使用'=='比较双精度值不是很可靠，应该避免（不仅在Dart中，而且在大多数语言中）。
你可以这样做

methodname(num radians) {
  // you can adjust this values according to your accuracy requirements
  const myPI = 3142; 
  int r = (radians * 1000).round();

  switch (r) {
    case 0:
      // do something
      break;
    case myPI: 
      // do something else
      break;
  }
}

此问题包含一些您可能感兴趣的附加信息

• comparing float/double values using == operator
• How should I do floating point comparison?

更多信息：

• https://www.dartlang.org/docs/spec/latest/dart-language-specification.html#h.50ae78s6gbw2
• http://floating-point-gui.de/errors/comparison/

以下是Dart中的开关案例。
问：写一个程序来打印给定数字的乘法表。接受用户的输入并显示其乘法表

import 'dart:io';

void main(List<String> args) {
  print('enter a number from 1 to 7');

  var input = stdin.readLineSync();

  int day = int.parse(input!);

  switch (day) {
    case 1:
      print('Sunday');
      break;

    case 2:
      print('Monday');
      break;

    case 3:
      print('Tuesday');
      break;

    case 4:
      print('Wednesday');
      break;
    case 5:
      print('Thursday');
      break;

    case 6:
      print('Friday');
      break;
    case 7:
      print('Saturday');
      break;
    default:
      print(' invalid entry');
  }
}

我认为Dart 3的switch expression为此提供了更简洁的语法。

bool methodname(num radians) {
  const myPI = 3142;
  int r = (radians * 1000).round();

  return switch (r) {
    myPI => true,
    _ => false,
  };
}