How to continuously update a graph in GUI according to a slider value

Hello,

I have a figure on my GUI and also a push button object. When I press the push button, after some calculations are done, a rectangle will be drawn on the figure. I added a sample GUI to this question. I need to add a slider object to continuously move the center of the rectangle according to the value of the slider.In other words, I need to add an offset value to the location of the center of my rectangle and execute my push button function after any change occurred in value of slider object. Any idea and advice is appreciated. Thanks