I have an NSTimer that I init with this code:
testTimer = [[NSTimer alloc] initWithFireDate:[new objectAtIndex:0] interval:0.0 target:self selector:#selector(works:) userInfo:nil repeats:NO];
[new objectAtIndex:0] is an NSDate in the past.
When I start up the app, the timer is getting created, with a fireDate of immediately (since the date is in the past), however it never calls my works method. (-(void)works:(id)sender
)
Anybody know why this is happening?
You will have to add it to the current run loop if you use initWith.. method to create the timer object.
NSRunLoop * theRunLoop = [NSRunLoop currentRunLoop];
[theRunLoop addTimer:testTimer forMode:NSDefaultRunLoopMode];
Or if you would like it set up for you, use the scheduled... methods to create your timer.
I just recently had an issue with NSTimer. In my case I didn't realize that the method scheduledTimerWithTimeInterval is not multi thread safe. Once I moved the timer to the main thread it started working.
I think I had the same problem as Dobler, but my solution was different.
The problem was that the timer was being created and scheduled in a GCD thread in a block within a
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0), ^{})
call (actually nested deep, so it wasn't obvious that this was the case).
Using NSTimer's scheduledTimerWithTimeInterval:... placed the timer into an invalid run loop.
The fix was to change to
timer = [NSTimer timerWithTimeInterval:1.0f target:self selector:#selector(...) userInfo:nil repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
Related
So I am using NSTimer to run a function every minute, it fires at the correct time for the first 3 or so attempts and then it suddenly starts firing every second. I have no idea why this is happening? Would anyone be able to let me know as to why NSTimer is firing inconsistently?
Here is the line where I have declared my timer.
[NSTimer scheduledTimerWithTimeInterval:60.0f target:self selector:#selector(checkForLocation) userInfo:nil repeats:YES];
It is worth noting that I have NSTimer declared inside of viewDidAppear.
Any help is appreciated,
Thank you.
Try to create a instance for NSTimer by declaring a property. Write a function which will initialize the timer and don’t forget to invalidate it before re-intializing it. Call initializeMyTimer in your -viewDidAppear.
-(void) initializeMyTimer
{
if(myTimer)
{
[myTimer invalidate];
myTimer = nil;
}
myTimer = [NSTimer scheduledTimerWithTimeInterval:60.0f
target:self
selector:#selector(checkForLocation)
userInfo:nil
repeats:YES];
}
I've added a timer with the runloopmode NSEventTrackingRunLoopMode like so:
NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:0.50
target:self
selector:#selector(targetMethod:)
userInfo:nil
repeats:YES];
[runLoop addTimer:timer forMode:NSEventTrackingRunLoopMode];
I thought this would only execute whilst for example a menu is open (modal), but it triggers the entire time, even when doing nothing. Is this the normal behavior?
Yes, this is normal behaviour. You add a timer to the runloopMode which is used for tracking events. This runloop runs all the time and is used to determine if there are events that needs to be processed and passed to your event handlers.
I have the following code to create an NSTimer which should update a label each time it fires:
.h file
#interface Game : UIViewController
{
NSTimer *updateTimer;
UILabel *testLabel;
int i;
}
-(void)GameUpdate;
#end
.m file
#implementation Game
-(void)GameUpdate
{
i++;
NSString *textToDisplay = [[NSString alloc] initWithFormat:#"Frame: %d", i];
[testLabel setText:textToDisplay];
NSLog(#"Game Updated");
}
- (void)viewDidLoad
{
[super viewDidLoad];
[[UIApplication sharedApplication] setStatusBarHidden:YES animated:NO];
updateTimer = [NSTimer scheduledTimerWithTimeInterval:0.01428 target:self selector:#selector(GameUpdate) userInfo:nil repeats:YES];
}
//other methods (viewDidUnload, init method, etc.)
#end
When I run it, a label appears in the top that says "0" but does not change. It makes me believe I missed something in how the NSTimer is to be setup. What did I miss?
I used breakpoints and (as you can see) logging to see if the method is actually running, rather than some other error.
I was having a similar problem, and it had a different root cause, related to the run loop. It's worth noting that when you schedule the Timer with the code:
updateTimer = [NSTimer scheduledTimerWithTimeInterval:0.01428 target:self selector:#selector(GameUpdate) userInfo:nil repeats:YES];
The timer will get scheduled with the current thread's runLoop. In your case, because you make this call within the viewDidLoad, it is the main thread, so you are are good to go.
However, if you schedule your timer with a thread other than the main thread, it will get scheduled on the runLoop for that thread, and not main. Which is fine, but on auxiliary threads, you are responsible for creating and starting the initial run loop, so if you haven't done that - your callback will never get called.
The solution is to either start the runLoop for your auxiliary thread, or to dispatch your timer start onto the main thread.
to dispatch:
dispatch_async(dispatch_get_main_queue(), ^{
updateTimer = [NSTimer scheduledTimerWithTimeInterval:0.01428 target:self selector:#selector(GameUpdate) userInfo:nil repeats:YES];
});
To start a runloop:
After creating a thread using your API of choice, call CFRunLoopGetCurrent() to allocate an initial run loop for that thread. Any future calls to CFRunLoopGetCurrent will return the same run loop.
CFRunLoopGetCurrent();
updateTimer = [NSTimer scheduledTimerWithTimeInterval:0.01428 target:self selector:#selector(GameUpdate) userInfo:nil repeats:YES];
Your callback must have this signature:
-(void)GameUpdate:(NSTimer *)timer
This is explicitly in the docs. And the #selector() reference when you setup the timer should be #selector(GameUpdate:) (notice the trailing :).
