四、結合SingleChildScrollView和Stack

我們也可以結合ScrollView和Stack來實現鍵盤頂起底部的效果。具體操作是將輸入框與底部內容放置在Stack中，并將Stack放置在SingleChildScrollView中。當鍵盤彈出時，可以與第一種方法類似地通過AnimationController將底部內容滑動到屏幕中央。

class MyWidget extends StatefulWidget {
  @override
  _MyWidgetState createState() => _MyWidgetState();
}

class _MyWidgetState extends State
    with SingleTickerProviderStateMixin {
  double _offset = 0.0;

  bool _isKeyboardShowing = false;

  late final AnimationController _controller = AnimationController(
      duration: const Duration(milliseconds: 200), vsync: this);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      resizeToAvoidBottomInset: false,
      appBar: AppBar(
        title: Text("Stack and SingleChildScrollView"),
      ),
      body: SingleChildScrollView(
        child: Stack(
          children: [
            Column(
              children: [
                Container(
                  height: 800,
                ),
              ],
            ),
            Positioned(
              bottom: _offset,
              left: 0,
              right: 0,
              child: Container(
                color: Colors.lightBlue,
                height: 140,
                child: Center(
                  child: GestureDetector(
                    onTap: () {
                      FocusScope.of(context).requestFocus(FocusNode());
                    },
                    child: Text(
                      "Input",
                      style: TextStyle(
                        fontSize: 30,
                        color: Colors.white,
                      ),
                    ),
                  ),
                ),
              ),
            ),
          ],
        ),
      ),
    );
  }

  @override
  void initState() {
    super.initState();
    _controller.addListener(() {
      setState(() {
        _offset =
            MediaQuery.of(context).viewInsets.bottom * _controller.value;
      });
    });
    _controller.addStatusListener((status) {
      if (status == AnimationStatus.completed) {
        setState(() {
          _isKeyboardShowing = true;
        });
      } else if (status == AnimationStatus.dismissed) {
        setState(() {
          _isKeyboardShowing = false;
        });
      }
    });
  }

  @override
  void dispose() {
    _controller.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      resizeToAvoidBottomInset: false,
      appBar: AppBar(
        title: Text("Stack and SingleChildScrollView"),
      ),
      body: SingleChildScrollView(
        child: Stack(
          children: [
            Column(
              children: [
                Container(
                  height: 800,
                ),
                GestureDetector(
                  onTap: () {
                    FocusScope.of(context).requestFocus(FocusNode());
                  }
                  child: // input widget
                ),
              ],
            ),
            Positioned(
              bottom: _offset,
              left: 0,
              right: 0,
              child: Container(
                color: Colors.lightBlue,
                height: 140,
                child: Center(
                  child: GestureDetector(
                    onTap: () {
                      FocusScope.of(context).requestFocus(FocusNode());
                    },
                    child: Text(
                      "Input",
                      style: TextStyle(
                        fontSize: 30,
                        color: Colors.white,
                      ),
                    ),
                  ),
                ),
              ),
            )
          ],
        ),
      ),
    );
  }

  void _handleFocusChange() {
    if (FocusScope.of(context).hasFocus != _isKeyboardShowing) {
      _isKeyboardShowing = FocusScope.of(context).hasFocus;
      _controller.animateTo(
          _isKeyboardShowing ? 1.0 : 0.0,
          duration: const Duration(milliseconds: 150),
          curve: Curves.linear);
    }
  }
}