iPhone: Tracking/Identifying individual touches

Question

I have a quick question regarding tracking touches on the iPhone and I seem to not be able to come to a conclusion on this, so any suggestions / ideas are greatly appreciated:

I want to be able to track and identify touches on the iphone, ie. basically every touch has a starting position and a current/moved position. Touches are stored in a std::vector and they shall be removed from the container, once they ended. Their position shall be updated once they move, but I still want to keep track of where they initially started (gesture recognition).

I am getting the touches from [event allTouches], thing is, the NSSet is unsorted and I seem not to be able to identify the touches that are already stored in the std::vector and refer to the touches in the NSSet (so I know which ones ended and shall be removed, or have been moved, etc.)

Here is my code, which works perfectly with only one finger on the touch screen, of course, but with more than one, I do get unpredictable results...

    - (void) touchesBegan:(NSSet*)touches withEvent:(UIEvent*)event
{
    [self handleTouches:[event allTouches]];
}

- (void) touchesEnded:(NSSet*)touches withEvent:(UIEvent*)event
{
    [self handleTouches:[event allTouches]];
}

- (void) touchesMoved:(NSSet*)touches withEvent:(UIEvent*)event
{
    [self handleTouches:[event allTouches]];
}

- (void) touchesCancelled:(NSSet*)touches withEvent:(UIEvent*)event
{
    [self handleTouches:[event allTouches]];
}

- (void) handleTouches:(NSSet*)allTouches
{   
    for(int i = 0; i < (int)[allTouches count]; ++i)
    {
        UITouch* touch = [[allTouches allObjects] objectAtIndex:i];
        NSTimeInterval timestamp = [touch timestamp];

        CGPoint currentLocation = [touch locationInView:self];
        CGPoint previousLocation = [touch previousLocationInView:self];

        if([touch phase] == UITouchPhaseBegan)
        {
            Finger finger;
            finger.start.x = currentLocation.x;
            finger.start.y = currentLocation.y;
            finger.end = finger.start;
            finger.hasMoved = false;
            finger.hasEnded = false;

            touchScreen->AddFinger(finger);
        }
        else if([touch phase] == UITouchPhaseEnded || [touch phase] == UITouchPhaseCancelled)
        {
            Finger& finger = touchScreen->GetFingerHandle(i);

            finger.hasEnded = true;
        }
        else if([touch phase] == UITouchPhaseMoved)
        {
            Finger& finger = touchScreen->GetFingerHandle(i);

            finger.end.x = currentLocation.x;
            finger.end.y = currentLocation.y;
            finger.hasMoved = true;
        }
    }

    touchScreen->RemoveEnded();
}

Thanks!

Answer 1

It appears the "proper" way to track multiple touches is by the pointer value of the UITouch event.

You can find more details in the "Handling a Complex Multi-Touch Sequence" section of this Apple Developer Documentation