问NSFileManager，将临时下载的文件移至永久目录的问题

EN

- (void)URLSession:(NSURLSession *)session downloadTask:(NSURLSessionDownloadTask *)downloadTask didFinishDownloadingToURL:(NSURL *)location
{
    NSLog(@"Finished Download");
    //NSLog(downloadTask.taskDescription);
    NSLog(location.absoluteString);
    NSFileManager* fileManager;
    NSURL* destUri = GetDestinationUri(downloadTask.taskDescription, &fileManager);
    NSLog(destUri.absoluteString);

    NSError *error;

    Boolean success = [fileManager replaceItemAtURL: destUri withItemAtURL: location backupItemName: nil options: NSFileManagerItemReplacementUsingNewMetadataOnly resultingItemURL: nil error: &error];

    if(success)
    {
        NSLog(@"success");
    }
    else
    {
        NSLog(@"Fail %@", error);
    }

    UnityBackgroundDownload* download = [backgroundDownloads objectForKey: downloadTask];
    download.status = kStatusDone;
}

static NSURL* GetDestinationUri(NSString* dest, NSFileManager** fileManager)
{
    NSFileManager* manager = [NSFileManager defaultManager];
    NSURL* documents = [[manager URLsForDirectory: NSDocumentDirectory inDomains: NSUserDomainMask] lastObject];
    NSURL* destUri = [documents URLByAppendingPathComponent: dest];
    if (fileManager != NULL)
        *fileManager = manager;
    return destUri;
}