NSURLSession全面学习笔记

@在将要向请求发送认证挑战时回调这个啊方法
- (void)connection:(NSURLConnection *)connection willSendRequestForAuthenticationChallenge:(NSURLAuthenticationChallenge *)challenge;

@当网络请求失败时会回调这个方法
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error;

NSURLConnectionDataDelegate

除非你是使用Newsstand这个框架，否则你也应该遵守 NSURLConnectionDataDelegate 这个协议，这个协议在上传文件时会提供进度信息，在下载数据时会周期性的回调下载的数据片等等。

主要的协议方法：

@当收到响应的时候会回调这个方法
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response;

@在获取从服务器端返回的数据时这个方法会被周期性的回调，每次的data都是服务器端新返回的数据，我们把这些数据拼接在一起就可以得到完整的数据。
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data;

@在上传请求体的数据时，回调这个方法来显示上传的进度
- (void)connection:(NSURLConnection *)connection didSendBodyData:(NSInteger)bytesWritten totalBytesWritten:(NSInteger)totalBytesWritten totalBytesExpectedToWrite:(NSInteger)totalBytesExpectedToWrite;

@网络请求成功完成的时候会回调这个方法
- (void)connectionDidFinishLoading:(NSURLConnection *)connection;

NSURLConnectionDownloadDelegate

如果使用了Newsstand这个框架，那么这个协议也应该遵守。

2.NSURLConnection的基础API

同步加载网络请求：

+ (NSData *)sendSynchronousRequest:(NSURLRequest *)request returningResponse:(NSURLResponse * _Nullable *)response error:(NSError * _Nullable *)error;

异步加载网络请求：

@使用NSURLRequest创建一个NSURLConnection对象，并且给这个对象指定代理，然后返回这个对象，并开始网络请求
+ (NSURLConnection *)connectionWithRequest:(NSURLRequest *)request delegate:(id)delegate;

@通过NSURLRequest创建一个NSURLConnection对象，并给它指定delegate，返回这个对象，并开始网络请求
- (instancetype)initWithRequest:(NSURLRequest *)request delegate:(id)delegate;

@和上面方法一样，只是多了一个是否立刻开始进行网络请求
- (instancetype)initWithRequest:(NSURLRequest *)request delegate:(id)delegate startImmediately:(BOOL)startImmediately;

@通过NSURLRequest进行异步请求，请求完成之后在执行的队列里执行回调的操作
+ (void)sendAsynchronousRequest:(NSURLRequest *)request queue:(NSOperationQueue *)queue completionHandler:(void (^)(NSURLResponse *response, NSData *data, NSError *connectionError))handler;

开始和取消网络请求：

@开始网络请求
- (void)start;

@取消网络请求，注意只有在异步的时候才能取消，同步请求的时候是不能取消网络请求的。
- (void)cancel;

3.NSURLConnection的简单使用

1.get请求

//由于NSURLRequest默认的就是get请求，所以这里不需要设置HTTPmethod
    NSString *urlString = @"http://www.qingmooc.com";
    NSURL *url = [NSURL URLWithString:urlString];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    NSURLResponse *response;
    NSError *error = 0;
    //NSURLConnection 发送同步请求
    /*
     @param1:请求对象
     @param2:响应头
     @param3:错误信息
     @return:响应体-返回的数据
     **/
    NSData *data = [NSURLConnection sendSynchronousRequest:request returningResponse:&response error:&error];

2.异步post请求

NSString *urlString = @"http://www.qingmooc.com";
    NSURL *url = [NSURL URLWithString:urlString];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    //由于方法不是默认的get方法，所以要设置方法参数
    request.HTTPMethod = @"POST";
    //设置请求超时时间
    request.timeoutInterval = 10.0;
    //设置请求体
    NSString *params = [NSString stringWithFormat:@"username=%@", @"pdd"];
    request.HTTPBody = [params dataUsingEncoding:NSUTF8StringEncoding];
    //设置请求头
    [request setValue:[[UIDevice currentDevice] systemVersion] forHTTPHeaderField:@"User-Agent"];
    //NSURLConnection 发送异步请求
    /*
     @param1:请求对象
     @param2:队列，决定block在哪个队列调用
     @param3:block块，当请求结束之后j就会i调用block 参数：response：响应头 data：响应体
     **/
    [NSURLConnection sendAsynchronousRequest:request queue:[NSOperationQueue mainQueue] completionHandler:^(NSURLResponse * _Nullable response, NSData * _Nullable data, NSError * _Nullable connectionError) {

