            public void onClick(View view) 
                Log.d(Tag, "onClick");
            
        );

        view.setOnTouchListener(new View.OnTouchListener() 
            @Override
            public boolean onTouch(View view, MotionEvent motionEvent) 
                Log.d(Tag, "onTouch");
                return true;
            
        );
    

EventDispatchView.java

package com.dsliang.eventdispatch;

import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;

/**
 * Created by dsliang on 16-7-31.
 */
public class EventDispatchView extends View 

    public static String Tag = EventDispatchView.class.getSimpleName();

    public EventDispatchView(Context context) 
        super(context);
    

    public EventDispatchView(Context context, AttributeSet attrs) 
        super(context, attrs);
    

    public EventDispatchView(Context context, AttributeSet attrs, int defStyleAttr) 
        super(context, attrs, defStyleAttr);
    

    private OnTouchListener mTouchListener = null;

    /*
    onTouch子类无法访问,当设置onTouch的时候保存对象的引用
     */
    @Override
    public void setOnTouchListener(OnTouchListener l) 
        super.setOnTouchListener(l);
        this.mTouchListener = l;
    

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) 

        boolean result;
        Log.d(Tag, "dispatchTouchEvent: " + event.getAction());

//        result = super.dispatchTouchEvent(event);

        if (null != this.mTouchListener && this.mTouchListener.onTouch(this, event)) 
            return true;
        

        result = doOnDispatchTouchEvent(event);


        Log.d(Tag, "dispatchTouchEvent result: " + result);

        return result;
    

    private boolean doOnDispatchTouchEvent(MotionEvent event) 
        return onTouchEvent(event);
    

    public void callOnClickListener() 

        /*
        performClick()已经封装了怎么调用onclick函数
         */
        if (isClickable()) 
            performClick();
        
    

    @Override
    public boolean onTouchEvent(MotionEvent event) 


        Log.d(Tag, "onTouchEvent: " + event.getAction());

//        result = super.onTouchEvent(event);


        /*
        可以点击,可以长按
         */
        if (isClickable() || isLongClickable()) 

            switch (event.getAction()) 
                case MotionEvent.ACTION_DOWN:
                    ;
                    break;
                case MotionEvent.ACTION_UP:
                    callOnClickListener();
                    break;
                case MotionEvent.ACTION_MOVE:
                    ;
                    break;
                case MotionEvent.ACTION_CANCEL:
                    ;
                    break;

            

            return true;
        

        return false;

    

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
    android:orientation="vertical">

    <com.dsliang.eventdispatch.EventDispatchView
        android:id="@+id/viewEventDispatchView"
        android:layout_width="match_parent"
        android:layout_height="60dp"
        android:background="@android:color/darker_gray" />

</LinearLayout>

理论上现在我们的EventDispatchView控件就拥有了系统默认的行为了.(在事件派发方面)

现在然我们总结一下view在事件派发方面的几个关键地方:

1,事件派发首先调用doOnDispatchTouchEvent函数,然后调用onTouchEvent函数
2,根据ACTION_DOWN事件是否给消耗判,断接下来能否接收其余的一连串事件.
3,onClick回调函数在ACTION_UP事件中才调用
4,系统在没有设置点击回调函数/长按回调函数的情况下view不会消耗事件.(ACTION_DOWN事件)
5,onTouch回调函数的返回值会影响点击回调函数/长按回调函数的调用