How do I write GCD asyncAfter in Swift 4?

Question

In earlier versions of Swift this code works perfectly.

DispatchQueue.main.asyncAfter(deadline: .now() + delay) { timer in self.setOriginalState() self.shakeAnimation() }

But in Swift 4 the following error appears:

Ambiguous reference to member 'asyncAfter(deadline:qos:flags:execute:)'

How can one create a delay before running a sequence of code in Swift 4?

"In earlier versions of Swift this code works perfectly" Nevertheless, it was always wrong. All that happened is that the compiler stopped being so forgiving. — matt
– matt, Commented Sep 23, 2017 at 17:38

Andrea · Accepted Answer · 2017-09-23 09:55:48Z

Trying in playground it doesn't give any issue, that is just "missing" is the "timer" reference.

DispatchQueue.main.asyncAfter(deadline: .now() + 3) { print("Dispatching after") } DispatchQueue.main.asyncAfter(deadline: .now() + 3, qos: .userInteractive, flags: []) { print("Dispatching after") }

They both seems to work, are you sure that the problem isn't somewhere else?

Tom E · Accepted Answer · 2018-05-30 15:34:09Z

The compiler doesn’t seem to be able to infer the type of parameters in the asyncAfter call. So you might want to specify the type like this:

DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + delay)

If you still get the same error make sure delay is of type DispatchTimeInterval. Here’s another example:

DispatchQueue.main.asyncAfter(deadline: DispatchTime.now() + DispatchTimeInterval.milliseconds(300)

This should eventually silence the compiler.

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