afn文件上传实现

1. 定义一个全局的AFHttpClient：包含有
    1> baseURL
    2> 请求
    3> 操作队列 NSOperationQueue
2. 由AFHTTPRequestOperation负责所有的“网络”操作请求

完整demo：文件上传

关键代码：

- (IBAction)upload {
    // 1.设置基准路径
    AFHTTPClient *client = [AFHTTPClient clientWithBaseURL:[NSURL URLWithString:@"http://192.168.178.47:8080/MyServer"]];
    
    // 2.初始化请求参数
    NSURLRequest *request = [client multipartFormRequestWithMethod:@"POST" path:@"upload" parameters:@{
                     @"username" : @"carl",
                     @"pwd":@"123"}
        constructingBodyWithBlock:^(id<AFMultipartFormData> formData) {
        // 上传Default.png
        [formData appendPartWithFileURL:[[NSBundle mainBundle] URLForResource:@"Default" withExtension:@"png"] name:@"file" error:nil];
        
        // 上传新获得的图片文件
        NSData *data = UIImagePNGRepresentation(_imageView.image);
        [formData appendPartWithFileData:data name:@"file" fileName:@"456.png" mimeType:@"image/png"];
            
        // 上传artifacts.xml
        [formData appendPartWithFileURL:[[NSBundle mainBundle] URLForResource:@"artifacts" withExtension:@"xml"] name:@"file" error:nil];
        
        // 上传epl-v10.html
        [formData appendPartWithFileURL:[[NSBundle mainBundle] URLForResource:@"epl-v10" withExtension:@"html"] name:@"file" error:nil];
    }];
    
    
    // 发送请求上传文件
    AFHTTPRequestOperation *operation = [client HTTPRequestOperationWithRequest:request success:nil failure:nil];
    [operation start];