捕获Swift中的闭包值(Capturing closure values in Swift)

 我的问题与其他几个人非常相似，但我无法实现。 我正在通过我编写的帮助程序类进行API调用。 
 
 首先，我尝试了一个带有返回值的标准函数，结果与预期一致。 我厌倦分配结果后完成后台任务。 
 
 现在我正在使用闭包，并且可以将值返回到视图控制器中，但它仍然停留在闭包中，我也遇到了同样的问题。 我知道我需要使用GCD来将任务发生在主队列中。 
 
 这是我在视图控制器中所拥有的 
 
var artists = [String]()
let api = APIController()
    api.getArtistList("foo fighters") { (thelist) -> Void in
        if let names = thelist {
            dispatch_async(dispatch_get_main_queue()) {
                artists = names
                print("in the closure: \(artists)")
            }
        }
    }

    print ("method 1 results: \(artists)")
 
 结果是： 
 
method 1 results: []
in the closure: [Foo Fighters & Brian May, UK Foo Fighters, John Fogerty with Foo Fighters, Foo Fighters, Foo Fighters feat. Norah Jones, Foo Fighters feat. Brian May, Foo Fighters vs. Beastie Boys]
 
 我知道为什么会发生这种情况，我只是不知道如何解决这个问题:( API调用需要是异步的，那么捕获这些结果的最佳做法是什么？根据用户在表视图中选择的内容，我将进行后续的api调用，因此它不像我可以处理闭包内的所有内容 

My question is very similar to several others here but I just can't get it to work. I'm making an API call via a helper class that I wrote. 
 
First I tried a standard function with a return value and the result was as expected. The background task completed after I tired to assign the result.
 
Now I'm using a closure and I can get the value back into my view controller but its still stuck in the closure, I have the same problem. I know I need to use GCD to get the assignment to happen in the main queue.
 
this is what I have in my view controller
 
var artists = [String]()
let api = APIController()
    api.getArtistList("foo fighters") { (thelist) -> Void in
        if let names = thelist {
            dispatch_async(dispatch_get_main_queue()) {
                artists = names
                print("in the closure: \(artists)")
            }
        }
    }

    print ("method 1 results: \(artists)")
 
as the results are:
 
method 1 results: []
in the closure: [Foo Fighters & Brian May, UK Foo Fighters, John Fogerty with Foo Fighters, Foo Fighters, Foo Fighters feat. Norah Jones, Foo Fighters feat. Brian May, Foo Fighters vs. Beastie Boys]
 
I know why this is happening, I just don't know how to fix it :( The API calls need to be async, so what is the best practice for capturing these results? Based on what the user selects in the table view I'll be making subsequent api calls so its not like I can handle everything inside the closure

原文：https://stackoverflow.com/questions/31279369