Flutter 布局参考手册：Stack

Stack

非常适用于将部件叠加在一起

@override
Widget build(BuildContext context) {
  Widget main = Scaffold(
    appBar: AppBar(title: Text('Stack')),
  );

  return Stack(
    fit: StackFit.expand,
    children: <Widget>[
      main,
      Banner(
        message: "Top Start",
        location: BannerLocation.topStart,
      ),
      Banner(
        message: "Top End",
        location: BannerLocation.topEnd,
      ),
      Banner(
        message: "Bottom Start",
        location: BannerLocation.bottomStart,
      ),
      Banner(
        message: "Bottom End",
        location: BannerLocation.bottomEnd,
      ),
    ],
  );
}
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如果想使用自己的部件，需要将它们放置在 Positioned 里面

Widget build(BuildContext context) {
  return Scaffold(
    appBar: AppBar(title: Text('Stack')),
    body: Stack(
      fit: StackFit.expand,
      children: <Widget>[
        Material(color: Colors.yellowAccent),
        Positioned(
          top: 0,
          left: 0,
          child: Icon(Icons.star, size: 50),
        ),
        Positioned(
          top: 340,
          left: 250,
          child: Icon(Icons.call, size: 50),
        ),
      ],
    ),
  );
}
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如果你不想去猜测 top 或 bottom 的值，你可以使用 LayoutBuilder 来检索它们

Widget build(BuildContext context) {
  const iconSize = 50;
  return Scaffold(
    appBar: AppBar(title: Text('Stack with LayoutBuilder')),
    body: LayoutBuilder(
      builder: (context, constraints) =>
        Stack(
          fit: StackFit.expand,
          children: <Widget>[
            Material(color: Colors.yellowAccent),
            Positioned(
              top: 0,
              child: Icon(Icons.star, size: iconSize),
            ),
            Positioned(
              top: constraints.maxHeight - iconSize,
              left: constraints.maxWidth - iconSize,
              child: Icon(Icons.call, size: iconSize),
            ),
          ],
        ),
    ),
  );
}