函數在NSURLSession之前完成 - dataTaskWithRequest完成

Question

我在ViewDidLoad（）下調用了以下方法。我明白，session.dataTaskWithRequest會自動在後臺線程中運行。由於相同，ViewDidLoad（）中此方法後面的代碼不會等待此過程完成並開始執行。

有什麼辦法，我可以確保在執行其他方法之前在後臺線程完成？

func getCoordinatesFromServer() { 
     let request = NSMutableURLRequest(URL: NSURL(string: constants.urlName.loadData)!) 
     request.HTTPMethod = "POST" 
     request.addValue("multipart/form-data", forHTTPHeaderField: "Accept") 
     request.setValue("keep-Alive", forHTTPHeaderField: "Connection") 
     request.HTTPBody = (constants.requestTag.getCoordinates).data 

     let session = NSURLSession.sharedSession() 
     let task = session.dataTaskWithRequest(request, completionHandler: {(data, response ,error) in 
      if let response = response { 
       let httpResponse = response as! NSHTTPURLResponse 

       print("response code = \(httpResponse.statusCode)") 
       if (httpResponse.statusCode == 200) { 
        dispatch_async(dispatch_get_main_queue(), { 
         let decodedData = NSData(base64EncodedData: data!, options: NSDataBase64DecodingOptions([])) 
         let jsonText = NSString(data: decodedData!, encoding: NSASCIIStringEncoding) as! String 
         do { 
         let json = try NSJSONSerialization.JSONObjectWithData(jsonText.data, options: NSJSONReadingOptions.init(rawValue: 0)) 
         self.parseJsonData(json["Datalist"] as! NSArray) 
         } catch { 
         print("Error:\n \(error)") 
         } 
        }) 
       } 
      } 
     }) 
     task.resume() 
    } 

問候，

Answer 1

，如果我明白你的問題，你可以在這樣 解決這個問題，例如：

class func ConnectedToNetwork(completionHandler: ((Status: Bool) -> Void)) 
    { 
    let url = NSURL(string: "http://google.com") 
    let request = NSMutableURLRequest(URL: url!) 
    request.HTTPMethod = "HEAD" 
    request.timeoutInterval = 0.2 
     let task = NSURLSession.sharedSession().dataTaskWithURL(url!) {(data,response, error) in 
      let httpResponse = response as! NSHTTPURLResponse 
       if httpResponse.statusCode == 200 
       { completionHandler(Status: true) 
        return 
       } 
     } 
     task.resume() 
    } 

，然後，你可以用這個

Checks.ConnectedToNetwork({ Status in dispatch_async(dispatch_get_main_queue()) 
     { 
      if Status == true 
      { 
       //do what you want 
      } 
}); 

Answer 2

dataTaskWithRequest是assync呼叫，並且它具有completionHandler塊。因此，數據的任務結束後，你裏面寫的所有代碼將被執行：

let request = NSURLRequest(URL: NSURL(string: "http://google.com")!) 
let task = NSURLSession.sharedSession().dataTaskWithRequest(request, completionHandler: {(data, response ,error) in 
    print("3") // executed after data task is finished 
    print("4") // executed after data task is finished 
}) 
task.resume() 
print("1") 
print("2") 

Answer 3

import Foundation 

// some aync function with completition handler, i MUST USE AS IT IS 
func f(completitionHandler:()->()) { 
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0)) {() -> Void in 
     print("running concurrently") 
     sleep(1) 
     print("finished") 
     completitionHandler() 
    } 
} 

// some function running on main queue 
func foo() { 
    // create dispatch group 
    let group = dispatch_group_create() 
    let myCompletitionHandler:()->() = { 
     dispatch_group_leave(group) 
    } 
    let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0) 
    dispatch_group_async(group, queue) {() -> Void in 
     dispatch_group_enter(group) 
     f(myCompletitionHandler) 
    } 
    dispatch_group_wait(group, DISPATCH_TIME_FOREVER) 
} 

foo() 
print("foo finished") 

這是不是最好的，在所有的，更好的工作SOLUT離子是這個「處理方法」的:-)