Play reverse button?

Hey there, i have a few questions.

1- I have a button in my project. When i click this button, i am changing an objects opacity to %0. Now i want to when i click the same button, if i click before, play reverse from the end. I mean user clicks, object disappears. When user clicks again, object appears. Like on/off toggle button. How to do that?

2- Can i apply a transition effect to basic toggle function in Actions panel? Like fade-in/out effects?

Thanks!