Question

I am trying to create a loop like this:

while (TRUE){
  dispatch_after(...{
    <some action>
  });
}

After a viewDidLoad. The idea is to repeat the dispatch_after repeatedly. The dispatch_after waits two seconds before doing the action.

This does not work – the screen just blanks? Is it stuck in looping or …?

Answer 1

The dispatch_after(...) call returns immediately no matter when it is scheduled to run. This means that your loop is not waiting two seconds between dispatching them. Instead you are building an infinite queue of things that will happen two seconds from now, not two seconds between each other.

So yes, you are stuck in an infinite loop of adding more and more blocks to be executed. If you want something to happen every two second then you could use a repeating NSTimer or have the block dispatch_after inside itself (so that the second block runs two seconds after the first).