ios - 如何使用 Alamofire 制定一个良好的模式来控制多个请求依赖关系？比如request2需要request1的响应

Question

我使用 Alamofire 同时发送多个请求。但是请求A需要请求B的响应名为token。我举个例子:

var token = "111111111111"

let URLString1 = "http://httpbin.org/get?token=\(token)"
Alamofire.request(.GET, URLString1, parameters:  nil, encoding:.JSON).responseJSON { response in
    switch response.result {
    case .Success(let JSON):
        print("http1: \(JSON)")
        token = "22222222222"
    case .Failure(let error):
        print("Request failed with error: \(error)")
    }
}

//I want to wait for request1's response and get the new token value.
let URLString2 = "http://httpbin.org/get?token=\(token)"
Alamofire.request(.GET, URLString2, parameters:  nil, encoding:.JSON).responseJSON { response in
    switch response.result {
    case .Success(let JSON):
        print("http2: \(JSON)")
        print("token: \(token)")
    case .Failure(let error):
        print("Request failed with error: \(error)")
    }
}

我不想将 request2 放在 request1 的成功中。所以现在我的解决方案是:我给出一个名为 tokenChange 的变量。我有一个数组来存储所有需要 token 的请求。当 token 更改时，我从数组中将它们一一发送。但这个解决方案并不优雅。那么有没有一个好的模式来控制这个呢？

Answer 1

我发现这个方法dispatch_semaphore_signal。它可以解决我的问题。那么还有其他方法吗？

var token = "111111"

let group = dispatch_group_create();

dispatch_group_async(group, dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) { () -> Void in
    let semaphore = dispatch_semaphore_create(0)
    //token is 111111
    let URLString = "http://httpbin.org/get?token=\(token)"
    Alamofire.request(.GET, URLString, parameters:  nil, encoding:.JSON).responseJSON { response in
        switch response.result {
        case .Success(let JSON):
            print("http1: \(JSON)--class:")
            token = "222222"
            print("\n")
            dispatch_semaphore_signal(semaphore)
        case .Failure(let error):
            print("Request failed with error: \(error)")
        }
    }
    dispatch_semaphore_wait(semaphore, DISPATCH_TIME_FOREVER)

    //token is 222222
    let URLString2 = "http://httpbin.org/get?token=\(token)"
    Alamofire.request(.GET, URLString2, parameters:  nil, encoding:.JSON).responseJSON { response in
        switch response.result {
        case .Success(let JSON):
            print("http2: \(JSON)--class:")
            print("\n")
            print ("token is:\(token)")
        case .Failure(let error):
            print("Request failed with error: \(error)")
        }
    }

    //token is 2222222
    let URLString3 = "http://httpbin.org/get?token=\(token)"
    Alamofire.request(.GET, URLString3, parameters:  nil, encoding:.JSON).responseJSON { response in
        switch response.result {
        case .Success(let JSON):
            //                    token = (JSON["args"]!!["value"]) as! String
            print("http3: \(JSON)--class:")
            print("\n")
            print ("token is:\(token)")
        case .Failure(let error):
            print("Request failed with error: \(error)")
        }
    }
}

dispatch_group_notify(group,dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0)) { () -> Void in
    NSLog("finish");
}