Objective-C delay action with blocks

Question

I know that there are several ways of delaying an action in Objective-C like:

performSelector:withObject:afterDelay:

or using NSTimer.

But there is such a fancy thing called blocks where you can do something like this:

[UIView animateWithDuration:1.50 delay:0 options:(UIViewAnimationOptionCurveEaseOut|UIViewAnimationOptionBeginFromCurrentState) animations:^{

    }completion:^(BOOL finished){
}];

Unfortunately, this method applies only to animating things.

How can I create a delay with a block in one method so I don't have to use all those @selectors and without the need to create a new separate method? Thanks!

Engaging

Will this help you ? #15219361 – Deme

why do you afraid of creating a separate method ? this will solve the problem immediately. – Oppose

@ShivanRaptor because I have a lot of methods already and I wanted to find a better way – Engaging

i dont sure it will work but you can try calling methods inside completion:^(BOOL finished){ } block – Lindberg

Is your problem a warning or error you're not mentioning here? – Haustellum

@StevenFisher the problem is written in the end of the post – Engaging

Ah, my problem was just that I misread your code sample. :) You discovered things in a very strange order, but this is a good question. Thanks for posting it. – Haustellum

Answer 1

use dispatch_after:

double delayInSeconds = 2.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
    //code to be executed on the main queue after delay
    [self doSometingWithObject:obj1 andAnotherObject:obj2];
});

Iou

well it improves readability a lot - especially when you use blocks as method parameters – Iou

It would be nice to hide this (especially popTime calculation) in a function/method, e.g [NSObject performBlock:afterDelay:]; – Mosaic

Answer 2

Expanding on the accepted answer, I created a Helper function for anyone who doesn't care to memorize the syntax each time they want to do this :) I simply have a Utils class with this:

Usage:

[Utils delayCallback:^{
     //--- code here
} forTotalSeconds:0.3];

Helper method:

+ (void) delayCallback: (void(^)(void))callback forTotalSeconds: (double)delayInSeconds{

     dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, delayInSeconds * NSEC_PER_SEC);
     dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
           if(callback){
                callback();
           }
      });
}

Infection

Answer 3

Xcode 11.3.1 (at least, and also other versions of Xcode) provides a code snippet to do this where you just have to enter the delay value and the code you wish to run after the delay.

1. click on the + button at the top right of Xcode.
2. search for after
3. It will return only 1 search result, which is the desired snippet (see screenshot). Double click it and you're good to go.

Trowbridge

Wow! The crazy stuff you find hidden in XCode! – Useful

Answer 4

Here is how you can trigger a block after a delay in Swift:

runThisAfterDelay(seconds: 4) { () -> () in
    print("Prints this 4 seconds later in main queue")
    // Or just call animatedMyObject() right here
}

/// EZSwiftExtensions
func runThisAfterDelay(seconds seconds: Double, after: () -> ()) {
    let time = dispatch_time(DISPATCH_TIME_NOW, Int64(seconds * Double(NSEC_PER_SEC)))
    dispatch_after(time, dispatch_get_main_queue(), after)
}

Its included as a standard function in my repo: https://github.com/goktugyil/EZSwiftExtensions

Joeannjoed

Wrong language. Question was about Obj-C – Gow