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

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];
});

Answer 2

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

Answer 3

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();
           }
      });
}

Answer 4

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.