Dialogs' Default BorderRadius

Summary

Instances of Dialog, as well as SimpleDialog, AlertDialog, and showTimePicker, now have a default shape of a RoundedRectangleBorder with a BorderRadius of 4.0 pixels. This matches the current specifications of Material Design. Prior to this change, the default behavior for Dialog.shape’s BorderRadius was 2.0 pixels.

Context

Dialogs and their associated subclasses (SimpleDialog, AlertDialog, and showTimePicker), appears slightly different as the border radius is larger. if you have master golden file images that have the prior rendering of the Dialog with a 2.0 pixel border radius, your widget tests will fail. These golden file images can be updated to reflect the new rendering, or you can update your code to maintain the original behavior.

The showDatePicker dialog already matched this specification and is unaffected by this change.

Migration guide

If you would prefer to maintain the old shape, you can use the shape property of your Dialog to specify the original 2.0 pixel radius.

Setting the Dialog shape to the original radius:

import 'package:flutter/material.dart';

void main() => runApp(Foo());

class Foo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        floatingActionButton: FloatingActionButton(onPressed: () {
          showDialog(
            context: context,
            builder: (BuildContext context) {
              return AlertDialog(
                content: Text('Alert!'),
                shape: RoundedRectangleBorder(
                    borderRadius: BorderRadius.all(Radius.circular(2.0))),
              );
            },
          );
        }),
      ),
    );
  }
}

If you prefer the new behavior and have failing golden file tests, you can update your master golden files using this command:

flutter test --update-goldens

Timeline

This change was introduced in June 2020, in 1.20.0-0.0.pre.

References

API documentation:

Relevant PR: