ios - 如何覆盖 Alamofire SessionManager 以修改响应以添加 header ？

Question

所以，我正在使用 Alamofire 发出一些 HTTP 请求，并且我正在尝试使用缓存策略，但服务器的 header 中没有“Cache-Control”标志。所以我想使用 session 管理器添加这个标志 delegate method dataTaskWillCacheResponse 基于此answer here.

为了做到这一点，我想创建一个带有 SessionManager 静态共享实例的类(我不想在 AppDelegate 上创建一个全局变量。我认为这不是一个好的做法)并在此类中重写委托(delegate)方法，但我做不到。

这是我的代码:

public class Manager: SessionDelegate {
    var manager: SessionManager?
    weak var sessionDelegate: SessionDelegate?
    override init() {
        super.init()
        let configuration = URLSessionConfiguration.default
        configuration.urlCache = URLCache(memoryCapacity: 20 * 1024 * 1024, diskCapacity: 100 * 1024 * 1024, diskPath: nil)
        configuration.requestCachePolicy = .returnCacheDataElseLoad
        configuration.timeoutIntervalForRequest = 35
        self.manager = SessionManager(configuration: configuration)
        self.manager = Alamofire.SessionManager(configuration: configuration)
        self.manager?.delegate = self
    }
}

在 self.manager.delegate = self 上我得到错误:无法分配给属性:'delegate' is a 'let' constant

我对 Swift 和 Alamofire 比较陌生。我究竟做错了什么？我怎样才能实现我想要做的事情？

编辑:我看到我无法创建单例，但我能够使用共享实例并覆盖方法。检查下面的答案

Answer 1

经过更多的研究，我发现了一些东西:
1 - Advanced usage override closures
2 - Found this answer that creates a Session Manager
3 - Found this solution在 dataTaskWillCacheResponse 委托(delegate)方法中为我的响应添加 header 。

这是我的解决方案:

class MyService {
    static let shared = MyService()

    //The manager with the cache policy
    private let manager: Alamofire.SessionManager = {
        let configuration = URLSessionConfiguration.default
        configuration.requestCachePolicy = .useProtocolCachePolicy
        configuration.timeoutIntervalForRequest = 35
        return Alamofire.SessionManager(configuration: configuration)
    }()

    init() {
        let delegate: Alamofire.SessionDelegate = manager.delegate
        //Overriding delegate to add headers
        delegate.dataTaskWillCacheResponseWithCompletion = { session, datatask, cachedResponse, completion in
            let response = cachedResponse.response  as! HTTPURLResponse
            var headers = response.allHeaderFields as! [String: String]
            print(headers.keys.contains("Cache-Control"))
            headers["Cache-Control"] = "max-age=30"
            let modifiedResponse = HTTPURLResponse(
                url: response.url!,
                statusCode: response.statusCode,
                httpVersion: "HTTP/1.1",
                headerFields: headers)

            let modifiedCachedResponse = CachedURLResponse(
                response: modifiedResponse!,
                data: cachedResponse.data,
                userInfo: cachedResponse.userInfo,
                storagePolicy: cachedResponse.storagePolicy)
            completion(modifiedCachedResponse)
        }
    }
}