NSURLSession是苹果ios7后提供的api，用来替换 NSURLConnection
会话指的是程序和服务器的通信对象
//一.简单会话不可以配合会话（get请求）

- (void)startRequest
{
    NSString *strURL = [[NSString alloc] initWithFormat:@"http://www.51work6.com/service/mynotes/WebService.php?email=%@&type=%@&action=%@", @"414875346@qq.com", @"JSON", @"query"];
    //1.将字符串转化成URL字符串
    strURL = [strURL stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];
    NSURL *url = [NSURL URLWithString:strURL];
    NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url];

    //2.用单列创建简单会话
    NSURLSession *session = [NSURLSession sharedSession];
    //3.会话任务（会话都是基于会话任务的）
    NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:
        ^(NSData *data, NSURLResponse *response, NSError *error) {
        NSLog(@"请求完成...");
        if (!error) {
            NSDictionary *resDict = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:nil];
            //页面交互放在主线程进行
            dispatch_async(dispatch_get_main_queue(), ^{
                [self reloadView:resDict];
            });
        } else {
            NSLog(@"error : %@", error.localizedDescription);
        }
    }];

    //4.新建任务默认是暂停的 要自己执行
    [task resume];
}

//二.默认会话,可以对会话进行配置（GET）

- (void)startRequest
{
    NSString *strURL = [[NSString alloc] initWithFormat:@"http://www.51work6.com/service/mynotes/WebService.php?email=%@&type=%@&action=%@", @"414875346@qq.com", @"JSON", @"query"];

    strURL = [strURL stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];
    NSURL *url = [NSURL URLWithString:strURL];
    NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url];

    //1.创建默认会话配置对象
    NSURLSessionConfiguration *defaultConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
    //2.1创建默认会话 （主线程中执行）
    NSURLSession *session = [NSURLSession sessionWithConfiguration: defaultConfig delegate: nil delegateQueue: [NSOperationQueue mainQueue]];

    NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:
        ^(NSData *data, NSURLResponse *response, NSError *error) {
        NSLog(@"请求完成...");
        if (!error) {
            NSDictionary *resDict = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:nil];
            //2.2不需要再次设置在主线程中执行
            //dispatch_async(dispatch_get_main_queue(), ^{
            [self reloadView:resDict];
            //});
        } else {
            NSLog(@"error : %@", error.localizedDescription);
        }
    }];

    //3.执行会话任务
    [task resume];
}

//三.默认会话 (POST)[和get的主要区别是NSMutableURLRequest]

- (void)startRequest
{
    NSString *strURL = @"http://www.51work6.com/service/mynotes/WebService.php";
    NSURL *url = [NSURL URLWithString:strURL];

    //1.构建NSMutableURLRequest对象
    NSString *post = [NSString stringWithFormat:@"email=%@&type=%@&action=%@", @"414875346@qq.com", @"JSON", @"query"];
    NSData *postData = http://www.mamicode.com/[post dataUsingEncoding:NSUTF8StringEncoding];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request setHTTPMethod:@"POST"];
    [request setHTTPBody:postData];

    //2.构建默认会话
    NSURLSessionConfiguration *defaultConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration: defaultConfig delegate: nil delegateQueue: [NSOperationQueue mainQueue]];

    //3.构建会话任务
    NSURLSessionDataTask *task = [session dataTaskWithRequest:request completionHandler:
        ^(NSData *data, NSURLResponse *response, NSError *error) {
        NSLog(@"请求完成...");
        if (!error) {
            NSDictionary *resDict = [NSJSONSerialization JSONObjectWithData:data options:NSJSONReadingAllowFragments error:nil];
            //dispatch_async(dispatch_get_main_queue(), ^{
            [self reloadView:resDict];
            //});
        } else {
            NSLog(@"error : %@", error.localizedDescription);
        }
    }];

    //4.执行会话任务
    [task resume];
}

四.下载文件或图片，用的是下载会话任务（一般get post用的都是数据任务NSURLSessionDataTask）支持后台下载

//四.下载图片或文件，用会话下载任务NSURLSessionDownloadTask（支持后台下载）
- (IBAction)onClick:(id)sender
{
    NSString *strURL = [[NSString alloc] initWithFormat:@"http://www.51work6.com/service/download.php?email=%@&FileName=test1.jpg", @"414875346@qq.com"];
    NSURL *url = [NSURL URLWithString:strURL];

    //1.构造默认会话 （基于委托代理非block回调模式）
    NSURLSessionConfiguration *defaultConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:defaultConfig delegate:self delegateQueue:[NSOperationQueue mainQueue]];//1.1主线程执行

