GestureDetector - 检测 GridView 项目中的双击，尽管在 onTouchEvent() 中返回 false

Question

我写了一个简单的ImageView 子类，我想用它来检测对GridView-items 的双击：

public class DoubleClickImageView extends ImageView {

public interface ClickListener {
    void onSingleClick();
    void onDoubleClick();
}

private ClickListener imageClickReceiver;
private GestureDetector gestureDetector;

@Override
public boolean onTouchEvent(MotionEvent event) {
    gestureDetector.onTouchEvent(event);
    // return super.onTouchEvent(event); does not work with gestureDetector
    // return false; does not work with gestureDetector
    return true; // works but breaks the rest of the application
}

public void setDoubleClickListener(ClickListener listener) {
    imageClickReceiver = listener;
}

public DoubleClickImageView(Context cx, AttributeSet attrs) {
    super(cx, attrs);
    gestureDetector = new GestureDetector(cx, new InternalClickListener());
}

private class InternalClickListener extends GestureDetector.SimpleOnGestureListener {

    @Override
    public boolean onSingleTapConfirmed(MotionEvent event) {
        if (imageClickReceiver != null) {
            imageClickReceiver.onSingleClick();
        }
        return true;
    }

    @Override
    public boolean onDoubleTap(MotionEvent e) {
        if (imageClickReceiver != null) {
            imageClickReceiver.onDoubleClick();
        }
        return true;
    }

    @Override
    public boolean onDown(MotionEvent event) {
        //return true for onDown is required according to docs but does not help
        return true;
    }
}

}

GridView 由使用此类显示的图像组成。

问题是双击检测只有在onTouchEvent返回true时有效，否则gestureDetector不会检测到任何点击事件。

但是，当我在 onTouchEvent 中返回 true 时，它会破坏我的应用程序的其余部分，因为我有一个全局 onTouchListener 来检测对整个 GridView 的滑动和一个多选选择模式与 long按下。

我怎样才能解决这个问题，让所有这三个功能一起工作？

更新：我能够通过调试日志追踪问题。如果初始 onTouchEvent-call (MotionEvent.ACTION_DOWN) 返回 false，则相关的后续事件不会传递到 ImageView。因此，GestureDetector 无法理解它，因为它需要给定手势的所有相关 MotionEvent。

Answer 1

在阅读了http://balpha.de/2013/07/android-development-what-i-wish-i-had-known-earlier/ 的触摸处理部分后，我终于找到了解决方法。

解决方法包括手动将 MotionEvent 传递给 GridView 的图像。 因此我扩展了 DoubleClickImageView 类和我的 GridView 的适配器类如下：

 

    /**
     * A workaround to get all touch events of a gesture delivered to GridView-images,
     * although the onTouchEvent-callback has to return false to prevent breaking the
     * rest of the GridView-functionality. (these are swipe gestures and a contextual action bar in our case)
     * See http://stackoverflow.com/questions/39107566/detect-double-click-on-imageview-works-only-when-ontouchevent-returns-true#
     * http://stackoverflow.com/questions/39100565/gesturedetector-detect-doubleclick-on-gridview-items
     * for more information
     */
    public class DoubleClickImageView extends ImageView {

        private TouchEventForwarder touchEventForwarder;
        private ClickListener imageClickListener;
        private GestureDetector gestureDetector;

        /**
         * This needs to be called in the parent GridView adapter's getView() method
         **/
        public void setListeners(ClickListener dest, TouchEventForwarder src) {
            imageClickListener = dest;
            touchEventForwarder = src;
        }

        /**
         * The parent GridView adapter has to maintain an instance of this class
         **/
        public static class TouchEventForwarder {

            private DoubleClickImageView currentlyClickedImage;

            /**
             * This needs to be called on each touch event received by the parent GridView
             **/
            public void forwardTouchEvent(MotionEvent event) {
                if (currentlyClickedImage != null) {
                    currentlyClickedImage.onForwardedTouchEvent(event);
                }
            }

            private void setNewReceiver(DoubleClickImageView doubleClickImageView) {
                currentlyClickedImage = doubleClickImageView;
            }
        }

        public interface ClickListener {
            void onSingleClick();
            void onDoubleClick();
        }

        private void onForwardedTouchEvent(MotionEvent event) {
            /** Use only forwarded events for gesture detection
             * to prevent the evaluation of duplicate events **/
            gestureDetector.onTouchEvent(event);
        }

        @Override
        public boolean onTouchEvent(MotionEvent event) {
            /** Use the system listener to register the view at the event forwarder**/
            if (touchEventForwarder != null) {
                touchEventForwarder.setNewReceiver(this);
            }
            return super.onTouchEvent(event); // always false
        }

        public DoubleClickImageView(Context cx, AttributeSet attrs) {
            super(cx, attrs);
            gestureDetector = new GestureDetector(cx, new InternalClickListener());
        }

        private class InternalClickListener extends GestureDetector.SimpleOnGestureListener {
            @Override
            public boolean onSingleTapConfirmed(MotionEvent event) {
                if (imageClickListener != null) {
                    imageClickListener.onSingleClick();
                }
                return true;
            }

            @Override
            public boolean onDoubleTap(MotionEvent event) {
                if (imageClickListener != null) {
                    imageClickListener.onDoubleClick();
                }
                return true;
            }
        }
    }