How to update a UI label from a non UI thread in iOS

Question

I am new to iOS development, I have plain objective -c class \"MoneyTimer.m\" for running timer, from there i want to update the an UI label with the changing value of timer.

Answer 1

Your question doesn't give much info or detail so it is hard to know exactly what you need to do (e.g. if there is a "thread" issue at all, etc.).

At any rate, assuming your MoneyTimer instance has a reference to the current viewController you can use performSelectorOnMainThread.

//

- (void)performSelectorOnMainThread:(SEL)aSelector withObject:(id)arg waitUntilDone:(BOOL)wait;

Answer 2

I've done something identical in the past.

I used a function to set the label text:

- (void)updateLabelText:(NSString *)newText {
    yourLabel.text = newText;
}

and then called this function on the main thread with performSelectorOnMainThread

NSString* myText = @"new value";
[self performSelectorOnMainThread:(@selector)updateLabelText withObject:myText waitUntilDone:NO];

Answer 3

This is the quickest and simplest way to do it is:

- (void) countUpH{

   sumUp = sumUp + rateInSecH;
   //Accessing UI Thread
   [[NSOperationQueue mainQueue] addOperationWithBlock:^{

      //Do any updates to your label here
      yourLabel.text = newText;

   }];
}

If you do it this way you don't have to switch to a different method.

Hope this helps.

Sam

Answer 4

The proper way is this:

- (void) countUpH  {
   sumUp = sumUp + rateInSecH;
   //Accessing UI Thread
   dispatch_async(dispatch_get_main_queue(), ^{

   //Do any updates to your label here
    yourLabel.text = newText;
   });
}

Answer 5

Assuming that label lives in the same class:

    if(nsTimerUp == nil){
        nsTimerUp = [NSTimer scheduledTimerWithTimeInterval: 1.0 target:self selector:@selector(countUpH) userInfo:nil repeats: YES];
    [self performSelectorOnMainThread:@selector(updateLabel)
                                           withObject:nil
                                        waitUntilDone:NO];

    }

-(void)updateLabel {
    self.myLabel.text = @"someValue";
}