    //2.创建会话下载任务
    NSURLSessionDownloadTask *downloadTask = [session downloadTaskWithURL:url];
    //3.执行任务
    [downloadTask resume];
}

//4.实现回调接口，显示进度条
#pragma mark -- 实现NSURLSessionDownloadDelegate委托协议
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didWriteData:(int64_t)bytesWritten totalBytesWritten:(int64_t)totalBytesWritten totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite {

    float progress = totalBytesWritten * 1.0 / totalBytesExpectedToWrite;
    //1.2 不用再次单独设置在主进程里进行
    [_progressView setProgress:progress animated:TRUE];
    NSLog(@"完成进度= %.2f%%", progress * 100);
    NSLog(@"当前接收: %lld 字节 (累计已下载: %lld 字节)  期待: %lld 字节.", bytesWritten, totalBytesWritten, totalBytesExpectedToWrite);
}
//5.下载完成时回调
- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{
    //6.将临时文件保存到沙盒中
    NSLog(@"临时文件: %@\\n", location);

    //6.1构建保存到沙盒的文件的路径
    NSString *downloadsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, TRUE) objectAtIndex:0];
    NSString *downloadStrPath = [downloadsDir stringByAppendingPathComponent:@"test1.jpg"];
    NSURL *downloadURLPath = [NSURL fileURLWithPath:downloadStrPath];

    //6.2如果已经存在先删除
    NSFileManager *fileManager = [NSFileManager defaultManager];
    NSError *error = nil;
    if ([fileManager fileExistsAtPath:downloadStrPath]) {
        [fileManager removeItemAtPath:downloadStrPath error:&error];
        if (error) {
            NSLog(@"删除文件失败: %@", error.localizedDescription);
        }
    }

    //6.3将文件保存到沙盒中
    error = nil;
    if ([fileManager moveItemAtURL:location toURL:downloadURLPath error:&error]) {
        NSLog(@"文件保存成功: %@", downloadStrPath);
        UIImage *img = [UIImage imageWithContentsOfFile:downloadStrPath];
        self.imageView1.image = img;
    } else {
        NSLog(@"保存文件失败: %@", error.localizedDescription);
    }
}

2.AFNetwork使用模板(AFNetwork3 底层也是NSURLSession) <swift推荐用Alamofire>

//一.get请求（AFNetworking）

- (void)startRequest
{
    NSString *strURL = [[NSString alloc] initWithFormat:@"http://www.51work6.com/service/mynotes/WebService.php?email=%@&type=%@&action=%@", @"414875346@qq.com", @"JSON", @"query"];

    strURL = [strURL stringByAddingPercentEncodingWithAllowedCharacters:[NSCharacterSet URLQueryAllowedCharacterSet]];
    NSURL *url = [NSURL URLWithString:strURL];
    NSURLRequest *request = [[NSURLRequest alloc] initWithURL:url];

    //1.默认配置
    NSURLSessionConfiguration *defaultConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
    //2.构建AF会话AFURLSessionManager  （其实就是将NSURLSession对象换掉，其他函数接口都一样）
    AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:defaultConfig];
    //3.构建AF生产的会话任务
    NSURLSessionDataTask *task = [manager dataTaskWithRequest:request completionHandler:^(NSURLResponse *response, id responseObject, NSError *error) {
        //3.1注意responseObject可以是字典或数组，不需要我们自己解析

        NSLog(@"请求完成...");
        if (!error) {
            [self reloadView:responseObject];
        } else {
            NSLog(@"error : %@", error.localizedDescription);
        }
    }];
    //4.执行任务
    [task resume];
}

//二.post请求（AFNetworking）

- (void)startRequest
{
    NSString *strURL = @"http://www.51work6.com/service/mynotes/WebService.php";
    NSURL *url = [NSURL URLWithString:strURL];

    //1.设置参数构建NSMutableURLRequest
    NSString *post = [NSString stringWithFormat:@"email=%@&type=%@&action=%@", @"414875346@qq.com", @"JSON", @"query"];
    NSData *postData = http://www.mamicode.com/[post dataUsingEncoding:NSUTF8StringEncoding];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    [request setHTTPMethod:@"POST"];
    [request setHTTPBody:postData];