Try that.
Just in case anyone stumbles across this, I want to point out that this:
[[NSString alloc] initWithFormat:#"Frame: %d", i];
Needs memory management.
Safely replace with:
[NSString stringWithFormat:#"Frame: %d", i];
for the same effect but no need for memory management.
P.S. At time of writing I cannot comment on the original post, so I've added this as an answer.
EDIT: As adam waite pointed out below, this isn't really relevant anymore with the widespread usage of ARC.
I have had a little bit different issue with NSTimer - scheduled method call was ignored during UITableView scrolling.
Timer had been started from main thread. Adding timer explicitly to main run loop resolved the problem.
[[NSRunLoop mainRunLoop] addTimer:playbackTimer forMode:NSRunLoopCommonModes];
Solution found here https://stackoverflow.com/a/2716605/1994889
UPD: CADisplayLink fits much better for updating UI.
According official documentation, CADisplayLink is a:
Class representing a timer bound to the display vsync.
And can be easily implemented like:
playbackTimer = [CADisplayLink displayLinkWithTarget:self selector:#selector(updateUI)];
[playbackTimer addToRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
and removed like
if (playbackTimer) {
[playbackTimer removeFromRunLoop:[NSRunLoop mainRunLoop] forMode:NSRunLoopCommonModes];
playbackTimer = nil;
}
I'm trying to debug my application.
I've been using some NSTimer instances in my non-arc code like this (from the main thread):
[NSTimer scheduledTimerWithTimeInterval:5 target:musicPlayer selector:#selector(playPause:) userInfo:nil repeats:NO];
This works fine if I assign this code to a button and click a button. The timer fires.
I've also tried:
if( self.deliveryTimer == nil)
{
self.deliveryTimer = [NSTimer scheduledTimerWithTimeInterval:10 target:self selector:#selector(playPause:) userInfo:nil repeats:NO];
}
-(void)playPause:(NSTimer*)timer
{
[deliveryTimer invalidate];
deliveryTimer = nil;
//more code here
}
I would expect the timer to execute, hit the play/pause method below, then turn to nil, so I can reset the timer later. The reason why I'm checking for nil is because I have 3 different code paths that may set the timer. Each one has an NSLog statement indicating that the timer has been scheduled.
My code runs, and I see that the timers are being scheduled, but they don't seem to fire in the course of normal app execution. I'm investigating why. Short term timers, using the same logic fire fine. It is when I let the app run for a while that I'm running into issues.
Could the NSTimers be reclaimed by ARC?
Does it matter if I set the timer from a performSelectorInBackground? As I was writing up this question, I noticed that some of my timers were created from a code path that is being called through:
[self performSelectorInBackground:#selector(notifyDelegateOfDataPoint:) withObject:data];
could the background selector be the reason why my timers do not fire/get reclaimed earlier?
Any help is appreciated, this bug has been bugging me for over 2 weeks!
Update: after changing the code to use the main thread for NSTimers, the timers fire correctly, causing the music to play:
[self performSelectorOnMainThread:#selector(deliverReminder:) withObject:nil waitUntilDone:NO];
-(void)deliverReminder:(id)sender{
[ NSTimer scheduledTimerWithTimeInterval:10 target:reminderDeliverySystem selector:#selector(playAfterDelay:) userInfo:nil repeats:NO];
[self postMessageWithTitle:nil message:#"Deliver Reminder Called" action:kNoContextAction];
}
-(void)playAfterDelay:(id)sender
{
int reminderDelay = reminder.delayValue.intValue;
[playTimers addObject:[NSTimer scheduledTimerWithTimeInterval:reminderDelay target:self selector:#selector(appMusicPlayerPlay:) userInfo:nil repeats:NO]];
}
Here I have a whole bunch of timers, which is because I don't know how to pass a primitive to a target with a selector.
An NSTimer requires a run loop to be running in that background thread for it to keep firing. The main thread already has an active run loop, which is why your timers work fine when executed on it.
If you want to use your timers within a background thread, you can do something like the following:
NSRunLoop* runLoop = [NSRunLoop currentRunLoop];
self.deliveryTimer = [NSTimer scheduledTimerWithTimeInterval:10 target:self selector:#selector(playPause:) userInfo:nil repeats:NO];
[runLoop run];
What was probably happening with your short duration timers firing, but the longer ones not, was that they were firing while the thread was still active, but without a run loop to keep it going, were failing after the thread reached the end of its execution.
I don't believe this is ARC-related, although there may be something there you'll have to watch for, because the NSRunLoop holds on to a timer that is attached to it. Following standard procedure with NSTimers should avoid ARC problems.
What is the meaning of this statement given?
NSTimer *timer ,[timer invalidate]
It's an objective C timer statement that cancels a running timer.
Normally it would be expressed as:
NSTimer* myTimer = [NSTimer timerWithTimeInterval:1.0 target:self
selector:#selector(calculateTLE) userInfo:nil repeats:YES];
[[NSRunLoop currentRunLoop] addTimer:myTimer forMode: NSDefaultRunLoopMode];
..
[myTimer invalidate];
It looks as though you're creating an instance of NSTimer without defining it, and then in the same line for whatever reason stopping that same timer. Waste of memory allocation resources, unless you're planning to use the timer at a later time, in which case you should trigger the timer then.