How is the better way to create background loop routines in objective-c?

Question

I need to create a routine that save automatically a file content in a constant time period, ie, a backgroung loop that perform the save instructions. I thinked in use a recursive call of performSelector like below:

- (void)viewWillAppear:(BOOL)animated{

    [super viewWillAppear:animated];

    [self performSelector:@selector(saveMethod) withObject:nil afterDelay:kTimeConstant];

}

- (void)saveMethod{

     //The save logic should to be here

     [self performSelector:@selector(saveMethod) withObject:nil afterDelay:kTimeConstant];

}

It works, but when I get out of viewController, it still running, and it must to stop. are there any better way to execute it? Thank you!

The code you've posted doesn't do anything in the background (ie. in a separate thread). Do you actually want to the save to happen on a non-main thread? — Andrew Madsen, Jun 27 '13 at 16:59
If you don't want it to be execute, then you can cancel @selector method in `viewWillDissapear:` method. And this is not background method. It will call in main thread after delay. — TheTiger, Jun 27 '13 at 17:03
I have a RichtextEditor, and I want to implement a autosaving that in a time period save the html content, but it doesn`t can lock the execution, to be invisible to the user, so I think that it should`t run in the Main Thread. — Lucio Fonseca, Jun 27 '13 at 17:05
Thank you The Tiger for the explanation. I really don't know much about it. — Lucio Fonseca, Jun 27 '13 at 17:10
And why it shouldn't run in main thread ?? Have you done anything for this ? If you want it in background then you should use [– performSelectorInBackground:withObject:](http://developer.apple.com/library/ios/#documentation/Cocoa/Reference/Foundation/Classes/NSObject_Class/Reference/Reference.html#//apple_ref/occ/instm/NSObject/performSelectorInBackground:withObject:) — TheTiger, Jun 27 '13 at 17:10
Your requirement is not possible with single line method. You will have to run delay method in background. See below answer for how to run method in background. — TheTiger, Jun 27 '13 at 17:22
The Tiger, the used cancelPreviousPerformRequestsWithTarget and it works fine! I still use the recursive call. Do you Agree that it is the best way? — Lucio Fonseca, Jun 27 '13 at 17:46

score 2 · Answer 1 · answered Jun 27 '13 at 17:04

There is a function NSRunLoop cancelPreviousPerformRequestsWithTarget:selector:object: which allows you to cancel the performSelector call. Call this when you unload the view controller

ie.

 [NSRunLoop cancelPreviousPerformRequestsWithTarget:self selector:@selector(saveMethod) object:nil];

Firo · Accepted Answer · 2013-06-27T18:45:36.577

2

This is probably a better implementation:

- (void)viewWillAppear:(BOOL)animated {

    [super viewWillAppear:animated];

    // Start timer and sets it to a property called saveTimer
    self.saveTimer = [NSTimer scheduledTimerWithTimeInterval:2.0
                              target:self
                            selector:@selector(saveMethod:)
                            userInfo:nil
                             repeats:YES];
}

- (void)saveMethod:(NSTimer*)theTimer {
     // The save logic should to be here
     // No recursion
}

- (void)viewWillDisappear:(BOOL)animated {
    [super viewWillDisappear:animated];

    // Stop timer
    [self.saveTimer invalidate];
}

This is running on the main thread so it is probably not the best implementation but it should work better than what you currently have.

edited Jun 27 '13 at 18:45

answered Jun 27 '13 at 17:17

Firo

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it looks interesting for me. Thank you Firo! – Lucio Fonseca Jun 27 '13 at 17:26
I would not say it better implementation. – TheTiger Jun 27 '13 at 17:28
It really works fine, but the invalidade does't is stopping the timer =( – Lucio Fonseca Jun 27 '13 at 17:36
Thats what I'm trying to tell. Happy you got it :) – TheTiger Jun 27 '13 at 17:41
I know that it works like above, yet the documentation on `NSTimer` clearly states "The selector must correspond to a method that returns void and takes a single argument". – Nikolai Ruhe Jun 27 '13 at 18:03
@LucioFonseca I made a correction, thanks @NikolaiRuhe. It looks like `invalidate` works only if the method parameter list is correct. Look at my fix on the method (also make sure you add the `:` to `@selector(saveMethod:)`. If the `invalidate` still does not work for some reason try setting the timer to nil. – Firo Jun 27 '13 at 18:46

How is the better way to create background loop routines in objective-c?

2 Answers2