在Swift中进行异步GET/POST请求

Question

我已经为make GET请求写了这个类

    class GETReq{
func HTTPsendRequest(request: NSMutableURLRequest, callback: (String, String?) -> Void) {
            let task = NSURLSession.sharedSession().dataTaskWithRequest(request) {  (data, response, error) -> Void in

                dispatch_async(dispatch_get_main_queue()) {
                    if (error != nil) {
                        callback("", error.localizedDescription)
                    } else {
                        callback(NSString(data: data,encoding: NSUTF8StringEncoding)!, nil)
                    }
                }
            }
            task.resume()
    }   

func HTTPGet(url: String, callback: (String, String?) -> Void) {
    var request = NSMutableURLRequest(URL: NSURL(string: url)!)
    HTTPsendRequest(request, callback) }
}

在另一个名为"ManageData"的类中

class ManageData{

    func makeTheRequest()->String{
        var makeReq:GETReq=GETReq();
        var ret:String="";

        makeReq.HTTPGet("http://www.example.com/fileExample.php") { (data:String, error:String?) -> Void in
            if(error==nil){ ret="error"; } else { ret="ok"; }
        }
        return ret;
    }
}

问题是在ViewController类中make

 var result:String =  manageData.makeTheRequest();

"result"变量始终为空,因为makeTheRequest函数在完成get请求之前返回"ret".

Answer 1

您应该makeTheRequest采用与其他地方相同的完成闭包模式.因此,更改makeTheRequest为不返回任何值,而是采用一个callback参数,该参数是在请求完成时将调用的闭包:

func makeTheRequest(callback: (String, String?) -> Void) {
    var makeReq:GETReq=GETReq();
    var ret:String="";

    makeReq.HTTPGet("http://www.example.com/fileExample.php", callback)
}

你可能会这样称呼它:

makeTheRequest() { string, error in 
    if error != nil {
        println(error)
        return
    }

    // if you got here, you can use `string`

    println(string)
}