我想在单击应用栏上的按钮时创建一个弹出菜单.. 我希望出现这样的东西:

有没有办法在 flutter 中做到这一点？包什么的？

最佳答案

我试过了，但我在以这种方式显示子小部件时遇到了一些问题。所以，这里有两个解决方案:

class TestScreen extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _TestScreenState();
}

class _TestScreenState extends State<TestScreen> with SingleTickerProviderStateMixin {
  AnimationController animationController;
  bool _menuShown = false;

  @override
  void initState() {
    animationController = AnimationController(vsync: this, duration: Duration(milliseconds: 500));
    super.initState();
  }

  @override
  Widget build(BuildContext context) {    
    Animation opacityAnimation = Tween(begin: 0.0, end: 1.0).animate(animationController);
    if (_menuShown)
      animationController.forward();
    else
      animationController.reverse();
    return Scaffold(
      appBar: AppBar(
        actions: <Widget>[IconButton(icon: Icon(Icons.menu), onPressed: (){
          setState(() {
            _menuShown = !_menuShown;
          });
        })],
      ),
      body: Stack(
        overflow: Overflow.visible,
        children: <Widget>[
          Positioned(
            child: FadeTransition(
              opacity: opacityAnimation,
              child: _ShapedWidget(),
            ),
            right: 4.0,
            top: 16.0,
          ),
        ],
      ),
    );
  }
}

class _ShapedWidget extends StatelessWidget {
  _ShapedWidget();
  final double padding = 4.0;

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Material(
          clipBehavior: Clip.antiAlias,
          shape:
          _ShapedWidgetBorder(borderRadius: BorderRadius.all(Radius.circular(padding)), padding: padding),
          elevation: 4.0,
          child: Container(
            padding: EdgeInsets.all(padding).copyWith(bottom: padding * 2),
            child: SizedBox(width: 150.0, height: 250.0, child: Center(child: Text('ShapedWidget'),),),
          )),
    );
  }
}

class _ShapedWidgetBorder extends RoundedRectangleBorder {
  _ShapedWidgetBorder({
    @required this.padding,
    side = BorderSide.none,
    borderRadius = BorderRadius.zero,
  }) : super(side: side, borderRadius: borderRadius);
  final double padding;

  @override
  Path getOuterPath(Rect rect, {TextDirection textDirection}) {
    return Path()
      ..moveTo(rect.width - 8.0 , rect.top)
      ..lineTo(rect.width - 20.0, rect.top - 16.0)
      ..lineTo(rect.width - 32.0, rect.top)
      ..addRRect(borderRadius
          .resolve(textDirection)
          .toRRect(Rect.fromLTWH(rect.left, rect.top, rect.width, rect.height - padding)));
  }
}

在这种情况下，子小部件位于 appbar 下方

class TestScreen extends StatefulWidget {
  @override
  State<StatefulWidget> createState() => _TestScreenState();
}

class _TestScreenState extends State<TestScreen> with SingleTickerProviderStateMixin {
  AnimationController animationController;
  bool _menuShown = false;

  @override
  void initState() {


    animationController = AnimationController(vsync: this, duration: Duration(milliseconds: 500));
    super.initState();
  }

  @override
  Widget build(BuildContext context) {

    Animation opacityAnimation = Tween(begin: 0.0, end: 1.0).animate(animationController);
    if (_menuShown)
      animationController.forward();
    else
      animationController.reverse();
    return Scaffold(
      appBar: AppBar(
        elevation: 0.0,
        actions: <Widget>[Stack(
          overflow: Overflow.visible,
          children: <Widget>[IconButton(icon: Icon(Icons.menu), onPressed: (){
          setState(() {
            _menuShown = !_menuShown;
          });    
        }),
          Positioned(
            child: FadeTransition(
              opacity: opacityAnimation,
              child: _ShapedWidget(onlyTop: true,),
            ),
            right: 4.0,
            top: 48.0,
          ),    
          ],)],
      ),
      body: Stack(
        overflow: Overflow.visible,
        children: <Widget>[
          Positioned(
            child: FadeTransition(
              opacity: opacityAnimation,
              child: _ShapedWidget(),
            ),
            right: 4.0,
            top: -4.0,
          ),
        ],
      ),
    );
  }
}  

class _ShapedWidget extends StatelessWidget {
  _ShapedWidget({this.onlyTop = false});
  final double padding = 4.0;
  final bool onlyTop;

  @override
  Widget build(BuildContext context) {
    return Center(
      child: Material(
          clipBehavior: Clip.antiAlias,
          shape:
          _ShapedWidgetBorder(borderRadius: BorderRadius.all(Radius.circular(padding)), padding: padding),
          elevation: 4.0,
          child: Container(
            padding: EdgeInsets.all(padding).copyWith(bottom: padding * 2),
            child: onlyTop ? SizedBox(width: 150.0, height: 20.0,) :  SizedBox(width: 150.0, height: 250.0, child: Center(child: Text('ShapedWidget'),),),
          )),
    );
  }
}

class _ShapedWidgetBorder extends RoundedRectangleBorder {
  _ShapedWidgetBorder({
    @required this.padding,
    side = BorderSide.none,
    borderRadius = BorderRadius.zero,
  }) : super(side: side, borderRadius: borderRadius);
  final double padding;

  @override
  Path getOuterPath(Rect rect, {TextDirection textDirection}) {
    return Path()
      ..moveTo(rect.width - 8.0 , rect.top)
      ..lineTo(rect.width - 20.0, rect.top - 16.0)
      ..lineTo(rect.width - 32.0, rect.top)
      ..addRRect(borderRadius
          .resolve(textDirection)
          .toRRect(Rect.fromLTWH(rect.left, rect.top, rect.width, rect.height - padding)));
  }
}

在这种情况下，子小部件的顶部位于 appbar 上，但 appbar 的高度必须为 0.0

其实我觉得这两种解决方案都不完整，但是可以帮助你找到你需要的东西

关于dart - 如何使用 flutter 创建自定义弹出菜单，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/53811115/