    }];

@interface NSURLConnectionDemoViewController ()<NSURLConnectionDelegate, NSURLConnectionDataDelegate>

@property (nonatomic, strong)NSURLConnection *connection;
@property (nonatomic, strong)NSFileHandle *handle;
@property (nonatomic, assign)NSInteger currentLength;
@property (nonatomic, assign)NSInteger totalLength;
@property (nonatomic, strong)NSString *filePath;

@end

@implementation NSURLConnectionDemoViewController

- (void)viewDidLoad {
    [super viewDidLoad];

}
- (void)touchesBegan:(NSSet<UITouch *> *)touches withEvent:(UIEvent *)event
{
    NSString *urlString = @"http://www.qingmooc.com";
    NSURL *url = [NSURL URLWithString:urlString];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    //设置请求超时时间
    request.timeoutInterval = 10.0;
    //设置请求体
    NSString *params = [NSString stringWithFormat:@"username=%@", @"pdd"];
    request.HTTPBody = [params dataUsingEncoding:NSUTF8StringEncoding];
    //设置请求头
    [request setValue:[[UIDevice currentDevice] systemVersion] forHTTPHeaderField:@"User-Agent"];
    //通过Content-rRange请求头部来进行断点下载
    [request setValue:[NSString stringWithFormat:@"bytes=%zd-", self.currentLength] forHTTPHeaderField:@"Content-Range"];
    self.connection = [[NSURLConnection alloc] initWithRequest:request delegate:self];
}

#pragma mark - 
  
- (void)connection:(NSURLConnection *)connection didFailWithError:(NSError *)error
{
    NSLog(@"网络请求失败了");
}

#pragma mark - 
  
//收到响应的时候回调这个方法
- (void)connection:(NSURLConnection *)connection didReceiveResponse:(NSURLResponse *)response
{
    //只在第一次开始下载的时候才进行下面的操作
    if (self.currentLength > 0) {
        return;
    }
    //创建文件
    NSString *caches = NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES).lastObject;
    NSString *filePath = [caches stringByAppendingString:response.suggestedFilename];
    self.filePath = filePath;
    [[NSFileManager defaultManager] createFileAtPath:self.filePath contents:nil attributes:nil];
    //得到文件的总长度，为了显示下载进度
    self.totalLength = response.expectedContentLength;
}
- (void)connection:(NSURLConnection *)connection didReceiveData:(NSData *)data
{
    //使用文件句柄把数据b拼接到文件结尾
    self.handle = [NSFileHandle fileHandleForWritingAtPath:self.filePath];
    [self.handle seekToEndOfFile];
    [self.handle writeData:data];
    //由于又获取了新的数据，所以更新currentLength
    NSData *fileData = [[NSFileManager defaultManager] contentsAtPath:self.filePath];
    self.currentLength = fileData.length;
    //显示下载进度
    NSLog(@"progress = %ld", self.currentLength / self.totalLength);
}
- (void)connectionDidFinishLoading:(NSURLConnection *)connection
{
    [self.handle closeFile];
    self.handle = nil;
}
@end

@property NSURLRequestCachePolicy cachePolicy;

typedef enum NSURLRequestCachePolicy : NSUInteger {
    NSURLRequestUseProtocolCachePolicy = 0,
    NSURLRequestReloadIgnoringLocalCacheData = 1,
    NSURLRequestReloadIgnoringLocalAndRemoteCacheData = 4,
    NSURLRequestReloadIgnoringCacheData = NSURLRequestReloadIgnoringLocalCacheData,
    NSURLRequestReturnCacheDataElseLoad = 2,
    NSURLRequestReturnCacheDataDontLoad = 3,
    NSURLRequestReloadRevalidatingCacheData = 5
} NSURLRequestCachePolicy;

设置请求方法和请求体：

//默认方法是get
@property(copy) NSString *HTTPMethod;
@property(copy) NSData *HTTPBody;

