对于iOS天气应用程序，我在尝试使用swift中的dispatch async逐个运行多个异步任务时遇到问题。我想要'update（）'函数：
（对我来说很容易，我是一名最近自学成才的编码员，所以我假设你们经验丰富，可以指出各种错误！任何帮助都会受到大力赞赏。）
var latitude: String = ""
var longitude: String = ""
var locationManager: CLLocationManager!
var forecastData: Weather = Weather() // the weather class has it's own asynchronous NSURLSession called retrieveForecast()
// which calls the Open Weather Map API and parses the XML
func refresh() {
// Here's where I don't know what I'm doing:
let group = dispatch_group_create()
dispatch_group_enter(group)
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) {
self.getLocation()
dispatch_group_leave(group)
}
dispatch_group_notify(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) {
self.getWeather()
}
self.updateUI() // ...and I know that this is in totally the wrong place!
}
// function(s) to get phone's location:
func getLocation() {
locationManager = CLLocationManager()
locationManager.delegate = self
locationManager.desiredAccuracy = kCLLocationAccuracyHundredMeters
locationManager.requestWhenInUseAuthorization()
locationManager.distanceFilter = 100.0
locationManager.startUpdatingLocation()
}
func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
self.locationManager.stopUpdatingLocation()
manager.stopUpdatingLocation()
for item: AnyObject in locations {
if let location = item as? CLLocation {
if location.horizontalAccuracy < 1000 {
manager.stopUpdatingLocation()
self.latitude = String(location.coordinate.latitude)
self.longitude = String(location.coordinate.longitude)
}
}
}
}
// function to download and parse the weather data within forecastData object
func getWeather() {
let apiCall = "http://api.openweathermap.org/data/2.5/forecast?lat=" + self.latitude
+ "&lon=" + self.longitude + "&mode=xml&appid=" + self.openWeatherMapAPIKey
NSLog("getWeather called with api request: \(apiCall)")
self.forecastData.retrieveForecast(apiCall)
}
答案 0 :(得分：3)
对于任何异步操作，最好有一个完成回调。
在您的情况下，如果您已为getLocation和getWeather实施了回调，那么您将永远不需要dispatch_groups，只需从getWeather＆＃拨打getLocation即可39; s回调，然后你只需从refreshUI的回调中拨打getWeather。
var latitude: String = ""
var longitude: String = ""
var locationManager: CLLocationManager!
var forecastData: Weather = Weather() // the weather class has it's own asynchronous NSURLSession called retrieveForecast()
// which calls the Open Weather Map API and parses the XML
func refresh() {
self.getLocation()
}
// function(s) to get phone's location:
func getLocation() {
locationManager = CLLocationManager()
locationManager.delegate = self
locationManager.desiredAccuracy = kCLLocationAccuracyHundredMeters
locationManager.requestWhenInUseAuthorization()
locationManager.distanceFilter = 100.0
locationManager.startUpdatingLocation()
}
func locationManager(manager: CLLocationManager, didUpdateLocations locations: [CLLocation]) {
self.locationManager.stopUpdatingLocation()
manager.stopUpdatingLocation()
for item: AnyObject in locations {
if let location = item as? CLLocation {
if location.horizontalAccuracy < 1000 {
manager.stopUpdatingLocation()
self.latitude = String(location.coordinate.latitude)
self.longitude = String(location.coordinate.longitude)
self.getWeather()
}
}
}
}
// function to download and parse the weather data within forecastData object
func getWeather() {
let apiCall = "http://api.openweathermap.org/data/2.5/forecast?lat=" + self.latitude
+ "&lon=" + self.longitude + "&mode=xml&appid=" + self.openWeatherMapAPIKey
NSLog("getWeather called with api request: \(apiCall)")
self.forecastData.retrieveForecast(apiCall)
// assuming that self.forecastData.retrieveForecast(apiCall) is completely synchronous, we can call updateUI below
self.updateUI()
}
以下是代码，演示如何正确使用dispatch_group：
func refetchOrdersAndChats(remoteNotificationData: [NSObject : AnyObject], completion: ((Bool)->())?) {
var overallSuccess: Bool = true
let refetchGroup = dispatch_group_create();
dispatch_group_enter(refetchGroup);
CPChatController.sharedInstance.updateChat(remoteNotificationData, completion: { success in
overallSuccess = success && overallSuccess
dispatch_group_leave(refetchGroup);
})
dispatch_group_enter(refetchGroup);
CPChatController.sharedInstance.fetchNewOrdersWithNotification(remoteNotificationData, completion: { success in
overallSuccess = success && overallSuccess
dispatch_group_leave(refetchGroup);
})
dispatch_group_notify(refetchGroup,dispatch_get_main_queue(), {
completion?(overallSuccess)
})
}
答案 1 :(得分：1)
在开始学习关闭/阻塞之后，我终于找到了我的答案，以为我会分享。我需要做的是为我的Weather类中的参数添加一个闭包，它在XML解析完成时返回一个布尔值，并允许我在更新UI之前在我的View Controller中等待它。我希望这可以帮助其他人寻找类似的答案，如果有任何专业人士能够使这个代码更好，请添加评论！
...
// getWeather function in my View Controller (called from location manager)
func getWeather() {
let apiCall = "http://api.openweathermap.org/data/2.5/forecast?lat=" + self.latitude
+ "&lon=" + self.longitude + "&mode=xml&appid=" + self.openWeatherMapAPIKey
NSLog("getWeather called with api request: \(apiCall)")
self.forecastData.retrieveForecast(apiCall, completion: { success in
if success {
self.updateUI()
} else {
NSLog("Parse unsuccessful")
// I'll handle the issue here
}
});
}
...在Weather类功能中：
func retrieveForecast(url: String, completion: ((Bool)->())?) {
self.reset()
let apiCall = NSURL(string: url)
let urlRequest: NSURLRequest = NSURLRequest(URL: apiCall!)
let session = NSURLSession.sharedSession()
let task = session.dataTaskWithRequest(urlRequest) {
(data, response, error) -> Void in
self.xmlParser = NSXMLParser(data: data!)
self.xmlParser.delegate = self
let success: Bool = self.xmlParser.parse()
if !success {
NSLog("Did not parse. \(error?.localizedDescription)")
completion?(false)
} else {
self.currentParsedElement = ""
self.retrievingForecast = false
completion?(true)
}
}
task.resume()
}