I am making an iphone app and have scheduled an event called gameOver to occur after 15 seconds(when the game is over).
[self performSelector:#selector(gameOver) withObject:nil afterDelay:15.0];
How can I unschedule this event so that if someone wanted to press a reset button and start the game over, this scheduled event would be deleted and another one would be created.
I would use an NSTimer
with the retain-property NSTimer *myTimer
-(void) startTimer
{
self.myTimer = [NSTimer scheduledTimerWithTimeInterval:myDelay target:self selector:#selector(myTimerExpiredMethod:) userInfo:nil repeats:NO];
}
-(void) myTimerExpiredMethod:(id)aSender
{
NSLog(#"timer expired");
self.myTimer = nil;
}
-(void) cancelTimer
{
[self.myTimer invalidate];
self.myTimer = nil;
}
Try
+ (void)cancelPreviousPerformRequestsWithTarget:(id)aTarget
aTarget would be the object the selector should be performed on. self in your example.
Edit:
This method is defined on NSObject so:
[NSObject cancelPreviousPerformRequestsWithTarget:myObject]
would be the syntax.
Edit 2:
Use
+ (void)cancelPreviousPerformRequestsWithTarget:(id)aTarget selector:(SEL)aSelector object:(id)anArgument
to only unschedule calls to this specific selector.
Related
I am adding
[self performSelector:#selector(showLyrics) withObject:nil afterDelay:20];
but if user restart the song then the this selector should not get performed. So I just want to
know how I can cancel that. Because after 20 second it will get invoked but I don't want that, and reschedule
[self performSelector:#selector(showLyrics) withObject:nil afterDelay:20];
I'v so many
[self performSelector:#selector(showLyrics) withObject:nil afterDelay:2];
I want to cancel all those, which I've scheduled before.
[[NSRunLoop currentRunLoop] cancelPerformSelector:#selector(showLyrics)
target:self
argument:nil];
You can use NSTimer instead of performSelector:withObject:afterDelay:
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:20 target:self selector:#selector(showLyrics) userInfo:nil repeats:NO];
To cancel:
[timer invalidate];
But you may want to invalidate before you start each time or keep timers in an array and iterate through them to cancel all of them.
Use an NSTimer and save a reference to it instead of performSelector. Afaik performSelector can't be cancelled. Edit: Apparently it can be cancelled, see omz's answer...
self.showLyricsTimer = [NSTimer scheduledTimerWithTimeInterval:20.0
target:self
selector:#selector(showLyrics)
userInfo:nil
repeats:NO];
To cancel the timer you use:
[self.showLyricsTimer invalidate];
But be careful to also invalidate the timer when your view disappears f.e. in the viewWillDisappear callback, since NSTimer retains it's target.
Cancels perform requests previously registered with performSelector:withObject:afterDelay:
+ (void)cancelPreviousPerformRequestsWithTarget:(id)aTarget selector:(SEL)aSelector object:(id)anArgument
It seems this is what you are looking for or what you were looking for~~
I have an NSTimer declared in my .h and in the viewDidLoad of the /m I have the code:
timer = [NSTimer scheduledTimerWithTimeInterval:kComplexTimer target:self selector:#selector (main) userInfo:nil repeats:YES];
I also have [timer release]; in my dealloc.
However when I exit the view and return to it, the timer has not in fact released, it has doubles in speed! How do I solve this & what am I doing wrong???
Thanks
you don't need to release it as you have not retained it - as a rule.
all you need to do is just call [timer invalidate]; which will stop your timer.
Nice Answer , but good to check whether the time is nil or not to avoid unwanted exception..
if( timer ! = nil )
{
[timer invalidate];
timer = nil;
}
Thank you...
[timer invalidate];
timer = nil;
The second line is important if you want to reset the NSTimer
You must not call release on a object that it not be created by "new", "alloc", "retain", "copy".
In this case, you had created a Timer by scheduledTimerWithTimeInterval method, So you must not call release method but call [timer invalidate] to stop the timer.
Following is my sample code.
#interface TrackTimer : NSObject {
NSTimer *timer;
}
#property (nonatomic, retain) NSTimer *timer;
- (void) startTimer;
- (void) stopTimer;
- (void) timerFired;
#end
TrackTimer.m
#synthesize timer;
- (void) startTimer
{
NSLog(#"Timer started ...");
if(timer)
{
timer = nil;
}
timer = [NSTimer scheduledTimerWithTimeInterval:30.0 target:self selector:#selector(timerFired) userInfo:nil repeats:NO];
}
- (void) stopTimer
{
NSLog(#"Timer stoped ...");
[tTimer invalidate];
}
- (void) timerFired
{
NSLog(#"Timer Fired ... :)");
}
I have to use the same timer object from 3 different view controllers, my problem is startTimer method do not invoke timerFired method in 2nd UIViewController. Its works perfectly on 1st and 3rd View Controller.
appln Flow : 1stView -> 2ndView -> 3rdView
You are doing everything right... almost.
Your timer does not fire, because of the "if" statement.
if (timer) {
timer = [NSTimer scheduledTimerWithTimeInterval:5 target:self selector:#selector(boom) userInfo:nil repeats:NO];
}
Here, the "if" statement returns NO, because the timer is not yet initialized..
