第一篇文章,请温和。我在Swift 3,Xcode 8.1中玩弄了JSON数据。我特别从http://forecast.weather.gov/MapClick.php?lat=38.9782&lon=-76.4933&FcstType=json获取我的数据。我的代码如下:无法从Swift 3的dataTask中获取JSON数据
private func getWeatherData(url:URL) -> (currentObservation:Dictionary<String, AnyObject>, currentData:Dictionary<String, AnyObject>) {
var currentObservation:Dictionary = [:] as Dictionary<String, AnyObject>
var currentData:Dictionary = [:] as Dictionary<String, AnyObject>
let task = URLSession.shared.dataTask(with: url) { (data, response, error) in
if error != nil {
print ("Error retrieving URLSession")
}
else
{
if let content = data
{
do
{
let JSONData = try JSONSerialization.jsonObject(with: content, options: JSONSerialization.ReadingOptions.mutableContainers) as AnyObject
if let observation = JSONData["currentobservation"] as? Dictionary<String, AnyObject> {
currentObservation = observation
print("currentObservation inside of task: \(currentObservation)\n\n")
}
if let data = JSONData["data"] as? Dictionary<String, AnyObject> {
currentData = data
print("currentData inside of task: \(currentData)")
}
}
catch
{
print("Error in trying JSONSerialization")
}
}
}
}
task.resume()
print("currentObservation outside of task: \(currentObservation) \n\n")
print("currentData outside of task: \(currentData)")
return (currentObservation , currentData)
}
我得到的输出是:
currentObservation outside of task: [:]
currentData outside of task: [:]
currentObservation: [:]
currentData: [:]
currentObservation inside of task: ["state": MD, "name": Annapolis, United States Naval Academy, "longitude": -76.49, "elev": 3, "Relh": 79, "WindChill": NA, "Weather": Fair, "Altimeter": 1028.7, "latitude": 38.99, "Temp": 46, "SLP": 30.37, "id": KNAK, "timezone": EST, "Weatherimage": nsct.png, "Windd": 0, "Winds": 0, "Visibility": 10.00, "Gust": 0, "Dewp": 40, "Date": 7 Nov 20:54 pm EST]
currentData inside of task: ["hazard": <__NSArrayM 0x60800005a520>(
Frost Advisory, Hazardous Weather Outlook), "weather": <__NSArrayM 0x60800005a490>(
Clear then Areas Frost, Areas Frost then Sunny,
Partly Cloudy then Slight Chance Showers, etc.(edited for brevity)]
我得到一个JSON数据的反应,但我似乎无法保持数据的保持。
我很困惑的几件事情。首先,为什么URLSession.shared.dataTask之外的打印语句在打印语句之前打印?
此外,“currentObservation”和“currentData”的打印语句在函数外调用,并且它们打印在URLSession.shared.dataTask中的打印语句之前。这是为什么?
最后,最重要的是,为什么JSON数据没有超出URLSession.shared.dataTask块呢?
任何洞察将有所帮助。谢谢。
编辑: 这是我现在的代码基于维诺德的回应。当我打印它们时,currentObservation和currentData仍然是空的。
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
var currentObservation:Dictionary = [:] as Dictionary<String, AnyObject>
var currentData:Dictionary = [:] as Dictionary<String, AnyObject>
let serverURL = URL(string:"http://forecast.weather.gov/MapClick.php?lat=38.9782&lon=-76.4933&FcstType=json")
getWeatherData(serverURL: serverURL!, completion: { serverResponse in
if let observation = serverResponse["currentobservation"] as? Dictionary<String, AnyObject> {
currentObservation = observation
print("currentObservation inside of task: \(currentObservation)\n\n")
}
if let data = serverResponse["data"] as? Dictionary<String, AnyObject> {
currentData = data
print("currentData inside of task: \(currentData)\n\n")
}
})
print("currentObservation outside of task: \(currentObservation)\n\n")
print("currentData outside of task: \(currentData)")
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
private func getWeatherData(serverURL:URL, completion:@escaping (AnyObject) ->()){
let task = URLSession.shared.dataTask(with: serverURL) { (data, response, error) in
if error != nil {
print ("Error retrieving URLSession")
}
else
{
if let content = data
{
do
{
let JSONData = try JSONSerialization.jsonObject(with: content, options: JSONSerialization.ReadingOptions.mutableContainers) as AnyObject
completion(JSONData)
}
catch
{
print("Error in trying JSONSerialization")
}
}
}
}
task.resume()
}
}
是的,我知道我不应该在所有的视图控制器违反了MVC的可以这样做,但我只是玩弄的努力得到它添加的复杂工作之前数据模型和控制器以及UI。谢谢。
'dataTask'以异步方式工作。您不能从包含异步任务的方法返回任何内容。 – vadian
我想这是有道理的。如果在函数调用完成时已完成采样,那么如何返回任何内容。谢谢。 – Yrb
Vinod的答案提供了一种使用回调闭包异步返回数据的解决方案。此外,在这里有几百个相关的主题。 – vadian