问题 I would like to be able to change the navigation bar tab programmatically. I have a button inside Page1 that navigates to Page2. When I perform this, the navigation bar disappears because I didn't select page2 using the navigation bar. I have 4 dart files along the lines of navigationbar.dart, page1.dart, page2.dart, page3.dart The Navigation page is the home page of the application with the children: final List<Widget> _children = [ Page1(), Page2(), Page3(), ]; return Scaffold(