Question

I started using the MoveMe sample to get touch input working.

basically, I define these two callback functions to get my touch input:

- (void)touchesBegan:(NSSet *)touches withEvent:(UIEvent *)event 
{

    for ( UITouch* touch in touches )
    {
        printf("touch down");
    }
}



- (void)touchesEnded:(NSSet *)touches withEvent:(UIEvent *)event 
{
    for ( UITouch* touch in touches )
    {
        printf("touch up");
    }
}

This works fine, until you have more than 5 touches on the screen at once. then it stops working properly, you won’t get the “touch down” message if there are more than 5 touches on the screen. what is even worse is that you won’t reliably get all of the “touch up” messages until you have removed ALL your fingers from the screen.

If you touch with 6 fingers, then release 3, then touch again with the other 3 still down, you will get the “touch down” but if you release it, some times you get the “touch up” sometimes you don’t.

This pretty much makes it impossible to track touches, and usually results in a touch getting ‘stuck’ permanently down, when passed to my Touch Manager.

Are there some better apis to use to get touch input? is there at very least a function you can call to reliably get whether the screen is currently touched or not? that way I could reset my manager when all fingers are released.

EDIT:

right, there must be something I’m missing. because currently the calculator does something I cannot do with those callbacks.

it only accepts one touch at a time, if there is more than one touch on the screen it “cancels” all touches, but it must keep track of them to know that there is “more than one” touch on the screen.

if I touch the screen the button goes down, now if I add another touch to the screen, the button releases, cool, not allowed more than one touch. now, if I add 4 more fingers to the screen, for a total of 6, the screen should break, and when I release those 6 fingers, the app shouldn’t get any of the “up” callbacks. yet when I release all of them and touch again, the button depresses, so it knows I released all those fingers!! how??

Answer 1

The problem you have is that the iPhone and iPod touch only support up to five touches at the same time (being fingers still touching the screen). This is probably a hardware limit.
(As St3fan told you already.)

The system will cancel all touches if there are more than 5 at the same time:
touchesCancelled:withEvent:
(This is probably what causes the odd behavior with only some touches calling touchesEnded:withEvent:)

If you want to know if a touch ended and it ended because it was lifted then make sure to check the UITouch’s phase property.