如何在Swift中将completionHandler Closure与Return结合使用？

Question

我正在尝试向我们提供一个RESTful
API，该API返回一些json数据。我想封装创建HTTP请求并在其自己的方法中设置标头的代码，以便可以通过输入url
String来调用它，然后让该方法返回JSON对象。

在下面的代码片段中，我已经创建了请求对象并设置了标头，并将该变量称为“
req”。我尚未声明任何名为data，response或error的对象。我有以下代码可以正确打印出JSON对象

let sesh = NSURLSession.sharedSession()
    let dataTask = sesh.dataTaskWithRequest(req, completionHandler: {(data, response, error) in
        var jsonError : NSError?
        let jsonBlob = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableLeaves, error: &jsonError)
        println(jsonBlob)
        });

    dataTask.resume()

所以这是我的问题。我如何做到这一点，使该completeHandler块能够返回类型为“
AnyObject！”的jsonBlob？如果我将代码稍微修改为以下内容：

let sesh = NSURLSession.sharedSession()
    let dataTask = sesh.dataTaskWithRequest(req, completionHandler: {(data, response, error) -> AnyObject! in
        var jsonError : NSError?
        let jsonBlob : AnyObject! = NSJSONSerialization.JSONObjectWithData(data, options: NSJSONReadingOptions.MutableLeaves, error: &jsonError)
        return jsonBlob
        });

    dataTask.resume()

那么该程序将不会编译，因为对dataTaskWithRequest：completionHandler的调用会给出编译器警告，提示：

 Could not find an overload for 'dataTaskWithRequest' that accepts the supplied arguments

我不明白 我正在使用正确的语法来返回闭包，如Swift Docs的此页面所述：

https://developer.apple.com/library/content/documentation/Swift/Conceptual/Swift_Programming_Language/Closures.html

Answer 1

func getSomething(callback: (Array<AnyObject>) -> ()) {
    var dataTask = NSURLSessionDataTask()
    dataTask = session.dataTaskWithRequest(request) { (data, response, error) in
        if (error == nil) {
            var callbackArray = Array<MyObject>()
            let responseDict = NSJSONSerialization.JSONObjectWithData(data, options: .MutableContainers, error: nil) as NSDictionary
            let response = responseDict.objectForKey("response_key") as NSDictionary
            let array = response.objectForKey("array_key") as NSArray

            for item: AnyObject in array {
                var arrayItem = MyObject(dict: item as NSDictionary)
                callbackArray.append(arrayItem)
            }

            callback(callbackArray)
        } else {
            // handle an error
        }
    }
    dataTask.resume()
}

然后，您可以执行以下操作：

getSomething() { (response) in
    if let responseArray = response as? Array<MyObject> {
        self.somethings = responseArray
    }
}