Save/load parameters of a window after being closed

I have a mainwindow on which I have a "Edit" pushButton. Once clicked on this button, a new window "dialog" is opened ( see the picture ) All 96 buttons are initially green, when I click on a button it becomes red. After selecting the buttons that I want ( red ones ), once I click "OK" button, this window should close. The problem is when I click again on "Edit" from the first window ( mainwindow ), the "dialog" window is opened but all modifications are lost ( All buttons are green ) Is there a way to save those modifications so that if I re-open the dialog window by clicking on "edit", the selected buttons stay red ? What I wanna do is to save the state of the "dialog" window even if it is closed.