AFNetworking實現程序從新啓動時的斷點續傳

今天須要用AFNetworking實現斷點續傳的功能，可是在進行了一番研究以後，發現AFNetworking雖然支持下載文件的暫停和繼續，可是程序從新啓動後再次下載沒法進行續傳。網上有說能夠經過AFDownloadRequestOperation這個AFNetworking的擴展庫來實現從新啓動後的續傳，可是通過本人測試，這個庫在最新的AFNetworking上會報錯，無奈之下，參考他的代碼，本身實現了一個，在這裏分享給你們。

實現的代碼以下：

 

//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];
}

須要注意的是，此種寫法僅適用於下載zip包，由於下載其餘格式的文件有可能出現數據過多的狀況。當文件已經下載完成時，再次調用該函數，沒法判斷文件是否已經下載完整，因而會再次下載，此時服務器會報416錯，同時返回也會輸出到文件中，使得文件大小異常。可是zip格式不受影響。

 

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