紧约束（Tight Constraints）

定义：紧约束指的是父组件对其子组件施加了严格的大小限制。例如，如果一个父组件给子组件提供了具体的宽度和高度，那么子组件只能在这个范围内绘制。

例子：使用 SizedBox、Container 指定 width 和 height。

例子

不使用ConstrainedBox

import 'package:flutter/material.dart';

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return  MaterialApp(
      home: Scaffold(
        body: Container(
          color: Colors.blue,
          width: 59,
          height: 50,
        ),
      ),
    );
  }
}

使用ConstrainedBox

import 'package:demo/pages/home_page.dart';
import 'package:flutter/material.dart';

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return  MaterialApp(
      home: Scaffold(
        body: ConstrainedBox(
          constraints: const BoxConstraints(
            maxWidth: 25,
            maxHeight: 25,
          ),
          child: Container(
            color: Colors.blue,
            width: 59,
            height: 50,
          ),
        ),
      ),
    );
  }
}

import 'package:demo/pages/home_page.dart';
import 'package:flutter/material.dart';

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return  MaterialApp(
      home: Scaffold(
        body: Center(
          child: ConstrainedBox(
            constraints: const BoxConstraints(
              minWidth: 200,
              minHeight: 200
            ),
            child: Container(
              color: Colors.blue,
              width: 100,
              height: 100,
            ),
          ),
        ),
      ),
    );
  }
}

import 'package:demo/pages/home_page.dart';
import 'package:flutter/material.dart';

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    // TODO: implement build
    return  MaterialApp(
      home: Scaffold(
        body: Center(
          child: ConstrainedBox(
            constraints: const BoxConstraints.tight(Size(200, 200)),
            child: Container(
              color: Colors.blue,
              width: 100,
              height: 100,
            ),
          ),
        ),
      ),
    );
  }
}