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详细解析几个和网络请求有关的类 （一） —— NSURLSess

2018-03-08  本文已影响129人  刀客传奇

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版本号 时间
V1.0 2018.03.08

前言

我们做APP发起网络请求，一般都是使用框架，这些框架的底层也都是苹果的API，接下来几篇就一起来看一下和网络有关的几个类。

NSURLSession

这个类是网络请求相关的最重要的类，可以说是网络请求的基础，任何请求都是在一个特定的会话中完成的。

NSURLSession是NSURLConnection的替代API。它提供影响政策的各种选择，以及各方面的政策从中检索NSURLRequest对象的机制网络。

NSURLSession可以绑定到代理对象。代理是在会话的整个生命周期中为某些事件调用，例如服务器认证或确定是否加载资源应该转换成下载。

NSURLSession实例是线程安全的。

默认的NSURLSession使用系统提供的代理并且是适合用来代替使用的现有代码
+ [NSURLConnection sendAsynchronousRequest：queue：completionHandler：]

NSURLSession创建表示NSURLSessionTask对象代表正在加载资源的操作。这些与之类似NSURLConnection对象，但提供更多的控制和统一委托模型。

NSURLSessionTask对象始终以挂起状态创建必须在执行之前发送- resume消息。

NSURLSessionTask的子类用于语法区分数据和文件下载。

NSURLSessionDataTask以一系列调用的形式接收资源
URLSession：dataTask：didReceiveData：代理方法。这是一种通常与检索对象关联的任务类型，以便立即解析对象。

NSURLSessionUploadTask与NSURLSessionDataTask不同在它的实例是如何构建的。上传任务通过引用要上传的文件或数据明确创建对象，或通过利用 - URLSession：task：needNewBodyStream：代理消息提供上传主体。

NSURLSessionDownloadTask将直接写入响应数据到一个临时文件。完成后，代理发送URLSession：downloadTask：didFinishDownloadingToURL：并给予机会将此文件移动到其沙盒容器中的永久位置，或读取文件。如果取消，NSURLSessionDownloadTask可以产生一个数据blob，可用于稍后恢复下载时间。

从iOS 9和Mac OS X 10.11开始，NSURLSessionStream就是可用作的任务类型。这允许直接的TCP / IP连接到一个给定的主机和端口与可选的安全握手和代理的导航。数据任务也可能通过HTTP Upgrade升级到NSURLSessionStream任务：头和适当的使用NSURLSessionConfiguration的流水线选项。请参阅RFC 2817和RFC 6455以获取有关Upgrade：header的信息以及关于将数据任务转换为流任务的注释。

NSURLSession 的优势

NSURLSession API

1. NSURLSession类

NS_CLASS_AVAILABLE(NSURLSESSION_AVAILABLE, 7_0)
@interface NSURLSession : NSObject

/*
 * The shared session uses the currently set global NSURLCache,
 * NSHTTPCookieStorage and NSURLCredentialStorage objects.
 */
@property (class, readonly, strong) NSURLSession *sharedSession;

/*
 * Customization of NSURLSession occurs during creation of a new session.
 * If you only need to use the convenience routines with custom
 * configuration options it is not necessary to specify a delegate.
 * If you do specify a delegate, the delegate will be retained until after
 * the delegate has been sent the URLSession:didBecomeInvalidWithError: message.
 */
+ (NSURLSession *)sessionWithConfiguration:(NSURLSessionConfiguration *)configuration;
+ (NSURLSession *)sessionWithConfiguration:(NSURLSessionConfiguration *)configuration delegate:(nullable id <NSURLSessionDelegate>)delegate delegateQueue:(nullable NSOperationQueue *)queue;

@property (readonly, retain) NSOperationQueue *delegateQueue;
@property (nullable, readonly, retain) id <NSURLSessionDelegate> delegate;
@property (readonly, copy) NSURLSessionConfiguration *configuration;

/*
 * The sessionDescription property is available for the developer to
 * provide a descriptive label for the session.
 */
@property (nullable, copy) NSString *sessionDescription;

/* -finishTasksAndInvalidate returns immediately and existing tasks will be allowed
 * to run to completion.  New tasks may not be created.  The session
 * will continue to make delegate callbacks until URLSession:didBecomeInvalidWithError:
 * has been issued. 
 *
 * -finishTasksAndInvalidate and -invalidateAndCancel do not
 * have any effect on the shared session singleton.
 *
 * When invalidating a background session, it is not safe to create another background
 * session with the same identifier until URLSession:didBecomeInvalidWithError: has
 * been issued.
 */
- (void)finishTasksAndInvalidate;

/* -invalidateAndCancel acts as -finishTasksAndInvalidate, but issues
 * -cancel to all outstanding tasks for this session.  Note task 
 * cancellation is subject to the state of the task, and some tasks may
 * have already have completed at the time they are sent -cancel. 
 */
- (void)invalidateAndCancel;

