Objective-C 创建会话和数据任务

NSURL *url = [NSURL URLWithString:@"http://www.example.com/"];
NSURLSessionConfiguration *configuration = [NSURLSessionConfiguration defaultSessionConfiguration];

// Configure the session here.

NSURLSession *session = [NSURLSession sessionWithConfiguration:configuration];
    
[[session dataTaskWithURL:url
        completionHandler:^(NSData *data, NSURLResponse *response, NSError *error)
{
    // The response object contains the metadata (HTTP headers, status code)

    // The data object contains the response body

    // The error object contains any client-side errors (e.g. connection
    // failures) and, in some cases, may report server-side errors.
    // In general, however, you should detect server-side errors by
    // checking the HTTP status code in the response object.
}] resume];