今天需要用AFNetworking实现断点续传的功能,但是在进行了一番研究之后,发现AFNetworking虽然支持下载文件的暂停和继续,但是程序重新启动后再次下载无法进行续传。网上有说可以通过AFDownloadRequestOperation这个AFNetworking的扩展库来实现重新启动后的续传,但是经过本人测试,这个库在最新的AFNetworking上会报错,无奈之下,参考他的代码,自己实现了一个,在这里分享给大家。
实现的代码如下:
1 //获取已下载的文件大小 2 - (unsigned long long)fileSizeForPath:(NSString *)path { 3 signed long long fileSize = 0; 4 NSFileManager *fileManager = [NSFileManager new]; // default is not thread safe 5 if ([fileManager fileExistsAtPath:path]) { 6 NSError *error = nil; 7 NSDictionary *fileDict = [fileManager attributesOfItemAtPath:path error:&error]; 8 if (!error && fileDict) { 9 fileSize = [fileDict fileSize]; 10 } 11 } 12 return fileSize; 13 } 14 //开始下载 15 - (void)startDownload { 16 NSString *downloadUrl = @"http://www.xxx.com/xxx.zip"; 17 NSString *cacheDirectory = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) objectAtIndex:0]; 18 NSString *downloadPath = [cacheDirectory stringByAppendingPathComponent:@"xxx.zip"]; 19 NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:downloadUrl]]; 20 //检查文件是否已经下载了一部分 21 unsigned long long downloadedBytes = 0; 22 if ([[NSFileManager defaultManager] fileExistsAtPath:downloadPath]) { 23 //获取已下载的文件长度 24 downloadedBytes = [self fileSizeForPath:downloadPath]; 25 if (downloadedBytes > 0) { 26 NSMutableURLRequest *mutableURLRequest = [request mutableCopy]; 27 NSString *requestRange = [NSString stringWithFormat:@"bytes=%llu-", downloadedBytes]; 28 [mutableURLRequest setValue:requestRange forHTTPHeaderField:@"Range"]; 29 request = mutableURLRequest; 30 } 31 } 32 //不使用缓存,避免断点续传出现问题 33 [[NSURLCache sharedURLCache] removeCachedResponseForRequest:request]; 34 //下载请求 35 AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request]; 36 //下载路径 37 operation.outputStream = [NSOutputStream outputStreamToFileAtPath:downloadPath append:YES]; 38 //下载进度回调 39 [operation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead) { 40 //下载进度 41 float progress = ((float)totalBytesRead + downloadedBytes) / (totalBytesExpectedToRead + downloadedBytes); 42 }]; 43 //成功和失败回调 44 [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) { 45 46 } failure:^(AFHTTPRequestOperation *operation, NSError *error) { 47 48 }]; 49 [operation start]; 50 }
需要注意的是,此种写法仅适用于下载zip包,因为下载其他格式的文件有可能出现数据过多的情况。当文件已经下载完成时,再次调用该函数,无法判断文件是否已经下载完整,于是会再次下载,此时服务器会报416错,同时返回也会输出到文件中,使得文件大小异常。但是zip格式不受影响。
如果大家觉得对自己有帮助的话,还希望能帮顶一下,谢谢:)
转载请注明出处,谢谢!