"Zone mismatch" message

The best way to silence this message is to remove use of Zones from within the application. Zones can be very hard to debug, because they are essentially global variables, and break encapsulation. Best practice is to avoid global variables and zones.

If removing zones is not an option (for example because the application depends on a third-party library that relies on zones for its configuration), then the various calls into the Flutter framework should be moved to all be in the same zone. Typically, this means moving the call to WidgetsFlutterBinding.ensureInitialized() to the same closure as the call to runApp().

This can be awkward when the zone in which runApp is run is being initialized with zoneValues obtained from a plugin (which requires WidgetsFlutterBinding.ensureInitialized() to have been called).

One option in this kind of scenario is to place a mutable object in the zoneValues, and update that object with the value once the value is available.

import 'dart:async';
import 'package:material_ui/material_ui.dart';

class Mutable<T> {
  Mutable(this.value);
  T value;
}

void main() {
  var myValue = Mutable<double>(0.0);
  Zone.current.fork(
    zoneValues: {
      'myKey': myValue,
    }
  ).run(() {
    WidgetsFlutterBinding.ensureInitialized();
    var newValue = ...; // obtain value from plugin
    myValue.value = newValue; // update value in Zone
    runApp(...);
  });
}

In code that needs to use myKey, it can be obtained indirectly using Zone.current['myKey'].value.

When such a solution does not work because a third-party dependency requires the use of a specific type for a specific zoneValues key, all calls into the dependency can be wrapped in Zone calls that provide suitable values.

It is strongly recommended that packages that use zones in this way migrate to more maintainable solutions.