json - 从内部循环返回 JSON 数据

Question

我正在尝试返回从 JSON 响应中获取的值

    func getAsset(imageId: String) -> String{
    let url = "https://myimage.com"
    Alamofire.request(.GET, url).responseJSON { response in
        switch response.result {
        case .Success:
            if let value = response.result.value {
                dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) {
                    let json = JSON(value)
                    let singleAsset = json["fields"]["file"]["url"].string
                    print(singleAsset)
                }
            }
        case .Failure(let error):
            print(error)
        }
    }
}

我试图返回值(singleAsset)但不能，因为我不断收到错误未解析的标识符。我整晚都在尝试，但无法恢复值(value)。

Answer 1

您应该使用完成处理程序:
请参阅:https://thatthinginswift.com/completion-handlers/

func getAsset(imageId: String, completion: (String) -> Void) {
    let url = "https://myimage.com"
    Alamofire.request(.GET, url).responseJSON { response in
        switch response.result {
        case .Success:
            if let value = response.result.value {
                dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) {
                    let json = JSON(value)
                    let singleAsset = json["fields"]["file"]["url"].string
                    print(singleAsset)
                    completion(singleAsset)
                }
            }
        case .Failure(let error):
            print(error)
            completion(nil);
        }
    }

用法:

getAsset(imageId) {result in
    println("got back: \(result)")
}