在請求到服務器iOS的void函數中發生意外的非void返回值Swift 3

Question

我嘗試使請求到服務器的方法包含Background和Main隊列。最後，這個方法應該從服務器返回我的響應的NSDictionary。

func sendRequest(UrlString urlString:String,MethodString method:String)->(NSDictionary) { 

    DispatchQueue.global(qos: .background).async { 
     var request = URLRequest(url: URL(string:urlString)!) 
     request.httpMethod = method 
     //let postString = "id=13&name=Jack" 
     //request.httpBody = postString.data(using: .utf8) 
     let task = URLSession.shared.dataTask(with: request) { data, response, error in 
      guard let data = data, error == nil else {             // check for fundamental networking error 
       print("error=\(error)") 
       return 
      } 

      if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 {   // check for http errors 
       print("statusCode should be 200, but is \(httpStatus.statusCode)") 
       print("response = \(response)") 
      } 

      let responseString = String(data: data, encoding: .utf8) 
      print("responseString = \(responseString)") 

     DispatchQueue.main.async { 

      do { 
       let jsonDictionary:NSDictionary = try JSONSerialization.jsonObject(with: data, options: []) as! [String: AnyObject] as NSDictionary 

       return jsonDictionary 

      } catch { 
       //Handle the error 
      } 

      //return airports 
     } 

    } 

    task.resume() 
} 

現在當嘗試在主隊列返回jsonDictionary，它表明我這個錯誤：

Unexpected non-void return value in void function

現在我不知道如何解決這個問題。我正在使用Xcode 8,iOS8和Swift 3。
請幫幫我。
謝謝。

Answer 1

您已經實現了至少兩個異步操作並且它們不能返回值。對於異步操作，你應該使用像這樣的完成處理程序：

func sendRequest(urlString: String, method: String, completion: @escaping (_ dictionary: NSDictionary?, _ error: Error?) -> Void) { 

    DispatchQueue.global(qos: .background).async { 
     var request = URLRequest(url: URL(string:urlString)!) 
     request.httpMethod = method 
     let task = URLSession.shared.dataTask(with: request) { data, response, error in 
      guard let data = data, error == nil else {             // check for fundamental networking error 
       print("error=\(error)") 
       completion(nil, error) 
       return 
      } 

      if let httpStatus = response as? HTTPURLResponse, httpStatus.statusCode != 200 {   // check for http errors 
       print("statusCode should be 200, but is \(httpStatus.statusCode)") 
       print("response = \(response)") 
       // make error here and then 
       completion(nil, error) 
       return 
      } 

      let responseString = String(data: data, encoding: .utf8) 
      print("responseString = \(responseString)") 

      DispatchQueue.main.async { 
       do { 
        let jsonDictionary:NSDictionary = try JSONSerialization.jsonObject(with: data, options: []) as! [String: Any] as NSDictionary 

        completion(jsonDictionary, nil) 

       } catch { 
        completion(nil, error) 
       } 
      } 

     } 

     task.resume() 
    } 
}