flutter -如何在顶部和底部对齐(这是问题所在)-和列的中间部分

import 'package:flutter/material.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: Text('Flutter Alignment'),
        ),
        body: Container(
          child: Column(
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: [
              Container(
                color: Colors.blue,
                height: 100,
                child: Center(
                  child: Text('顶部对齐'),
                ),
              ),
              Expanded(
                child: Container(
                  color: Colors.green,
                  child: Center(
                    child: Text('中间部分'),
                  ),
                ),
              ),
              Container(
                color: Colors.red,
                height: 100,
                child: Center(
                  child: Text('底部对齐'),
                ),
              ),
            ],
          ),
        ),
      ),
    );
  }
}