如何在Android touchlistener中同时检测到触摸屏幕上的次要手指？

Question

How to detect an additional finger on the screen? Eg I touch the screen using one finger and after sometime I keep the first finger on screen and then touch the screen using other finger while keeping first finger as it is? How to detect the second finger touch in Touch Listener?

Answer 1

The MotionEvent.ACTION_POINTER_DOWN and MotionEvent.ACTION_POINTER_UP are send starting with the second finger. For the first finger MotionEvent.ACTION_DOWN and MotionEvent.ACTION_UP are used.

The getPointerCount() method on MotionEvent allows you to determine the number of pointers on the device. All events and the position of the pointers are included in the instance of MotionEvent which you receive in the onTouch() method.

To track the touch events from multiple pointers you have to use the MotionEvent.getActionIndex() and the MotionEvent.getActionMasked() methods to identify the index of the pointer and the touch event which happened for this pointer.

    int action = MotionEventCompat.getActionMasked(event);
// Get the index of the pointer associated with the action.
int index = MotionEventCompat.getActionIndex(event);
int xPos = -1;
int yPos = -1;

Log.d(DEBUG_TAG,"The action is " + actionToString(action));

if (event.getPointerCount() > 1) {
    Log.d(DEBUG_TAG,"Multitouch event"); 
    // The coordinates of the current screen contact, relative to 
    // the responding View or Activity.  
    xPos = (int)MotionEventCompat.getX(event, index);
    yPos = (int)MotionEventCompat.getY(event, index);

} else {
    // Single touch event
    Log.d(DEBUG_TAG,"Single touch event"); 
    xPos = (int)MotionEventCompat.getX(event, index);
    yPos = (int)MotionEventCompat.getY(event, index);
}
...

// Given an action int, returns a string description
public static String actionToString(int action) {
    switch (action) {

        case MotionEvent.ACTION_DOWN: return "Down";
        case MotionEvent.ACTION_MOVE: return "Move";
        case MotionEvent.ACTION_POINTER_DOWN: return "Pointer Down";
        case MotionEvent.ACTION_UP: return "Up";
        case MotionEvent.ACTION_POINTER_UP: return "Pointer Up";
        case MotionEvent.ACTION_OUTSIDE: return "Outside";
        case MotionEvent.ACTION_CANCEL: return "Cancel";
    }
    return "";
}

For more details please visit Google Handling Multi-Touch Gestures .

Answer 2

If you need to process multi touch events you should check PointerCount.

    public boolean onTouchEvent(MotionEvent event) {    
        if (event.getPointerCount() > 1) {
            Log.d(DEBUG_TAG,"Multitouch event"); 
            // The coordinates of the current screen contact, relative to 
            // the responding View or Activity.  
            xPos = (int)MotionEventCompat.getX(event, index);
            yPos = (int)MotionEventCompat.getY(event, index);

        } else {
            // Single touch event
            Log.d(DEBUG_TAG,"Single touch event"); 
            xPos = (int)MotionEventCompat.getX(event, index);
            yPos = (int)MotionEventCompat.getY(event, index);
        }
...

    }

You can find more information here: https://developer.android.com/training/gestures/multi.html