Question

Newbie obj-c question.
I am writing a simple iPad presentation not for Appstore. My task is to implement few methods executed one after another with little pauses between them. Main structure looks like this:

• view loads
• two seconds pause, then executing method1
• two seconds pause, then executing method2
• two seconds pause, then executing method3
  etc…

First method I am calling from -viewDidLoad:

NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:2.0 target:self selector:@selector(firstCountStarts) userInfo:nil repeats:NO];

Everything is ok here, method starts 2 seconds after view loads.
From inside method1 I try to call method 2 in the same way but it start to execute simultaneously with method1. Same way triggered method3 (called from method2) and all methods after them not executed at all. I tried to situate all this methods in -ViewDidLoad and to call them with delays:

 [self method1];
 [self performSelector:@selector(method2) withObject:nil afterDelay:2];
 [self performSelector:@selector(method3) withObject:nil afterDelay:4];
 etc...

But after method2 is calling all methods after didn’t executed. If I understand right the issue in threads. Do I need to use GCD to execute methods in different queues? Or maybe problem in else?

Thanks, colleagues!

Answer 1

You could add these to an NSOperation queue…

NSOperationQueue *queue = [NSOperationQueue new];

queue.maxConcurrentOperationCount = 1;

[queue  addOperationWithBlock:^{
    [self method1];
}];

[queue  addOperationWithBlock:^{
    [NSThread sleepForTimeInterval:2.0];
    [self method2];
}];

[queue  addOperationWithBlock:^{
    [NSThread sleepForTimeInterval:2.0];
    [self method3];
}];

...

This will then run each one only after the previous one has finished and put the 2 second delay in for you.

Careful about using this to do an UI stuff though. This will run in a Background thread so you may need to deal with that.

Maybe this might work better you could do it by subclassing NSOperation but that’s a lot of work for not much benefit.

Run this from where ever you want, I suggest putting all this into a function called setUpQueue or something.

Then from viewWillAppear or viewDidLoad or somewhere else, on a button press, etc… do…

[self setUpQueue];

All you have to do is add stuff to the queue, the queue will then manage itself.