How to Delay a Return-Statement in Swift

Is there a way to delay a return-Statement in Swift?

You are looking for a closure, a.k.a. completion handler.

return executes immediately and there is no way to delay that. Instead, you can use completion handlers, which work by passing in a closure as a parameter. This closure can then be called after a delay.

                            /// closure here!
func returnLate(completion: @escaping ((String) -> Void)) {
    var string = "Wrong"
    DispatchQueue.main.asyncAfter(deadline: .now() + 1) {
        string = "right"
        completion(string) /// similar to `return string`
    }
}

override func viewDidLoad() {
    super.viewDidLoad()
    returnLate { string in
        print("String is \(string)") /// String is right
    }
}

How to create a delay in Swift?

Instead of a sleep, which will lock up your program if called from the UI thread, consider using NSTimer or a dispatch timer.

But, if you really need a delay in the current thread:

do {
    sleep(4)
}

This uses the sleep function from UNIX.

Delay the return value instead of whole method

Use a block to call back with return value with delay;

- (void)ayncGetValue:(void(^)(id value))returnBlock {

  dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, 10.f * NSEC_PER_SEC); // delay 10 seconds
  dispatch_after(popTime, dispatch_get_main_queue(), ^{
    returnBlock(@"hello block");
  });
}
// Usage
[obj ayncGetValue:^(id value) {
  // continue  
}];

How to program a delay in Swift 3

After a lot of research, I finally figured this one out.

DispatchQueue.main.asyncAfter(deadline: .now() + 2.0) { // Change `2.0` to the desired number of seconds.
   // Code you want to be delayed
}

This creates the desired "wait" effect in Swift 3 and Swift 4.

Inspired by a part of this answer.

How can I put a time delay within an IF statement in Swift?

Taking aheze's code suggestion and adding it to my program in the proper position has worked, and now the app pauses for a second upon successful login. This doesn't work entirely as I need it to, as the successful login message simply does not appear now, probably due to the time delay, however I'm sure I can work around this as it appears to be simple issue!

aheze's code inserted into my program:

if self.username == storedUsername && self.password == storedPassword {
    
    DispatchQueue.main.asyncAfter(deadline: .now() + 1.0) {
    
    self.authenticationDidSucceed = true
}

Once again, thanks for the help, and I hope I've done it right!

Delaying function in swift

You can use GCD (in the example with a 10 second delay):

Swift 2

let triggerTime = (Int64(NSEC_PER_SEC) * 10)
dispatch_after(dispatch_time(DISPATCH_TIME_NOW, triggerTime), dispatch_get_main_queue(), { () -> Void in
    self.functionToCall()
})

Swift 3 and Swift 4

DispatchQueue.main.asyncAfter(deadline: .now() + 10.0, execute: {
    self.functionToCall()
})

Swift 5 or Later

 DispatchQueue.main.asyncAfter(deadline: .now() + 10.0) {
        //call any function
 }

Adding delay between execution of two following lines

You can use gcd to do this without having to create another method

// ObjC

NSTimeInterval delayInSeconds = 2.0;
dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC));
dispatch_after(popTime, dispatch_get_main_queue(), ^(void){
  NSLog(@"Do some work");
});

// Swift

DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
    print("Do some work)
}

You should still ask yourself "do I really need to add a delay" as it can often complicate code and cause race conditions

How to put delay for each iteration of loop

Your current code doesn't work because you are doing the increment asynchronously. This means that the for loop will still run at its normal speed.

To achieve what you want, you can use a timer like this:

var count = 0
let timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true){ _ in
    count += 1
    print(count)
}

If you want it to stop after 5 times, do this:

var count = 0
var timer = Timer.scheduledTimer(withTimeInterval: 1, repeats: true){ t in
    count += 1
    print(count)
    if count >= 5 {
        t.invalidate()
    }
}

How can I call a function after a time delay in the main thread in Swift 3?

I don't think it needs to be anywhere near that complicated. You can just use a Timer;

class MyClass: UIViewController {

    var tapCount = 0
    var tapTimer: Timer?

    @IBAction tapped(_ sender: Any) {
        if tapCount < 3 {
            tapCount += 1
            tapTimer?.invalidate()
            tapTimer = Timer.scheduledTimer(withTimeInterval: 0.5, repeats: false, block: { (timer) in
                switch (self.tapCount) {
                    case 1:
                      self.f1()
                    case 2:
                      self.f2()
                    case 3:
                      self.f3()
                    default:
                      // Hmm, shouldn't happen
                }
                self.tapCount = 0
            })
    }
}

The timer will be scheduled on the main queue by default, so there is no need to dispatch anything on the main queue specifically

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