Question

How can I pass a parameter to the method called by a NSTimer? My timer looks like this:

[NSTimer scheduledTimerWithTimeInterval:4 target:self selector:@selector(updateBusLocation) userInfo:nil repeats:YES];

and I want to be able to pass a string to the method updateBusLocation. Also, where am supposed to define the method updateBusLocation? In the same .m file that I create the timer?

EDIT:

Actually I am still having problems. I am getting the error message:

Terminating app due to uncaught exception ‘NSInvalidArgumentException’, reason: ‘* -[MapKitDisplayViewController updateBusLocation]: unrecognized selector sent to instance 0x4623600′

Here is my code:

- (IBAction) showBus {

//do something

[NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:@selector(updateBusLocation) userInfo:txtFieldData repeats:YES];
[txtFieldData release];
 }


 - (void) updateBusLocation:(NSTimer*)theTimer
 {
      NSLog(@"timer method was called");
      NSString *txtFieldData = [[NSString alloc] initWithString:(NSString*)[theTimer userInfo]];
if(txtFieldData == busNum.text) {
    //do something else
    }
    }

EDIT #2:
Never mind your example code works fine thanks for the help.

Answer 1

You need to define the method in the target. Since you set the target as ‘self’, then yes that same object needs to implement the method. But you could have set the target to anything else you wanted.

userInfo is a pointer that you can set to any object (or collection) you like and that will be passed to the target selector when the timer fires.

EDIT: … Simple Example:

Set up the timer:

    NSTimer* timer = [NSTimer scheduledTimerWithTimeInterval:2.0 
                              target:self 
                              selector:@selector(handleTimer:) 
                              userInfo:@"someString" repeats:NO];

and implement the handler in the same class (assuming you’re setting the target to ‘self’):

- (void)handleTimer:(NSTimer*)theTimer {
 
   NSLog (@"Got the string: %@", (NSString*)[theTimer userInfo]);
 
}