iPhone - ignoring the second touch on an area - iphone

Question

I have a view that the users are allowed to finger paint. The code is working perfectly if the area is touched with one finger. For example: I touch it with one finger and move the finger. Then, a line is drawn as I move the first finger. If I touch with a second finger the same view, the line that was being drawn by the first finger stops.
I would like to ignore any touch beyond the first, i.e., to track the first touch but ignore all others to the same view.
I am using touchesBegan/moved/ended.
I have used this to detect the touches
UITouch *touch = [[event allTouches] anyObject];
lastPoint = [touch locationInView:myView];
I have also tried this
lastPoint = [[touches anyObject] locationInView:myView];
but nothing changed.
How do I do that - track the first touch and ignore any subsequent touch to a view?
thanks.
NOTE: the view is NOT adjusted to detect multiple touches.

Answer 1

A given touch will maintain the same memory address as long as it is in contact with the screen. This means you can save the address as an instance variable and ignore any events from other objects. However, do not retain the touch. If you do, a different address will be used and your code won't work.
Example:
Add currentTouch to your interface:
#interface MyView : UIView {
UITouch *currentTouch;
...
}
...
#end
Modify touchesBegan: to ignore the touch if one is already being tracked:
- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event {
if(currentTouch) return;
currentTouch = [touches anyObject];
...
}
Modify touchesMoved: to use currentTouch instead of getting a touch from the set:
- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event {
if(!currentTouch) return;
CGPoint currentPoint = [currentTouch locationInView:myView];
...
}
Modify touchesEnded: and touchesCancelled: to clear currentTouch, but only if currentTouch has ended or been cancelled.
- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event {
if(currentTouch && currentTouch.phase == UITouchPhaseEnded) {
...
currentTouch = nil;
}
}
- (void)touchesCancelled:(NSSet *)touches withEvent:(UIEvent *)event {
if(currentTouch && currentTouch.phase == UITouchPhaseCancelled) {
...
currentTouch = nil;
}
}

Answer 2

yourView.multipleTouchEnabled = NO;
From the reference documents on UIView
multipleTouchEnabled
A Boolean value that indicates whether
the receiver handles multitouch
events.
#property(nonatomic, getter=isMultipleTouchEnabled) BOOL
multipleTouchEnabled Discussion
When set to YES, the receiver receives
all touches associated with a
multitouch sequence. When set to NO,
the receiver receives only the first
touch event in a multitouch sequence.
The default value of this property is
NO.
Other views in the same window can
still receive touch events when this
property is NO. If you want this view
to handle multitouch events
exclusively, set the values of both
this property and the exclusiveTouch
property to YES.