Countdown Timer

cocoa, objective-c

Solution

You're on the right track so far.

Sticking with the code you already have, here is how `advanceTimer` method should look to make it work:

- (void)advanceTimer:(NSTimer *)timer
{
    [countdown setIntegerValue:([countdown integerValue] - 1)];
    if ([countdown integerValue] == 0)
    {
        // code to stop the timer
    }
}

edit: To make the whole thing more object-oriented, and to avoid converting from strings to numbers and back every time, I would instead do something like this:

// Controller.h:
@interface Controller
{
    int counter;
    IBOutlet NSTextField * countdownField;
}
@property (assign) int counter;
- (IBAction)startCountdown:(id)sender;
@end

``

// Controller.m:
@implementation Controller

- (IBAction)startCountdown:(id)sender
{
    counter = 60;

    NSTimer *countdownTimer = [NSTimer scheduledTimerWithTimeInterval:1
                                         target:self
                                       selector:@selector(advanceTimer:)
                                       userInfo:nil
                                        repeats:YES];
}

- (void)advanceTimer:(NSTimer *)timer
{
    [self setCounter:(counter -1)];
    [countdownField setIntegerValue:counter];
    if (counter <= 0) { [timer invalidate]; }
}

@end

And, if you can make use of bindings, you could simply bind the text field's `intValue` to the `counter` property of the `Controller`. This would allow you to elminate the `IBOutlet` in the class interface, and the `setIntegerValue:` line in `advanceTimer`.

update: Removed the code which adds the timer to the run loop twice. Thank you to Nikolai Ruhe and nschmidt for noticing that error.

update: Used the `setIntegerValue` method to simplify the code, as per nschmidt.

edit: Typo in definition of (void)advanceTimer:(NSTimer *)timer ... caused annoying 'unrecognized selector sent to instance' exception

Problem

Original source

Related problems

• How Do I write a Timer in Objective-C?