NSURLSession 通过session创建任务
@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;
- (void)flushWithCompletionHandler:(void (^)(void))completionHandler;
- (void)getTasksWithCompletionHandler:(void (^)(NSArray<NSURLSessionDataTask *> *dataTasks, NSArray<NSURLSessionUploadTask *> *uploadTasks, NSArray<NSURLSessionDownloadTask *> *downloadTasks))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.
- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request;
- (NSURLSessionDataTask *)dataTaskWithURL:(NSURL *)url;
- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromFile:(NSURL *)fileURL;
- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromData:(NSData *)bodyData;
- (NSURLSessionUploadTask *)uploadTaskWithStreamedRequest:(NSURLRequest *)request;
- (NSURLSessionDownloadTask *)downloadTaskWithRequest:(NSURLRequest *)request;
- (NSURLSessionDownloadTask *)downloadTaskWithURL:(NSURL *)url;
- (NSURLSessionDownloadTask *)downloadTaskWithResumeData:(NSData *)resumeData;
- (NSURLSessionStreamTask *)streamTaskWithHostName:(NSString *)hostname port:(NSInteger)port API_AVAILABLE(macos(10.11), ios(9.0), tvos(9.0)) __WATCHOS_PROHIBITED;
- (NSURLSessionStreamTask *)streamTaskWithNetService:(NSNetService *)service API_AVAILABLE(macos(10.11), ios(9.0), tvos(9.0)) __WATCHOS_PROHIBITED;
NSURLSessionConfiguration 通过configuration创建session
NSURLSessionTask 任务
NSURLSessionDataTask : NSURLSessionTask 普通任务
NSURLSessionUploadTask : NSURLSessionDataTask 上传任务
NSURLSessionDownloadTask : NSURLSessionTask 下载任务
NSURLSessionStreamTask : NSURLSessionTask
NSURLSessionDelegate session代理
NSURLSessionTaskDelegate <NSURLSessionDelegate>
NSURLSessionDataDelegate <NSURLSessionTaskDelegate>
NSURLSessionDownloadDelegate <NSURLSessionTaskDelegate>
NSURLSessionStreamDelegate <NSURLSessionTaskDelegate>
NSURLSession各文件关系
原文地址：http://www.cnblogs.com/yang-shuai/p/7872023.html