Comments on: Queued Background Tasks for Cocoa

By: MGC

MGC — Sat, 18 Dec 2010 19:38:44 +0000

Great example. It looks like what I need.

So how do I integrate this into my project code?
I included the files into my project, but how do I call it from my view controller?

Do I #import on every View Controller where I want to use this? If I do that will it all be the same queue?

Essentially I want to use this to line up all of my methods in order no matter where I call them in my project. But they will sequentially execute based upon the order they were invoked.

Right now it looks like I need to include this file in every view controller, but I am not sure if that is the right thing to do.

By: Fredrik Olsson

Fredrik Olsson — Mon, 09 Nov 2009 15:55:32 +0000

The reason is that all methods in UIKit should be called on the main thread. So updating the UI directly from the background task is not a good thing, sometimes it works, sometimes you crash, and sometimes just nothing happens. This is why the Apple documentation says you must always call fromt he main thread.

Try to use performSelectorOnMainThread:withObject:waitUntilDone:.

By: John

John — Wed, 04 Nov 2009 17:29:14 +0000

I’m getting the following error when using:

[self performSelectorInBackgroundQueue:@selector(methodName:) withObject:nil];

bool _WebTryThreadLock(bool), 0x487aa0: Tried to obtain the web lock from a thread other than the main thread or the web thread. This may be a result of calling to UIKit from a secondary thread. Crashing now…

By: Marc Love

Marc Love — Sat, 18 Jul 2009 04:08:56 +0000

Thanks Fredrik, this is an excellent resource…especially for those of us just getting started with iPhone development and unfamiliar with such resource-constrained environments.

This should be really helpful for an app I’m working on that makes heavy use of some web services.