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AFNetworking实现程序重新启动时的断点续传

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    • 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:

       

      view sourceprint?
      01.//获取已下载的文件大小
      02.- (unsigned long long)fileSizeForPath:(NSString *)path {
      03.signed long long fileSize = 0;
      04.NSFileManager *fileManager = [NSFileManager new]; // default is not thread safe
      05.if ([fileManager fileExistsAtPath:path]) {
      06.NSError *error = nil;
      07.NSDictionary *fileDict = [fileManager attributesOfItemAtPath:path error:&error];
      08.if (!error && fileDict) {
      09.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。

AFNetworking实现程序重新启动时的断点续传