void main() {
  final p = PortType.fromString('USB-C');
  print(p);
  print(p.isUSB);
}

enum PortType {
  usbA('USB-A', isUSB: true),
  usbC('USB-C', isUSB: true),
  lightning('LIGHTNING'),
  unknown('UNKNOWN');

  final String name;
  final bool isUSB;

  const PortType(this.name, {this.isUSB = false});

  static PortType fromString(String name) {
    return values.firstWhere((v) => v.name == name,
        orElse: () => PortType.unknown);
  }
}

Waiting for connection from debug service on Chrome...
Error: Cannot run with sound null safety, because the following dependencies
don't support null safety:

 - package:xxxx

void main() {
    print("准备 GZip压缩");

    //原始字符串
    const testString = '测试一下GZip压缩字符串';
    //GZip 压缩后的文本
    final zipString = GzipUtil.gzipEncode(testString);

    print("GZip 编码-$zipString");

    //GZip 解压
    final zipString2 = GzipUtil.gzipDecode(zipString);

    print("GZip 解码-$zipString2");
  
}

import 'dart:convert';
import 'dart:io';

class GzipUtil {
  ///GZIP 压缩
  static String? gzipEncode(String? str) {
    if (str == null) return str;
    //先来转换一下
    final stringBytes = utf8.encode(str);
    //然后使用 gzip 压缩
    final gzipBytes = GZipCodec().encode(stringBytes);
    //然后再编码一下进行网络传输
    final compressedString = base64UrlEncode(gzipBytes);
    return compressedString;
  }

  ///GZIP 解压缩
  static String? gzipDecode(String? str) {
    if (str == null) return str;
    //先来解码一下
    final List<int> stringBytes = base64Url.decode(str);
    //然后使用 gzip 压缩
    final gzipBytes = GZipCodec().decode(stringBytes);
    //然后再编码一下
    final compressedString = utf8.decode(gzipBytes);
    return compressedString;
  }
}

/// Creates a stack layout widget.
///
/// By default, the non-positioned children of the stack are aligned by their
/// top left corners.
Stack({
  Key? key,
  this.alignment = AlignmentDirectional.topStart,
  this.textDirection,
  this.fit = StackFit.loose,
  @Deprecated(
    'Use clipBehavior instead. See the migration guide in flutter.dev/go/clip-behavior. '
    'This feature was deprecated after v1.22.0-12.0.pre.'
  )
  this.overflow = Overflow.clip,
  this.clipBehavior = Clip.hardEdge,
  List<Widget> children = const <Widget>[],
})

import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(title: 'Stack Demo', home: StackDemo()),
  );
}

class StackDemo extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text('Stack 组件'),
      ),
      body: Stack(
        children: <Widget>[
          Container(
            width: 100,
            height: 100,
            color: Colors.red,
          ),
          Container(
            width: 90,
            height: 90,
            color: Colors.blue,
          ),
          Container(
            width: 80,
            height: 80,
            color: Colors.green,
          ),
        ],
      ),
    );
  }
}

void main() {
  double price = 100 / 3;

  //原始值， 结果为 33.333333333333336。
  print("price = $price");

  //舍弃当前变量的小数部分，结果为 33。返回值为 int 类型。
  print("price.truncate() = ${price.truncate()}");

  //舍弃当前变量的小数部分，浮点数形式表示，结果为 33.0。返回值为 double。
  print("price.truncateToDouble() = ${price.truncateToDouble()}");

  //舍弃当前变量的小数部分，结果为 33。返回值为 int 类型。
  print("price.toInt() = ${price.toInt()}");

  //小数部分向上进位，结果为 34。返回值为 int 类型。
  print("price.ceil() = ${price.ceil()}");

  //小数部分向上进位，结果为 34.0。返回值为 double。
  print("price.ceilToDouble() = ${price.ceilToDouble()}");

  //当前变量四舍五入后取整，结果为 33。返回值为 int 类型。
  print("price.round() = ${price.round()}");

  //当前变量四舍五入后取整，结果为 33.0。返回值为 double 类型。
  print("price.roundToDouble() = ${price.roundToDouble()}");

  //取整: 忽略小数位,返回int整数，结果为 33。
  final int number = 100 ~/ 3;
  print("number = $number");
}

void main() {
  Animal animal = new Animal('cat');
  Animal empty = null;

  //animal 非空，返回 animal.name 的值 cat
  print(animal?.name);
  //empty 为空，返回 null
  print(empty?.name);

  //animal 非空，可以直接访问 animal.name 的值 cat
  print(animal.name);
  //empty 为空，抛出异常
  print(empty.name);
}

class Animal {
  final String name;
  Animal(this.name);
}