CODEWITHSUNDEEP
iosswiftuialertaction
Zhang
Zhang

Reputation: 11607

Swift alert handler syntax odd

One of my Swift code block is an alert popup:

func alertNewBillCreated() {
    let alert = UIAlertController(title: "Success", message: "Bill created and ready to be paid", preferredStyle: UIAlertControllerStyle.Alert)

    let actionOK = UIAlertAction(title: "OK", style: UIAlertActionStyle.Default) { (UIAlertAction) in

        self.navigationController?.popViewControllerAnimated(true)

    }

    alert.addAction(actionOK)

    self.presentViewController(alert, animated: true, completion: nil)
}

Reading other SO posts like this: Writing handler for UIAlertAction

They all gave examples where the handler part is inclusive and explicitly defined, e.g.:

UIAlertAction(title: "Okay",
                      style: UIAlertActionStyle.Default,
                    handler: {(alert: UIAlertAction!) in println("Foo")

However, in my above code which I used Xcode's autocomplete to help me write the alert block, my version doesn't have the comma followed the handler key.

These two variations also works (in addition to my first block of code above):

let actionOK = UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: { (action: UIAlertAction) in
        ...            
    })

and

let actionOK = UIAlertAction(title: "OK", style: UIAlertActionStyle.Default, handler: { (UIAlertAction) in
        ...
    })

What is this odd Swift syntax exception rule ?

Isn't this a bug ?

Do we not separate function parameters with commas ?

It looks to me like I'm calling a function UIAlertAction() and only passing it two parameters - title and style since there are only 2 commas:

UIAlertAction(__ , __ ) { ... }

Or is...this...the Swift equivalent of Ruby blocks? (Best explanation of Ruby blocks?)

My alert code works, it's not broken, in case anyone is curious.

Seems a bit inconsistent with so many rules and odd syntax, making it hard/harder to remember the rules for Swift syntax and learning Swift.

Hopefully by Swift 4.0, all these things are ironed out...

Maybe I'm complaining too much :D

Upvotes: 0

Views: 148

Answers (1)

Tommy Sadiq Hinrichsen
Tommy Sadiq Hinrichsen

Reputation: 804

If the last parameter is a block it can be appended like a method body.

Read more.

https://developer.apple.com/library/prerelease/content/documentation/Swift/Conceptual/Swift_Programming_Language/Closures.html#//apple_ref/doc/uid/TP40014097-CH11-ID94 Trailing Closures

Upvotes: 1

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