Problems with UILabel and while loop

[matsoftware]

Hi everybody,

I'm currenlty developing a simple test software for iPhone that use only an UILabel and an UIButton. The button is linked to the "writeresult" action that contains the following code:

	while (i<1000)
	{	
		NSString *text = [[NSString alloc] initWithFormat: @"Number: %d", i];
		labelOutput.text = text;
		[text release];
		i++;
	}

with "labelOutput" declared in the class.h file as:

@property (nonatomic, retain) UILabel *labelOutput;

and @syntetize labelOutput; in class.m file.

The problem is that when the user tap the button, it will show only the last number. The label doesn't appear with the value increasing (i think, it doesn't "reload" its content) and the software seems like freezing during the cycle (no user interaction till the loop ending).

How to show updated text in the UILabel when "i" increase (ie: "Number: 1" then "Number: 2" .... etc) ?

Thanks :-)

[JoeBlaze]

Try this

while (i<1000)
	labelOutput.text = [labelOutput.text stringByAppendingFormat:@"Number: %d ", i++];

i++ will not be performed until after that line of code is executed so you should get your expected results

[Oliver Drobnik]

Originally Posted by JoeBlaze

Try this

while (i<1000)
	labelOutput.text = [labelOutput.text stringByAppendingFormat:@"Number: %d ", i++];

i++ will not be performed until after that line of code is executed so you should get your expected results

Generally you have to allow your apps to get into the run loop for UI elements to be updated. Never write any functions that will take too long unless you do them with NSOperation or multithreaded.

A easy way around this is to do the updating in NSTimer method.

[JoeBlaze]

Yes Oliver is right, for some reason I thought you were trying to add onto the string. NSTimer seems like your best option because you probably want it to update the display at some set interval such as 1 second.

[matsoftware]

Originally Posted by Oliver Drobnik

Generally you have to allow your apps to get into the run loop for UI elements to be updated. Never write any functions that will take too long unless you do them with NSOperation or multithreaded.

A easy way around this is to do the updating in NSTimer method.

You're right :-)

I've read the NSTimer description in the xcode documentation but I didn't understand how to use it .. I'm a newbie with objective - c :-P

[matsoftware]

I tried with the following code:

	NSTimer *timer;
	timer = [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(testFunction:) userInfo: nil repeats: YES];

before the "while" loop and then in the class.m file I wrote (out of the "writeresult" function) the following:

-(void)testFunction:(NSTimer*)timer {
	//
	fooLabel.text = @"Yes, timer activated!";
}

where fooLabel is a new UILabel with the same declaration of labelOutput.

But it doesn't behave how I would .. it shows the 999 number (the last "i" value) yet and the string in fooLabel AFTER the ending of the while loop..:-(

[Oliver Drobnik]

Originally Posted by matsoftware

I tried with the following code:

	NSTimer *timer;
	timer = [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(testFunction:) userInfo: nil repeats: YES];

before the "while" loop and then in the class.m file I wrote (out of the "writeresult" function) the following:

-(void)testFunction:(NSTimer*)timer {
	//
	fooLabel.text = @"Yes, timer activated!";
}

where fooLabel is a new UILabel with the same declaration of labelOutput.

But it doesn't behave how I would .. it shows the 999 number (the last "i" value) yet and the string in fooLabel AFTER the ending of the while loop..:-(

You also need to move the incrementing to the testFunction!

[matsoftware]

Originally Posted by Oliver Drobnik

You also need to move the incrementing to the testFunction!

Do you mean put the "i++" in the testFunction?

I think I've some problems with the NSTimer.
To figure out with it I tried using the following:

- (IBAction)writeresult:(id)sender {
	
	NSTimer *timer;
	timer = [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(testFunction:) userInfo: nil repeats: YES];
	
	[timer release];
	
}

and

-(void)testFunction:(NSTimer*)timer {

	NSLog(@"Timer activated");
}

but I receive this error in gdb:

MyTest(770,0xa06f2720) malloc: *** error for object 0x542e00: double free
*** set a breakpoint in malloc_error_break to debug

without any NSLog printed

[Oliver Drobnik]

[quote=matsoftware;67763]Do you mean put the "i++" in the testFunction?

	[timer release];

UAAAAA. Don't release stuff that you don't own!! Only release objects that you yourself have instantiated with alloc/init.

The scheduleTimer... method is autoreleased at the end of the function and if you have an additional release you get a double release crash.

Yes, the increment and setting of the label has to go into the timer function.

[matsoftware]

Mea culpa, mea culpa, mea grandissima culpa!

Thank you very much!!
I figured out by removing the [timer release] and by putting in testFunction the following code:

		NSString *text = [[NSString alloc] initWithFormat: @"Number: %d", i];
		labelOutput.text = text;
		[text release];
		i++;

if (i == 1000) [timer invalidate];

and it works :-) Again thank you!

[Vitamblu]

Originally Posted by matsoftware

Mea culpa, mea culpa, mea grandissima culpa!

Thank you very much!!
I figured out by removing the [timer release] and by putting in testFunction the following code:

		NSString *text = [[NSString alloc] initWithFormat: @"Number: %d", i];
		labelOutput.text = text;
		[text release];
		i++;

if (i == 1000) [timer invalidate];

and it works :-) Again thank you!

is that code you put in the testFunction within the while loop? Could you provide the whole tesFunction code, I couldn't figure out how you get it to work. I probably misunderstood somewhere.

I tried the following:

-(void)testFunction:(NSTimer*)timer
{
    NSLog(@"Timer activated");

    int i = 0;
    while (i<1000) {
        NSString *text = [[NSString alloc] initWithFormat: @"Number: %d", i];
        _labelOutput.text = text;
        [text release];
        i++;
        
    
        if (i == 1000)
        {
            [timer invalidate];
        }
    }
}

-(void)writeResult:(id)sender
{   
    NSTimer *timer;
	timer = [NSTimer scheduledTimerWithTimeInterval:0.1 target:self selector:@selector(testFunction:) userInfo: nil repeats: YES];
}