How do I use NSTimer

Question

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

User · Answer

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
}

User · Answer

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

User · Answer

Firstly I d like to draw your attention to the Cocoa CF documentation  which is always a great first port of call   The Apple docs have a section at the top of each reference article called  Companion Guides   which lists guides for the topic being documented  if any exist   For example  with NSTimer  the documentation lists two companion guides    Timer Programming Topics for Cocoa Threading Programming Guide   For your situation  the Timer Programming Topics article is likely to be the most useful  whilst threading topics are related but not the most directly related to the class being documented  If you take a look at the Timer Programming Topics article  it s divided into two parts    Timers Using Timers   For articles that take this format  there is often an overview of the class and what it s used for  and then some sample code on how to use it  in this case in the  Using Timers  section  There are sections on  Creating and Scheduling a Timer    Stopping a Timer  and  Memory Management   From the article  creating a scheduled  non-repeating timer can be done something like this    NSTimer scheduledTimerWithTimeInterval 2 0     target self     selector  selector targetMethod       userInfo nil     repeats NO     This will create a timer that is fired after 2 0 seconds and calls targetMethod  on self with one argument  which is a pointer to the NSTimer instance   If you then want to look in more detail at the method you can refer back to the docs for more information  but there is explanation around the code too   If you want to stop a timer that is one which repeats   or stop a non-repeating timer before it fires  then you need to keep a pointer to the NSTimer instance that was created  often this will need to be an instance variable so that you can refer to it in another method  You can then call invalidate on the NSTimer instance    myTimer invalidate   myTimer   nil    It s also good practice to nil out the instance variable  for example if your method that invalidates the timer is called more than once and the instance variable hasn t been set to nil and the NSTimer instance has been deallocated  it will throw an exception    Note also the point on Memory Management at the bottom of the article      Because the run loop maintains the timer  from the perspective of memory management there s typically no need to keep a reference to a timer after you   ve scheduled it  Since the timer is passed as an argument when you specify its method as a selector  you can invalidate a repeating timer when appropriate within that method  In many situations  however  you also want the option of invalidating the timer   perhaps even before it starts  In this case  you do need to keep a reference to the timer  so that you can send it an invalidate message whenever appropriate  If you create an unscheduled timer  see    Unscheduled Timers      then you must maintain a strong reference to the timer  in a reference-counted environment  you retain it  so that it is not deallocated before you use it

User · Answer

NSTimer  timer    NSTimer scheduledTimerWithTimeInterval 60 target self selector  selector timerCalled  userInfo nil repeats NO    - void timerCalled        NSLog   Timer Called            Your Code

User · Answer

Something like this      NSTimer  timer       timer    NSTimer scheduledTimerWithTimeInterval  0 5                      target  self                      selector   selector handleTimer                        userInfo  nil                      repeats  YES

User · Answer

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

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