NSURLSession 简介

步骤:
(1) 得到 session 对象, NSURLSession *session = [NSURLSession sharedSession];
(2) 创建一个task, 任何一个请求都是一个任务

NSURLSessionDataTask // 普通任务
NSURLSessionDownLoadTask // 文件下载任务
NSURLSessionUploadTask // 文件上传任务

NSURLSession 实现 GET 请求

- (IBAction)login {
    //判断账号与密码是否为空
    NSString *name = _accountText.text;
    if (name == nil || name.length == 0){
        NSLog(@"请输入账号");
        return;
    }

    NSString *pwd = _pwdText.text;
    if (pwd == nil || pwd.length == 0){
        NSLog(@"请输入密码");
        return;
    }

    //创建URL
    NSString *urlStr = [NSString stringWithFormat:@"http://localhost:8080/Server/login?username=%@&pwd=%@", name, pwd];

    //用NSURLSession实现登录
    [self sessionWithUrl:urlStr];
}

- (void)sessionWithUrl:(NSString *)urlStr{
    NSURL *url = [NSURL URLWithString:urlStr];

    //用NSURLConnection实现登录
     NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    request.HTTPMethod = @"GET";

    NSURLSession *session = [NSURLSession sharedSession];
    NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        if (data == nil || error != nil) {
            NSLog(@"请求失败");
            return;
        }

        //JSON解析
        NSError *error2;
        NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableLeaves error:&error2];
        if (error2) {
            NSLog(@"解析失败 -- %@", error2);
        }
        NSLog(@"数据为 -- %@", dict);
    }];
    [task resume];

}

NSURLSession 实现 POST 请求:

- (IBAction)login {
    //判断账号与密码是否为空
    NSString *name = _accountText.text;
    if (name == nil || name.length == 0){
        NSLog(@"请输入账号");
        return;
    }

    NSString *pwd = _pwdText.text;
    if (pwd == nil || pwd.length == 0){
        NSLog(@"请输入密码");
        return;
    }


    //用NSURLSession实现登录
    //创建URL
    NSString *urlStr = @"http://localhost:8080/Server/login";
    [self sessionWithUrl:urlStr];
}

- (void)sessionWithUrl:(NSString *)urlStr{
    NSURL *url = [NSURL URLWithString:urlStr];

    //用NSURLConnection实现登录
     NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    //POST请求
    request.HTTPMethod = @"POST";
    NSString *prama = [NSString stringWithFormat:@"username=%@&pwd=%@", _accountText.text, _pwdText.text];
    //中文转码
    [prama stringByAddingPercentEscapesUsingEncoding:NSUTF8StringEncoding];
    //转码
    request.HTTPBody = [prama dataUsingEncoding:NSUTF8StringEncoding];

    NSURLSession *session = [NSURLSession sharedSession];
    NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        if (data == nil || error != nil) {
            NSLog(@"请求失败");
            return;
        }

        //JSON解析
        NSError *error2;
        NSDictionary *dict = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingMutableLeaves error:&error2];
        if (error2) {
            NSLog(@"解析失败 -- %@", error2);
        }
        NSLog(@"数据为 -- %@", dict);
    }];
    [task resume];

}

NSURLSession 实现 断点续传:

//断点下载
@property (nonatomic, strong) NSURLSession *session;
@property (nonatomic, strong) NSURLSessionDownloadTask *task;
@property (nonatomic, strong) NSData *resumeData;
@property (weak, nonatomic) IBOutlet UIProgressView *progressView;

//懒加载
- (NSURLSession *)session{
    if (!_session) {
        NSURLSessionConfiguration *cfg = [NSURLSessionConfiguration defaultSessionConfiguration];
        _session = [NSURLSession sessionWithConfiguration:cfg delegate:self delegateQueue:[NSOperationQueue mainQueue]];
    }
    return _session;
}

/**
 *  NSURLSession实现断点下载
 */
- (IBAction)startDowbLoad:(id)sender {
    NSURL *url = [NSURL URLWithString:@"http://localhost:8080/Server/resources/videos/minion_01.mp4"];
    self.task = [self.session downloadTaskWithURL:url];
    //开始下载
    [self.task resume];
}

/**
 *  暂停下载
 */
- (IBAction)pauseDownLoad:(id)sender{
    __weak typeof (self) vc = self;
    /**
     *  @param resumeData 包含了继续下载开始的位置和下载的URL
     */
    [self.task cancelByProducingResumeData:^(NSData * _Nullable resumeData) {
        vc.resumeData = resumeData;
        self.task = nil;
    }];
}

/**
 *  恢复下载
 */
- (IBAction)resumeDownLoad:(id)sender {
    //传入上次下载的数据
    self.task = [self.session downloadTaskWithResumeData:self.resumeData];
    //开始下载
    [self.task resume];
    //清空
    self.resumeData = nil;
}

#pragma mark - NSURLSessionDelegate 代理方法
//下载完成调用
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location{
    //下载完成后,写入 caches 文件中
    NSString *cachesFile = [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:downloadTask.response.suggestedFilename];

    NSFileManager *mgr = [NSFileManager defaultManager];
    [mgr moveItemAtPath:location.path toPath:cachesFile error:nil];
}

/**
 *  下载过程中调用这个方法, 每当下载完(写完)一部分时会调用, (可能被调用多次)
 *
 *  @param bytesWritten              这次写了多少
 *  @param totalBytesWritten         累计写了多少
 *  @param totalBytesExpectedToWrite 文件的总长度
 */
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{
    self.progressView.progress = (double)totalBytesWritten / totalBytesExpectedToWrite;
}

//恢复下载的时候调用
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didResumeAtOffset:(int64_t)fileOffset expectedTotalBytes:(int64_t)expectedTotalBytes{

}