Android View事件传递机制

view事件传递机制，在很多面试中会问道，我曾经也被问道，却没有回答上来。

写这篇博客前参考了https://blog.csdn.net/zuguorui/article/details/76862816。在这里感谢该作者，写的很详细。

今天我在这里写了一个demo去理解这个view的事件传递机制。

首先这个view包括两种，viewGroup和普通view。viewGroup就是里面还可以包含子控件的那种，如LinearLayout，ViewPager；view是指不能包含子view的那种，如Button，TextView，ImageView 等。

viewGroup的view传递事件按顺序是：

dispatchTouchEvent（分发）
onInterceptTouchEvent（拦截）
onTouchEvent（触摸）

view的事件传递顺序是

dispatchTouchEvent（分发）
onTouchEvent（触摸）

两者结合的一般顺序是

如果子控件没有消费掉触摸事件

viewPager: dispatchTouchEvent
viewPager: onInterceptTouchEvent
myImageView: dispatchTouchEvent
myImageView: onTouchEvent
viewPager: onTouchEvent

如果子控件消费掉触摸事件，比如执行了onClick方法，执行完onClick后，就不会再执行父控件的onTouchEvent

viewPager: dispatchTouchEvent
viewPager: onInterceptTouchEvent
myImageView: dispatchTouchEvent
myImageView: onTouchEvent
myImageView: onclick

如果onInterceptTouchEvent 返回true，则父控件消费触摸事件

如果onInterceptTouchEvent 返回false，则子控件消费触摸事件

我们来写demo看看，这个机制到底是怎么实现的。我使用viewPage和image做的测试。

我自己测试发现一个有趣的事情，

1、onInterceptTouchEvent 不做任何修改，

return super.onInterceptTouchEvent(ev)

a 子view的onTouchEvent 不做任何修改

     return super.onTouchEvent(event);

如果子view不消费onTouchEvent 事件，则一次滑动中，父控件不会多次调用onInterceptTouchEvent

09-13 16:55:21.427 6089-6089/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 16:55:21.428 6089-6089/ylj.com.vieweventapplication E/view_event_viewPager: onInterceptTouchEvent
09-13 16:55:21.429 6089-6089/ylj.com.vieweventapplication E/view_event_myImageView: dispatchTouchEvent
09-13 16:55:21.429 6089-6089/ylj.com.vieweventapplication E/view_event_myImageView: onTouchEvent
09-13 16:55:21.429 6089-6089/ylj.com.vieweventapplication E/view_event_viewPager: onTouchEvent
09-13 16:55:21.438 6089-6089/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 16:55:21.438 6089-6089/ylj.com.vieweventapplication E/view_event_viewPager: onTouchEvent
09-13 16:55:21.452 6089-6089/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 16:55:21.452 6089-6089/ylj.com.vieweventapplication E/view_event_viewPager: onTouchEvent
09-13 16:55:21.460 6089-6089/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 16:55:21.460 6089-6089/ylj.com.vieweventapplication E/view_event_viewPager: onTouchEvent
09-13 16:55:21.468 6089-6089/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 16:55:21.468 6089-6089/ylj.com.vieweventapplication E/view_event_viewPager: onTouchEvent
09-13 16:55:21.476 6089-6089/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 16:55:21.477 6089-6089/ylj.com.vieweventapplication E/view_event_viewPager: onTouchEvent

b 如果子控件onTouchEvent 返回true，view group 则会多次调用onInterceptTouchEvent。

09-13 17:12:47.652 7371-7371/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 17:12:47.652 7371-7371/ylj.com.vieweventapplication E/view_event_viewPager: onInterceptTouchEvent
09-13 17:12:47.652 7371-7371/ylj.com.vieweventapplication E/view_event_myImageView: dispatchTouchEvent
09-13 17:12:47.652 7371-7371/ylj.com.vieweventapplication E/view_event_myImageView: onTouchEvent
09-13 17:12:47.727 7371-7371/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 17:12:47.727 7371-7371/ylj.com.vieweventapplication E/view_event_viewPager: onInterceptTouchEvent
09-13 17:12:47.727 7371-7371/ylj.com.vieweventapplication E/view_event_myImageView: dispatchTouchEvent
09-13 17:12:47.727 7371-7371/ylj.com.vieweventapplication E/view_event_myImageView: onTouchEvent
09-13 17:12:47.738 7371-7371/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 17:12:47.738 7371-7371/ylj.com.vieweventapplication E/view_event_viewPager: onInterceptTouchEvent
09-13 17:12:47.738 7371-7371/ylj.com.vieweventapplication E/view_event_myImageView: dispatchTouchEvent
09-13 17:12:47.738 7371-7371/ylj.com.vieweventapplication E/view_event_myImageView: onTouchEvent
09-13 17:12:47.760 7371-7371/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 17:12:47.760 7371-7371/ylj.com.vieweventapplication E/view_event_viewPager: onTouchEvent
09-13 17:12:47.776 7371-7371/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 17:12:47.776 7371-7371/ylj.com.vieweventapplication E/view_event_viewPager: onTouchEvent
09-13 17:12:47.777 7371-7371/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 17:12:47.777 7371-7371/ylj.com.vieweventapplication E/view_event_viewPager: onTouchEvent

