Completion Handlers in Swift

Question

I'm fairly new at swift development and trying to get a handle on closures and completion handlers. I have a function with the following declaration inside a struct called ObjectData

func getData(id1:Int, id2:Int, completion: (dataObject? -> Void))

I am trying to call this function like

ObjectData.getData(1, id2: 2){
    (let myObject) in
}

but i get the following error

Cannot invoke 'getData' with an argument list of type '(NSNumber, id2: NSNumber, (_) -> _)'

Please can someone help

yes dataObject is another struct, i dont know why it doest show as the light blue color @nkukushkin — c11ada, Jul 23 '15 at 06:40
It does not show because it does not start with capital (I am guessing). You should always name your objects starting with capital letter, CamelCase :) — Jiri Trecak, Jul 23 '15 at 07:00

score 4 · Accepted Answer · answered Jul 22 '15 at 12:01

4

For better readability, change the header to this. Remember that you have to declare types, not variable names:

func getData(id1:Int, id2:Int, completion: (ObjectData?) -> (Void))

Now I personally use this syntax to use closures:

self.getData(1, id2: 1) { (data) -> (Void) in

     // Some code executed in closure
}

If you want to study further, you can find full syntax of closures here (notice appropriate name of the website). Hope it helps!

answered Jul 22 '15 at 12:01

Jiri Trecak

5,092
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hi Jiri, in my code dataObject is a data type. Thats why i am confused iv done something similar to this elsewhere and it worked. – c11ada Jul 23 '15 at 06:58
nope that didn't work ... everything code wise looks ok ... but t just doesn't want to work :(. – c11ada Jul 24 '15 at 07:21
So what exactly is the problem? can you provide more code, and what exactly did not work so I can help you? Either update the question, or post more code on https://gist.github.com/ – Jiri Trecak Jul 24 '15 at 07:51
This was right ... rookie mistake on my behalf ... my syntax was right !! the issue was in my function declaration i had Int, but in my function call i was passing through NSNumber. Hence the error. – c11ada Jul 24 '15 at 08:54

maxpovver · Answer 2 · 2015-07-22T12:09:30.870

1

Far away from my Mac now, so I can't test, but try this:

ObjectData.getData(1, id2: 2, (dataObject) -> { 
...code...
});

Also can't check now, but I think this also should work:

    ObjectData.getData(1, id2: 2)(dataObject){ 
...code...
}

edited Jul 22 '15 at 12:09

answered Jul 22 '15 at 11:20

maxpovver

1,580
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25

score 0 · Answer 3 · answered Jul 22 '15 at 11:48

0

try to initialize your class first (ex. var objectData = ObjectData()) , and then call function with objectData.getData... it should work that way ..

answered Jul 22 '15 at 11:48

Kristijan Delivuk

1,253
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score 0 · Answer 4 · answered Nov 04 '16 at 11:59

In SWIFT 3,It is known as completion closure.

func getData(id1:Int, id2:Int, completion:@escaping(dataObject?) -> (Void)) {

    //Do the stuff before calling completion closure
    completion(value as? dataObject)   
}

ObjectData.getData(id1:1, id2: 2,completion:{(data) -> (Void) in
    //Do the completion stuff here
}

Completion Handlers in Swift

4 Answers4