请求过程
Alamofire中的静态方法都是调用SessionManager里面的方法，SessionManager的default里存放着默认的session，而SessionDelegate则实现了session的代理。
SessionDelegate类中:
1.声明了许多闭包，如果你想自定义接收响应的逻辑可以实现闭包
open var sessionDidBecomeInvalidWithError: ((URLSession, Error?) -> Void)?
/// Overrides default behavior for URLSessionDelegate method `urlSession(_:didReceive:completionHandler:)`.
open var sessionDidReceiveChallenge: ((URLSession, URLAuthenticationChallenge) -> (URLSession.AuthChallengeDisposition, URLCredential?))?
/// Overrides all behavior for URLSessionDelegate method `urlSession(_:didReceive:completionHandler:)` and requires the caller to call the `completionHandler`.
open var sessionDidReceiveChallengeWithCompletion: ((URLSession, URLAuthenticationChallenge, @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void) -> Void)?
2.看下回调的代理方法的实现
open func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
if let dataTaskDidReceiveData = dataTaskDidReceiveData {
dataTaskDidReceiveData(session, dataTask, data)
} else if let delegate = self[dataTask]?.delegate as? DataTaskDelegate {
delegate.urlSession(session, dataTask: dataTask, didReceive: data)
}
}
如果外界实现闭包dataTaskDidReceiveData,就直接回调闭包dataTaskDidReceiveData,不再下发到具体的代理DataTaskDelegate执行。
否则将任务下发到DataTaskDelegate去执行。DataTaskDelegate是怎么处理的？
func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
if initialResponseTime == nil { initialResponseTime = CFAbsoluteTimeGetCurrent() }
if let dataTaskDidReceiveData = dataTaskDidReceiveData {
dataTaskDidReceiveData(session, dataTask, data)
} else {
if let dataStream = dataStream {
dataStream(data)
} else {
mutableData.append(data)
}
let bytesReceived = Int64(data.count)
totalBytesReceived += bytesReceived
let totalBytesExpected = dataTask.response?.expectedContentLength ?? NSURLSessionTransferSizeUnknown
progress.totalUnitCount = totalBytesExpected
progress.completedUnitCount = totalBytesReceived
if let progressHandler = progressHandler {
progressHandler.queue.async { progressHandler.closure(self.progress) }
}
}
}
Request初探
明白Alamofire中一个请求的过程，是非常有必要的。先看下边的代码：
SessionManager.default.request(myGetUrlString, method: .get, parameters: ["array":getJsonFromArray(array)])
.response { (response) in
debugPrint(response)
}
上边的代码是最简单的一个请求，我们看看Alamofire.request中究竟干了什么？
open func request(
_ url: URLConvertible,
method: HTTPMethod = .get,
parameters: Parameters? = nil,
encoding: ParameterEncoding = URLEncoding.default,
headers: HTTPHeaders? = nil)
-> DataRequest
{
var originalRequest: URLRequest?
do {
originalRequest = try URLRequest(url: url, method: method, headers: headers)
let encodedURLRequest = try encoding.encode(originalRequest!, with: parameters)
return request(encodedURLRequest)
} catch {
return request(originalRequest, failedWith: error)
}
}
1.创建URLRequest
2.encoding是URLEncoding类型的.encoding.encode会调用到
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
}
urlRequest是URLRequestConvertible协议类型,URLRequestConvertible协议的目的是对URLRequest进行自定义的转换。
判断method,如果method是.get, .head, .delete类型,需要urlComponents.percentEncodedQuery进行百分号编码,并且query(parameters)参数拼接。
如果是post,需要设置请求头application/x-www-form-urlencoded; charset=utf-8", forHTTPHeaderField: "Content-Type,然后拼接参数query(parameters),将参数转换为二进制并赋值到urlRequest.httpBody
我们看看query(parameters)的实现:
private func query(_ parameters: [String: Any]) -> String {
var components: [(String, String)] = []
for key in parameters.keys.sorted(by: <) {
let value = parameters[key]!
components += queryComponents(fromKey: key, value: value)
}
return components.map { "\($0)=\($1)" }.joined(separator: "&")
}
(1)将所有参数的keys按照ASCII码排序
(2)创建components数组,遍历parameters,取出每一对ket-value
(3)调用queryComponents(key,value)，返回一个元祖，并添加到数组components
public func queryComponents(fromKey key: String, value: Any) -> [(String, String)] {
var components: [(String, String)] = []
if let dictionary = value as? [String: Any] {
for (nestedKey, value) in dictionary {
components += queryComponents(fromKey: "\(key)[\(nestedKey)]", value: value)
}
} else if let array = value as? [Any] {
for value in array {
components += queryComponents(fromKey: arrayEncoding.encode(key: key), value: value)
}
} else if let value = value as? NSNumber {
if value.isBool {
components.append((escape(key), escape(boolEncoding.encode(value: value.boolValue))))
} else {
components.append((escape(key), escape("\(value)")))
}
} else if let bool = value as? Bool {
components.append((escape(key), escape(boolEncoding.encode(value: bool))))
} else {
components.append((escape(key), escape("\(value)")))
}
return components
}
如果是dictionary和array类型，继续递归调用queryComponents,如果是NSNumber,Bool,String类型,将数据添加到components。
(4).components.map { "\($0)=\($1)" }转化为key-vaue的字符串数组,然后调用joined(separator: "&"),&作为分隔符，连接成我们需要的数据并返回
Request内部关系
open func request(_ urlRequest: URLRequestConvertible) -> DataRequest {
var originalRequest: URLRequest?
