Question

我试图从JSON文件加载数据以在我的tableview中使用。然而，当我在viewdidload中调用此函数时，我想要填充数据，不包含任何数据，并返回一个空数组。

class CompanyModel {

func getJSON() -> NSMutableArray() {

let companyArray: NSMutableArray = NSMutableArray()

let requestURL: NSURL = NSURL(string: "http://localhost/Companies/JSON.php")!
let urlRequest: NSMutableURLRequest = NSMutableURLRequest(URL: requestURL)
let session = NSURLSession.sharedSession()

let task = session.dataTaskWithRequest(urlRequest) { <- does not enter bracket?
    (data, response, error) -> Void in

    let httpResponse = response as! NSHTTPURLResponse
    let statusCode = httpResponse.statusCode

    if (statusCode == 200) {
        print("Everyone is fine, file downloaded successfully.")

        do{

            let json = try NSJSONSerialization.JSONObjectWithData(data!, options:.AllowFragments)

            if let companies = json["companies"] as? [[String: AnyObject]] {

                for company in companies {

                    if let name = company["name"] as? String,
                        let phoneNumber = company["phone_number"] as? String,
                        let website = company["website"] as? String,
                        let email = company["email"] as? String,
                        let address = company["address"] as? String

                    {
                    let company = CompanyModel()

                        company.name = name
                        company.phoneNumber = phoneNumber
                        company.website = website
                        company.email = email
                        company.address = address
                    }
                    companyArray.addObject(company)
                    print(companyArray)
                }
            }
        } catch {
            print("Error with Json: \(error)")
        }

    }
    print(companyArray) <- array is populated
}
print(companyArray) <- array is empty
task.resume()
return companyArray
}
}

当我运行调试会话时，它似乎没有进入我上面所述的括号。相反，它直接跳转到返回函数，然后返回一个空数组。我相信没有从JSON文件中获取数据，但我不太清楚为什么。

Answer 1

您的第二个print(companyArray)代码在调用可以返回来自服务器的数据之前运行，因为请求是作为后台任务完成的。您应该在成功代码中写return companyArray，否则return在发生故障时清空数组。

Answer 2

在您的代码中，您创建了一个在不同线程上运行的数据任务。

    print(companyArray) <- this one is after request returns a response
}
print(companyArray) <- this comes before the array is populated
task.resume() <- And here is where you start the data task
return companyArray

您可以在完成方法时更改逻辑以返回companyArray。

    print(companyArray) <- and for the love of God, don't put return here! 
}
print(companyArray) <- this comes before the array is populated
task.resume() <- And here is where you start the data task
return companyArray

Answer 3

在您的代码localhost中创建了一个问题，您将response作为nil。因此，在检查任何内容之前，最好print(data)，print(response)，print(error)。要检查使用此网址：https://httpbin.org/get以及稍后的网址，请将您的localhost替换为您的网址中的IP或domain。

以下是上述更新代码：

func getWebServiceWithURL(strUrl: String, completionHandler: (NSDictionary?, NSError?) -> ()) -> (){

    let getTask = NSURLSession.sharedSession().dataTaskWithURL(NSURL(string: strUrl)!) { (responseData, _, error) -> Void in

        dispatch_async(dispatch_get_main_queue(), { () -> Void in

            do{
                if responseData != nil{

                    let json = try NSJSONSerialization.JSONObjectWithData(responseData!, options: NSJSONReadingOptions.AllowFragments) as? NSDictionary

                    if let parseJSON = json {

                        // Parsed JSON
                        completionHandler(parseJSON, nil)
                    }
                    else {
                        // Woa, okay the json object was nil, something went worng. Maybe the server isn't running?
                        let jsonStr = NSString(data: responseData!, encoding: NSUTF8StringEncoding)

                        #if DEBUG
                            print("Error could not parse JSON: \(jsonStr)")
                        #endif
                    }
                }else{

                    completionHandler(nil, error)
                }

            }catch let error as NSError{

                print(error.localizedDescription)
                completionHandler(nil, error)
            }
        })
    }

    getTask.resume()
}

Answer 4

doc of NSURLSession的一部分：

与大多数网络API一样，NSURLSession API非常高的异步即可。它以两种方式之一将数据返回到您的应用程序，取决于您调用的方法：
To a completion handler block that is called when a transfer finishes successfully or with an error.

By calling methods on the session’s delegate as data is received and when the transfer is complete.

和代码中的一部分：

   print(companyArray) <- array is populated
}
print(companyArray) <- array is empty

异步过程完成后，您的完成处理程序中会填充companyArray，并且在完成处理程序之外它是空的，因为代码：

print(companyArray) <- array is empty

紧接着这一行：

let task = session.dataTaskWithRequest(urlRequest) {

并且尚未评估完成处理程序。使用完成处理程序来获得实际结果。

Answer 5

您的return companyArray在响应来自服务器之前被调用。所以你不应该像数组那样创建一个返回类型的方法！您应该将companyArray作为公共变量或实例变量，并且可以从webservice调用的完成块设置它的值，并且可以在需要的地方使用。

希望这会有所帮助：）

函数返回一个空数组而不是填充它

5 个答案: