To which source file does NSRunLoop/NSTimer belong? - iphone

Question

I've been trying to figure out how to setup an NSTimer to allow me to print the current time in a UILabel within a View, and have it update every second (no finer resolution required - just a simple clock).
At first, I wasn't using a NSRunLoop, but if I try and include one, the execution just "spins" inside the loop, blocking further execution. I have posted my code below.
-(id) printCurrentTime {
now = [NSDate date];
dateFormat = [[NSDateFormatter alloc] init];
[dateFormat setTimeStyle:NSDateFormatterMediumStyle];
NSString *nowstr = [dateFormat stringFromDate:now];
[dateFormat release];
NSLog(#"Current time is: %#",nowstr);
return nowstr;
}
And in the ViewController source file, I execute as per:
TimeStuff *T = [[TimeStuff alloc] init];
NSString *thetime = [T printCurrentTime];
[timelabel setText:thetime];
[T release];
[self.view addSubview:timelabel];
NSTimer *timmeh = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:#selector(printCurrentTime) userInfo:nil repeats:YES];
[[[NSRunLoop currentRunLoop] addTimer:timmeh forMode:NSDefaultRunLoopMode] run];
The "TimeStuff" class is effectively an empty class, save for the printCurrentTime function.
Questions:
1) Should I be including the RunLoop in the AppDelegate class? I am having trouble visualising how this all should hang together, as in - what are the steps to achieving a Loop based on Timer to update a text label with the up-to-second time. Pretty stumped.
2) In the event that I should use a NSThread, should that also be in it's own class / the Delegate class.
3) Is the ViewController class totally out of bounds for looping/timers, and simply the "eye candy" class, with callbacks to functions in the Delegate class?
Thank you for your time and patience.

Answer 1

You don't need to deal with run loops at all.
This line :
NSTimer *timmeh = [NSTimer scheduledTimerWithTimeInterval:1.0 target:self selector:#selector(printCurrentTime) userInfo:nil repeats:YES];
will create a timer and attach it to the current thread's run loop for you. You don't need the [NSRunLoop addTimer:forMode:] call at all - you can delete that line.
PS You certainly don't need to go as far as NSThreads!
EDIT Regarding your comment :
You will need to make an instance of your TimeStuff class for the timer to use if that's where your printCurrentTime method is. i.e.
#interface MyViewController : UIViewcontroller {
TimeStuff *timeStuff
}
and in your viewDidLoad method:
- (void)viewDidLoad {
[super viewDidLoad];
...
// Create our timestuff if we don't have one already
if (nil == timeStuff)
timeStuff = [[TimeStuff alloc] init];
// Start the timer
[NSTimer scheduledTimerWithTimeInterval:1.0 target:timeStuff selector:#selector(printCurrentTime) userInfo:nil repeats:YES];
and not forgetting dealloc
- (void)dealloc {
[timeStuff release];
...
[super dealloc];
}
Passing in the timeStuff as the target for the timer tells it where to look for the printCurrentTime method!
Hope that helps,
PS All the line #class TimeStuff does is tell the compiler that there is a class called TimeStuff. It has no idea that you want to use it for your timer's selector!