Flutter Routing Issue and Duplicate GlobalKey

Issue

I’m having an issue with Flutter routes and a duplicate GlobalKey in the widget tree.

My app does the following:

Screen_A -> Screen_B -> Screen_C

In each case, the navigation (->) is done via the following (where * is B or C):

Navigator.push(context, MaterialPageRoute(builder: (context) => Screen_*()));

I then navigate from Screen_C -> Screen_A via:

Navigator.pushAndRemoveUntil(context, 
    MaterialPageRoute(builder: (context) => Screen_A()), 
    (Route<dynamic> route) => false);

Finally, I navigate from Screen_A -> Screen_B using the original Navigator.push method. I’m getting the following error:

‘package:flutter/src/widgets/will_pop_scope.dart’: Failed assertion: line 135 pos 12: ‘route == ModalRoute.of(context)’: is not true.

Exception caught by widgets library: Duplicate GlobalKey detected in widget tree.

For reference, Screen_B is a form wherein I define a GlobalKey via:

GlobalKey<FormState> formKey = GlobalKey<FormState>();

I can’t figure out why this is occurring. It appears where I define the GlobalKey and how I route is the proper way. Shouldn’t Navigator.pushAndRemoveUntil remove the route stack history, thereby removing the old GlobalKey in Screen_B?

Solution

SOLVED: The solution turned out to to be where I was putting the GlobalKey declaration. I previously had it outside of my stateful widget like so:

GlobalKey<FormState> formKey = GlobalKey<FormState>();
class Screen_B extends StatefulWidget { (etc.) }
class _Screen_B extends State<Screen_B > { (etc.) }

But upon moving it into the State<Screen_B>, my issue was solved. Like so:

class Screen_B extends StatefulWidget { (etc.) }
class _Screen_B extends State<Screen_B > { 
    GlobalKey<FormState> formKey = GlobalKey<FormState>();
    (etc.) 
}

=====
Additionally, as ikerfah noted above, using pushReplacement() would have worked as well from Screen_A -> Screen_B -> Screen_C.

Answered By – usafutb0l3r

Answer Checked By – Katrina (FlutterFixes Volunteer)