我寫了一個函數,該函數應該返回一個值,但值來自閉包。問題是,如果我試圖從閉包中返回一個值,它將它視爲來自完成處理程序的返回值。從包含閉包的Swift函數返回一個值
private func loadData() throws -> [Item] {
var items = [Item]()
let jsonUrl = "http://api.openweathermap.org/data/2.5/forecast/daily?units=metric&cnt=7&q=coventry,uk"
print(jsonUrl)
let session = NSURLSession.sharedSession()
guard let shotsUrl = NSURL(string: jsonUrl) else {
throw JSONError.InvalidURL(jsonUrl)
}
session.dataTaskWithURL(shotsUrl, completionHandler: {(data, response, error) -> Void in
do {
let json = try NSJSONSerialization.JSONObjectWithData(data!, options: [])
print(json)
guard let days:[AnyObject] = (json["list"] as! [AnyObject]) else {
throw JSONError.InvalidArray
}
for day in days {
guard let timestamp:Double = day["dt"] as? Double else {
throw JSONError.InvalidKey("dt")
}
print(timestamp)
let date = NSDate(timeIntervalSince1970: NSTimeInterval(timestamp))
guard let weather:[AnyObject] = day["weather"] as? [AnyObject] else {
throw JSONError.InvalidArray
}
guard let desc:String = weather[0]["description"] as? String else {
throw JSONError.InvalidKey("description")
}
guard let icon:String = weather[0]["icon"] as? String else {
throw JSONError.InvalidKey("icon")
}
guard let url = NSURL(string: "http://openweathermap.org/img/w/\(icon).png") else {
throw JSONError.InvalidURL("http://openweathermap.org/img/w/\(icon).png")
}
guard let data = NSData(contentsOfURL: url) else {
throw JSONError.InvalidData
}
guard let image = UIImage(data: data) else {
throw JSONError.InvalidImage
}
guard let temp:AnyObject = day["temp"] else {
throw JSONError.InvalidKey("temp")
}
guard let max:Float = temp["max"] as? Float else {
throw JSONError.InvalidKey("max")
}
let newDay = Item(date: date, description: desc, maxTemp: max, icon: image)
print(newDay)
items.append(newDay)
}
return items // this line fails because I'm in the closure. I want this to be the value returned by the loadData() function.
} catch {
print("Fetch failed: \((error as NSError).localizedDescription)")
}
})
}
您可以傳遞閉包作爲回調或完成處理程序,您可以在要返回項目的位置調用該閉包程序。你需要寫出你願意如何處理你傳遞給loadData()函數的閉包中的數據。 – iamyogish