Is it possible to call my function in the background after certain interval programmatically in iPhone SDK development? I want to call one particular function in the background for certain time intervals(may be every 10 mins) during my app in on running..
Could you please share your ideas.
thanks.
Clave/
Easiest way is to schedule a NSTimer on the main threads run-loop. I suggest that the following code is implemented on your application delegate, and that you call setupTimer from applicationDidFinishLaunching:.
-(void)setupTimer;
{
NSTimer* timer = [NSTimer timerWithTimeInterval:10 * 60
target:self
selector:#selector(triggerTimer:)
userInfo:nil
repeats:YES];
[[NSRunLoop mainRunLoop] addTimer:timer forMode:NSRunLoopCommonModes];
}
-(void)triggerTimer:(NSTimer*)timer;
{
// Do your stuff
}
If your stuff here takes a long time, and you can not hold up the main thread then either call your stuff using:
[self performSelectorInBackground:#selector(myStuff) withObject:nil];
Or you could run the NSTimer on a background thread by with something like this (I am intentionally leaking the thread object):
-(void)startTimerThread;
{
NSThread* thread = [[NSThread alloc] initWithTarget:self
selector:#selector(setupTimerThread)
withObject:nil];
[thread start];
}
-(void)setupTimerThread;
{
NSAutoreleasePool* pool = [[NSAutoreleasePool alloc] init];
NSTimer* timer = [NSTimer timerWithTimeInterval:10 * 60
target:self
selector:#selector(triggerTimer:)
userInfo:nil
repeats:YES];
NSRunLoop* runLoop = [NSRunLoop currentRunLoop];
[runLoop addTimer:timer forModes:NSRunLoopCommonModes];
[runLoop run];
[pool release];
}
-(void)triggerTimer:(NSTimer*)timer;
{
// Do your stuff
}
You can have a timer, look into NSTimer for that that will fire off every 10 minutes, in order to make i t happen i n the background you have a few options ill name two.
First of note that any UI work should not be done in another thread since UIKit is not thread safe.
You can subclass NSThread and use it to do you process in the background
You can use NSObjects performSelectorInBackground method which basically creates a thread and executes the method. Heres a reference http://developer.apple.com/iphone/library/documentation/Cocoa/Reference/Foundation/Classes/NSObject_Class/Reference/Reference.html#//apple_ref/occ/instm/NSObject/performSelectorInBackground:withObject:
NSThread reference here http://developer.apple.com/iphone/library/documentation/Cocoa/Reference/Foundation/Classes/NSThread_Class/Reference/Reference.html
NSTimer reference here
http://developer.apple.com/iphone/library/documentation/Cocoa/Reference/Foundation/Classes/NSTimer_Class/Reference/NSTimer.html
To call the function on the main thread, use an NSTimer.
To call it on another thread, create an NSOperation and set up an NSOperationQueue to call it.
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 am working on an application where i have to call a thread repeatedly. In that thread we have to parse an XML and i have to get updated data from that xml. now please guide me how to call that thread repeatedly? if my thread is in working and my code calls it again, then i think it will have a crash on it.
Separate the code into a new method
-(void) thisMethodWillRunAsASeparateThread
{
//Threads need their own pool.
NSAutoreleasePool *pool = [NSAutoreleasePool new];
while (thisThreadShouldRun)
{
// run xml parsing code
}
[pool release];
}
and to start the thread:
[NSThread detachNewThreadSelector:#selector(thisMethodWillRunAsASeparateThread) toTarget:self withObject:nil];
To call any code repeatedly you must NSTimer like:
NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:0.10f target:self
selector:#selector(methodName) userInfo:nil repeats:YES];
you should to invalidate the timer after use. while if you wan to execute the code using background thread you must this code but this will not repeat multiple times.
[NSThread detachNewThreadSelector:#selector(methodName:) toTarget:self withObject:objName,nil]];
I am using Background Thread to update one of my label
I am using the following code. But in iOS 4.0 i have learn that application saves its states and goes to background. and my application also did that work but the thread i am using stops working when i hide the application and again resumes from where i left when i reopen it. Can anybody please tell me what do I need to change in code in order to make the thread keep on running in background and change my GUI while my application is hidden. I am using this code..
