AFNetworking下载网络相关的附件（音视频）等到本地app包中做离线来提高用户体验

使用场景:

      有时我们做的app在请求网络相关的附件资源时有图片的也有音视频的，请求图片我们常用的第三方库一般是

SDWebImage就足够了，但SDWebImage不支持对像音频、视频及压缩zip等附件的下载支持，这时我们可以利用

AFNetworking的AFHTTPRequestOperation类来完成下载并保存到指定的app的Caches目录下，底层对这块的封装

代码如下:

.h头文件接口

/**
 * 下载文件
 * 
 * @param string aUrl 请求文件地址
 * @param string aSavePath 保存地址
 * @param string aFileName 文件名 
 * @param int aTag tag标识
 */
- (void)downloadFileURL:(NSString *)aUrl savePath:(NSString *)aSavePath fileName:(NSString *)aFileName tag:(NSInteger)aTag;

.m实现代码如下:

/**
 * 下载文件
 */
- (void)downloadFileURL:(NSString *)aUrl savePath:(NSString *)aSavePath fileName:(NSString *)aFileName tag:(NSInteger)aTag
{
    NSFileManager *fileManager = [NSFileManager defaultManager];
    
    //检查本地文件是否已存在
    NSString *fileName = [NSString stringWithFormat:@"%@/%@", aSavePath, aFileName];
    
    //检查附件是否存在
    if ([fileManager fileExistsAtPath:fileName]) {
        NSData *audioData = [NSData dataWithContentsOfFile:fileName];
        [self requestFinished:[NSDictionary dictionaryWithObject:audioData forKey:@"res"] tag:aTag];
    }else{
        //创建附件存储目录
        if (![fileManager fileExistsAtPath:aSavePath]) {
            [fileManager createDirectoryAtPath:aSavePath withIntermediateDirectories:YES attributes:nil error:nil];
        }
        
        //下载附件
        NSURL *url = [[NSURL alloc] initWithString:aUrl];
        NSURLRequest *request = [NSURLRequest requestWithURL:url];
        
        AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];
        operation.inputStream   = [NSInputStream inputStreamWithURL:url];
        operation.outputStream  = [NSOutputStream outputStreamToFileAtPath:fileName append:NO];
        
        //下载进度控制
        /*
        [operation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead) {
            NSLog(@"is download：%f", (float)totalBytesRead/totalBytesExpectedToRead);
        }];
        */
        
        //已完成下载
        [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {
            
            NSData *audioData = [NSData dataWithContentsOfFile:fileName];
            //设置下载数据到res字典对象中并用代理返回下载数据NSData
            [self requestFinished:[NSDictionary dictionaryWithObject:audioData forKey:@"res"] tag:aTag];
        } failure:^(AFHTTPRequestOperation *operation, NSError *error) {

            //下载失败
            [self requestFailed:aTag];
        }];
        
        [operation start];
    }
}