Alamofire(3)SessionManager

SessionManager

先来一张思维导图

SenssionManager.jpg

1：'default'

/// A default instance ofSessionManager, used by top-level Alamofire request methods, and suitable for use
/// directly for any ad hoc requests.

 public static let `default`: SessionManager = {
        let configuration = URLSessionConfiguration.default
        configuration.httpAdditionalHeaders = SessionManager.defaultHTTPHeaders

        return SessionManager(configuration: configuration)
    }()

'default'是个单利模式，默认设置编码方式、语言、和配置信息等。会在这里标入一些自己的特殊标记进行安全的校验，非法信息的拦截。

2:init

  private func commonInit(serverTrustPolicyManager: ServerTrustPolicyManager?) {
        session.serverTrustPolicyManager = serverTrustPolicyManager

        delegate.sessionManager = self

        delegate.sessionDidFinishEventsForBackgroundURLSession = { [weak self] session in
            guard let strongSelf = self else { return }
            DispatchQueue.main.async { strongSelf.backgroundCompletionHandler?() }
        }
    }

DispatchQueue.main.async when finished返回主线程操作。

If you need to handle your own events before the handler is called, then you need to override the
/// SessionDelegatesessionDidFinishEventsForBackgroundURLSessionand manually call the handler when finished.

3: download

 open func download(
        _ url: URLConvertible,
        method: HTTPMethod = .get,
        parameters: Parameters? = nil,
        encoding: ParameterEncoding = URLEncoding.default,
        headers: HTTPHeaders? = nil,
        to destination: DownloadRequest.DownloadFileDestination? = nil)
        -> DownloadRequest
    {
        do {
            let urlRequest = try URLRequest(url: url, method: method, headers: headers)
            let encodedURLRequest = try encoding.encode(urlRequest, with: parameters)
            return download(encodedURLRequest, to: destination)
        } catch {
            return download(nil, to: destination, failedWith: error)
        }
    }

下载请求默认get方法。parameters参数需要转成json格式与后台进行交互。否则会有编码格式问题。

4:encode

 public func encode(_ urlRequest: URLRequestConvertible, with parameters: Parameters?) throws -> URLRequest {
        var urlRequest = try urlRequest.asURLRequest()

        guard let parameters = parameters else { return urlRequest }

        if let method = HTTPMethod(rawValue: urlRequest.httpMethod ?? "GET"), encodesParametersInURL(with: method) {
            guard let url = urlRequest.url else {
                throw AFError.parameterEncodingFailed(reason: .missingURL)
            }

            if var urlComponents = URLComponents(url: url, resolvingAgainstBaseURL: false), !parameters.isEmpty {
                let percentEncodedQuery = (urlComponents.percentEncodedQuery.map { $0 + "&" } ?? "") + query(parameters)
                urlComponents.percentEncodedQuery = percentEncodedQuery
                urlRequest.url = urlComponents.url
            }
        } else {
            if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
                urlRequest.setValue("application/x-www-form-urlencoded; charset=utf-8", forHTTPHeaderField: "Content-Type")
            }

            urlRequest.httpBody = query(parameters).data(using: .utf8, allowLossyConversion: false)
        }

        return urlRequest
    }

GET方法会在url连接中拼接"&"符号。POST方法会在body里添加数据。
let percentEncodedQuery = (urlComponents.percentEncodedQuery.map { $0 + "&" } ?? "") + query(parameters)
5:upload

  open func upload(
        _ fileURL: URL,
        to url: URLConvertible,
        method: HTTPMethod = .post,
        headers: HTTPHeaders? = nil)
        -> UploadRequest
    {
        do {
            let urlRequest = try URLRequest(url: url, method: method, headers: headers)
            return upload(fileURL, with: urlRequest)
        } catch {
            return upload(nil, failedWith: error)
        }
    }