"Apply" button in custom Dialog

[Sergi Gàmiz Ribelles]

Hi. I have a large custom  dialog with a lot  of variables; I want to configure an <"Apply"> button that assigns modified values to their variables but preserve the dialog; later if user press <ESC> or <CANCEL> button "aplied" values must be kept but those changes not "applied" would  be lost.

Do I need something such as mirror-variables?; I mean, a copy for each variable while the dialog is shown?

Any idea, please?

Thank you.

SGR