Exception Thrown

[jkears]

This line of code throws an exception in emulator...

Navigator.pushReplacementNamed(context, '/topics');

Looking up a deactivated widget's ancestor is unsafe.
At this point the state of the widget's element tree is no longer stable. To safely refer to a widget's ancestor in its dispose() method, save a reference to the ancestor by calling inheritFromWidgetOfExactType() in the widget's didChangeDependencies() method