如何在Swift中从闭包中获取数据

Question

我写了RetrieveUrl类来从URL获取JSON数据。这一切都按预期工作，我可以看到闭包中的数据变量返回了一个值。但我想在MasterViewController.swift的表格中显示这些数据，但尝试了几件事情，但似乎我对Swift闭包知之甚少。

import Foundation 

class RetrieveUrl { 

func httpGet(request: NSURLRequest!, callback: (String, String?) -> Void)     
{ 
    var session = NSURLSession.sharedSession() 
    var task = session.dataTaskWithRequest(request){ 
     (data, response, error) -> Void in 
     if error != nil { 
      callback("", error.localizedDescription) 
     } else { 
      var result = NSString(data: data, encoding: 
       NSASCIIStringEncoding)! 
      callback(result, nil) 
     } 
    } 
    task.resume() 

} 

func makeRequest() ->() { 

    var request = NSMutableURLRequest(URL: NSURL(string: "http://someapi_url")!) 

    var result:String = "" 

    httpGet(request){ 
     (data, error) -> Void in 
     if error != nil { 
      result = error! 
     } else { 
      result = data 
     } 
    } 

    } 
} 

MasterViewController.swift代码，我想将此数据

override func tableView(tableView: UITableView, cellForRowAtIndexPath indexPath: NSIndexPath) -> UITableViewCell { 
    let cell = tableView.dequeueReusableCellWithIdentifier("Cell", forIndexPath: indexPath) as UITableViewCell 
    let object = objects[indexPath.row] as NSDate 

    // Showing data from URL 
    var getUrlObject = RetrieveUrl() 
    getUrlObject.makeRequest() 

    cell.textLabel!.text = object.description 

    return cell 
} 

Answer 1

更新代码： 类RetrieveUrl {

func httpGet(request: NSURLRequest!, callback: (NSString, NSString?) -> Void) 
{ 
    var session = NSURLSession.sharedSession() 
    var task = session.dataTaskWithRequest(request){ 
     (data, response, error) -> Void in 
     if error != nil { 
      callback("", error.localizedDescription) 
     } else { 
      var result = NSString(data: data, encoding: 
       NSASCIIStringEncoding)! 
      callback(result, nil) 
     } 
    } 
    task.resume() 

} 

func makeRequest(callback: (NSString) ->Void) -> Void { 

    var request = NSMutableURLRequest(URL: NSURL(string: "http://sample_url")!) 

    var result:NSString = "" 


    httpGet(request){ 
     (data, error) -> Void in 

     if error != nil { 
      result = error! 
     } else { 
      result = data 
     } 


     callback(data) 
    } 

} 

}

用法：

let retrieveObj = RetrieveUrl() 
    retrieveObj.makeRequest(){ 
     (data) -> Void in 
     println("response data:\(data)") 

    } 

}