在Swift中添加完成塊功能

Question

我是新來的Swift，我試圖添加一個完成塊。我記得在Objective-C中這很簡單，但我有點在這裏的語法丟失。該函數解析一些json並將相關內容添加到數組中。一旦函數完成，我需要刷新一個tableview，因爲我不能在塊內完成這個工作，我需要添加一個完成塊。

如何在Swift中爲此函數添加完成塊，以及新的方法調用將如何？

func getSetParameter() 
{ 
    let param = ["format":"json"] 
    let jsonUrl: String! = "http://somewebsite.com" 

    let manager: AFHTTPSessionManager = AFHTTPSessionManager() 
    manager.GET(jsonUrl, parameters: param, success: { 
     (task: NSURLSessionDataTask!, JSONResponse: AnyObject!) in 

      let responseDictionary = JSONResponse as! NSDictionary 
      let responseArray = responseDictionary.objectForKey("response") as! NSArray 
      for thumbnailsOnVideoDictionary in responseArray 
      { 
       let thumbnailsOnVideoArray = thumbnailsOnVideoDictionary.objectForKey("thumbnails") as! NSArray 
       if thumbnailsOnVideoArray.count == 0 { 
        self.thumbnails.append(nil) 
       } 
       else { 
        let smallThumbnail = thumbnailsOnVideoArray[1]; 
        let aspect_ratio: Float = (smallThumbnail.objectForKey("aspect_ratio") as! Float) 
        let height: UInt = (smallThumbnail.objectForKey("height") as! UInt) 
        let name: AnyObject = smallThumbnail.objectForKey("name")! 
        let url: String = (smallThumbnail.objectForKey("url") as! String) 
        let width: UInt = (smallThumbnail.objectForKey("width") as! UInt) 

        let newThumbnail = Thumbnail(aspect_ratio: aspect_ratio, height: height, name: name, url: url, width: width) 
        self.thumbnails.append(newThumbnail) 
       } 
      } 
     }, failure: {(task: NSURLSessionDataTask?, error: NSError!) in 

    }) 
} 

Answer 1

用handler的參數更新你的函數。在這個例子中，我使用的則傳遞縮略圖的陣列封閉，並且沒有返回值：

func getSetParameter(handler:([Thumbnail]) ->()) { 

    // generate an array of Thumbnails 
    let someArray = [Thumbnail(), Thumbnail()] 

    // call the handler, passing the array 
    handler(someArray) 
} 

由於最後一個參數是一個閉包，你可以使用雨燕的尾部封語法：

// call the function 

getSetParameter { thumbnails in 
    print(thumbnails) 
} 

或者更簡潔：

getSetParameter { 
    print($0) 
} 

更詳細的版本的這個（沒有尾隨閉包語法）也適用：

getSetParameter({ (thumbnails) ->() in 
    print(thumbnails) 
}) 

但在我看來，這是非常醜陋的。

Answer 2

不知道如何在處理程序中使用閉包，self.getSetParameter函數的括號中的代碼在函數本身之前被調用。而不是完成該功能。

override func viewDidLoad() 
{ 
    self.getSetParameter { (thumbnails: [Thumbnail?]) ->() in 
     for var index = 0; index < thumbnails.count; ++index { 
      let currentThumbnail = thumbnails[index] 

      var title: String 
      var image: UIImage 
      if currentThumbnail!.isKindOfClass(Thumbnail) { 
       title = "Title " + String(index) 
       image = currentThumbnail!.image 
      } 
      else { 
       title = "Nil" 
       image = UIImage(named: "image0")! 
      } 

      self.models.append(CustomCell(title: title, image: image)) 
     } 
    } 
} 

func getSetParameter(handler:([Thumbnail?]) ->()) { 
    var thumbnails = [Thumbnail?]() 
    let param = ["format":"json"] 
    let jsonUrl: String! = "http://somewebsite.com" 

    let manager: AFHTTPSessionManager = AFHTTPSessionManager() 
    manager.GET(jsonUrl, parameters: param, success: { 
     (task: NSURLSessionDataTask!, JSONResponse: AnyObject!) in 

      let responseDictionary = JSONResponse as! NSDictionary 
      let responseArray = responseDictionary.objectForKey("response") as! NSArray 
      for thumbnailsOnVideoDictionary in responseArray 
      { 
       let thumbnailsOnVideoArray = thumbnailsOnVideoDictionary.objectForKey("thumbnails") as! NSArray 
       if thumbnailsOnVideoArray.count == 0 { 
        thumbnails.append(nil) 
       } 
       else { 
        let smallThumbnail = thumbnailsOnVideoArray[1]; 
        let aspect_ratio: Float = (smallThumbnail.objectForKey("aspect_ratio") as! Float) 
        let height: UInt = (smallThumbnail.objectForKey("height") as! UInt) 
        let name: AnyObject = smallThumbnail.objectForKey("name")! 
        let url: String = (smallThumbnail.objectForKey("url") as! String) 
        let width: UInt = (smallThumbnail.objectForKey("width") as! UInt) 

        let newThumbnail = Thumbnail(aspect_ratio: aspect_ratio, height: height, name: name, url: url, width: width) 
        thumbnails.append(newThumbnail) 
       } 
       handler(thumbnails) 
      } 
     }, failure: {(task: NSURLSessionDataTask?, error: NSError!) in 

    }) 
}