NSTimer in NSOperation main method? - objective-c

Question

I want to set up a timer in -(void) main {} method of a NSOperation subclass. However, I the timer doesn't fire. I tried [[NSRunLoop currentRunLoop] addTimer:timer forMode: NSDefaultRunLoopMode]; with no success. Am I missing smth?
[EDIT] Will this run the timer on the main thread or on NSOperation's thread? (guessing NSOperation, but I'm not sure)

Answer 1

I found what need to be done to start the timer. I'll put it here if anyone ever needs it:
[[NSRunLoop currentRunLoop] run];
However, I'm still not sure if this will run in the NSOperation's thread.

Answer 2

I find that it is sometimes useful to wrap an NSOperation around a method that is fired by a timer, like you are doing, to take advantage of the dependencies, cancellation, and other features provided by the operations queue. It is however not usually necessary for the timer to run in a separate thread, nor is it usually necessary for the method that the timer invokes to be running in a background thread. In fact, most of the time it shouldn't run in a background thread because the method updates the UI. If this is true for you too a setup like this should work:
#import <Foundation/Foundation.h>
#interface TimerOperation : NSOperation {
#private
NSTimer* _timer;
}
#property (nonatomic, readonly) BOOL isExecuting;
#property (nonatomic, readonly) BOOL isFinished;
#end
(Add in your own state, custom constructor, etc.).
#implementation TimerOperation
#synthesize isExecuting = _executing;
#synthesize isFinished = _finished;
- (id) init {
if ((self = [super init])) {
_executing = NO;
_finished = NO;
}
return self;
}
- (void) dealloc {
[_timer release];
[super dealloc];
}
- (BOOL) isConcurrent {
return YES;
}
- (void) finish {
[self willChangeValueForKey:#"isFinished"];
[self willChangeValueForKey:#"isExecuting"];
_executing = NO;
_finished = YES;
[self didChangeValueForKey:#"isExecuting"];
[self didChangeValueForKey:#"isFinished"];
}
- (void) start {
if ([self isCancelled]) {
[self willChangeValueForKey:#"isFinished"];
_finished = YES;
[self didChangeValueForKey:#"isFinished"];
} else {
[self willChangeValueForKey:#"isExecuting"];
[self performSelectorOnMainThread:#selector(main)
withObject:nil
waitUntilDone:NO];
_executing = YES;
[self didChangeValueForKey:#"isExecuting"];
}
}
- (void) timerFired:(NSTimer*)timer {
if (![self isCancelled]) {
// Whatever you want to do when the timer fires
}
}
- (void) main {
_timer = [[NSTimer scheduledTimerWithTimeInterval:1.0
target:self
selector:#selector(timerFired:)
userInfo:nil
repeats:YES] retain];
}
- (void) cancel {
[_timer invalidate];
[super cancel];
}
#end
Of course, if the main thread is blocked (for instance, because of a long database save) you will not see the timer firing, but most of the time this works fine.
You can use the same setup to deal with asynchronous APIs inside NSOperations.