设置请求头

//字典类型，返回所有的请求头
@property(copy) NSDictionary<NSString *,NSString *> *allHTTPHeaderFields;
//添加请求头，注意 ，只添加key，不设置value
- (void)addValue:(NSString *)value forHTTPHeaderField:(NSString *)field;
//为请求头设值
- (void)setValue:(NSString *)value forHTTPHeaderField:(NSString *)field;

设置请求行为：

//设置请求超时时间
timeoutInterval
//布尔值，设置是否使用默认的Cookie处理方法，默认是YES
HTTPShouldHandleCookies
//布尔值，设置是否支持蜂窝网络，默认是YES
allowsCellularAccess

//预期的响应的实体的长度，常用它来显示进度
expectedContentLength
//响应数据的建议的文件名，常用它来拼接成存放实体文件的路径
suggestedFilename
//响应的MIME类型
MIMEType
//响应的URL
URL

NSURLRsponse的相关属性非常有限，下面看一下NSHTTPURLResponse，通过NSHTTPURLResponse可以获取响应的起始行的状态码和描述短语，还有响应头的信息。

//字典类型，返回响应头的信息
allHeaderFields
//通过状态码返回描述性短语
+ (NSString *)localizedStringForStatusCode:(NSInteger)statusCode;
//返回响应的状态码
statusCode

@创建一个默认的session Configuration对象
    [NSURLSessionConfiguration defaultSessionConfiguration];

@创建一个暂时性的session Configuration对象
    [NSURLSessionConfiguration ephemeralSessionConfiguration];

@创建一种background session Configuration对象，使用这种Configuration对象初始化的session对象，允许upload task和download task在后台运行
//identifier:创建的Configuration对象的唯一标识，主要用在当应用重启时使用这个identifier再创建一个新的Configuration对象
+ (NSURLSessionConfiguration *)backgroundSessionConfigurationWithIdentifier:(NSString *)identifier;

• 设置一些通用的属性

//这个属性用来设置请求头，设置的请求头会应用到由session创建的所有task中去。
HTTPAdditionalHeaders
//设置是否支持蜂窝网络
allowsCellularAccess
//设置网络服务的类型，是一个枚举值
networkServiceType
//等待数据的超时时间
timeoutIntervalForRequest
//设置传输整个资源的超时时间
timeoutIntervalForResource

• 设置Cookie策略

//枚举类型，设置Cookie是否应该被接受
NSHTTPCookieAcceptPolicy
//设置请求时是否应该带上Cookie
HTTPShouldSetCookies

• 设置缓存策略

//设置请求的缓存策略，它是一个枚举值，决定了什么时候从缓存中返回response
requestCachePolicy

- (NSURLSessionDataTask *)dataTaskWithURL:(NSURL *)url

创建。

• upload task

  upload task一般是以文件的形式上传数据，并且它支持在后台上传数据。使用

- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromData:(NSData *)bodyData

创建

• download task

  download task是以文件的形式获取从服务器返回的数据，并且存储到磁盘，支持后台下载。使用

- (NSURLSessionDownloadTask *)downloadTaskWithURL:(NSURL *)url;

//当session对象失效时会调用这个方法。
- (void)URLSession:(NSURLSession *)session didBecomeInvalidWithError:(nullable NSError *)error;

//当发生session级别的认证挑战时会调用这个方法
- (void)URLSession:(NSURLSession *)session didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge
                                             completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential * _Nullable credential))completionHandler;
//当session队列中的所有消息都分发完成时调用这个方法
- (void)URLSessionDidFinishEventsForBackgroundURLSession:(NSURLSession *)session;

NSURLSessionTaskDelegate

这是一个task-level的协议，它可以处理所以task的回调，包括data task，upload task，download task。这个协议方法主要处理的是所有task的一些公共的问题。其主要的API如下：

1.处理task的生命周期改变

//网络请求完成时调用
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error;

2.处理重定向

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task willPerformHTTPRedirection:(NSHTTPURLResponse *)response newRequest:(NSURLRequest *)request completionHandler:(void (^)(NSURLRequest *))completionHandler;

