IOS 3dtouch 获取不到对应的ndexPath

为什么获取不到对应的indexPath
    - (UIViewController *)previewingContext:(id)context viewControllerForLocation:(CGPoint) point
    {
    NSIndexPath *indexPath = [owntableView indexPathForCell:(StyleTableViewCell* )[context sourceView]];

}
获取不到呀，cell是自定义的

记得 delegate!!!!!!!!!!!!!!!!

http://www.jianshu.com/p/b552bedbc3ef