android - 在 Android 中使用多点触控实现拖放

Question

我正在寻找一种在我的应用程序中通过多点触控实现拖放的方法。我有很多 View ，我希望第一个用户拖动一个 View 的时间与第二个用户拖动另一个 View 的时间相同。

我的单点触摸拖放效果很好，这是我的代码的一部分(我的 View 正在实现这个监听器。onDragStart 记录触摸点，onDragContinuing 改变 View 的位置，onDrop 检查位置是否有效):

public boolean onTouch(View v, MotionEvent event) {

    if (event.getAction() == MotionEvent.ACTION_DOWN) {
        return onDragStart(event.getX(), event.getY());
    }

    else if (event.getAction() == MotionEvent.ACTION_MOVE){
        return onDragContinuing(event.getRawX(), event.getRawY());                      
    }

    else if (event.getAction() == MotionEvent.ACTION_UP){
        return onDrop(event.getRawX(), event.getRawY());
    }

    else{
        return false;
    }

}

我试过像那样实现多点触控，但它不起作用:

private static final int INVALID_POINTER_ID = -1;
// The ‘active pointer’ is the one currently moving our object.
private int mActivePointerId = INVALID_POINTER_ID;

public boolean onTouch(View v, MotionEvent event) {

    int action = event.getAction();
    int actionCode = action & MotionEvent.ACTION_MASK;

    switch(actionCode){

        case MotionEvent.ACTION_DOWN :{
            Toast.makeText(getContext(), "down", Toast.LENGTH_SHORT).show();
            // Save the ID of this pointer
            mActivePointerId = event.getPointerId(0);
            return onDragStart(event.getX(), event.getY());
        }

        case MotionEvent.ACTION_POINTER_DOWN :{
            Toast.makeText(getContext(), "pointer down", Toast.LENGTH_SHORT).show();
            // Save the ID of this pointer
            // Extract the index of the pointer that left the touch sensor
            final int pointerIndex = (action & MotionEvent.ACTION_POINTER_ID_MASK) >> MotionEvent.ACTION_POINTER_ID_SHIFT;
            mActivePointerId = event.getPointerId(pointerIndex);
            return onDragStart(event.getX(mActivePointerId), event.getY(mActivePointerId));
        }

        case MotionEvent.ACTION_MOVE :{
            Toast.makeText(getContext(), "move", Toast.LENGTH_SHORT).show();
            final int pointerIndex = (action & MotionEvent.ACTION_POINTER_ID_MASK) >> MotionEvent.ACTION_POINTER_ID_SHIFT;
            final int mCurrentPointerId = event.getPointerId(pointerIndex);
            if (mActivePointerId == mCurrentPointerId){
                return onDragContinuing(getRawX(event, mActivePointerId), getRawY(event, mActivePointerId));
            }
            else return false;
        }

        case MotionEvent.ACTION_UP :{
            Toast.makeText(getContext(), "up", Toast.LENGTH_SHORT).show();
            final int pointerIndex = (action & MotionEvent.ACTION_POINTER_ID_MASK) >> MotionEvent.ACTION_POINTER_ID_SHIFT;
            final int mCurrentPointerId = event.getPointerId(pointerIndex);

            if (mActivePointerId == mCurrentPointerId){
                return onDrop(event.getRawX(), event.getRawY());
            }
            else return false;

        }

        case MotionEvent.ACTION_POINTER_UP :{
            Toast.makeText(getContext(), "pointer up", Toast.LENGTH_SHORT).show();
            final int pointerIndex = (action & MotionEvent.ACTION_POINTER_ID_MASK) >> MotionEvent.ACTION_POINTER_ID_SHIFT;
            final int mCurrentPointerId = event.getPointerId(pointerIndex);

            if (mActivePointerId == mCurrentPointerId){
                return onDrop(getRawX(event, pointerIndex), getRawY(event, pointerIndex));
            }
            else return false;

        }

        default :{
            return false;
        }

    }

}

/**
 * MotionEvent has no getRawX(int) method; simulate it pending future API approval. 
 */
private static float getRawX(MotionEvent event, int pointerIndex) {
    float offset = event.getX() - event.getRawX();
    return event.getX(pointerIndex) + offset;
}

/**
 * MotionEvent has no getRawY(int) method; simulate it pending future API approval. 
 */
private static float getRawY(MotionEvent event, int pointerIndex) {
    float offset = event.getY() - event.getRawY();
    return event.getY(pointerIndex) + offset;
}

怎么了？你能帮助我吗 ？谢谢!

Answer 1

我找到了解决方案和解释。

Android 不支持多屏多点触控，多点触控只针对单屏。因此，要为多 View 提供多点触控，我们必须在主 Activity 中捕获触摸事件并为 subview 生成新事件。

感谢 Pascal Welsch 和他的博客 (http://www.passsy.de/multitouch-for-all-views/)，以及我发现的对他代码中错误的修改 (http://code.google.com/p/friendbattle/issues/detail?id=19)，我已经解决了我的问题。

希望这对其他人有帮助:-)