    //2.就NSMutableURLRequest对象不一样，其他都和get一样
    NSURLSessionConfiguration *defaultConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
    AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:defaultConfig];
    //3.
    NSURLSessionDataTask *task = [manager dataTaskWithRequest:request completionHandler:^(NSURLResponse *response, id responseObject, NSError *error) {
        NSLog(@"请求完成...");
        if (!error) {
            [self reloadView:responseObject];
        } else {
            NSLog(@"error : %@", error.localizedDescription);
        }
    }];
    //4.
    [task resume];
}

//三.下载文件或图片（AFNetworking）<不用委托代理的模式，直接在block里处理>（既不是POST也不是GET）

- (IBAction)onClick:(id)sender
{
    NSString *strURL = [[NSString alloc] initWithFormat:@"http://www.51work6.com/service/download.php?email=%@&FileName=test1.jpg", @"414875346@qq.com"];

    NSURL *url = [NSURL URLWithString:strURL];
    NSURLRequest *request = [NSURLRequest requestWithURL:url];

    //1.构建会话AFURLSessionManager
    NSURLSessionConfiguration *defaultConfig = [NSURLSessionConfiguration defaultSessionConfiguration];
    AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:defaultConfig];
    //2.构建AF创建的会话下载任务
    NSURLSessionDownloadTask *downloadTask = [manager downloadTaskWithRequest:request progress:^(NSProgress *downloadProgress) {
        //3.设置进度条（需要设置在主线程进行）
        NSLog(@"本地化信息=%@", [downloadProgress localizedDescription]);//完成百分比
        dispatch_async(dispatch_get_main_queue(), ^{
            [self.progressView setProgress:downloadProgress.fractionCompleted animated:TRUE];
        });

    } destination:^NSURL *(NSURL *targetPath, NSURLResponse *response) {
        //4.指定文件下载好后的保存路径即可。不用自己操作（带返回参数的block）
        NSString *downloadsDir = [NSSearchPathForDirectoriesInDomains(NSDocumentDirectory, NSUserDomainMask, TRUE) objectAtIndex:0];
        NSString *downloadStrPath = [downloadsDir stringByAppendingPathComponent:[response suggestedFilename]];//4.1服务器端存储的文件名
        NSURL *downloadURLPath = [NSURL fileURLWithPath:downloadStrPath];

        return downloadURLPath;

    } completionHandler:^(NSURLResponse *response, NSURL *filePath, NSError *error) {
        //5.服务器返回数据后调用
        NSLog(@"File downloaded to: %@", filePath);
        NSData *imgData = http://www.mamicode.com/[[NSData alloc] initWithContentsOfURL:filePath];
        UIImage *img = [UIImage imageWithData:imgData];
        self.imageView1.image = img;

    }];
    //6.执行会话下载任务
    [downloadTask resume];
}

//四.上传文件或图片（AFNetworking）(也用POST)

- (IBAction)onClick:(id)sender
{
    _label.text = @"上传进度";
    _progressView.progress = 0.0;

    NSString *uploadStrURL = @"http://www.51work6.com/service/upload.php";
    NSDictionary *params = @{@"email" : @"414875346@qq.com"};

    NSString *filePath = [[NSBundle mainBundle] pathForResource:@"test2" ofType:@"jpg"];

    //1.构建NSMutableURLRequest（带上传文件对象）
    NSMutableURLRequest *request = [[AFHTTPRequestSerializer serializer] multipartFormRequestWithMethod:@"POST"
                  URLString:uploadStrURL parameters:params
                  constructingBodyWithBlock:^(id <AFMultipartFormData> formData) {
                      [formData appendPartWithFileURL:[NSURL fileURLWithPath:filePath] name:@"file" fileName:@"1.jpg" mimeType:@"image/jpeg" error:nil];
                  } error:nil];
    //2.创建会话
    AFURLSessionManager *manager = [[AFURLSessionManager alloc] initWithSessionConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration]];
    //3.创建会话上传任务（用AF构建）
    NSURLSessionUploadTask *uploadTask = [manager uploadTaskWithStreamedRequest:request
                   progress:^(NSProgress *uploadProgress) {
                       //3.1 上传进度条（主进程中显示）
                       NSLog(@"上传: %@", [uploadProgress localizedDescription]);
                       dispatch_async(dispatch_get_main_queue(), ^{
                           [_progressView setProgress:uploadProgress.fractionCompleted];
                       });
                   }
                  completionHandler:^(NSURLResponse *response, id responseObject, NSError *error) {
                      //3.2 上传完后操作
                      if (!error) {
                          NSLog(@"上传成功");
                          [self download];
                      } else {
                          NSLog(@"上传失败: %@", error.localizedDescription);
                      }
                  }];
    //4.执行任务
    [uploadTask resume];
}