Alamofire4.x开源代码分析(五)进阶用法

Alamofire基于URLSession和Foundation URL的加载机制,为了更充分的了解和使用本框架,建议大家深刻的学习底层的网络实现.

建议阅读

Session Manager

Alamofire.request就是我们最外层的方法方法,内部通过Alamofire.SessionManager和默认的URLSessionConfiguration实现
下面两者是等价的

1Alamofire.request("https://httpbin.org/get") 
2
3
4let sessionManager = Alamofire.SessionManager.default
5sessionManager.request("https://httpbin.org/get")

通过URLSessionConfiguration我们可以自由的修改http请求头,超时时间等.应用程序可以未后台和临时会话创建管理器

Creating a Session Manager with Default Configuration

1let configuration = URLSessionConfiguration.default
2let sessionManager = Alamofire.SessionManager(configuration: configuration)

Creating a Session Manager with Background Configuration

1let configuration = URLSessionConfiguration.background(withIdentifier: "com.example.app.background")
2let sessionManager = Alamofire.SessionManager(configuration: configuration)

Creating a Session Manager with Ephemeral Configuration

1let configuration = URLSessionConfiguration.ephemeral
2let sessionManager = Alamofire.SessionManager(configuration: configuration)

自定义Session Configuration

1var defaultHeaders = Alamofire.SessionManager.defaultHTTPHeaders
2defaultHeaders["DNT"] = "1 (Do Not Track Enabled)"
3
4let configuration = URLSessionConfiguration.default
5configuration.httpAdditionalHeaders = defaultHeaders
6
7let sessionManager = Alamofire.SessionManager(configuration: configuration)

对于Authorization和Content-Type,不建议通过configuration来修改,Alamofire.request API提供的header来配置.

Session Delegate

默认情况下，Alamofire SessionManager会创建一个SessionDelegate对象来处理URLSession生成的所有各种回调,从中抽出最简单的实现方法. 对于特定需求的开发者,需要覆盖这些方法. ####重写闭包第一种自定义SessionDelegate方法是重写闭包,每个闭包都对应着SessionDelegate的实现. 举例

1/// Overrides default behavior for URLSessionDelegate method `urlSession(_:didReceive:completionHandler:)`.
2open var sessionDidReceiveChallenge: ((URLSession, URLAuthenticationChallenge) -> (URLSession.AuthChallengeDisposition, URLCredential?))?
3
4/// Overrides default behavior for URLSessionDelegate method `urlSessionDidFinishEvents(forBackgroundURLSession:)`.
5open var sessionDidFinishEventsForBackgroundURLSession: ((URLSession) -> Void)?
6
7/// Overrides default behavior for URLSessionTaskDelegate method `urlSession(_:task:willPerformHTTPRedirection:newRequest:completionHandler:)`.
8open var taskWillPerformHTTPRedirection: ((URLSession, URLSessionTask, HTTPURLResponse, URLRequest) -> URLRequest?)?
9
10/// Overrides default behavior for URLSessionDataDelegate method `urlSession(_:dataTask:willCacheResponse:completionHandler:)`.
11open var dataTaskWillCacheResponse: ((URLSession, URLSessionDataTask, CachedURLResponse) -> CachedURLResponse?)?
12

以下是如何使用taskWillPerformHTTPRedirection避免重定向到任何apple.com的问题

1let sessionManager = Alamofire.SessionManager(configuration: URLSessionConfiguration.default)
2let delegate: Alamofire.SessionDelegate = sessionManager.delegate
3
4delegate.taskWillPerformHTTPRedirection = { session, task, response, request in
5    var finalRequest = request
6
7    if
8        let originalRequest = task.originalRequest,
9        let urlString = originalRequest.url?.urlString,
10        urlString.contains("apple.com")
11    {
12        finalRequest = originalRequest
13    }
14
15    return finalRequest
16}

###子类覆盖父类方法另一种方法就是通过子类来重写父类方法

1class LoggingSessionDelegate: SessionDelegate {
2    override func urlSession(
3        _ session: URLSession,
4        task: URLSessionTask,
5        willPerformHTTPRedirection response: HTTPURLResponse,
6        newRequest request: URLRequest,
7        completionHandler: @escaping (URLRequest?) -> Void)
8    {
9        print("URLSession will perform HTTP redirection to request: \(request)")
10
11        super.urlSession(
12            session,
13            task: task,
14            willPerformHTTPRedirection: response,
15            newRequest: request,
16            completionHandler: completionHandler
17        )
18    }
19}

####Request request,download, upload stream这四个方法的返回值分别为DataRequest, DownloadRequest, UploadRequest StreamRequest，并且他们都继承自Request.每个子类都有专用的方法,如authenticate，validate，responseJSON和uploadProgress，都会返回调用者的实例，方便使用. Request可以被暂停,恢复,取消:

suspend() 暂停
resume() 恢复，在SessionManager中有一个属性：startRequestsImmediately。他控制这请求是不是立刻发起，默认的值为true。
cancel() 取消同时该请求的每一个监听对象都会受到一个错误回调

####Routing Requests 随着应用程序的扩展，在构建网络堆栈时，采用通用模式很重要. 该设计的重要部分是如何路由您的请求. Alamofire URLConvertible和URLRequestConvertible协议以及路由器设计模式就是为之设计的. 路由的概念就是中转站的意思，在Alamofire中，String, URL, URLComponents实现了URLConvertible协议.

1let urlString = "https://httpbin.org/post"
2Alamofire.request(urlString, method: .post)
3
4let url = URL(string: urlString)!
5Alamofire.request(url, method: .post)
6
7let urlComponents = URLComponents(url: url, resolvingAgainstBaseURL: true)!
8Alamofire.request(urlComponents, method: .post)

采用URLConvertible协议的类型可用于构造URL，然后用于内部构造URL请求。默认情况下，string，URL和URLComponent准守URLConvertible协议，允许将任何一个作为URL参数传递发送请求，上传和下载等方法：

1let urlString = "https://httpbin.org/post"
2Alamofire.request(urlString, method: .post)
3
4let url = URL(string: urlString)!
5Alamofire.request(url, method: .post)
6
7let urlComponents = URLComponents(url: url, resolvingAgainstBaseURL: true)!
8Alamofire.request(urlComponents, method: .post)

遵守URLConvertible协议,可以方便我们便捷的使用model与服务器生成映射关系.

1extension User: URLConvertible {
2    static let baseURLString = "https://example.com"
3
4    func asURL() throws -> URL {
5    	let urlString = User.baseURLString + "/users/\(username)/"
6        return try urlString.asURL()
7    }
8}
9let user = User(username: "mattt")
10Alamofire.request(user) // https://example.com/users/mattt