in flutter page textfield hidden by keyboard

问题

I'm using flutter to make a page that someone can comment.And the page is shown by showModalBottomSheet. but the textfield is hidden by the keyboard when the keyboard showing in the front.

    flutter doctor output:
    Doctor summary (to see all details, run flutter doctor -v):
    [✓] Flutter (Channel stable, v1.0.0, on Mac OS X 10.14 18A391, locale zh-Hans-CN)
    [!] Android toolchain - develop for Android devices (Android SDK 28.0.3)
     ✗ Android license status unknown.
    [✓] iOS toolchain - develop for iOS devices (Xcode 10.1)
    [✓] Android Studio (version 3.1)
    [!] VS Code (version 1.30.0)
    [✓] Connected device (1 available)

---

Code snippet:

showModalBottomSheet(
            context: context,
            builder: (BuildContext sheetContext) {
              return new Container(
                height: 230.0,
                padding: const EdgeInsets.all(20.0),
                child: ListView(
                  children: <Widget>[
                    new Column(
                      children: <Widget>[
                        new Row(
                          children: <Widget>[
                            new Text(isMainFloor ? "reply author" :"reply"),
                            new Expanded(
                                child: new Text(
                              title,
                              style: new TextStyle(color: const Color(0xFF63CA6C)),
                            )),
                            new InkWell(
                              child: new Container(
                                padding:
                                    const EdgeInsets.fromLTRB(10.0, 6.0, 10.0, 6.0),
                                decoration: new BoxDecoration(
                                    border: new Border.all(
                                      color: const Color(0xFF63CA6C),
                                      width: 1.0,
                                    ),
                                    borderRadius: new BorderRadius.all(
                                        new Radius.circular(6.0))),
                                child: new Text( "send",
                                  style:
                                      new TextStyle(color: const Color(0xFF63CA6C)),
                                ),
                              ),
                              onTap: () {

                                sendReply(authorId);
                              },
                            )
                          ],
                        ),
                        new Container(
                          height: 10.0,
                        ),
                        new TextFormField(
                          maxLines: 5,
                          controller: _inputController,
                          focusNode: _focusNode,
                          decoration: new InputDecoration(
                              hintText: "balabala……",
                              hintStyle:
                                  new TextStyle(color: const Color(0xFF808080)),
                              border: new OutlineInputBorder(
                                borderRadius: const BorderRadius.all(
                                    const Radius.circular(10.0)),
                              )),
                        ),
                        new Padding(
                            padding: EdgeInsets.only(
                                bottom: MediaQuery.of(context).viewInsets.bottom)),
                      ],
                    )
                  ],
                ),
              );
            });
      }

来源：https://stackoverflow.com/questions/54196213/in-flutter-page-textfield-hidden-by-keyboard