Add event to call one procedure from another

I am trying to make a GUI. I have multiple buttons that increment and decrement a page number. I have a variable that stores the data that will be shown on the page. This variable is set in a series of if else functions in a procedure that is called when the GUI is drawn. 

however, i do not have a nice, neat little event that can refer back to the if else functions. I have to lock my button functions and copy-paste a line from the original call to the if else function. Then, if i want to edit the buttons at any point, i need to unlock, edit, then repeat the process.