Flutter BottomSheet change width

Question

I want the bottom sheet to look like the one in Angular Material.
The sheet instead expands to the maximum width. The problem is that I cannot configure the width of the bottom sheet. It currently looks like this

My code looks like this:

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      theme: ThemeData.dark().copyWith(scaffoldBackgroundColor: darkBlue),
      debugShowCheckedModeBanner: false,
      home: Scaffold(
        body: ...,
        floatingActionButton: FloatingActionButton(
          child: Icon(Icons.add),
          tooltip: 'Add File',
          onPressed: () => showModalBottomSheet(
            context: context,
            builder: (context) => AddFileBottomSheet(),
            shape: RoundedRectangleBorder(
              borderRadius: BorderRadius.only(
                topLeft: Radius.circular(10),
                topRight: Radius.circular(10),
              ),
            ),
            // backgroundColor: Colors.transparent,
            isScrollControlled: true,
          ),
        ),
      ),
    );
  }
}

class AddFileBottomSheet extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          Container(
            padding: EdgeInsets.symmetric(vertical: 20, horizontal: 5),
            alignment: Alignment.center,
            child: Text(
              'Create New File',
              style: Theme.of(context).textTheme.headline5,
            ),
          ),
          GridView.count(
            shrinkWrap: true,
            crossAxisCount: 3,
            children: [
              _gridTile(
                context: context,
                icon: Icon(Icons.file_upload),
                text: 'Upload File',
                callback: () => print('lel'),
              ),
              _gridTile(
                context: context,
                icon: Icon(Icons.create),
                text: 'Create Text File',
                callback: () => print('lel'),
              ),
            ],
          ),
        ],
    );
  }

  Widget _gridTile({
    @required BuildContext context,
    @required Icon icon,
    @required String text,
    @required void callback(),
  }) {
    return InkWell(
        onTap: () => callback(),
        child: Container(
          padding: EdgeInsets.all(15),
          alignment: Alignment.center,
          height: double.infinity,
          width: double.infinity,
          child: Column(
            mainAxisSize: MainAxisSize.min,
            children: <Widget>[
              icon,
              Text(text, style: Theme.of(context).textTheme.subtitle2),
            ],
          ),
        ),
    );
  }
}

I know I can fake it having a smaller width when making some of it transparent, but I have round edges and they won't get preserved.

Workaround #1

I managed to do it by changing the canvasColor to transparent and making the borders rounded in the widget: This way, however I need to do additional logic to dismiss it when the user clicks the fake transparent area.

First add the canvasColor to the context somehow:

...
      floatingActionButton: Theme(
        data: Theme.of(context).copyWith(canvasColor: Colors.transparent),
        child: Builder(
          builder: (context) => FloatingActionButton(
            child: Icon(Icons.add),
            tooltip: 'Add File',
            onPressed: () => showModalBottomSheet(
              context: context,
              builder: (context) => AddFileBottomSheet(),
              // shape: RoundedRectangleBorder(
              //   borderRadius: BorderRadius.only(
              //     topLeft: Radius.circular(10),
              //     topRight: Radius.circular(10),
              //   ),
              // ),
              // backgroundColor: Colors.transparent,
              isScrollControlled: true,
            ),
          ),
        ),
      ),
...

Then fake the width

    return Container(
      padding: EdgeInsets.symmetric(horizontal: 300),
      child: Container(
        decoration: BoxDecoration(
          color: Colors.white,
          shape: BoxShape.rectangle,
          borderRadius: BorderRadius.only(
            topLeft: Radius.circular(10),
            topRight: Radius.circular(10),
          ),
        ),
        // backgroundColor: Colors.transparent,
        child: Column(
          mainAxisSize: MainAxisSize.min,
          children: <Widget>[
            Container(
              padding: EdgeInsets.symmetric(vertical: 20, horizontal: 5),
              alignment: Alignment.center,
              child: Text(
                'Create New File',
                style: Theme.of(context).textTheme.headline5,
              ),
            ),
            GridView.count(
              shrinkWrap: true,
              crossAxisCount: 3,
              children: [
                _gridTile(
                  context: context,
                  icon: Icon(Icons.file_upload),
                  text: 'Upload File',
                  callback: () => print('lel'),
                ),
                _gridTile(
                  context: context,
                  icon: Icon(Icons.create),
                  text: 'Create Text File',
                  callback: () => print('lel'),
                ),
              ],
            ),
          ],
        ),
      ),
    );

I wonder if there is a standard approach to this and I need your help. I tried making a DartPad example, but it gives me Script error.

My idea was to try and make it mobile friendly with something like this:

    final isMobile = MediaQuery.of(context).size.width < 700;
    return Container(
      padding: EdgeInsets.symmetric(horizontal: isMobile ? 0: 300),
      child: ...
    )

This will make it full-width when mobile and with some padding when desktop.

Autogenous

As of now adding a constraint to showModalBottomSheet is the right way to go. – Terra

Answer 1

UPDATE : Flutter now support constraints property in showModalBottomSheet

showModalBottomSheet(
  context: context,
  constraints: BoxConstraints(
     maxWidth: Responsive.isMobile(context) ? Get.width : 600,              
  ),
  builder: ...
),

Zoochore

Answer 2

UPDATE

Flutter added constraints to showModalBottomSheet and it's available on master, dev and beta :)

Mcclinton

Answer 3

You can wrap your widget with an Align widget and set the alignment to bottom center, then you can set box constraints if you want to have a maximum width

Align(
  alignment: Alignment.bottomCenter,
  child: ConstrainedBox(
    constraints: BoxConstraints(...),
    child: ...
  ),
)

Habitforming

looks promising, but I cannot test it rn. I will accept your answer if you are sure it works – Autogenous

Yeah, I had the same problem as you, as I wanted not to have full width bottom sheet on tablets. You can try it your self some day, thanks – Habitforming

This solution is not working. I've created a feature request on Flutter repo. Hope for the best. – Mcclinton