Cannot keep track of the value of my property in Objective-c

Question

I have a problem with one property in one class. I am coding with iOS 6.1 if it makes any difference.

The class is UIViewController and the property is the declared in the header file like so:

// Keeps track of time in seconds
@property (nonatomic, strong) NSNumber *timeInSeconds;

In my implementation file I use the property during 3 occasions:

• one is to add time with the method - (void)addTime

• one is to subtract time with the method - (void)subtractTime

Those two methods use the property like so:

- (void)addTime
{
    CGFloat timeFloat = [self.timeInSeconds floatValue];

    // Here I set the value of the property timeInSeconds, but I can't access that value later on in the code!

    self.timeInSeconds = [NSNumber numberWithFloat:timeFloat +5];
    NSLog(@"Total Time:%@", self.timeInSeconds);
}

The two methods addTime and subtractTime do what they are supposed to do, and they keep a good track of the property timeInSeconds value as I add then subtract then add...

The problem is when I call in the same implementation file the third method which is:

- (void)updateLabelTime
{
   self.label.attributedText = [[NSAttributedString alloc]initWithString:[self.timeInSeconds stringValue]];


   [self.label setNeedsDisplay];

   [NSTimer scheduledTimerWithTimeInterval:0.8 target:self selector:@selector(updateLabelTime) userInfo:nil repeats:YES];
}

I also tried to create a the NSAttributedString with stringWithFormat instead of initWithString but the problem persists which is that instead of returning the value of the property timeInSeconds which i previously set using addTime and subtractTime, it calls the getter which creates a new instance of timeInSeconds since in my getter I have lazy instantiation.

I tried to not write the getter/setter for the property (since I am using iOS 6.1) but it makes no difference.

If I just set the label to some random string, it would work. The problem is that if I know the value of timeInSeconds is 55, it would still create a new _timeInSeconds.

I tried my best with my English since I am French, please don't answer if the question was already asked by a beginner iOS developer and just redirect me. I couldn't find an answer though, thanks!

EDIT: Here is the custom getter

- (float)timeInSeconds
{
if (!_timeInSeconds) {
    _timeInSeconds = 0;
}

return _timeInSeconds;
}

SECOND EDIT:

The stupid beginner mistake that I made was that addTime and subtractTime are actually implementing a protocol and they set the property which "lives" in another class which is why I could not access it! That other class that needs the protocol was creating a new instance of the class where addTime and subtractTime is written.

What needs to be done is to set the controller as the delegate for the protocol. I did this in the viewDidLoad method with something like:

self.view.delegate = self;

Thanks for all the help.

Answer 1

In your header file, declare this property:

@property (assign) float timeInSeconds;

In the implementation file:

@synthesize timeInSeconds = _timeInSeconds;

- (void)viewDidLoad
{
    [super viewDidLoad];
    _timeInSeconds = 0.0f;
}

- (void)addTime
{
    _timeInSeconds += 5.0f;
}

This should initialize timeInSeconds to zero and then increment its value by 5 each time you call addTime. To use its value in the label:

- (void)updateLabelTime
{
   self.label.text = [NSString stringWithFormat:@"%f", _timeInSeconds];
}

Answer 2

In your custom getter you are assigning a scalar value to an object property. In fact assigning zero to an object property is the equivalent of setting the object to nil.

What you need to do is this:

- (float)timeInSeconds
{
    if (!_timeInSeconds) {
        _timeInSeconds = [NSNumber numberWithFloat:0.0f];
        // or alternatively with the latest version of objective c
        // you can more simply use:
        // _timeInSeconds = @(0.0f);
    }

    return _timeInSeconds;
}