如何在Interface Builder中使用自定义UIButton类别？

I'm coding a simple card game for my younger sister on a whim. I'm using UIButtons: default state is face down, selected state is face up. I need the buttons to have a boolean property that tells me if they've ever been flipped over. If not, it gets set to true (that way I'm not just drawing random cards on each flip). I tried creating a category of UIButton called CardGameButton. In the .h file:I'm coding a simple card game for my younger si