Exception with touches set...

[Johanovski]

Hi there!

I'm trying to get multitouch working in my app but when there's more than one finger on the screen the app crashes when trying to access them. In touches moved, if number of touches is higher than 1 (so there are at least two fingers in the screen) the app tries to access the two fingers, but throws an NSException error. Here's the code and after it the error:

Code:

// In touchesMoved event

NSLog(@"Touches:%d",[[event allTouches] count]);

if ([[event allTouches] count] > 1) {
	for(UITouch *t in [touches allObjects])
	{
		NSLog(@"Luke, I'm your father!");
	}
			
	UITouch *t2 = [[touches allObjects] objectAtIndex:1];
	CGPoint touchPos2 = [t2 locationInView:t2.view];

	(...irrelevant code...)
}

And here's what I get in the console:

2010-02-23 10:04:23.694 provaObjectes3D[1909:207] Touches:2
2010-02-23 10:04:24.106 provaObjectes3D[1909:207] Luke, I'm your father!
2010-02-23 10:04:24.130 provaObjectes3D[1909:207] *** Terminating app due to uncaught exception 'NSRangeException', reason: '*** -[NSCFArray objectAtIndex:]: index (1) beyond bounds (1)'
2010-02-23 10:04:24.157 provaObjectes3D[1909:207] Stack: (
    853417245,
    845594132,
    852966195,
    852966099,
    871671569,
    871826727,
    13227,
    818194628,
    818192276,
    818173840,
    818172052,
    834382224,
    853165355,
    853163039,
    834376564,
    817839152,
    817832496,
    9127,
    9060
)
terminate called after throwing an instance of 'NSException'
Program received signal:  “SIGABRT”.
kill

So seems that just the first object position is accessible... However, count says that there are two objects... Argh, it have no sense! :S

Any help please? Thanks in advance!

[Mr Jack]

Try not switching back and forth between touches allObjects and event allTouches.

[Johanovski]

Hi Mr. Jack!

I've tried this but the problem is that by using "[touches allObjects]" the counter is always one, so seems that there's only one finger on the screen, but by using "[event allTouches]" I can't compile because I can't access to the touch via the "[[event allTouches] objectAtIndex:n]" method...

I've tried replacing all my code by the "[touches allObjects]" and the result is:

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
	if ([[touches allObjects] count] > 0) {
		// Hi ha 1 dit a la pantalla
		
		UITouch *t1 = [[touches allObjects] objectAtIndex:0];
		CGPoint touchPos1 = [t1 locationInView:t1.view];
		CGPoint touchPosAnt1 = [t1 previousLocationInView:t1.view];
		
		NSLog(@"1");
		
		if ([[touches allObjects] count] > 1) {
			// Hi ha 2 dits a la pantalla
			
			NSLog(@"2");
	
			for(UITouch *t in [touches allObjects])
			{
				NSLog(@"Luke, I'm your father!");
			}
			
			UITouch *t2 = [[touches allObjects] objectAtIndex:1];
			CGPoint touchPos2 = [t2 locationInView:t2.view];
		}
	}
}

And the console shows:

2010-02-23 10:36:49.175 provaObjectes3D[1996:207] 1
2010-02-23 10:36:49.331 provaObjectes3D[1996:207] 1
2010-02-23 10:36:49.354 provaObjectes3D[1996:207] 1
(repeat ad infinitum...)

So seems that counter is never > 1...

Any clue about this?

[Johanovski]

Solved!

You were on the right way, Mr. Jack!

What I've done is to simply create a new NSSet from the event (to ensure that initial data won't be modified during the method) and then everything worked! Here's the new code:

- (void)touchesMoved:(NSSet *)touches withEvent:(UIEvent *)event
{
	NSSet *touchSet = [event allTouches];  // <--- This is the happy line!
	
	if ([touchSet count] > 0) {
		// Hi ha 1 dit a la pantalla
		
		UITouch *t1 = [[touchSet allObjects] objectAtIndex:0];
		CGPoint touchPos1 = [t1 locationInView:t1.view];
		CGPoint touchPosAnt1 = [t1 previousLocationInView:t1.view];
		
		if ([touchSet count] > 1) {
			// Hi ha 2 dits a la pantalla
	
			for(UITouch *t in [touchSet allObjects])
			{
				NSLog(@"Luke, I'm your father!");
			}
			
			UITouch *t2 = [[touchSet allObjects] objectAtIndex:1];
			CGPoint touchPos2 = [t2 locationInView:t2.view];
		}
	}
}

Thanks for your time Mr. Jack!