Cocoa threads being cantankerous - objective-c

Question

In short, I would like to, in Objective-C cocoa, program something that functions the same way as the following Java pseudocode:
public class MainClass
{
public void mainmethod() //Gets called at start of program
{
UILabel label = CreateAButton();
new DaemonClass(label).start();
//Do things without being interrupted by the Daemon class sleeping or lagging
}
}
public class DaemonClass extends Thread
{
public UILabel label;
public DaemonClass(UILabel lbl)
{
setDaemon(true);
label = lbl;
}
public void run()
{
int i = 0;
while(true)
{
i++;
i = i%2;
UILabel.setText("" + i);
Thread.sleep(1000);
}
}
}
In other words... I'd like to spawn a daemon thread that can be as slow as it likes, without interrupting the progress or speed of any other threads, INCLUDING, the main one.
I have tried using things like the Dispatch Queue, as well as NSThread.
When using either of these, I tried to create a simple label-changer thread that toggled the label's text from 1 to 0, indefinitely. It appeared to me, the user, to constantly be locked either at 1, or 0, randomly chosen at startup.
When using either of these, and attempting to use [NSThread sleepForTimeInterval:1];, the thread would stop executing all together after the sleepForTimeInterval call.
Furthermore, having skimmed the docs, I picked up on the fact that the run loop is not called while [NSThread sleep... is sleeping!
If it is any help, I was invoking my threads from the - (void)viewDidLoad; method.
My question for you is:
How do I stop [NSThread sleepForTimeInterval:1]; from crashing my thread, OR:
How do I start a daemon thread that invokes a method or code block (preferably a code block!)
P.S. if it makes any difference, this is for iOS

Answer 1

The reason for the problems you've seen is most likely that UIKit isn't thread-safe, i.e. you can only use a UILabel from the main thread. The easiest way to do that is to enqueue a block on the main queue (which is associated with the main thread) using GCD:
dispatch_async(dispatch_get_main_queue(), ^{
myLabel.text = #"whatever";
});

Answer 2

First of all you cannot manage UIKit in the background threads. In order to set the text to UILabel you need to use main thread.
Judging by the type of task you want to achieve, you should use NSTimer. You can set the time interval it should be called and stop and resume it anytime.
#property (strong, nonatomic) NSTimer *timer; //in your .h file
- (void)startChangingLabelText {
self.timer = [NSTimer scheduledTimerWithTimeInterval:1.0
target:self
selector:#selector(checkTime:)
userInfo:nil
repeats:YES];
}
- (void)stopChangingLabelText {
[timer invalidate], self.timer = nil;
}
- (void)checkTime:(NSTimer *)timer {
int rand = arc4random() % 2;
if (rand)
label.text = #"true";
else
label.text = #"false";
}