3.处理upload task相关

//在上传文件的过程中这个方法会被周期性的回调
bytesSent:自上次调用这个方法以来，总共传送的数据的字节数
totalBytesSent:所有已传送的数据的字节数
totalBytesExpectedToSend:期望发送的数据的总字节数
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didSendBodyData:(int64_t)bytesSent totalBytesSent:(int64_t)totalBytesSent totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend;

4.处理认证挑战

- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didReceiveChallenge:(NSURLAuthenticationChallenge *)challenge completionHandler:(void (^)(NSURLSessionAuthChallengeDisposition disposition, NSURLCredential *credential))completionHandler;

• NSURLSessionDownloadDelegate

  这是一个task-level的协议，专门用来处理NSURLSessionDownloadTask相关的回调。主要的API如下：

  1.处理download task的生命周期改变

//这个方法是必须实现的，当下载完成的时候调用这个方法
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location;

2.继续已经暂停的下载

fileOffset：这个字节长度是已经下载在磁盘中的数据大小，这部分不需要再重新下载，如果缓存策略不允许使用已经存在的内容，则这个值为0
expectedTotalbytes：想要下载的这个文件的总长度
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didResumeAtOffset:(int64_t)fileOffset expectedTotalBytes:(int64_t)expectedTotalBytes;

3.提供下载的进度

//这个方法是在下载的过程中华周期性的调用的
bytesWritten：从上一次调用到这一次调用这期间下载的数据的字节数
totalBytesWritten：总共下载的数据的字节数
totalBytesExpectedToWrite：预期要下载的数据的总长度
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite;

• NSURLSessionDataTask

  这是一个task-level的协议，用来处理NSURLSessionDataTask和NSURLSessionUploadTask相关的额回调。主要API如下：

  1.处理task的生命周期变化

当data task收到了来自服务器的响应头时会回调这个方法
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler;

当data task转变成了download task时会调用这个方法
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didBecomeDownloadTask:(NSURLSessionDownloadTask *)downloadTask;

2.获取数据

这个方法会周期性的调用，data task每收到一部分数据就会调用一次 这个方法，把所有的数据拼接在一起就能获得完整的数据
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data;

3.处理缓存

询问代理data task或upload task是否应该将响应存储在缓存中
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask willCacheResponse:(NSCachedURLResponse *)proposedResponse completionHandler:(void (^)(NSCachedURLResponse *cachedResponse))completionHandler;

5.NSURLSession的基础API

• 创建一个session对象

sharedSession
+ (NSURLSession *)sessionWithConfiguration:(NSURLSessionConfiguration *)configuration;

这个初始化方法可以指定session的代理以及代理的回调方法在哪个队列中执行
+ (NSURLSession *)sessionWithConfiguration:(NSURLSessionConfiguration *)configuration delegate:(nullable id <NSURLSessionDelegate>)delegate delegateQueue:(nullable NSOperationQueue *)queue;

• 创建data task

- (NSURLSessionDataTask *)dataTaskWithRequest:(NSURLRequest *)request;

- (NSURLSessionDataTask *)dataTaskWithURL:(NSURL *)url;

- (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;

• 创建download task

- (NSURLSessionDownloadTask *)downloadTaskWithRequest:(NSURLRequest *)request;

- (NSURLSessionDownloadTask *)downloadTaskWithURL:(NSURL *)url;

用这个resume data去创建一个之前取消了或者失败了的download task，再下载的时候就不用下载这部分数据
- (NSURLSessionDownloadTask *)downloadTaskWithResumeData:(NSData *)resumeData;

- (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;

• 创建upload task

- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromFile:(NSURL *)fileURL;

- (NSURLSessionUploadTask *)uploadTaskWithRequest:(NSURLRequest *)request fromData:(NSData *)bodyData;

- (NSURLSessionUploadTask *)uploadTaskWithStreamedRequest:(NSURLRequest *)request;

- (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;

6.使用NSURLSession进行简单的网络请求

• 简单的get请求

NSURLSession *session = [NSURLSession sharedSession];
    NSURL *url = [NSURL URLWithString:@"http://120.25.226.186.32812/login"];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];
    /**
     data:响应实体
     response:响应，包括响应起始行和响应头
     error:出现错误时error不为nil
     */
    NSURLSessionDataTask *dataTask =[session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {

