NSTimer countdown not functioning correctly - ios

Question

I am trying to do the difference between time and display the countdown timer to the user in a ui label
declaration of NSTimer
#property (strong, nonatomic)NSTimer *timer;
this is my timer in view did load
_timer = [NSTimer scheduledTimerWithTimeInterval: 1.0 target:self selector:#selector(updateCountdown:) userInfo:nil repeats: YES];
and this is my updateCountdown method
-(void) updateCountdown:(int)secondsLeft {
int hours, minutes, seconds;
secondsLeft--;
hours = secondsLeft / 3600;
minutes = (secondsLeft % 3600) / 60;
seconds = (secondsLeft %3600) % 60;
_countDownlabel.text = [self timeFormatted:secondsLeft];///[NSString stringWithFormat:#"%02d:%02d:%02d", hours, minutes, seconds];
NSLog(#"%#",[NSString stringWithFormat:#"%02d:%02d:%02d", hours, minutes, seconds]);
if ( secondsLeft == 0 ) {
[_timer invalidate];
}
}
and my log details are
2017-06-30 09:49:34.070 Barebones[845:56963] requestReply cust liqour category: {
date = "30-6-2017";
"end_time" = "11:41";
"market_crash" = true;
"start_time" = "09:41";
}
2017-06-30 09:49:34.070 Barebones[845:56963] true
2017-06-30 09:49:34.070 Barebones[845:56963] 09:41
2017-06-30 09:49:34.070 Barebones[845:56963] 11:41
2017-06-30 09:49:34.070 Barebones[845:56963] 30-6-2017
2017-06-30 09:49:34.073 Barebones[845:56963] 2016-12-25 08:58:00 +0000
2017-06-30 09:49:34.073 Barebones[845:56963] 2016-12-25 12:15:00 +0000
2017-06-30 09:49:34.073 Barebones[845:56963] 197.000000 is the time difference
2017-06-30 09:49:34.073 Barebones[845:56963] 00:03:17
2017-06-30 09:49:35.075 Barebones[845:56963] 991:05:35
2017-06-30 09:49:36.075 Barebones[845:56963] 991:05:35
2017-06-30 09:49:37.075 Barebones[845:56963] 991:05:35
2017-06-30 09:49:38.075 Barebones[845:56963] 991:05:35
and this value goes on executing
Aim:- to countdown till zero and stop the timer actually I ll be hiding the label once the countdown is over
Update:-
int secondsLeft=[self timeFormatted:[date2 timeIntervalSinceDate:date1]/60];
have initialised this above timer
this is my updated timer:-
int secondsLeft=[date2 timeIntervalSinceDate:date1]/60;
NSDictionary *userInfo = [NSDictionary dictionaryWithObjectsAndKeys:
[NSNumber numberWithInt:secondsLeft], #"cID", nil];
_timer = [NSTimer scheduledTimerWithTimeInterval: 1.0 target:self selector:#selector(updateCountdown:) userInfo:userInfo repeats: YES];
and this is my updated timer method :-
- (void)updateCountdown:(NSTimer *)timer{
int hours, minutes, seconds;
NSDictionary *userInfo = [timer userInfo];
int secondsLeft = [[userInfo objectForKey:#"cID"] intValue];
secondsLeft--;
hours = secondsLeft / 3600;
minutes = (secondsLeft % 3600) / 60;
seconds = (secondsLeft %3600) % 60;
_countDownlabel.text = [self timeFormatted:secondsLeft];///[NSString stringWithFormat:#"%02d:%02d:%02d", hours, minutes, seconds];
NSLog(#"%#",[NSString stringWithFormat:#"%02d:%02d:%02d", hours, minutes, seconds]);
if ( secondsLeft == 0 ) {
[_timer invalidate];
}
}

