How to separate program logic from GUI

Hello I`m trying to separate programm logic from the GUI, I want to have multiwindowed application with logi placed in my class not MainWindow like it is in most example cases. And I want to start my windows, give them a pointers to Data, they would fill the data, close and next window would be run. What to do in such situation try to override the qapplication(If yes where should i put my logic in which QApplication method) or it can be done by "just like that"

Code:

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QApplication a(argc,argv);
MainWindow *w = new MainWindow();
w->show();
a->exec();
//Here to place the loop of comunication beetwen this and windows 
//Main loop of gui communication with logic
//Start windows, close windows, switch results, make actions
//MAIN LOOP
return 0;

---

if this loop is posiblle to create pls tell my how. Should i make some signals to comunicate with my window or in other way.I achiewed that signals are protected by default so is it possible or there is a better way to sepate the logic from window pls help, give me some clues, or examples.

You don't need another loop (you already have one)

Just code your classes that will contain and work the with data you need.

Also you can take a look at the Model View Programming, it may be what you are looking for.