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iOS Build a Weather App with Swift Managing Complexity Callback Methods With Closures

Marcos Reboucas
Marcos Reboucas
12,890 Points
Posted by Marcos Reboucas
Marcos Reboucas
12,890 Points

Any idea what's wrong with my closure?

func fetchTreehouseBlogPosts(completion:{(data:NSData!, response:NSURLResponse!, error:NSError!)->Void in})

Callbacks.swift 
import Foundation

// Add your code below

func fetchTreehouseBlogPosts(completion:{(data:NSData!, response:NSURLResponse!, error:NSError!)->Void in})

2 Answers

Roberta Voulon
Roberta Voulon
5,792 Points
Roberta Voulon
Roberta Voulon
5,792 Points

I think a ton of people are stuck on this, I finally got a hint from somewhere and it worked for me, so I'm re-posting this where I can: What made it work for me in the end was wrap the signature in outer parenthesis like this:

typealias BlogPostCompletion = ((NSData!, NSURLResponse!, NSError!) -> Void)
func fetchTreehouseBlogPosts(completion: BlogPostCompletion) {}

It's really silly, I was stuck on this for days, I didn't even know this is correct syntax, and they're not necessary!

Richard Lu
Richard Lu
20,185 Points
Richard Lu
Richard Lu
20,185 Points

The problem here is that your defining the closure. To fix this problem you have to declare it, like this:

import Foundation

// remove the 'in' keyword
func fetchTreehouseBlogPosts(completion: (NSData!, NSURLResponse!, NSError!)->Void) {}

When you pass the closure onto the function, it should look like this:

fetchTreehouseBlogPosts {
   (Data, response, error) -> Void in {
      // do something
   }
}

Let me know how this works out for you (:

Marcos Reboucas
Marcos Reboucas
12,890 Points
Marcos Reboucas
Marcos Reboucas
12,890 Points

Hello Richard and thank you for helping. Unfortunately it didn't work for me. What I'm doing is:

import Foundation

typealias BlogPostCompletion = (data:NSData!, response:NSURLResponse!, error:NSError!) -> Void

func fetchTreehouseBlogPosts (completion: BlogPostCompletion) { }

But I'm getting: Make sure the method is named fetchTreehouseBlogPosts and has the correct syntax!

Also the preview:

swift_lint.swift:7:45: error: expected ',' separator typealias BlogPostCompletion = (data:NSData!; response:NSURLResponse!; error:NSError!) -> Void ^ , swift_lint.swift:7:45: error: expected type typealias BlogPostCompletion = (data:NSData!; response:NSURLResponse!; error:NSError!) -> Void ^ swift_lint.swift:7:45: error: expected ',' separator typealias BlogPostCompletion = (data:NSData!; response:NSURLResponse!; error:NSError!) -> Void ^ ,