    }];
    [dataTask resume];

• 简单的post请求

//创建Configuration对象，并设置各种属性
    NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];
    configuration.timeoutIntervalForRequest = 10.0;
    configuration.allowsCellularAccess = YES;
    NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration];
    NSURL *url = [NSURL URLWithString:@"http://120.25.226.186.32812/login"];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    request.HTTPMethod = @"POST";
    request.HTTPBody = [@"username=520it&pwd=520it&type=JSON" dataUsingEncoding:NSUTF8StringEncoding];
    NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        //通过打印发现回调方法是在子线程中调用，所以如果要在回调方法中拿到数据刷新UI，必须要回到主线程刷新UI
    }];
    [dataTask resume];

7.使用NSURLSessionDownloadTask进行断点下载

使用NSURLSessionDownloadTask进行断点下载非常方便，因为它提供了两个便捷的API：

取消下载：

- (void)cancelByProducingResumeData:(void (^)(NSData * _Nullable resumeData))completionHandler;

利用已经下载的数据，创建一个新的task，继续下载：

- (NSURLSessionDownloadTask *)downloadTaskWithResumeData:(NSData *)resumeData;

具体代码如下：

@interface NSURLSessionDownloadTaskViewController2 ()<NSURLSessionDownloadDelegate>
@property (nonatomic, strong)NSURLSessionDownloadTask *downloadTask;
@property (nonatomic, strong)NSURLSession *session;
@property (nonatomic, strong)NSData *currentData;
@end

@implementation NSURLSessionDownloadTaskViewController2

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
}

- (NSURLSessionDownloadTask *)downloadTask
{
    if (!_downloadTask) {
        _session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[NSOperationQueue mainQueue]];
        NSURL *url = [NSURL URLWithString:@"https://qingmooc-v1.oss-cn-qingdao.aliyuncs.com/zips/4b0bb06ebae3ff517069a36f6acbd514.zip"];
        NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
        _downloadTask = [_session downloadTaskWithRequest:request];

    }
    return _downloadTask;
}

#pragma mark - 
  
//在下载完成的时候调用
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location
{
    NSString *documentPath = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES).lastObject;
    NSString *filePath = [documentPath stringByAppendingPathComponent:@"file.zip"];
    NSError *error;

    [[NSFileManager defaultManager] moveItemAtURL:location toURL:[NSURL fileURLWithPath:filePath] error:&error];
    if (!error) {
        NSLog(@"成功");
    }else {
        NSLog(@"失败");
    }
}

//周期性的调用这个方法传送下载进度
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
      didWriteData:(int64_t)bytesWritten
 totalBytesWritten:(int64_t)totalBytesWritten
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite
{
    //显示下载进度
    _progress.progress = totalBytesWritten*1.0 / totalBytesExpectedToWrite;
}


- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask
 didResumeAtOffset:(int64_t)fileOffset
expectedTotalBytes:(int64_t)expectedTotalBytes
{

}
- (IBAction)start:(id)sender {
    [self.downloadTask resume];
    NSLog(@"开始");
}

- (IBAction)pause:(id)sender {
    __weak typeof(self) weakSelf = self;
    [self.downloadTask cancelByProducingResumeData:^(NSData * _Nullable resumeData) {
        weakSelf.currentData = resumeData;
    }];
    NSLog(@"暂停");
}

- (IBAction)restart:(id)sender {
    _downloadTask = [_session downloadTaskWithResumeData:_currentData];

    [_downloadTask resume];
    NSLog(@"重新开始");
}

@end

有非常重要的一点是，如果我们在创建task的时候使用了有block的API，那么使用这种方式创建的task，是不会调用它的代理方法的。

8.使用NSURLSessionDataTask进行断点下载

使用NSURLSessionDataTask进行断点下载主要是运用HTTP请求的一个请求头，这个请求头是用来进行范围请求的，就是Content-Range，下面是具体的代码：

