swift - 从快速关闭中获取数据

Question

我很难理解 Swift 闭包，尤其是如何从中获取数据。以下代码发出 http get 请求并从 URL 检索数据。这一切都很好。我可以在闭包中打印出这些数据，但无法确定如何存储到外部变量或返回数据。代码完成时，routes变量为零。有谁知道我做错了什么和/或如何从关闭中获取数据。

var routes: [String]?

let task = URLSession.shared.dataTask(with: url, completionHandler: { data, response, error in
    guard let data = data, error == nil else {
        print(error ?? "Unknown error")
        return
    } //end let
    do {
    if let jsonDict = try JSONSerialization.jsonObject(with: data, options: []) as? NSDictionary {
        if let response = jsonDict.value(forKey: "response") as? NSArray {
            for i in 0..<response.count {
                let route = response.object(at: i) as! NSDictionary
                print(route.value(forKey: "route_id")!)
                routes?.append(route.value(forKey: "route_id")! as! String)

            }
        self.routes = routes
        print(self.routes)
        }
    }
    } catch let error as NSError {
        print(error.localizedDescription)
    }
})
task.resume()

输出：

11201-20180605110613_v67.1

11202-20180524131340_v66.89

11201-20180524131340_v66.89

11202-20180605110613_v67.1

nil

标签： swift