AFNetworking實現程序從新啟動時的斷點續傳

tags:    時間:2014-03-23 19:21:02
AFNetworking實現程序重新啟動時的斷點續傳

今天需要用AFNetworking實現斷點續傳的功能,但是在進行了一番研究之後,發現AFNetworking雖然支持下載文件的暫停和繼續,但是程序重新啟動后再次下載無法進行續傳。網上有說可以通過AFDownloadRequestOperation這個AFNetworking的擴展庫來實現重新啟動后的續傳,但是經過本人測試,這個庫在最新的AFNetworking上會報錯,無奈之下,參考他的代碼,自己實現了一個,在這裡分享給大家。

實現的代碼如下:

//獲取已下載的文件大小 - (unsigned long long)fileSizeForPath:(NSString *)path {     signed long long fileSize = 0;     NSFileManager *fileManager = [NSFileManager new]; // default is not thread safe     if ([fileManager fileExistsAtPath:path]) {         NSError *error = nil;         NSDictionary *fileDict = [fileManager attributesOfItemAtPath:path error:&error];         if (!error && fileDict) {             fileSize = [fileDict fileSize];         }     }     return fileSize; } //開始下載 - (void)startDownload {     NSString *downloadUrl = @"http://www.xxx.com/xxx.zip";     NSString *cacheDirectory = [NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) objectAtIndex:0];     NSString *downloadPath = [cacheDirectory stringByAppendingPathComponent:@"xxx.zip"];     NSURLRequest *request = [NSURLRequest requestWithURL:[NSURL URLWithString:downloadUrl]];     //檢查文件是否已經下載了一部分     unsigned long long downloadedBytes = 0;     if ([[NSFileManager defaultManager] fileExistsAtPath:downloadPath]) { 	//獲取已下載的文件長度         downloadedBytes = [self fileSizeForPath:downloadPath];         if (downloadedBytes > 0) {             NSMutableURLRequest *mutableURLRequest = [request mutableCopy];             NSString *requestRange = [NSString stringWithFormat:@"bytes=%llu-", downloadedBytes];             [mutableURLRequest setValue:requestRange forHTTPHeaderField:@"Range"];             request = mutableURLRequest;         }     }     //不使用緩存,避免斷點續傳出現問題     [[NSURLCache sharedURLCache] removeCachedResponseForRequest:request];     //下載請求     AFHTTPRequestOperation *operation = [[AFHTTPRequestOperation alloc] initWithRequest:request];     //下載路徑     operation.outputStream = [NSOutputStream outputStreamToFileAtPath:downloadPath append:YES];     //下載進度回調     [operation setDownloadProgressBlock:^(NSUInteger bytesRead, long long totalBytesRead, long long totalBytesExpectedToRead) {         //下載進度         float progress = ((float)totalBytesRead + downloadedBytes) / (totalBytesExpectedToRead + downloadedBytes);     }];     //成功和失敗回調     [operation setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {                  } failure:^(AFHTTPRequestOperation *operation, NSError *error) {                  }];     [operation start]; }

需要注意的是,此種寫法僅適用於下載zip包,因為下載其他格式的文件有可能出現數據過多的情況。當文件已經下載完成時,再次調用該函數,無法判斷文件是否已經下載完整,於是會再次下載,此時伺服器會報416錯,同時返回也會輸出到文件中,使得文件大小異常。但是zip格式不受影響。

如果大家覺得對自己有幫助的話,還希望能幫頂一下,謝謝:)
個人博客:http://blog.csdn.net/zhaoxy2850
本文地址:http://blog.csdn.net/zhaoxy_thu/article/details/21383515
轉載請註明出處,謝謝!

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