The fact that you make it a property and synthesize it does not mean that (timer != nil)
If you remove the "if" statement it should work...
From the Apple docs on NSTimer:
The message to send to target when the timer fires. The selector must have the following signature:
- (void)timerFireMethod:(NSTimer*)theTimer
So, it looks like the signature of your timerFired method needs to be expanded to include one parameter '(NSTimer*)theTimer' and your selector needs to be #selector(timerFired:)
Don't really know how you do that, but NStimer has a class method called
+ (NSTimer *)scheduledTimerWithTimeInterval:(NSTimeInterval)seconds target:(id)target selector:(SEL)aSelector userInfo:(id)userInfo repeats:(BOOL)repeats. So you can do it like this:
timer=[NSTimer scheduledTimerWithTimeInterval:2 target:self
selector:#selector(timerFired)
userInfo:nil
repeats:YES];
This will invoke the timerFired method for you.
P.S.Here's the link to a simple app that does just what you want.
http://www.mediafire.com/?8uz115drqzb2nan
I'm trying to invalidate a timer when my app goes into background. The timer gets invoked when you hit a button that starts the timer and is in the TimerController.m file. Here is how it gets invoked.
mytimer = [NSTimer timerWithTimeInterval:1 target:self selector:#selector(updateTime) userInfo:nil repeats:YES];//Timer with interval of one second
[[NSRunLoop mainRunLoop] addTimer:mytimer forMode:NSDefaultRunLoopMode];
Now, I'd like to invalidate mytimer when the app goes into background, so I tried putting
[mytimer invalidate];
into the - (void)applicationDidEnterBackground:(UIApplication *)application method the apps delegate. But this won't work since it's undeclared in the delegate. I thought by including TimerController.h into the delegate, this would work, but it won't.
So, I clearly don't know what I'm doing here. Can you help? How do it get it so that mytimer is invalidated when the app goes into background?
There’s also a UIApplicationDidEnterBackgroundNotification notification posted when the application goes into background. You can subscribe for this notification in your controller and handle the transition there:
[[NSNotificationCenter defaultCenter]
addObserver:self
selector:#selector(goBackground)
name:UIApplicationDidEnterBackgroundNotification
object:nil];
// and later:
- (void) goBackground {
[timer invalidate], timer = nil;
}
if (timer) {
[timer invalidate];
timer = nil;
}
in applicationReEnteredForeground notification method will also work
I'm pretty sure this is really simple, and I'm just missing something obvious. I have an app that needs to download data from a web service for display in a UITableView, and I want to display a UIAlertView if the operation takes more than X seconds to complete. So this is what I've got (simplified for brevity):
MyViewController.h
#interface MyViewController : UIViewController
<UITableViewDelegate, UITableViewDataSource> {
NSTimer *timer;
}
#property (nonatomic, retain) NSTimer *timer;
MyViewController.m
#implementation MyViewController
#synthesize timer;
- (void)viewDidLoad {
timer = [NSTimer scheduledTimerWithTimeInterval:20
target:self
selector:#selector(initializationTimedOut:)
userInfo:nil
repeats:NO];
[self doSomethingThatTakesALongTime];
[timer invalidate];
}
- (void)doSomethingThatTakesALongTime {
sleep(30); // for testing only
// web service calls etc. go here
}
- (void)initializationTimedOut:(NSTimer *)theTimer {
// show the alert view
}
My problem is that I'm expecting the [self doSomethingThatTakesALongTime] call to block while the timer keeps counting, and I'm thinking that if it finishes before the timer is done counting down, it will return control of the thread to viewDidLoad where [timer invalidate] will proceed to cancel the timer. Obviously my understanding of how timers/threads work is flawed here because the way the code is written, the timer never goes off. However, if I remove the [timer invalidate], it does.
I think there is a problem with scheduling a timer and doing a blocking call on the same thread. Until the blocking call is completed, the run-loop cannot fire the timer.
I suggest you to detach a thread to perform the long operation. Once the long operation is finished, call back on the main thread to invalidate the timer.
Note: it is important to invalidate the timer on the same thread it was scheduled.
- (void)viewDidLoad {
timer = [NSTimer scheduledTimerWithTimeInterval:20
target:self
selector:#selector(initializationTimedOut:)
userInfo:nil
repeats:NO];
[NSThread detachNewThreadSelector:#selector(doSomethingThatTakesALongTime:) toTarget:self withObject:nil];
}
- (void)doSomethingThatTakesALongTime:(id)arg {
sleep(30); // for testing only
// web service calls etc. go here
[self performSelectorOnMainThread:#selector(invalidate) withObject:nil waitUntilDone:NO];
}
- (void)invalidate {
[timer invalidate];
}
- (void)initializationTimedOut:(NSTimer *)theTimer {
// show the alert view
}
Have you tried to use [NSThread sleepforTimeInterval:30]; ?
The sleep() occurs on the main thread and the associated run loop never has the chance to invoke the selector for the timer.
If you would do real work in -doSomething that doesn't block the thread, e.g. non-blocking calls to web-services, it would work as expected. Blocking calls however would have to be done in a different thread so the main run loop does not get blocked.