Android的事件传递机制

android

前言

View可以监听交互事件（触碰，点击等），当View与ViewGroup之间重叠时，Android系统是怎么处理这些事件的呢？本文主要分析ACTION_DOWN事件（常用的有ACTION_UP,ACTION_MOVE等）在View之间的传递，涉及下面3个方法：

• public boolean dispatchTouchEvent(MotionEvent ev)
• public boolean onInterceptTouchEvent(MotionEvent ev) （注：ViewGroup中才有，View中不包含）
• public boolean onTouchEvent(MotionEvent event)

通过demo看规律

（代码附录在最后，迫不及待来分析吧）自定义了个LogButton，作为View这类。LogLinearLayout，作为ViewGroup这类，加上Activity，全部重写dispatchTouchEvent，onTouchEvent，onInterceptTouchEvent，并捕获ACTION_DOWN和ACTION_UP事件，输出log。布局就是把一个LogButton放入一个LogLinearLayout中。然后在Activity中监听onTouch事件。

首先自定义个LogButton，作为View这类

public class LogButton extends Button {
    private static final String TAG = "LogButton";
    public LogButton(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                Log.d(MainActivity.MY_TAG, TAG+" onTouchEvent :ACTION_DOWN");
                break;
            case MotionEvent.ACTION_UP:
                Log.d(MainActivity.MY_TAG, TAG+" onTouchEvent :ACTION_UP");
                break;
        }
        // 注意这里默认是true。
        return true; 
    }
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        switch (ev.getAction()) {
            case MotionEvent.ACTION_DOWN:
                Log.d(MainActivity.MY_TAG, TAG+" dispatchTouchEvent :ACTION_DOWN");
                break;
            case MotionEvent.ACTION_UP:
                Log.d(MainActivity.MY_TAG, TAG+" dispatchTouchEvent :ACTION_UP");
                break;
        }
        return super.dispatchTouchEvent(ev);
    }
}

然后定义个LogLinearLayout，作为ViewGroup这类

public class LogLinearLayout extends LinearLayout {
    private static final String TAG = "LogLinearLayout";
    public LogLinearLayout(Context context, AttributeSet attrs) {
        super(context, attrs);
    }
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                Log.d(MainActivity.MY_TAG, TAG+" onTouchEvent :ACTION_DOWN");
                break;
            case MotionEvent.ACTION_UP:
                Log.d(MainActivity.MY_TAG, TAG+" onTouchEvent :ACTION_UP");
                break;
        }
        // 这里默认是super.onTouchEvent(event)
        return super.onTouchEvent(event);
    }
    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        switch (ev.getAction()) {
            case MotionEvent.ACTION_DOWN:
                Log.d(MainActivity.MY_TAG, TAG+" onInterceptTouchEvent :ACTION_DOWN");
                break;
            case MotionEvent.ACTION_UP:
                Log.d(MainActivity.MY_TAG, TAG+" onInterceptTouchEvent :ACTION_UP");
                break;
        }
        return super.onInterceptTouchEvent(ev);
    }
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        switch (ev.getAction()) {
            case MotionEvent.ACTION_DOWN:
                Log.d(MainActivity.MY_TAG, TAG+" dispatchTouchEvent :ACTION_DOWN");
                break;
            case MotionEvent.ACTION_UP:
                Log.d(MainActivity.MY_TAG, TAG+" dispatchTouchEvent :ACTION_UP");
                break;
        }
        return super.dispatchTouchEvent(ev);
    }
}

主界面，其实是Activity类实现了Window的一个Callback接口，里面包含这2个方法。

public class MainActivity extends AppCompatActivity {
    private static final String TAG = "MainActivity";
    public static final String MY_TAG = "zero";
    private LogButton btn;
    private LogLinearLayout ly;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn = (LogButton) findViewById(R.id.log_btn);
        ly = (LogLinearLayout) findViewById(R.id.log_ly);
        btn.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View view, MotionEvent motionEvent) {
                switch (motionEvent.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        Log.d(MainActivity.MY_TAG, TAG+" btn onTouch :ACTION_DOWN");
                        break;
                    case MotionEvent.ACTION_UP:
                        Log.d(MainActivity.MY_TAG, TAG+" btn onTouch :ACTION_UP");
                        break;
                }
                return false;
            }
        });
        ly.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View view, MotionEvent motionEvent) {
                switch (motionEvent.getAction()) {
                    case MotionEvent.ACTION_DOWN:
                        Log.d(MainActivity.MY_TAG, TAG+" layout onTouch :ACTION_DOWN");
                        break;
                    case MotionEvent.ACTION_UP:
                        Log.d(MainActivity.MY_TAG, TAG+" layout onTouch :ACTION_UP");
                        break;
                }
                return false;
            }
        });
    }
    @Override
    public boolean dispatchTouchEvent(MotionEvent ev) {
        switch (ev.getAction()) {
            case MotionEvent.ACTION_DOWN:
                Log.d(MainActivity.MY_TAG, TAG+" dispatchTouchEvent :ACTION_DOWN");
                break;
            case MotionEvent.ACTION_UP:
                Log.d(MainActivity.MY_TAG, TAG+" dispatchTouchEvent :ACTION_UP");
                break;
        }
        return super.dispatchTouchEvent(ev);
    }
    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                Log.d(MainActivity.MY_TAG, TAG+" onTouchEvent :ACTION_DOWN");
                break;
            case MotionEvent.ACTION_UP:
                Log.d(MainActivity.MY_TAG, TAG+" onTouchEvent :ACTION_UP");
                break;
        }
        return super.onTouchEvent(event);
    }
}

布局文件

<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"
    tools:context="com.zero.eventdemo.MainActivity">
    <com.zero.eventdemo.LogLinearLayout
        android:id="@+id/log_ly"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <com.zero.eventdemo.LogButton
            android:id="@+id/log_btn"
            android:layout_width="200dp"
            android:layout_height="wrap_content"
            android:text="log button"/>
    </com.zero.eventdemo.LogLinearLayout>
</LinearLayout>

参考

1. 图解 Android 事件分发机制
2. 公共技术点之 View 事件传递