Display a timer for an iOS app that persists between view controllers

Question

I've been trying to get a timer to show at the bottom left corner of my app by using an NSTimer, and making the "elapsed time" show as UILabel on the bottom left corner but it hasn't been working for me.

-(void)viewDidLoad
{
    NSTimer *aTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(aTime) userInfo:nil repeats:YES];
}

-(void)aTime
{
    NSLog(@"....Update Function Called....");

    static int i = 1;

    Label.text = [NSString stringWithFormat:@"%d",i];

    i++;
}

The timer actually works but I can't get it to be triggered by a button. I'm trying to get the timer to continue and not restart at 1 when it enters to the next storyboard/xib file.

Can you please include your code so that we may look at it to determine why it is not working? — vcsjones, Sep 21 '12 at 16:04
Sorry for that. I was experimenting with different codes trying to see if I could make things work so I didn't really have a code to post a while back cause they were kind of just drafts. But I posted the code I'm using now. Hope that helps! Thanks. — user1677210, Sep 21 '12 at 16:39
@user1677210: now what is the issue ? Timer is not working or need to implement it in button click ? — Midhun MP, Sep 21 '12 at 16:42
If you want it triggered by a button, then put the timer creation code in the button method, not viewDidLoad. — rdelmar, Sep 21 '12 at 16:43
@MidhunMP the only issue now is how do I get the Timer to continue on even after going to another storyboard/xib. Like if it ends at 10 on the first storyboard/xib file it should continue to 11 at the next. — user1677210, Sep 21 '12 at 16:48

score 11 · Answer 1 · edited Sep 23 '13 at 04:39

11

For implementing the timer action on the button press, you need to write it on a IBAction method like:

- (IBAction) buttonPress
{
    NSTimer *aTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(aTime) userInfo:nil repeats:YES];
}

For storing the previous value, you can use NSUserDefaults or a SQLite database. For this purpose I'll suggest NSUserDefaults.

Change the aTime method like:

-(void)aTime
{
    NSUserDefaults *standardUserDefaults = [NSUserDefaults standardUserDefaults];
    id obj = [standardUserDefaults objectForKey:@"TimerValue"];
    int i = 0;

    if(obj != nil)
    {
        i = [obj intValue];
    }

    Label.text = [NSString stringWithFormat:@"%d",i];
    i++;

    [standardUserDefaults setObject:[NSNumber numberWithInt:i] forKey:@"TimerValue"];
    [standardUserDefaults synchronize];
}

edited Sep 23 '13 at 04:39

Adi Inbar

12,097
13
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answered Sep 21 '12 at 16:53

Midhun MP

103,496
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Do I just put this method on the first view controller? or should I put it as well to the other succeeding view controllers? – user1677210 Sep 21 '12 at 18:18
No, just replace your aTime in first view controller – Midhun MP Sep 21 '12 at 18:18
But then when I would switch to the next view the label with the time would disappear – user1677210 Sep 21 '12 at 18:21
wherever you are using the same timer for displaying the time, you need to use this – Midhun MP Sep 21 '12 at 18:22
Alright I did just that but when it moves to the next view the timer stops let's say if the last view lasted for 5 seconds it would just show "5" at the next view. – user1677210 Sep 21 '12 at 18:28
I set the the method on the next view right after -(void)viewDidLoad{ – user1677210 Sep 21 '12 at 18:28
then you need to set the timer again, because when you move to another view, the timer is getting released and set to nil. That's why it displays a constant value. – Midhun MP Sep 21 '12 at 18:30
Oh so with this method I can't have the timer continue counting time on the next view? So I would really need a singleton to do this? – user1677210 Sep 21 '12 at 18:32
ya, or use the timer on other thread. and don't release or don't set to nil in the first view. :) – Midhun MP Sep 21 '12 at 18:34
Ohh Alright man thanks :) But isn't the releasing automatic with Xcode 4 cause of ARC? – user1677210 Sep 21 '12 at 18:39

score 3 · Answer 2 · edited Mar 11 '13 at 15:06

I think the problem is that the method aTime is in your view controller, when you enters another view, this view controller is released and you can't perform selector aTime anymore.

so I suggest that you put your aTime method and i to a singleton(or any object that won't be released when you enter another view) and set the singleton as the target of your timer.

also you should keep code below in your view controller so that you can update your label properly when you came back to this view.

-(void)viewDidLoad
{
    NSTimer *aTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(aTime) userInfo:nil repeats:YES];
}

-(void)aTime
{
    NSLog(@"....Update Function Called....");

    Label.text = [NSString stringWithFormat:@"%d",theSingleton.i];
}

better choice:

You can declare i as a property of your singleton, and then add an observer to i, then you'll get your label updated on time. call -startTimer when you want to count time.

the singleton:

  @interface Singleton

  @property (nonatomic,retain) NSNumber *i;

  @end

  @implementation

+(Singleton*)instance
{
    //the singleton code here
}

-(void)startTimer
{
    NSTimer *aTimer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:@selector(aTime) userInfo:nil repeats:YES];
}

-(void)aTime
{
    NSInteger temp = [i integerValue];
    temp ++;
    self.i = [NSNumber numberWithInteger:temp];
}

the view controller:

-(void)viewDidLoad
{
    [super viewDidLoad];
    [[Singleton instance] addObserver:self forKeyPath:@"i" options:NSKeyValueObservingOptionNew context:NULL]];
}


- (void)observeValueForKeyPath:(NSString *)keyPath
                  ofObject:(id)object
                    change:(NSDictionary *)change
                   context:(void *)context
{
    NSLog(@"....Update Function Called....");

    Label.text = [NSString stringWithFormat:@"%@",[Singleton instance].i];
}

Thans for the help man. Singletons are pretty much new to me. I understand it in theory but I get lost a bit with the coding. How do I set up a Singleton for the time data? — user1677210, Sep 21 '12 at 17:25
You don't have to use a singleton then, you can just put i as a property in your application delegate. — CarmeloS, Sep 22 '12 at 00:34

Display a timer for an iOS app that persists between view controllers

2 Answers2