- (void)resetWithCompletionHandler:(void (^)(void))completionHandler;    /* empty all cookies, cache and credential stores, removes disk files, issues -flushWithCompletionHandler:. Invokes completionHandler() on the delegate queue if not nil. */
- (void)flushWithCompletionHandler:(void (^)(void))completionHandler;    /* flush storage to disk and clear transient network caches.  Invokes completionHandler() on the delegate queue if not nil. */

- (void)getTasksWithCompletionHandler:(void (^)(NSArray<NSURLSessionDataTask *> *dataTasks, NSArray<NSURLSessionUploadTask *> *uploadTasks, NSArray<NSURLSessionDownloadTask *> *downloadTasks))completionHandler; /* invokes completionHandler with outstanding data, upload and download tasks. */

- (void)getAllTasksWithCompletionHandler:(void (^)(NSArray<__kindof NSURLSessionTask *> *tasks))completionHandler API_AVAILABLE(macos(10.11), ios(9.0), watchos(2.0), tvos(9.0)); /* invokes completionHandler with all outstanding tasks. */

/* 
 * NSURLSessionTask objects are always created in a suspended state and
 * must be sent the -resume message before they will execute.
 */
// NSURLSessionTask对象必须在暂停状态下创建，必须发送- resume消息才执行。

/* Creates a data task with the given request.  The request may have a body stream. */
// 根据给定的请求创建数据任务，请求具有体流。
- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request;

/* Creates a data task to retrieve the contents of the given URL. */
// 创建数据任务以检索给定URL的内容
- (NSURLSessionDataTask *)dataTaskWithURL:(NSURL *)url;

/* Creates an upload task with the given request.  The body of the request will be created from the file referenced by fileURL */
// 根据给定的请求创建一个给定的上传任务，请求体根据fileURL文件引用创建
- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromFile:(NSURL *)fileURL;

/* Creates an upload task with the given request.  The body of the request is provided from the bodyData. */
// 根据给定的请求，创建一个上传任务，请求体根据bodyData提供
- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromData:(NSData *)bodyData;

/* Creates an upload task with the given request.  The previously set body stream of the request (if any) is ignored and the URLSession:task:needNewBodyStream: delegate will be called when the body payload is required. */
// 根据给定的请求创建上传任务，忽略以前请求的体流设置，当需要加载体的时候，
// 将会调用URLSession:task:needNewBodyStream: 代理方法。
- (NSURLSessionUploadTask *)uploadTaskWithStreamedRequest:(NSURLRequest *)request;

/* Creates a download task with the given request. */
// 根据指定的请求创建下载任务
- (NSURLSessionDownloadTask *)downloadTaskWithRequest:(NSURLRequest *)request;

/* Creates a download task to download the contents of the given URL. */
// 创建下载任务，下载给定URL的内容
- (NSURLSessionDownloadTask *)downloadTaskWithURL:(NSURL *)url;

/* Creates a download task with the resume data.  If the download cannot be successfully resumed, URLSession:task:didCompleteWithError: will be called. */
// 根据resume data创建一个下载任务，如果下载不能成功开始，那么会调用URLSession:task:didCompleteWithError: 
- (NSURLSessionDownloadTask *)downloadTaskWithResumeData:(NSData *)resumeData;

/* Creates a bidirectional stream task to a given host and port.
 */
// 创建给定主机和端口的双向流任务
- (NSURLSessionStreamTask *)streamTaskWithHostName:(NSString *)hostname port:(NSInteger)port API_AVAILABLE(macos(10.11), ios(9.0), tvos(9.0)) __WATCHOS_PROHIBITED;

/* Creates a bidirectional stream task with an NSNetService to identify the endpoint.
 * The NSNetService will be resolved before any IO completes.
 */
// 使用NSNetService识别端点以创建双向流任务。
// NSNetService将在任何IO完成之后解决
- (NSURLSessionStreamTask *)streamTaskWithNetService:(NSNetService *)service API_AVAILABLE(macos(10.11), ios(9.0), tvos(9.0)) __WATCHOS_PROHIBITED;

@end

下面我们就一起来看一下这些API的用法。

@property (class, readonly, strong) NSURLSession *sharedSession;

+ (NSURLSession *)sessionWithConfiguration:(NSURLSessionConfiguration *)configuration;
+ (NSURLSession *)sessionWithConfiguration:(NSURLSessionConfiguration *)configuration delegate:(nullable id <NSURLSessionDelegate>)delegate delegateQueue:(nullable NSOperationQueue *)queue;

@property (readonly, retain) NSOperationQueue *delegateQueue;
@property (nullable, readonly, retain) id <NSURLSessionDelegate> delegate;
@property (readonly, copy) NSURLSessionConfiguration *configuration;

