SizedOverflowBox 尺寸溢出盒

可容纳一个子组件，且子组件允许溢出父组件区域，可以通过size属性对子组件进行偏移，拥有对齐属性alignment。

相关组件

OverflowBox

SizedOverflowBox基本使用

   <br />【child】 : 孩子组件   【Widget】<br />【size】 : 尺寸偏移   【Size】<br />【alignment】 : 对齐方式   【AlignmentGeometry】<br />![194.gif](https://cdn.nlark.com/yuque/0/2020/gif/326147/1589508609454-b8ce3927-abd2-4dd1-93cc-bf381ccdd3fa.gif#align=left&display=inline&height=210&margin=%5Bobject%20Object%5D&name=194.gif&originHeight=210&originWidth=397&size=421860&status=done&style=none&width=397)

import 'package:flutter/material.dart';
class CustomSizedOverflowBox extends StatefulWidget {

  @override
  _CustomSizedOverflowBoxState createState() => _CustomSizedOverflowBoxState();
}

class _CustomSizedOverflowBoxState extends State<CustomSizedOverflowBox> {
  double _x = 50;
  double _y = 44;

  @override
  Widget build(BuildContext context) {
    var box = SizedOverflowBox(
      alignment: Alignment.bottomRight,
      size: Size(_x, _y),
      child: Container(width: 30, height: 50, color: Colors.orange),
    );
    return Column(
      children: <Widget>[
        Container(
            alignment: Alignment.topLeft,
            color: Colors.grey.withAlpha(88),
            width: 250,
            height: 60,
            child: box),
        _buildSlider()
      ],
    );
  }

  Widget _buildSlider() =>
      Column(
        children: <Widget>[
          Slider(
              divisions: 100,
              min: 0,
              max: 250,
              label: 'x:' + _x.toStringAsFixed(1),
              value: _x,
              onChanged: (v) => setState(() => _x = v)),
          Slider(
              divisions: 100,
              min: 0,
              max: 100,
              label: 'y:' + _y.toStringAsFixed(1),
              value: _y,
              onChanged: (v) => setState(() => _y = v)),

        ],
      );
}