如何确定以前是否加载了UITableViewCell?

您应该触发动画并跟踪哪些索引路径已经显示在 tableView:willDisplayCell:forRowAtIndexPath:

- (void)tableView:(UITableView *)tableView willDisplayCell:(UITableViewCell *)cell forRowAtIndexPath:(NSIndexPath *)indexPath
{
    // NSMutableSet *animatedIndexPaths; <-- this is an ivar.
    if (![animatedIndexPaths containsObject:indexPath])
    {
        [animatedIndexPaths addObject:indexPath];
        // Trigger your cell animation on cell.
    }
}