2、onInterceptTouchEvent 返回true

输出如下，不会调用子view的方法

09-13 16:52:34.841 4478-4478/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 16:52:34.841 4478-4478/ylj.com.vieweventapplication E/view_event_viewPager: onInterceptTouchEvent
09-13 16:52:34.842 4478-4478/ylj.com.vieweventapplication E/view_event_viewPager: onTouchEvent
09-13 16:52:34.848 4478-4478/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 16:52:34.848 4478-4478/ylj.com.vieweventapplication E/view_event_viewPager: onTouchEvent
09-13 16:52:34.864 4478-4478/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 16:52:34.864 4478-4478/ylj.com.vieweventapplication E/view_event_viewPager: onTouchEvent
09-13 16:52:34.871 4478-4478/ylj.com.vieweventapplication E/view_event_viewPager: dispatchTouchEvent
09-13 16:52:34.871 4478-4478/ylj.com.vieweventapplication E/view_event_viewPager: onTouchEvent

3、onInterceptTouchEvent 返回false，子view的onTouchevent

return super.onTouchEvent(event);

这个时候，viewPager 可以滑动

3、onInterceptTouchEvent 返回false，子view的onTouchevent

return true;

这个时候，viewPager 就不能滑动了

测试源码如下，复写的viewPager

package ylj.com.vieweventapplication;import android.content.Context;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v4.view.ViewPager;
import android.util.AttributeSet;
import android.view.MotionEvent;/*** Created by dfgx_yinlijuan on 2018/9/13.10:06*/public class MyViewPager extends ViewPager {String tag="viewPager";public MyViewPager(@NonNull Context context) {super(context);}public MyViewPager(@NonNull Context context, @Nullable AttributeSet attrs) {super(context, attrs);}@Overridepublic boolean dispatchTouchEvent(MotionEvent ev) {Tools.log(tag,"dispatchTouchEvent");return super.dispatchTouchEvent(ev);}@Overridepublic boolean onTouchEvent(MotionEvent ev) {Tools.log(tag,"onTouchEvent");return super.onTouchEvent(ev);}@Overridepublic boolean onInterceptTouchEvent(MotionEvent ev) {Tools.log(tag,"onInterceptTouchEvent");return super.onInterceptTouchEvent(ev);
//        return false;}
}

复写的ImageView

package ylj.com.vieweventapplication;import android.content.Context;
import android.support.annotation.Nullable;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.widget.ImageView;/*** Created by dfgx_yinlijuan on 2018/9/13.14:49*/public class MyImageView extends android.support.v7.widget.AppCompatImageView {String tag="myImageView";public MyImageView(Context context) {super(context);}public MyImageView(Context context, @Nullable AttributeSet attrs) {super(context, attrs);}public MyImageView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {super(context, attrs, defStyleAttr);}@Overridepublic boolean dispatchTouchEvent(MotionEvent event) {Tools.log(tag,"dispatchTouchEvent");return super.dispatchTouchEvent(event);}@Overridepublic boolean onTouchEvent(MotionEvent event) {Tools.log(tag,"onTouchEvent");return super.onTouchEvent(event);
//        return true;}}

activity 调用

package ylj.com.vieweventapplication;import android.graphics.Color;
import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.view.ViewGroup;import java.util.ArrayList;
import java.util.List;/*** view 事件传递机制demo*/
public class ViewEventActivty extends AppCompatActivity {final String tag = "button";ViewPager viewPager;List<View> views=new ArrayList<>();@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.actvity_view_event);MyViewPager viewPager = (MyViewPager) findViewById(R.id.viewPager);//        viewPager.setAdapter(new GuidePageAdapter());for (int i = 0; i < 3; i++) {MyImageView imageView = new MyImageView(this);if (i == 0) {imageView.setBackgroundColor(Color.RED);} else if (i == 1) {imageView.setBackgroundColor(Color.GREEN);} else if (i == 2) {imageView.setBackgroundColor(Color.BLUE);}imageView.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT));views.add(imageView);}GuideAdapter adapter = new GuideAdapter(views);viewPager.setAdapter(adapter);}class GuideAdapter extends PagerAdapter {List<View> mViews;GuideAdapter(List<View> views) {this.mViews = views;}@Overridepublic int getCount() {return mViews.size();}@Overridepublic boolean isViewFromObject(@NonNull View view, @NonNull Object object) {return view==object;}@Overridepublic void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {((ViewPager) container).removeView(mViews.get(position));}@Overridepublic Object instantiateItem(@NonNull ViewGroup container, int position) {((ViewPager)container).addView(mViews.get(position));return mViews.get(position);}}
}

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