Android中View的事件分发

案例

TestActivity

public class TestActivity extends AppCompatActivity {

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

        TouchView view = findViewById(R.id.touch_view);
        view.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                Log.e("xxx", "onTouch -> " + event.getAction());
                return false;       // @1
            }
        });

        view.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Log.e("xxx", "onClick");
            }
        });
    }

}

TouchView

public class TouchView extends View {

    // 在代码中创建 TouchView view = new TouchView(this); 实例时会调用
    public TouchView(Context context) {
        super(context);
    }

    // 在布局文件中引用（<com.zc.myapp.listener.TouchView />）时会调用
    public TouchView(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    // 在../res/values/styles.xml中定义样式时会调用
    public TouchView(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        Log.e("xxx","onTouchEvent -> " + event.getAction());
        return super.onTouchEvent(event);               // @2
    }

    @Override
    public boolean dispatchTouchEvent(MotionEvent event) {
        super.dispatchTouchEvent(event);                // @3
        return true;                                    // @4
    }

}

测试结论

1、TestActivity中有view.setOnTouchListener()方法，TouchView中覆写onTouchEvent()方法，没有覆写dispatchTouchEvent()方法
    1.1 @1处返回false，@2处返回super.onTouchEvent(event)，输出结果：OnTouchListener.DOWN -> OnTouch.DOWN -> OnTouchListener.MOVE -> OnTouch.MOVE -> OnTouchListener.UP -> OnTouch.UP -> OnClickListener
    1.2 @1处返回false，@2处返回true，输出结果：OnTouchListener.DOWN -> OnTouch.DOWN -> OnTouchListener.MOVE -> OnTouch.MOVE -> OnTouchListener.UP -> OnTouch.UP
    1.3 @1处返回false，@2处返回false，输出结果：OnTouchListener.DOWN -> OnTouch.DOWN
    1.4 @1处返回true，不管@2处返回super.onTouchEvent(event) / true / false，输出结果：OnTouchListener.DOWN -> OnTouchListener.MOVE -> OnTouchListener.UP

2、TestActivity中没有view.setOnTouchListener()方法，TouchView中覆写onTouchEvent()方法，没有覆写dispatchTouchEvent()方法
    2.1 @2处返回super.onTouchEvent(event)，输出结果：OnTouch.DOWN -> OnTouch.MOVE -> OnTouch.UP -> OnClickListener
    2.2 @2处返回true，输出结果：OnTouch.DOWN -> OnTouch.MOVE -> OnTouch.UP
    2.3 @2处返回false，输出结果：OnTouch.DOWN

3、TestActivity中有view.setOnTouchListener()方法，TouchView中覆写onTouchEvent()方法，也覆写dispatchTouchEvent()方法
    3.1 没有@3行，不管@4返回true / false，不管@1处返回true / false，不管@2处返回true / false，输出结果：没有任何输出
    3.2 有@3行，@4返回true，@1处返回false，@2处返回super.onTouchEvent(event)，输出结果：OnTouchListener.DOWN -> OnTouch.DOWN -> OnTouchListener.MOVE -> OnTouch.MOVE -> OnTouchListener.UP -> OnTouch.UP -> OnClickListener
    3.3 有@3行，@4返回true，@1处返回false，@2处返回true / false，输出结果：OnTouchListener.DOWN -> OnTouch.DOWN -> OnTouchListener.MOVE -> OnTouch.MOVE -> OnTouchListener.UP -> OnTouch.UP
    3.4 有@3行，@4返回false，@1处返回false，@2处返回super.onTouchEvent(event) / true / false，输出结果：OnTouchListener.DOWN -> OnTouch.DOWN

源码分析

View.dispatchTouchEvent(MotionEvent event)方法

public boolean dispatchTouchEvent(MotionEvent event) {
    ...
    boolean result = false;
    ...
    if (onFilterTouchEventForSecurity(event)) {
        /* 
         * ListenerInfo 是View中的静态内部类，存放着View的各种Listener
         * protected OnFocusChangeListener mOnFocusChangeListener;
         * protected OnScrollChangeListener mOnScrollChangeListener;
         * public OnClickListener mOnClickListener;
         * protected OnLongClickListener mOnLongClickListener;
         * 等等...
        */
        ListenerInfo li = mListenerInfo;
        if (li != null && li.mOnTouchListener != null && (mViewFlags & ENABLED_MASK) == ENABLED
                    && li.mOnTouchListener.onTouch(this, event)) {
            result = true;
        }
        if (!result && onTouchEvent(event)) {        // @1
            result = true;
        }
    }
    ...
    return result;
}

@1处的onTouchEvent(MotionEvent event)方法

public boolean onTouchEvent(MotionEvent event) {
    final float x = event.getX();
    final float y = event.getY();
    final int viewFlags = mViewFlags;
    final int action = event.getAction();
    ...
    if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {
        switch (action) {
            case MotionEvent.ACTION_UP:
                ...
                if (!post(mPerformClick)) {
                    performClickInternal();        // @2 View的点击事件
                }
                ...
                break;
            case MotionEvent.ACTION_DOWN:
                ...
                break;
            case MotionEvent.ACTION_CANCEL:
                ...
                break;
            case MotionEvent.ACTION_MOVE:
                ...
                break;
        }
        return true;
    }
    return false;
}

@2处的performClickInternal()方法

private boolean performClickInternal() {
    notifyAutofillManagerOnClick();
    return performClick();        // @3
}

@3处的performClick()方法 【执行View的点击事件】

/**
 * Call this view's OnClickListener, if it is defined.  Performs all normal
 * actions associated with clicking: reporting accessibility event, playing
 * a sound, etc.
 * @return True there was an assigned OnClickListener that was called, false
 *         otherwise is returned.
 */
// NOTE: other methods on View should not call this method directly, but performClickInternal()
// instead, to guarantee that the autofill manager is notified when necessary (as subclasses
// could extend this method without calling super.performClick()).
public boolean performClick() {
    notifyAutofillManagerOnClick();
    final boolean result;
    final ListenerInfo li = mListenerInfo;
    if (li != null && li.mOnClickListener != null) {
        playSoundEffect(SoundEffectConstants.CLICK);
        li.mOnClickListener.onClick(this);
        result = true;
    } else {
        result = false;
    }
    sendAccessibilityEvent(AccessibilityEvent.TYPE_VIEW_CLICKED);
    notifyEnterOrExitForAutoFillIfNeeded(true);
    return result;
}