@property (nullable, copy) NSString *sessionDescription;

- (void)finishTasksAndInvalidate;

- (void)invalidateAndCancel;

- (void)resetWithCompletionHandler:(void (^)(void))completionHandler;    
/* empty all cookies, cache and credential stores, removes disk files, issues -flushWithCompletionHandler:. Invokes completionHandler() on the delegate queue if not nil. */
// 清空所有的cookie、cache和凭证，移除磁盘文件，发送- flushWithCompletionHandler:消息，
// 如果代理队列不为空的话，就在代理队列中调用completionHandler()方法。

- (void)flushWithCompletionHandler:(void (^)(void))completionHandler;    
/* flush storage to disk and clear transient network caches.  Invokes completionHandler() on the delegate queue if not nil. */
// 将存储清空到磁盘并清除瞬态网络缓存。 如果不为nil，则在代理队列上调用completionHandler（）

- (void)getTasksWithCompletionHandler:(void (^)(NSArray<NSURLSessionDataTask *> *dataTasks, NSArray<NSURLSessionUploadTask *> *uploadTasks, NSArray<NSURLSessionDownloadTask *> *downloadTasks))completionHandler; 
/* invokes completionHandler with outstanding data, upload and download tasks. */
// 用数据，上传和下载任务调用completionHandler

- (void)getAllTasksWithCompletionHandler:(void (^)(NSArray<__kindof NSURLSessionTask *> *tasks))completionHandler API_AVAILABLE(macos(10.11), ios(9.0), watchos(2.0), tvos(9.0)); 
/* invokes completionHandler with all outstanding tasks. */
// 用所有未完成的任务调用completionHandler

2. NSURLSession分类NSURLSessionAsynchronousConvenience

/*
 * NSURLSession convenience routines deliver results to 
 * a completion handler block.  These convenience routines
 * are not available to NSURLSessions that are configured
 * as background sessions.
 *
 * Task objects are always created in a suspended state and 
 * must be sent the -resume message before they will execute.
 */
// NSURLSession便捷例程将结果传递给完成处理程序块。 这些便利例程不适用于配置为后台会话的NSURLSessions。 
// 任务对象总是在挂起状态创建，并且必须在执行之前发送-resume消息。

@interface NSURLSession (NSURLSessionAsynchronousConvenience)
/*
 * data task convenience methods.  These methods create tasks that
 * bypass the normal delegate calls for response and data delivery,
 * and provide a simple cancelable asynchronous interface to receiving
 * data.  Errors will be returned in the NSURLErrorDomain, 
 * see <Foundation/NSURLError.h>.  The delegate, if any, will still be
 * called for authentication challenges.
 */
// 数据任务的便利方法。 这些方法创建绕过普通代理调用进行响应和数据传递的任务，
// 并提供一个简单的可取消异步接口来接收数据。 错误将在NSURLErrorDomain中返回，
// 请参阅<Foundation / NSURLError.h>。 代理（如果有的话）仍将被要求认证挑战。
- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request completionHandler:(void (^)(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error))completionHandler;
- (NSURLSessionDataTask *)dataTaskWithURL:(NSURL *)url completionHandler:(void (^)(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error))completionHandler;

/*
 * upload convenience method.
 */
// 上传任务便利化方法
- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromFile:(NSURL *)fileURL completionHandler:(void (^)(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error))completionHandler;
- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromData:(nullable NSData *)bodyData completionHandler:(void (^)(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error))completionHandler;

/*
 * download task convenience methods.  When a download successfully
 * completes, the NSURL will point to a file that must be read or
 * copied during the invocation of the completion routine.  The file
 * will be removed automatically.
 */
// 下载任务便利化方法，当成功下载完成时，URL指向一个文件，
// 这个文件必须在完成调用中进行读和赋值，文件将被自动移除。
- (NSURLSessionDownloadTask *)downloadTaskWithRequest:(NSURLRequest *)request completionHandler:(void (^)(NSURL * _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error))completionHandler;
- (NSURLSessionDownloadTask *)downloadTaskWithURL:(NSURL *)url completionHandler:(void (^)(NSURL * _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error))completionHandler;
- (NSURLSessionDownloadTask *)downloadTaskWithResumeData:(NSData *)resumeData completionHandler:(void (^)(NSURL * _Nullable location, NSURLResponse * _Nullable response, NSError * _Nullable error))completionHandler;

@end

各种形形色色的任务

下面我们就看一下这些各种不同的任务。

这几个任务类的继承关系如下。

NSURLSessionTask 是一个抽象类，如果要使用那么只能使用它的子类，NSURLSessionTask 有两个子类。

各种形形色色的代理

我们看一下各种不同的代理。

大家可以很清楚看到其中的继承关系。

后记

本篇主要介绍了NSURLSession的各种API接口，以及几个任务类和代理的继承关系。

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