How to create a modal bottomsheet with circular corners in Flutter?

UPDATED ON 2019-08-05

You can now do it using the default showModalBottomSheet method that now supports adding a ShapeBorder and also backgroundColor!

showModalBottomSheet(
  shape: RoundedRectangleBorder(
     borderRadius: BorderRadius.circular(10.0),
  ),
  backgroundColor: Colors.white,
  ...
);

—

Instead of overriding the entire theme of the app (which caused problems in various parts of my app) as suggested by other answers, I decided to take a look at the implementation for showModalBottomSheet and find the problem myself. Turns out that all that was needed was wrapping the main code for the modal in a Theme widget that contains the canvasColor: Colors.transparent trick. I also made it easier to customize the radius and also the color of the modal itself.

You can use either the package on pub or a gist containing the same code. Don’t forget to import the proper package/file.

showRoundedModalBottomSheet(
    context: context,
    radius: 20.0,  // This is the default
    color: Colors.white,  // Also default
    builder: (context) => ???,
);