ios7.1点击collection中item里面的按钮的时候获取父视图中indexpath的时候奔溃

GoodsCollectionViewCell * cell = (GoodsCollectionViewCell *)[btn superview];
NSIndexPath * indexPath = [self.collectionview indexPathForCell:cell];
在ios7.1的模拟器上运行完这句代码就奔溃了。报的错误是： Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UIView _layoutAttributes]: unrecognized selector sent to instance 0x7bec0c10'
怎么能让collection的那个方法不走呢。各位大神帮帮忙。