Simple (hopefully) thread question

[DeeJay_CRO]

Hello!

I never needed to work with threads till now - my task shouldn't be complicated.

So, I have one label and I need to change label text every 10 seconds - in endless loop.

Something like this:

-(void) changeText {
    [myLabel setText:@"Text1"];

    <wait 10 seconds>

   [myLabel setText:@"Text2"];

    <wait 10 seconds>
}

And this Text1 and Text2 has to exchange each other constantly.
And application itself must not be frozen due to this text change.
(Therefore I suppose that this changing text should be in a thread).

Please, can you give me some instructions how to do it.

Thanks a lot!

[BrianSlick]

NSTimer

[RLScott]

As Brian said, "NSTimer" is what you should use. However you should also realize that this cannot be done with threads. The only thread that is allowed to touch the user interface (meaning the display screen) is the main user interface thread. Worker threads can do work, but they must not try to talk directly to the user.

If you look at how NSTimer can be made to send a message to the UI run loop every so often, you will see that threads are not even needed to do what you need to do.

[DeeJay_CRO]

Originally Posted by RLScott

As Brian said, "NSTimer" is what you should use. However you should also realize that this cannot be done with threads. The only thread that is allowed to touch the user interface (meaning the display screen) is the main user interface thread. Worker threads can do work, but they must not try to talk directly to the user.

If you look at how NSTimer can be made to send a message to the UI run loop every so often, you will see that threads are not even needed to do what you need to do.

Hello!

Thanks for the answers. I did it in the following way:

- (void) thisMethodIsTrigered {
NSLog(@"setMessage should be triggered now");
    NSTimer *messageTimer = [NSTimer scheduledTimerWithTimeInterval:3.0
                                    target: self
                                    selector:@selector(setMessageText:)
                                    userInfo:nil
                                    repeats:YES];
    
    [[NSRunLoop currentRunLoop] addTimer:messageTimer forMode:NSDefaultRunLoopMode];

    
}

- (void)setMessageText {
    NSLog(@"setMessage triggered !!!");
}

In the console, I see only:
2011-05-27 13:15:48.924 Zdravo_Budi[1100:207] setMessage should be triggered now
I expected that setMessage triggered !!! will be written every 3 seconds.

Any idea why this happens?

Thanks a lot!

[dany_dev]

- (void)setMessageText: (NSTimer *) timer {
    NSLog(@"setMessage triggered !!!");
}

[Duncan C]

Originally Posted by DeeJay_CRO

Hello!

Thanks for the answers. I did it in the following way:

- (void) thisMethodIsTrigered {
NSLog(@"setMessage should be triggered now");
    NSTimer *messageTimer = [NSTimer scheduledTimerWithTimeInterval:3.0
                                    target: self
                                    selector:@selector(setMessageText:)
                                    userInfo:nil
                                    repeats:YES];
    

    [[NSRunLoop currentRunLoop] addTimer:messageTimer forMode:NSDefaultRunLoopMode];


    
}

- (void)setMessageText {
    NSLog(@"setMessage triggered !!!");
}

In the console, I see only:
2011-05-27 13:15:48.924 Zdravo_Budi[1100:207] setMessage should be triggered now
I expected that setMessage triggered !!! will be written every 3 seconds.

Any idea why this happens?

Thanks a lot!

That second line doesn't belong there (I marked it in bold red.) The method scheduledTimerWithTimeInterval creates a timer and adds to the default run loop all in one step. I don't know what will happen when you then add the timer again, but it probably won't be good.

Dany's pointed out the other problem that your setMessageText method needs to have the timer as a parameter. Methods with different numbers of parameters (and different parameter names) are actually different methods in Objective C.

The selector for a method with one parameter looks like this:

@selector(setMessageText:)

(note the colon after the method name)

The selector for a method with no parameters looks like this:

@selector(setMessageText)

(note the lack of a colon after the method name)

The selector for a timer method needs to take one and only one parameter: the timer itself.

[DeeJay_CRO]

Thanks for very detailed explanation. It works great!.

Kind regards!