Question

I have a timer class set up that is basically handling all of count down timer logic. All it does is on button press – counts from 60 to 0 seconds.

I have the following code in a Timer.m class.

- (void)advanceTimer
{
    self.lengthOfTime = [NSNumber numberWithInt:self.lengthOfTime.intValue - 1];
    NSLog(@"%@",self.lengthOfTime);
    [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(advanceTimer) userInfo:nil repeats:NO];
}
- (void)startCountdown
{
    if (!self.lengthOfTime) self.lengthOfTime = [NSNumber numberWithInt:60];
    [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(advanceTimer) userInfo:nil repeats:NO];
}

What I am looking to do is create a timer object in my View Controller that will update a label from the ViewController.m. Currently – the class works because I can NSLog from the Timer class and it counts down correctly. I thought about having the advanceTimer method return – but I can’t seem to wrap my head around how to update the label in the ViewController with the returned data.

The only way I cold get the return to work was to have a button that refreshed the label to the correct countdown time… I can’t get it to automatically count down…

Answer 1

Well, if you know how to update a label by clicking a button, you have everything in place to connect everything else:

If your view controller has an IBOutlet for the label and an IBAction that updates it, why not call the view-controller’s action in your advanceTimer method?

Yet easier, you could connect your timer class to the label.
You might do it like this:

// Timer.h:
@interface Timer : NSObject

@property (retain, nonatomic) IBOutlet UILabel *timeLabel;
@property (assign, nonatomic) NSInteger secondsRemaining;
@property (assign, nonatomic) NSTimer *timer;

- (IBAction)startCountdown:(id)sender;
- (IBAction)stopCountdown:(id)sender;
- (void)timerFired:(NSTimer *)timer;

@end

// Timer.m
@implementation Timer

@synthesize timeLabel = timeLabel_;
@synthesize secondsRemaining = secondsRemaining;
@synthesize timer = timer_;

- (void)setTimer:(NSTimer *)timer
{
    if (timer = timer_)
        return;

    [timer_ invalidate];
    timer_ = timer;
}

- (void)scheduleTimer
{
    if (self.secondsRemaining <= 0) {
        self.timer = nil;
    } else {
        self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(timerFired:) userInfo:nil repeats:NO];
    }
}

- (void)timerFired:(NSTimer *)timer
{
    self.secondsRemaining -= 1;
    NSString *displayString = [NSString stringWithFormat:@"%d", self.secondsRemaining];
    self.timeLabel.text = displayString;
    [self scheduleTimer];
}

- (IBAction)startCountdown:(id)sender
{
    self.secondsRemaining = 60;
    [self scheduleTimer];
}

- (IBAction)stopCountdown:(id)sender
{
    self.timer = nil;
}

- (void)dealloc
{
    [timeLabel_ release];
    [super dealloc];
}

@end

This code has a two benefits:

• You can cancel your timer.
• Your view controller does not need to know anything about this — you can set this up in interface builder, entirely.