-(void)startThread
{
NSThread *thread = [[NSThread alloc] initWithTarget:self selector:#selector(setUpTimerThread) object:nil];
[thread start];
}
-(void)setUpTimerThread
{
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
NSTimer *timer = [NSTimer timerWithTimeInterval:3 target:self selector:#selector(triggerTimer) userInfo:nil repeats:YES];
NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
[runLoop addTimer:timer forMode:NSRunLoopCommonModes];
[runLoop run];
[pool release];
}
-(void)triggerTimer
{
NSLog(#"***Timer Called after 3 seconds*** %d",count);
self.label.text = [NSString stringWithFormat:#"count value = %d",count];
//self.titleLabel.text= [NSString stringWithFormat:#"count value = %d",count];
count = count +1;
}
Thanks
Timers won't work on relaunch of the application. What you need to do is reinitialize the timer from your appDelegate's applicationDidBecomeActive: method and make sure you shut down the timer from applicationWillEnterBackground: method
I am trying to schedule NSTimer on a separate thread and this is how i am doing it.
-(void) startSpinner {
#ifdef DEBUG_MODE
NSLog(#"Starting Spinner...");
#endif
self.spinnerThread = [[[NSThread alloc] initWithTarget:self selector:#selector(scheduleSpinner) object:nil] autorelease];
[spinnerThread start];
}
-(void) scheduleSpinner {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc] init];
NSTimer *_spinTimer = [NSTimer scheduledTimerWithTimeInterval:SPIN_FIRE_INTERVAL target:self selector:#selector(timerFireMethod:) userInfo:nil repeats:YES];
NSRunLoop *runLoop = [NSRunLoop currentRunLoop];
[runLoop addTimer:_spinTimer forMode:NSRunLoopCommonModes];
[runLoop addTimer:_spinTimer forMode:UITrackingRunLoopMode];
[runLoop run];
[pool release];
}
timerFireMethod spins my spinner and when a button is pressed (stop button), i invalidate the timer and exit the thread in this method. I do a polling here if spin button is pressed.
The problem is, my timerFireMethod gets called properly for the first time. Spinner spins for first time. But when i stop my spinner and start it again, spinner doesn't spins. The logs say that second time my "startSpinner" method gets called but "timerFireMethod" method is not called.
The worse is, the spinner works 5-6 times on simulator, 1 times on 2g device, 4-5 times on latest ipod. Its random.
How does this basically work? What could be the problem?
Make your NSTimer instance variable a class variable. When you invalidate it, set it to nil immediately afterwards.
I am aware of the many questions regarding this topic, as I myself have asked one previously however, my issue now seems to be more related to the threading part. I have the following 2 methods.
-(void) restartTimer {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init];
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.
target:self
selector:#selector(dim)
userInfo:nil
repeats:YES];
time = 31;
NSLog(#"calling restart timer");
[self performSelectorOnMainThread:#selector(timerImageUpdate) withObject:nil waitUntilDone:NO];
[[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];
[[NSRunLoop currentRunLoop] run];
[pool drain];
}
-(void) resumeTimer {
NSAutoreleasePool *pool = [[NSAutoreleasePool alloc]init];
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.
target:self
selector:#selector(dim)
userInfo:nil
repeats:YES];
NSLog(#"calling resume timer");
[[NSRunLoop currentRunLoop] addTimer:self.timer forMode:NSDefaultRunLoopMode];
[[NSRunLoop currentRunLoop] run];
[pool drain];
}
The restartTimer function is called when the game begins. This works fine and the timer fires the dim selector nicely. The problem occurs when the user clicks my skip button in quick succession. [skip] updates an MKMapView and in the delegate method mapdidfinishloading the follwing is called :
[NSThread detachNewThreadSelector:#selector(restartTimer) toTarget:self withObject:nil];
When this happens it seems several timers are created and thus my dim function is called far too often giving the appearance of the single timer running really fast? What is the best way to start and restart the timer using a secondary thread? Note this problem only seems to happen if the skip button is pressed repeatedly and quickly, while it works fine if just pressed now and again?
Anyone have any ideas? Many thanks
Jules
You can use a bool to know if you have a timer running or not. When you start the timer you set it to true, when you stop the timer you set it to false. When resume timer function is called you check this variable and if it's true you do not start a new timer.
Another solution would be to limit user interaction with the button. If the button is pressed you make it inactive for a time.