@interface NSURLSessionDataTaskViewController ()<NSURLSessionDataDelegate, NSURLSessionTaskDelegate>
@property (weak, nonatomic) IBOutlet UIProgressView *progress;
@property (nonatomic, strong)NSURLSessionDataTask *dataTask;
@property (nonatomic, assign)int currentLength;
@property (nonatomic, assign)int totalLength;
@property (nonatomic, strong)NSFileHandle *fileHandle;

@end

@implementation NSURLSessionDataTaskViewController

- (void)viewDidLoad {
    [super viewDidLoad];

}

- (NSURLSessionDataTask *)dataTask
{
    if (!_dataTask) {
        NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[NSOperationQueue mainQueue]];
        NSString *urlString = @"https://qingmooc-v1.oss-cn-qingdao.aliyuncs.com/zips/4b0bb06ebae3ff517069a36f6acbd514.zip";
        NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:urlString]];
        NSString *range = [NSString stringWithFormat:@"bytes=%d-", self.currentLength];
        [request setValue:range forHTTPHeaderField:@"Range"];
        _dataTask = [session dataTaskWithRequest:request];
    }
    return _dataTask;
}

#pragma mark - 
  
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
didReceiveResponse:(NSURLResponse *)response
 completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler
{
    _totalLength = (int)response.expectedContentLength;
    /**
    typedef NS_ENUM(NSInteger, NSURLSessionResponseDisposition) {
        NSURLSessionResponseCancel = 0,                            //取消(默认的做法)
        NSURLSessionResponseAllow = 1,                             //允许(接收数据)
        NSURLSessionResponseBecomeDownload = 2,
        NSURLSessionResponseBecomeStream API_AVAILABLE(macos(10.11), ios(9.0), watchos(2.0), tvos(9.0)) = 3,
    } NS_ENUM_AVAILABLE(NSURLSESSION_AVAILABLE, 7_0);
*/
    //注意，这句话非常重要，必须要实现，否则下面一个协议方法就不会被调用
    completionHandler(NSURLSessionResponseAllow);
}

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask
    didReceiveData:(NSData *)data
{
    NSString *document = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES).lastObject;
    NSString *filePath = [document stringByAppendingPathComponent:@"file.zip"];
    [[NSFileManager defaultManager] createFileAtPath:filePath contents:nil attributes:nil];
    _fileHandle = [NSFileHandle fileHandleForWritingAtPath:filePath];
    [_fileHandle seekToEndOfFile];
    [_fileHandle writeData:data];
    _currentLength += data.length;
    _progress.progress = _currentLength*1.0 / _totalLength;
}


#pragma mark - 
  
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
didCompleteWithError:(nullable NSError *)error
{

    if (!error) {
        [_fileHandle closeFile];
        _fileHandle = nil;
        NSLog(@"成功");
    }
}

- (IBAction)start:(id)sender
{
    [self.dataTask resume];
}
- (IBAction)pause:(id)sender
{
    [self.dataTask suspend];
}
- (IBAction)restart:(id)sender
{
    [self.dataTask resume];
}

@end

@interface NSURLSessionUploadTaskViewController ()<NSURLSessionTaskDelegate>
@property (weak, nonatomic) IBOutlet UIProgressView *progress;
@property (nonatomic, strong)NSURLSessionUploadTask *uploadTask;

@end

@implementation NSURLSessionUploadTaskViewController

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view from its nib.
}

- (NSURLSessionUploadTask *)uploadTask
{
    if (!_uploadTask) {
        NSURLSession *session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[NSOperationQueue mainQueue]];
        NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"http://120.25.226.186:32812/upload"]];
        request.HTTPMethod = @"POST";
        NSString *document = NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, YES).lastObject;
        NSString *filePath = [document stringByAppendingPathComponent:@"file.zip"];
        _uploadTask = [session uploadTaskWithRequest:request fromFile:[NSURL fileURLWithPath:filePath]];
    }
    return _uploadTask;
}

- (IBAction)upload:(id)sender
{
    [_uploadTask resume];
}

#pragma mark - 
  
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task
   didSendBodyData:(int64_t)bytesSent
    totalBytesSent:(int64_t)totalBytesSent
totalBytesExpectedToSend:(int64_t)totalBytesExpectedToSend
{
    _progress.progress = totalBytesSent*1.0 / totalBytesExpectedToSend;
}

@end