让最后一根手指触摸屏幕

Question

I need to do controls, and I am having problem with multi touch.

The concept is easy:

• if the user touches the left (half of the screen) side the ship go to the left
• if the user touches the right (half of the screen) side the ship go to the right.

The problems come when the user does the following:

• Put finger on left side
• Without removing left finger, put finger on the right side
• remove left finger
• Put again left finger (my code won't recognize it, there is the problem)

I want a code that only get the 'X' position of the last finger in the screen

My actual code:

    @Override
public boolean onTouchEvent(MotionEvent event)
{
    int index = MotionEventCompat.getPointerCount(event) - 1;

    float x = (int) MotionEventCompat.getX(event, index);       
    @SuppressWarnings("deprecation")
    int ancho = AEngine.display.getWidth();

    switch (MotionEventCompat.getActionMasked(event))
    {
        case MotionEvent.ACTION_DOWN:
            if (gameView != null)
                gameView.touchNave(x, ancho);
            break;
        case MotionEvent.ACTION_POINTER_DOWN:
            if (gameView != null)
                gameView.touchNave(x, ancho);
            break;
        case MotionEvent.ACTION_MOVE:
            if (gameView != null)
                gameView.touchNave(x, ancho);
            break;

        case MotionEvent.ACTION_UP:
            Nave.estado = AEngine.NAVE_STAY;
            break;
        case MotionEvent.ACTION_POINTER_UP:
            Nave.estado = AEngine.NAVE_STAY;
            break;
    }


    return false;
}

Answer 1

I think by "the LAST finger in the screen" you mean the finger with the latest ACTION_DOWN/ACTION_POINTER_DOWN time.

Each time you get a DOWN/POINTER_DOWN event, get the ID of the action pointer with the method getActionIndex() and then getPointerID() , keep that in a field "lastActionDownId".

Then, before you call touchNave() , get the index of the last down with findPointerIndex(lastActionDownId) . Then use the getX(int index) with the result of that method call.

Answer 2

I made it by using a LinkedHashMap and using the last item of it code:

LinkedHashMap<Integer, Float> al = new LinkedHashMap<Integer, Float>();
@Override
public boolean onTouchEvent(MotionEvent event)
{
    int index = MotionEventCompat.getActionIndex(event);
    int id = event.getPointerId(index);

    float x = (int) MotionEventCompat.getX(event, index);


    @SuppressWarnings("deprecation")
    int ancho = AEngine.display.getWidth();

    switch (MotionEventCompat.getActionMasked(event))
    {
        case MotionEvent.ACTION_DOWN:
            anadir(id,x);               
            break;
        case MotionEvent.ACTION_POINTER_DOWN:
            anadir(id,x);
            break;

        case MotionEvent.ACTION_UP:
            al.remove(id);
            break;
        case MotionEvent.ACTION_POINTER_UP:         
            al.remove(id);
            break;
    }

    if(al.size() > 0)
    {
        if (gameView != null)
            gameView.touchNave(getX(al), ancho);
    }
    else 
    {
        Nave.estado = AEngine.NAVE_STAY;
    }

    return false;
}
public float getX(LinkedHashMap<Integer,Float> map) {
    Iterator<Map.Entry<Integer,Float>> iterator = map.entrySet().iterator();
    float x = 0;
    while (iterator.hasNext()) {
        x = iterator.next().getValue();
    }
    return x;
}

public void anadir(int id,float x)
{
    if (al.size() > 0 || !al.containsKey(id))
    {
        al.put(id, x);  
        Log.e("WTF",Integer.toString(id)+ "añadido");
    } 
}

Answer 3

I never thought of a good solution for this, I ended up writing a rather lengthy class. It seems odd but when you want to count the fingers correctly and account for lifting fingers so if you give the touch event numbers like #1 and #2, #3 etc, you need to know that finger #2 was lifted and thus fingers #1 and #3 are the valid events and the next finger touch is finger #2 back again.

There's a lot of things with multiple fingers where doing it the naive way will suddenly teleport one finger location across the screen because you picked up the touches in different orders. Especially if you want to store information about these touches.

public class TouchTrack {

    private static final int INVALID = -1;
    private static final int POINTERMAX = 5;

    HashMap<Integer, TouchData> touches = new HashMap<>();
    ArrayList<TouchData> fingers = new ArrayList<>(POINTERMAX);


    public void setEventPointers(MotionEvent event) {
        int count = event.getPointerCount();
        count = Math.min(count, POINTERMAX);
        for (int i = 0; i < count; i++) {
            int id = event.getPointerId(i);
            TouchData td = touches.get(id);
            if (td == null) {
                //Log.e("Touch", "Log does not have records for ID: " + id);
                return;
            }
            td.x = event.getX(i);
            td.y = event.getY(i);
        }
    }

    public void setLostPointer(MotionEvent event) {
        int index = event.getActionIndex();
        if (index >= POINTERMAX) return;
        int id = event.getPointerId(index);
        TouchData finger = touches.get(id);
        finger.id = INVALID;
    }

    public void setNewPointer(MotionEvent event) {
        int index = event.getActionIndex();
        if (index >= POINTERMAX) return;
        int id = event.getPointerId(index);

        for (int i = 0; i < POINTERMAX; i++) {
            TouchData finger = fingers.get(i);
            if (finger.id == INVALID) {
                finger.id = id;
                finger.x = event.getX();
                finger.y = event.getY();
                touches.put(id, finger);
                break;
            }
        }
    }

    public double lastEventX(int requestIndex) {
        if ((requestIndex >= 0) && (requestIndex < POINTERMAX)) {
            TouchData td = fingers.get(requestIndex);
            if (td == null) return 0;
            return td.x;
        }
        return 0;
    }

    public double lastEventY(int requestIndex) {
        if ((requestIndex >= 0) && (requestIndex < POINTERMAX)) {
            TouchData td = fingers.get(requestIndex);
            if (td == null) return 0;
            return td.y;
        }
        return 0;
    }

    public boolean isPointerActive(int requestIndex) {
        if ((requestIndex >= 0) && (requestIndex < POINTERMAX)) {
            TouchData td = fingers.get(requestIndex);
            if (td == null) return false;
            return td.id != INVALID;
        }
        return false;
    }

    public void start(float x, float y) {
        touches.clear();
        fingers.clear();
        for (int i = 0; i < POINTERMAX; i++) {
            fingers.add(new TouchData(x, y));
        }
    }

    public void stop() {
        touches.clear();
        fingers.clear();
    }

    public class TouchData {
        static final int INVALID = -1;
        public int id = INVALID;
        public double x = 0;
        public double y = 0;

        public TouchData(double x, double y) {
            this.x = x;
            this.y = y;
        }
    }
}