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!

Will this help you ? http://stackoverflow.com/questions/15218861/call-function-only-after-reloaddata-has-finished/15218941#15218941 — Anoop Vaidya, Mar 14 '13 at 15:12
why do you afraid of creating a separate method ? this will solve the problem immediately. — Raptor, Mar 14 '13 at 15:12
@ShivanRaptor because I have a lot of methods already and I wanted to find a better way — Sergey Grischyov, Mar 14 '13 at 15:13
i dont sure it will work but you can try calling methods inside completion:^(BOOL finished){ } block — meth, Mar 14 '13 at 15:13
Is your problem a warning or error you're not mentioning here? — Steven Fisher, Mar 14 '13 at 15:15
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. — Steven Fisher, Mar 15 '13 at 01:53

score 142 · Accepted Answer · answered Mar 14 '13 at 15:13

142

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];
});

answered Mar 14 '13 at 15:13

Martin Ullrich

94,744
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well it improves readability a lot - especially when you use blocks as method parameters – Martin Ullrich Mar 14 '13 at 15:22
6

It would be nice to hide this (especially `popTime` calculation) in a function/method, e.g `[NSObject performBlock:afterDelay:];` – Sulthan Mar 14 '13 at 15:45

score 25 · Answer 2 · edited Jan 19 '16 at 13:05

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();
           }
      });
}

score 3 · Answer 3 · answered Jun 18 '20 at 13:20

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.

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

answered Jun 18 '20 at 13:20

auspicious99

3,902
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2

Wow! The crazy stuff you find hidden in XCode! – Neville Nason Dec 30 '20 at 22:01

score 1 · Answer 4 · answered Dec 01 '15 at 22:30

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

Wrong language. Question was about Obj-C – Cross_ Mar 29 '18 at 22:43 — Cross_, Mar 29 '18 at 22:43

Objective-C delay action with blocks

4 Answers4

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