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.so         


        

Answer 1

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
}

Answer 2

Here you go, this will compile

Swift 2

UIView.animateWithDuration(0.3, animations: {
    self.blurBg.alpha = 1
}, completion: {(_) -> Void in
    self.blurBg.hidden = true
})

Swift 3, 4, 5

UIView.animate(withDuration: 0.3, animations: {
    self.blurBg.alpha = 1
}, completion: {(_) -> Void in
    self.blurBg.isHidden = true
})

The reason I made the Bool area an underscore is because you not using that value, if you need it you can replace the (_) with (value : Bool)

Answer 3

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 4

Underscore by itself alongside the in keyword will ignore the input

Swift 2

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

Swift 3, 4, 5

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

Answer 5

Sometimes you want to throw this in a variable to animate in different ways depending on the situation. For that you need

 let completionBlock : (Bool) -> () = { _ in 
 }

Or you could use the equally verbose:

 let completionBlock = { (_:Bool) in 
 }

But in any case, you have have to indicate the Bool somewhere.

Answer 6

There is my solution above based on accepted answer above. It fades out a view and hiddes it once almost invisible.

Swift 2

func animateOut(view:UIView) {

    UIView.animateWithDuration (0.25, delay: 0.0, options: UIViewAnimationOptions.CurveLinear ,animations: {
        view.layer.opacity = 0.1
        }, completion: { _ in
            view.hidden = true
    })   
}

Swift 3, 4, 5

func animateOut(view: UIView) {

    UIView.animate(withDuration: 0.25, delay: 0.0, options: UIView.AnimationOptions.curveLinear ,animations: {
        view.layer.opacity = 0.1
    }, completion: { _ in
        view.isHidden = true
    })
}