Swift中的完成处理程序

Question

I have been searching for many hours trying to find the solution to this closure problem in swift. I have found many resources for explaining the closures but for some reason I can't seem to get this working.

This is the Objective-C code I am trying to convert into swift:

[direction calculateDirectionsWithCompletionHandler:^(MKDirectionsResponse *response, NSError *error) {
            NSLog(@"%@",[response description]);
            NSLog(@"%@",[error description]);

            }];

and the swift I am trying but is not working:

directions.calculateDirectionsWithCompletionHandler(response: MKDirectionsResponse?, error: NSError?) {
    println(response.description)
    println(error.description)
}

directions is an MKDirections object.

Thanks!

Answer 1

Try

directions.calculateDirectionsWithCompletionHandler ({
(response: MKDirectionsResponse?, error: NSError?) in 
        println(response?.description)
        println(error?.description)
    })

Answer 2

This is the general way a block/closure looks like in Swift.

if you don't need to use the parameters you can do it like this

directions.calculateDirectionsWithCompletionHandler ({
(_) in 
  // your code here
    })

Answer 3

regarding the syntax of Closures in Swift , and checking the MKDirections Class Reference:

it looks the proper closure here should be an MKDirectionHandler , which defined as:

therefore the completion handler should look like this:

direction.calculateDirectionsWithCompletionHandler( { (response: MKDirectionsResponse!, error: NSError!) -> () in
    println(response.description)
    println(error.description)
    } )