Answer 1

A couple of things.
As vadian said, if you use the selector-based timer, the timer handler function takes a single parameter which is a reference to the timer itself. If you want to keep track of the count down, you can have define properties to keep track of that:
#interface ViewController ()
#property (nonatomic, weak) IBOutlet UILabel *label;
#property (nonatomic, weak) NSTimer *timer;
#property (nonatomic, strong) NSDateComponentsFormatter *formatter;
#property (nonatomic, strong) NSDate *stopTime;
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
self.formatter = [[NSDateComponentsFormatter alloc] init];
self.formatter.allowedUnits = NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
self.formatter.unitsStyle = NSDateComponentsFormatterUnitsStylePositional;
self.formatter.zeroFormattingBehavior = NSDateComponentsFormatterZeroFormattingBehaviorPad;
self.stopTime = [[NSDate date] dateByAddingTimeInterval:5 * 60]; // in 5 minutes, for example
self.timer = [NSTimer scheduledTimerWithTimeInterval:1 target:self selector:#selector(handleTimer:) userInfo:nil repeats:true];
[self.timer fire]; // don't wait one second before firing the first time; fire now
}
- (void)handleTimer:(NSTimer *)timer {
NSDate *now = [NSDate date];
if ([now compare:self.stopTime] == NSOrderedDescending) {
// do whatever you want when timer stops
[timer invalidate];
return;
}
self.label.text = [self.formatter stringFromDate:now toDate:self.stopTime];
}
// Note, when the view disappears, invalidate the timer so the timer doesn't
// keep strong reference to the view controller. Note that in this selector-based
// pattern, I can't attempt to do this in `dealloc`, because the scheduled timer
// will keep a strong reference, preventing `dealloc` from getting called. So do
// this in `viewDidDisappear`.
- (void)viewDidDisappear:(BOOL)animated {
[self.timer invalidate];
}
#end
If only supporting iOS 10 and later, I'd suggest using the completion block timer, as it simplifies the process even further:
#interface ViewController ()
#property (nonatomic, weak) IBOutlet UILabel *label;
#property (nonatomic, weak) NSTimer *timer;
#end
#implementation ViewController
- (void)viewDidLoad {
[super viewDidLoad];
NSDateComponentsFormatter *formatter = [[NSDateComponentsFormatter alloc] init];
formatter.allowedUnits = NSCalendarUnitHour | NSCalendarUnitMinute | NSCalendarUnitSecond;
formatter.unitsStyle = NSDateComponentsFormatterUnitsStylePositional;
formatter.zeroFormattingBehavior = NSDateComponentsFormatterZeroFormattingBehaviorPad;
NSDate *stopTime = [[NSDate date] dateByAddingTimeInterval:5 * 60]; // in 5 minutes, for example
typeof(self) __weak weakSelf = self; // make sure to not reference `self` in block below, but only reference `weakSelf` to avoid timer from maintaining strong reference
self.timer = [NSTimer scheduledTimerWithTimeInterval:1 repeats:true block:^(NSTimer * _Nonnull timer) {
NSDate *now = [NSDate date];
if ([now compare:stopTime] == NSOrderedDescending) {
// do whatever you want when timer stops
[timer invalidate];
return;
}
weakSelf.label.text = [formatter stringFromDate:now toDate:stopTime];
}];
[self.timer fire]; // don't wait one second before firing the first time; fire now
}
// Because I was careful to not reference `self` inside the above block,
// this block-based timer will NOT keep a strong reference to the view
// controller. Nonetheless, when the view controller is dismissed, I want
// to stop the timer, to avoid wasting CPU cycles on a timer that isn't
// needed anymore.
- (void)dealloc {
[self.timer invalidate];
}
#end
Clearly, if you need to support iOS 9 and earlier, too, then you have to use the aforementioned selector-based solution.
I'd suggest not relying on the timer to adjust the time, as you're not assured that the timer will be called with the frequency you want. In both of the above examples, I capture to what time I'm counting down, and just display the amount of time between "now" and that scheduled "stop time".
Note, I'm also suggesting that you get out of the business of building the format string yourself. There's a convenient NSDateComponentsFormatter which can format this for you. Use it, if you can.
You made your timer reference strong. You can make it weak because a scheduled timer is not deallocated until it's invalidated. And once it's invalidated, it's convenient to have it be deallocated automatically for you.

Answer 2

Your action method cannot work.
If a parameter is passed it must be a NSTimer instance
- (void)updateCountdown:(NSTimer *)timer
To pass custom parameters use the userInfo argument.
Nevertheless a more suitable solution is to use an instance variable or property because the value of userInfo must be an object like NSNumber

Answer 3

Create property
#property (nonatomic) int secondsLeft;
in viewDidLoad
self.secondsLeft = 5 * 60; // 5 minutes
_timer = [NSTimer scheduledTimerWithTimeInterval: 1.0 target:self selector:#selector(updateCountdown) userInfo:nil repeats: YES];
Selector:
-(void)updateCountdown{
int secondsLeft = self.secondsLeft;
if (secondsLeft >= 0) {
int minutes, seconds;
int hours;
self.secondsLeft--;
hours = secondsLeft / 3600;
minutes = (secondsLeft % 3600) / 60;
seconds = (secondsLeft %3600) % 60;
NSString *time = [NSString stringWithFormat:#"%02d:%02d:%02d", hours, minutes, seconds];
_countDownlabel.text = [self timeFormatted:secondsLeft];
}
if (secondsLeft <= 0) {
NSLog(#"TIME ENDS");
if ([self.timer isValid]) {
[self.timer invalidate];
self.timer = nil;
}
}
}