Brix 310 mpl ui part2

so I get that you want me to make a handleFlipperClicked method rather than just stuffing it on the fly into the click handler.  But I see in Andrew's sketch code that there is the ability to pass it arguments. I just can't tell how he's doing that.  I'd really like to write one handler for both previous and next arrows, but I'd need to pass it a direction argument.  Instructions on how to do that?