How to call a method every x seconds in Objective-C using NSTimer?

Question

I am using Objective-C, Xcode 4.5.1 and working on an app for the iPhone.

I have a method A in which I want to call another method B to do a series of calculations e

Answer 1

try this

 NSTimer *aTimer = [NSTimer timerWithTimeInterval:(x) target:self selector:@selector(timerFired:) userInfo:nil repeats:YES];

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

- (void)timerFired:(NSTimer*)theTimer 
{
if(condition)
{
  [theTimer isValid]; //recall the NSTimer
   //implement your methods
}
else
{
  [theTimer invalidate]; //stop the NSTimer

}

}

Answer 2

Well you are trying to call an normal C method, NSTimer can't to that.

The target is the an instance of the class on which to call the selector, this selector adn not select. The selector here is a SEL type which you can create with the @selector(METHOD_NAME) function.

For example this will call the handleTimer : ever 0.1 second: (For this example the AppDelegate is used):

- (BOOL)application:(UIApplication *)application didFinishLaunchingWithOptions:(NSDictionary *)launchOptions {
    //SNIP, some code to setup the windos.   

    [NSTimer scheduledTimerWithTimeInterval:0.1f target:self selector:@selector(handleTimer:) userInfo:nil repeats:YES];
    return YES;
}

- (void) handleTimer:(NSTimer *)timer {
    // Hanlde the timed event.
}

Answer 3

If you look at your code and compared to the one below

[NSTimer scheduledTimerWithTimeInterval:0.1 target:self
select:@selector(targetMethod:myVolumeMonitor()) userInfo:nil repeats:YES];

self means that you are invoking a method in same instance of your class, in your example the method is myVolumeMonitor

[NSTimer scheduledTimerWithTimeInterval:0.1 target:self
selector:@selector(MethodB) userInfo:nil repeats:YES];

and you are good to go though

method be should look like this

- (void)MethodB:(NSTimer*)timer { 
// do something
}

Answer 4

Target is the recipient of the message named in select. In Objective-C functions are not called. There are rather messages sent to objects. The Object internally refers to its symbol table and determines which of its methods is being called. That is a selector. Your selector is @selector(MethodB). (BTW: you should start method names with lower case. "methodB" would be more appropriate here.) This leads to the question: how to determine the object to which the message is sent? That is the target. In your case, it is simply self.

BTW: In this case the selector is expected to return void and accept an id, which is the id of the NSTimer object itself. That will come handy if you want the timer to stop firing based on some conditions according to your program logic. Most important: Your selector is then methodB: rather than methodB.

- (void) methodA
{
//Start playing an audio file.

//NSTimer calling Method B, as long the audio file is playing, every 5 seconds.
[NSTimer scheduledTimerWithTimeInterval:5.0f 
target:self selector:@selector(methodB:) userInfo:nil repeats:YES];
}

- (void) methodB:(NSTimer *)timer
{
//Do calculations.
}