更新日期：

您需要使用StatefulBuilder更新底部表单的状态
下面是示例代码

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  bool setToMaxHeight = false;

  @override
  Widget build(BuildContext context) {
    return Center(
      child: ElevatedButton(
        child: const Text('showModalBottomSheet'),
        onPressed: () {
          showModalBottomSheet<void>(
            isScrollControlled: true,
            context: context,
            builder: (BuildContext context) {
              return StatefulBuilder(builder: (BuildContext context,
                  StateSetter setState) { //this
                return Container(
                  height: setToMaxHeight ? 600 : 300, //this
                  color: Colors.amber,
                  child: Center(
                    child: Column(
                      mainAxisAlignment: MainAxisAlignment.center,
                      mainAxisSize: MainAxisSize.min,
                      children: <Widget>[
                        Text('Max Height: ${setToMaxHeight ? 600 : 300}'),
                        const SizedBox(height: 12),
                        ElevatedButton(
                          child: const Text('Toggle BottomSheet Size'),
                          onPressed: () {
                            setState(() {
                              setToMaxHeight = !setToMaxHeight;
                            }); //this

                          },
                        ),
                        const SizedBox(height: 12),
                        ElevatedButton(
                          child: const Text('Close BottomSheet'),
                          onPressed: () => Navigator.pop(context),
                        ),
                      ],
                    ),
                  ),
                );
              });
            },
          );
        },
      ),
    );
  }
}

记下isScrollControlled属性并将其设置为true

对于底部图纸，需要设置图纸的高度。
和设置高度之前设置启用此选项

isScrollControlled: true,

height: MediaQuery.of(context).size.height - 100,