您可以将您的身体转换为新的小部件。
Dart Pad Example
完整代码：

import 'package:flutter/material.dart';

void main() => runApp(new MyApp());

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
        home: new Scaffold(
            appBar: new AppBar(title: const Text('Modal bottom sheet')),
            body: Sheet(), // new Widget
   ));
  }
}

class Sheet extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new Center(
      child: new RaisedButton(
          child: const Text('SHOW BOTTOM SHEET'),
          onPressed: () {
            // Show sheet here
            showModalBottomSheet<void>(
                context: context,
                builder: (BuildContext context) {
                  return new Container(
                    child: new Padding(
                      padding: const EdgeInsets.all(32.0),
                      child: new Text(
                        'This is the modal bottom sheet. Click anywhere to dismiss.',
                        textAlign: TextAlign.center,
                        style: new TextStyle(
                            color: Theme.of(context).accentColor,
                            fontSize: 24.0),
                      ),
                    ),
                  );
                });
          }),
    );
  }
}

大部分是因为上下文有问题，所以不起作用

make sour you给予context

_showBottomSheet(BuildContext context) {
showModalBottomSheet<void>(
    context: context,
    builder: (BuildContext context) {
      return new Container(
        child: new Padding(
          padding: const EdgeInsets.all(32.0),
          child: new Text(
            'This is the modal bottom sheet. Click anywhere to dismiss.',
            textAlign: TextAlign.center,
            style: new TextStyle(
                color: Theme.of(context).accentColor,
                fontSize: 24.0),
          ),
        ),
      );
    });
}

要解决这类问题，您必须延迟触发模态底表。

onTap :() {
    Future.dalayed(Duration(seconds: 0).then((value) {
      showModalBottomSheet<void>(
      context: context,
       builder: (BuildContext context) {
       return new Container(
        child: new Padding(
        padding: const EdgeInsets.all(32.0),
         child: new Text(
        'This is the modal bottom sheet. Click anywhere to dismiss.',
        textAlign: TextAlign.center,
        style: new TextStyle(
            color: Theme.of(context).accentColor,
            fontSize: 24.0),
                   ),
                  ),
                 );
                });

              }

          }