AFNetworking实现程序重新启动时的断点续传

浏览数：40 / 时间：2015年06月09日

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 }