Blocks on Swift (animateWithDuration:animations:completion:)

Question

I'm having trouble making the blocks work on Swift. Here's an example that worked (without completion block):

UIView.animateWithDuration(0.07) {     self.someButton.alpha = 1 } 

or alternatively without the trailing closure:

UIView.animateWithDuration(0.2, animations: {     self.someButton.alpha = 1 }) 

but once I try to add the completion block it just won't work:

UIView.animateWithDuration(0.2, animations: {     self.blurBg.alpha = 1 }, completion: {     self.blurBg.hidden = true }) 

The autocomplete gives me completion: ((Bool) -> Void)? but not sure how to make it work. Also tried with trailing closure but got the same error:

! Could not find an overload for 'animateWithDuration that accepts the supplied arguments

Update for Swift 3 / 4:

// This is how I do regular animation blocks UIView.animate(withDuration: 0.2) {     <#code#> }  // Or with a completion block UIView.animate(withDuration: 0.2, animations: {     <#code#> }, completion: { _ in     <#code#> }) 

I don't use the trailing closure for the completion block because I think it lacks clarity, but if you like it then you can see Trevor's answer below.

Answer 1

The completion is correct, the closure must accept a Bool parameter: (Bool) -> (). Try

UIView.animate(withDuration: 0.2, animations: {     self.blurBg.alpha = 1 }, completion: { finished in     self.blurBg.hidden = true }) 

Answer 2

The completion parameter in animateWithDuration takes a block which takes one boolean parameter. In Swift, like in Obj-C blocks, you must specify the parameters that a closure takes:

UIView.animateWithDuration(0.2, animations: {     self.blurBg.alpha = 1 }, completion: {     (value: Bool) in     self.blurBg.hidden = true }) 

The important part here is the (value: Bool) in. That tells the compiler that this closure takes a Bool labeled 'value' and returns Void.

For reference, if you wanted to write a closure that returned a Bool, the syntax would be

{(value: Bool) -> bool in     //your stuff }