do {
originalRequest = try urlRequest.asURLRequest()
let originalTask = DataRequest.Requestable(urlRequest: originalRequest!)
let task = try originalTask.task(session: session, adapter: adapter, queue: queue)
let request = DataRequest(session: session, requestTask: .data(originalTask, task))
delegate[task] = request
if startRequestsImmediately { request.resume() }
return request
} catch {
return request(originalRequest, failedWith: error)
}
}
1.首先创建一个Requestable结构体对象，使用Requestable创建task。
为什么要有Requestable这个层,不直接把task·放到DataRequest? (1)我们知道task和request是一一对应的关系,关系是平级的,如果直接把task放到DataRequest`中,体现的是一种归属关系。
(2)降低耦合性。任务分层，架构思路更清晰
2.delegate[task] = request,绑定task和request , 方便SessionDelegate下发任务，用task直接检索到request。
delegate[task] = request我们在OC中看到这种写法都是数组或者字典,而这里的delegate是一个类。这是Swift的下标法。我们看看实现:
var requests: [Int: Request] = [:]
private let lock = NSLock()
open subscript(task: URLSessionTask) -> Request? {
get {
lock.lock() ; defer { lock.unlock() }
return requests[task.taskIdentifier]
}
set {
lock.lock() ; defer { lock.unlock() }
requests[task.taskIdentifier] = newValue
}
}
类可以重写下标,支持get,get方法。这种方式SessionDelegate不直接持有Request可以降低耦合。
3.if startRequestsImmediately { request.resume() },满足startRequestsImmediately,就会发起请求。 open var startRequestsImmediately: Bool = true,startRequestsImmediately默认会true。为什么要这么设计?而不直接调用request.resume()。这里是为了让用户可以通过在外界对startRequestsImmediately控制,而达到控制请求发不发起。
4.Request有许多不同的子类实现。DataRequest,DownloadRequest,UploadRequest,StreamRequest。这里是任务细分。
func task(session: URLSession, adapter: RequestAdapter?, queue: DispatchQueue) throws -> URLSessionTask {
do {
let urlRequest = try self.urlRequest.adapt(using: adapter)
return queue.sync { session.dataTask(with: urlRequest) }
} catch {
throw AdaptError(error: error)
}
}
DataRequest初始化:调用父类Request的init方法
init(session: URLSession, requestTask: RequestTask, error: Error? = nil) {
self.session = session
switch requestTask {
case .data(let originalTask, let task):
taskDelegate = DataTaskDelegate(task: task)
self.originalTask = originalTask
case .download(let originalTask, let task):
taskDelegate = DownloadTaskDelegate(task: task)
self.originalTask = originalTask
case .upload(let originalTask, let task):
taskDelegate = UploadTaskDelegate(task: task)
self.originalTask = originalTask
case .stream(let originalTask, let task):
taskDelegate = TaskDelegate(task: task)
self.originalTask = originalTask
}
delegate.error = error
delegate.queue.addOperation { self.endTime = CFAbsoluteTimeGetCurrent() }
}
1.使用枚举requestTask标识不同的类型。是工厂设计模式,根据用户传进来的枚举标识,走不同的初始化。
2.保存相关信息originalTask(Requestable类型)
requestTask有如下几种:
enum RequestTask {
case data(TaskConvertible?, URLSessionTask?)
case download(TaskConvertible?, URLSessionTask?)
case upload(TaskConvertible?, URLSessionTask?)
case stream(TaskConvertible?, URLSessionTask?)
}
这里的根据枚举类型的不同,会初始化不同的代理,DataTaskDelegate,DownloadTaskDelegate,UploadTaskDelegate,TaskDelegate。疑问:为什么已经有SessionDelegate,还要有这些代理?这些代理与SessionDelegate是什么关系?
上面的请求流程我们有提到:
1.SessionDelegate是session的代理,那么所有的代理方法都会首先来到SessionDelegate
2.SessionDelegate下发响应到具体的任务实现者SessionDelegate,其实就是整体和局部关系.
3.所有的响应都会来到SessionDelegate，如果SessionDelegate将所有的响应都自己处理，那将会很复杂，混乱.根据不同的需求将具体实现下发到对应的代理中处理，耦合性大大降低，架构的分层更加明显。
如上述请求过程中提到的:
open func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
if let dataTaskDidReceiveData = dataTaskDidReceiveData {
dataTaskDidReceiveData(session, dataTask, data)
} else if let delegate = self[dataTask]?.delegate as? DataTaskDelegate {
delegate.urlSession(session, dataTask: dataTask, didReceive: data)
}
}
SessionDelegate可以快速方便的通过dataTask 获取到request。然后拿到具体的delegate,如DataTaskDelegate。然后下发具体的任务,至于DataTaskDelegate中做了什么SessionDelegate根本就不需要知道。
总结:
