还记得在使用Row和Column组件的时候，我们内部的内容都聚集在一起的的吗？如果要让他们占满一行或一列进行平均分配或比例分配就需要Expanded组件。

Expanded有一个flex属性比较常用。flex表示弹性系数，默认是1。

1、将一行的内容进行比例分配

import 'package:flutter/material.dart';

class LayoutExpandedWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text('弹性布局组件：Expanded'),
          elevation: 0.0,
          centerTitle: true,
        ),
        body: Column(
          children: [
            Text("等比分配"),
            Row(
              children: [
                Expanded(
                  child: Text("Row Text Left"),
                ),
                Expanded(
                  child: Icon(Icons.add),
                ),
                Expanded(
                  child: Text("Row Text Right"),
                ),
              ],
            ),
            Row(
              children: [
                Expanded(
                  child: Container(
                    height: 150,
                    child: Text("Row Text Left"),
                    color: Colors.red,
                  ),
                ),
                Expanded(
                  child: Container(
                    height: 150,
                    child: Icon(Icons.add),
                    color: Colors.blue,
                  ),
                ),
                Expanded(
                  child: Container(
                    height: 150,
                    child: Text("Row Text Right"),
                    color: Colors.yellow,
                  ),
                )
              ],
            ),
            Text("指定比例分配，需要设置flex：2:1:5"),
            Row(
              children: [
                Expanded(
                  flex: 2,
                  child: Container(
                    height: 150,
                    child: Text("Row Text Left"),
                    color: Colors.red,
                  ),
                ),
                Expanded(
                  flex: 1,
                  child: Container(
                    height: 150,
                    child: Icon(Icons.add),
                    color: Colors.blue,
                  ),
                ),
                Expanded(
                  flex: 5,
                  child: Container(
                    height: 150,
                    child: Text("Row Text Right"),
                    color: Colors.yellow,
                  ),
                )
              ],
            ),
          ],
        ));
  }
}

2、将一列的内容进行比例分配

import 'package:flutter/material.dart';

class LayoutExpandedWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('弹性布局组件：Expanded'),
        elevation: 0.0,
        centerTitle: true,
      ),
      body: Row(
        children: [
          Column(
            children: [
              Expanded(
                child: Text("Row Text Left"),
              ),
              Expanded(
                child: Icon(Icons.add),
              ),
              Expanded(
                child: Text("Row Text Right"),
              ),
            ],
          ),
          Column(
            children: [
              Expanded(
                child: Container(
                  height: 150,
                  child: Text("Row Text Left"),
                  color: Colors.red,
                ),
              ),
              Expanded(
                child: Container(
                  height: 150,
                  child: Icon(Icons.add),
                  color: Colors.blue,
                ),
              ),
              Expanded(
                child: Container(
                  height: 150,
                  child: Text("Row Text Right"),
                  color: Colors.yellow,
                ),
              )
            ],
          ),
          Column(
            children: [
              Expanded(
                flex: 2,
                child: Container(
                  height: 150,
                  child: Text("Row Text Left"),
                  color: Colors.red,
                ),
              ),
              Expanded(
                flex: 1,
                child: Container(
                  height: 150,
                  child: Icon(Icons.add),
                  color: Colors.blue,
                ),
              ),
              Expanded(
                flex: 5,
                child: Container(
                  height: 150,
                  child: Text("Row Text Right"),
                  color: Colors.yellow,
                ),
              )
            ],
          ),
        ],
      ),
    );
  }
}