Pause and stop a method - ios

Question

I am making a stopwatch, but I only have the start button working. When the start button is pressed it enters a loop:
- (void)stopwatch
{
NSInteger hourInt = [hourLabel.text intValue];
NSInteger minuteInt = [minuteLabel.text intValue];
NSInteger secondInt = [secondLabel.text intValue];
if (secondInt == 59) {
secondInt = 0;
if (minuteInt == 59) {
minuteInt = 0;
if (hourInt == 23) {
hourInt = 0;
} else {
hourInt += 1;
}
} else {
minuteInt += 1;
}
} else {
secondInt += 1;
}
NSString *hourString = [NSString stringWithFormat:#"%02d", hourInt];
NSString *minuteString = [NSString stringWithFormat:#"%02d", minuteInt];
NSString *secondString = [NSString stringWithFormat:#"%02d", secondInt];
hourLabel.text = hourString;
minuteLabel.text = minuteString;
secondLabel.text = secondString;
CGRect hourFrame = self->hourBar.frame;
CGRect minuteFrame = self->minuteBar.frame;
CGRect secondFrame = self->secondBar.frame;
if ((NSInteger)hourFrame.size.height != hourInt) { // check if we need to modify
hourFrame.origin.y -= ((hourInt * 10.0) - hourFrame.size.height);
hourFrame.size.height = (hourInt * 10.0);
self->hourBar.frame = hourFrame;
}
if ((NSInteger)minuteFrame.size.height != minuteInt) { // check if we need to modify
minuteFrame.origin.y -= ((minuteInt * 4.0) - minuteFrame.size.height);
minuteFrame.size.height = (minuteInt * 4.0);
self->minuteBar.frame = minuteFrame;
}
if ((NSInteger)secondFrame.size.height != secondInt) { // check if we need to modify
secondFrame.origin.y -= ((secondInt * 4.0) - secondFrame.size.height);
secondFrame.size.height = (secondInt * 4.0);
self->secondBar.frame = secondFrame;
}
[NSTimer scheduledTimerWithTimeInterval:1.0f target:self selector:#selector(stopwatch) userInfo:nil repeats:NO];
}
When the stop button is pressed, I want this loop to be paused so that when the user presses start, it resumes the stopwatch.
When the reset button is pressed, I want the loop to stop and reset back to 0.
If you could make your answer as simple as possible, that would be really great because I'm only a beginner!

Answer 1

You should take the timer out of your 'loop' method and make it repeating. It should be the thing that is driving the stopwatch, not that fact that you have started your 'loop'. Then, you can stop the timer when you need to and restart it later. You can also google to find out the correct way to pause the timer (you need to change the timer to start at a specified fire date to be 100% accurate, but just knowing how many seconds are left may be enough for your case).

Answer 2

Based on your previous question it sounds like you have moved your timer outside of your stopwatch method. Remember, timers and loops are two very different things.
You can stop an NSTimer by calling invalidate on it. Please read Apple's documentation for more details.

Answer 3

One way that might not be completely thread safe but I just tested it and it works is to have a variable that is set to true when you click start and false when you click stop.
For example, in my .h, I added #property (nonatomic) BOOL go;, then as the first line of the method you provided, add an if check that looks like this:
- (void)stopwatch {
if (!self.go) return;
//..do the rest of your stopwatch code
//the timer call
}
then my start and stop button calls look like:
- (void)start {
if (!self.go) { // Do not call the stopwatch method again if it is already going.
self.go = YES;
[self stopwatch];
}
}
- (void)stop {
self.go = NO;
}

Answer 4

Loop is the wrong construct for this type of operation. For better control, use NSTimer.
A relevant example can be found here.
EDIT:
My above answer was based on prior version of your question.
So yes, the NSTimer should be the controlling thing for your loop, not part of the loop.
General implementation:
Start should only mark timer starting. Also note the current time from system clock. (this is optional though)
Timer function should change value of the time variable, and compare it against the stopwatch set value. If time elapsed == set value, stop the timer using invalidate.
Stop should interrupt the timer and stop it, and also the elapsed time value should be set to 0. Time Variable should be reset too, if you do not want to reuse this same time value again.