[objective-c] How do I use NSTimer?

How do I use an NSTimer? Can anyone give me step by step instructions?

The answers are missing a specific time of day timer here is on the next hour:

NSCalendarUnit allUnits = NSCalendarUnitYear   | NSCalendarUnitMonth |
                          NSCalendarUnitDay    | NSCalendarUnitHour  |
                          NSCalendarUnitMinute | NSCalendarUnitSecond;

NSCalendar *calendar = [[ NSCalendar alloc]  
                          initWithCalendarIdentifier:NSGregorianCalendar];

NSDateComponents *weekdayComponents = [calendar components: allUnits 
                                                  fromDate: [ NSDate date ] ];

[ weekdayComponents setHour: weekdayComponents.hour + 1 ];
[ weekdayComponents setMinute: 0 ];
[ weekdayComponents setSecond: 0 ];

NSDate *nextTime = [ calendar dateFromComponents: weekdayComponents ];

refreshTimer = [[ NSTimer alloc ] initWithFireDate: nextTime
                                          interval: 0.0
                                            target: self
                                          selector: @selector( doRefresh )
                                          userInfo: nil repeats: NO ];

[[NSRunLoop currentRunLoop] addTimer: refreshTimer forMode: NSDefaultRunLoopMode];

Of course, substitute "doRefresh" with your class's desired method

try to create the calendar object once and make the allUnits a static for efficiency.

adding one to hour component works just fine, no need for a midnight test (link)

there are a couple of ways of using a timer:

1) scheduled timer & using selector

NSTimer *t = [NSTimer scheduledTimerWithTimeInterval: 2.0
                      target: self
                      selector:@selector(onTick:)
                      userInfo: nil repeats:NO];

• if you set repeats to NO, the timer will wait 2 seconds before running the selector and after that it will stop;
• if repeat: YES, the timer will start immediatelly and will repeat calling the selector every 2 seconds;
• to stop the timer you call the timer's -invalidate method: [t invalidate];

As a side note, instead of using a timer that doesn't repeat and calls the selector after a specified interval, you could use a simple statement like this:

[self performSelector:@selector(onTick:) withObject:nil afterDelay:2.0];

this will have the same effect as the sample code above; but if you want to call the selector every nth time, you use the timer with repeats:YES;

2) self-scheduled timer

NSDate *d = [NSDate dateWithTimeIntervalSinceNow: 60.0];
NSTimer *t = [[NSTimer alloc] initWithFireDate: d
                              interval: 1
                              target: self
                              selector:@selector(onTick:)
                              userInfo:nil repeats:YES];

NSRunLoop *runner = [NSRunLoop currentRunLoop];
[runner addTimer:t forMode: NSDefaultRunLoopMode];
[t release];

• this will create a timer that will start itself on a custom date specified by you (in this case, after a minute), and repeats itself every one second
  
  

3) unscheduled timer & using invocation

NSMethodSignature *sgn = [self methodSignatureForSelector:@selector(onTick:)];
NSInvocation *inv = [NSInvocation invocationWithMethodSignature: sgn];
[inv setTarget: self];
[inv setSelector:@selector(onTick:)];

NSTimer *t = [NSTimer timerWithTimeInterval: 1.0
                      invocation:inv 
                      repeats:YES];

and after that, you start the timer manually whenever you need like this:

NSRunLoop *runner = [NSRunLoop currentRunLoop];
[runner addTimer: t forMode: NSDefaultRunLoopMode];

And as a note, onTick: method looks like this:

-(void)onTick:(NSTimer *)timer {
   //do smth
}

Something like this:

NSTimer *timer;

    timer = [NSTimer scheduledTimerWithTimeInterval: 0.5
                     target: self
                     selector: @selector(handleTimer:)
                     userInfo: nil
                     repeats: YES];

NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:60 target:self selector:@selector(timerCalled) userInfo:nil repeats:NO];

-(void)timerCalled
{
     NSLog(@"Timer Called");
     // Your Code
}

#import "MyViewController.h"

@interface MyViewController ()

@property (strong, nonatomic) NSTimer *timer;

@end

@implementation MyViewController

double timerInterval = 1.0f;

- (NSTimer *) timer {
    if (!_timer) {
        _timer = [NSTimer timerWithTimeInterval:timerInterval target:self selector:@selector(onTick:) userInfo:nil repeats:YES];
    }
    return _timer;
}

- (void)viewDidLoad
{
    [super viewDidLoad];

    [[NSRunLoop mainRunLoop] addTimer:self.timer forMode:NSRunLoopCommonModes];
}

-(void)onTick:(NSTimer*)timer
{
    NSLog(@"Tick...");
}

@end