#2421 [Script] How to get dialog selected item before exec?

[SourceLee]

I have code.

> %SCRIPT
> dialog = new UniversalInputDialog()
> dialog.setWindowTitle("Form1")
> dialog.add(["A", "B","C"],"Choice 1","choicea")
> dialog.add(["AA","BB"],"Choice 2","choiceb")
> if (dialog.exec() != null) {
>...
>}

How to get dialog choiced before exec? Such as SelectedIndexChanged in VB.NET. I want to make 2 dialogs in one form. When selecting an item in dialog choicea, it will change the items in dialog choiceb.
Thanks. I use Google Translate.