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11143

answers:

5

Hey all,

How do I use an NSTimer. Can anyone give me step by step instructions?

Thanks,

Kevin

+2  A: 

Something like this:

NSTimer *timer;

    timer = [NSTimer scheduledTimerWithTimeInterval: 0.5
                     target: self
                     selector: @selector(handleTimer:)
                     userInfo: nil
                     repeats: YES];
ennuikiller
+27  A: 

Firstly I'd like to draw your attention to the Cocoa/CF documentation (which is always a great first port of call). The Apple docs have a section at the top of each reference article called "Companion Guides", which lists guides for the topic being documented (if any exist). For example, with NSTimer, the documentation lists two companion guides:

For your situation, the Timer Programming Topics article is likely to be the most useful, whilst threading topics are related but not the most directly related to the class being documented. If you take a look at the Timer Programming Topics article, it's divided into two parts:

  • Timers
  • Using Timers

For articles that take this format, there is often an overview of the class and what it's used for, and then some sample code on how to use it, in this case in the "Using Timers" section. There are sections on "Creating and Scheduling a Timer", "Stopping a Timer" and "Memory Management". From the article, creating a scheduled, non-repeating timer can be done something like this:

[NSTimer scheduledTimerWithTimeInterval:2.0
    target:self
    selector:@selector(targetMethod:)
    userInfo:nil
    repeats:NO];

This will create a timer that is fired after 2.0 seconds and calls targetMethod: on self with one argument, which is a pointer to the NSTimer instance.

If you then want to look in more detail at the method you can refer back to the docs for more information, but there is explanation around the code too.

If you want to stop a timer that is one which repeats, (or stop a non-repeating timer before it fires) then you need to keep a pointer to the NSTimer instance that was created; often this will need to be an instance variable so that you can refer to it in another method. You can then call invalidate on the NSTimer instance:

[myTimer invalidate];
myTimer = nil;

It's also good practice to nil out the instance variable (for example if your method that invalidates the timer is called more than once and the instance variable hasn't been set to nil and the NSTimer instance has been deallocated, it will throw an exception).

Note also the point on Memory Management at the bottom of the article:

Because the run loop maintains the timer, from the perspective of memory management there's typically no need to keep a reference to a timer after you’ve scheduled it. Since the timer is passed as an argument when you specify its method as a selector, you can invalidate a repeating timer when appropriate within that method. In many situations, however, you also want the option of invalidating the timer—perhaps even before it starts. In this case, you do need to keep a reference to the timer, so that you can send it an invalidate message whenever appropriate. If you create an unscheduled timer (see “Unscheduled Timers”), then you must maintain a strong reference to the timer (in a reference-counted environment, you retain it) so that it is not deallocated before you use it.

Perspx
Okk, one question, what would I put in as my code that would be executed every two seconds?
Kevin
You'd pass `YES` for `repeats:` when you call `scheduledTimerWithTimeInterval:target:selector:userInfo:repeats:`. If you do so then make sure to keep a reference to the `NSTimer` instance (it is returned by the method) and follow the point on Memory Management as I detailed above.
Perspx
No, where would I put my code that would be started every 2 seconds? For example, let's say I wanted it to make a beep noise every 2 seconds. where would I put the beep noise code..?
Kevin
In the method that you specify with the `target` and `selector`.For example, if your target is `self` and the selector is `timerMethod:`, the method called when the timer fires is `timerMethod:` defined on the `self`. You can then put whatever code you want in that method, and the method will be called whenever the timer fires. Note that the method called when the timer fires (that you pass in as the `selector:`) can only take one argument (which when called is a pointer to the `NSTimer` instance).
Perspx
Sorry, meant "defined on `self`"
Perspx
so would this coding be correct... (inputBox is a NSTextField)[NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(targetMethod:[inputBox setStringValue@"blah"]) userInfo:nil repeats:NO];
Kevin
No that's a method call, not a selector. And if you want to pass arguments to the timer method you have to use an `NSInvocation`. Take a look at this question, which might be more what you're looking for http://stackoverflow.com/questions/1349740/arguments-in-selector/1349800#1349800
Perspx
+1 for mentioning the memory management aspect of timers
DonnaLea
+27  A: 

there are a couple of ways of using a timer:

1) scheduled timer & using selector

NSTimer *t = [NSTimer scheduledTimerWithTimeInterval: 2.0
                      target: self
                      selector:@selector(onTick:)
                      userInfo: nil repeats:NO];
  • if you set repeats to NO, the timer will wait 2 seconds before running the selector and after that it will stop;
  • if repeat: YES, the timer will start immediatelly and will repeat calling the selector every 2 seconds;
  • to stop the timer you call the timer's -invalidate method: [t invalidate];

As a side note, instead of using a timer that doesn't repeat and calls the selector after a specified interval, you could use a simple statement like this:

[self performSelector:@selector(onTick:) withObject:nil afterDelay:2.0];

this will have the same effect as the sample code above; but if you want to call the selector every nth time, you use the timer with repeats:YES;

2) self-scheduled timer

NSDate *d = [NSDate dateWithTimeIntervalSinceNow: 60.0];
NSTimer *t = [[NSTimer alloc] initWithFireDate: d
                              interval: 1
                              target: self
                              selector:@selector(onTick:)
                              userInfo:nil repeats:YES];

NSRunLoop *runner = [NSRunLoop currentRunLoop];
[runner addTimer:t forMode: NSDefaultRunLoopMode];
[t release];
  • this will create a timer that will start itself on a custom date specified by you (in this case, after a minute), and repeats itself every one second

3) unscheduled timer & using invocation

NSMethodSignature *sgn = [self methodSignatureForSelector:@selector(onTick:)];
NSInvocation *inv = [NSInvocation invocationWithMethodSignature: sgn];
[inv setTarget: self];
[inv setSelector:@selector(onTick:)];

NSTimer *t = [NSTimer timerWithTimeInterval: 1.0
                      invocation:inv 
                      repeats:YES];

and after that, you start the timer manually whenever you need like this:

NSRunLoop *runner = [NSRunLoop currentRunLoop];
[runner addTimer: t forMode: NSDefaultRunLoopMode];



And as a note, onTick: method looks like this:

-(void)onTick:(NSTimer *)timer {
   //do smth
}
Woofy
Ok, but you see I want to lower the transparency of my app, so I don't know how to apply that with the NSTimer
Kevin
jeez, these people today.. vote down from me because you didn't specified that from the start and let us write in vain!
Woofy
You didn't write in vain. This is GOOD info!
willc2
A: 

Just a note to say THANK YOU!!!!!

I searched the entire net and read the doc's but, nothing was clear and as useful as these posts - esp post #5.

It worked beautifully!

Mr T
I think you meant Woofy's post, because it had a rating of "5" before it was voted up to 6.
Elliot
also, this is not an answer, it's a comment.
nornagon
A: 

I want to trigger a function at a particular date and particular time,when I run the following code,the app getting terminated. NSTimer *timeControl = [[NSTimer alloc]init]; [timeControl initWithFireDate:itemDate interval:1.0 target:self selector:@selector(scheduleAlarm) userInfo:nil repeats:NO];

[[NSRunLoop currentRunLoop] addTimer:timeControl forMode:NSDefaultRunLoopMode];
NSRunLoop *runner = [NSRunLoop currentRunLoop];
[runner addTimer:timeControl forMode: NSDefaultRunLoopMode];
[timeControl release];

how to do this?

Dinesh Kumar