从字符串枚举 [英] Enum from String

问题描述

我有一个 Enum 和一个函数从 String 创建它，因为我找不到一个

I have an Enum and a function to create it from a String because i couldn't find a built in way to do it

enum Visibility{VISIBLE,COLLAPSED,HIDDEN}

Visibility visibilityFromString(String value){
  return Visibility.values.firstWhere((e)=>
      e.toString().split('.')[1].toUpperCase()==value.toUpperCase());
}

//used as
Visibility x = visibilityFromString('COLLAPSED');

但似乎我必须为每个Enum重写这个函数，写相同的函数，它需要Enum类型作为参数？我试图，但我想出，我不能转换到枚举。

but it seems like i have to rewrite this function for every Enum i have, is there a way to write the same function where it takes the Enum type as parameter? i tried to but i figured out that i can't cast to Enum.

//is something with the following signiture actually possible?
     dynamic enumFromString(Type enumType,String value){

     }

推荐答案

使用镜像可以强制某些行为。我有两个想法。不幸的是，Dart不支持类型化函数：

Using mirrors you could force some behaviour. I had two ideas in mind. Unfortunately Dart does not support typed functions:

import 'dart:mirrors';

enum Visibility {VISIBLE, COLLAPSED, HIDDEN}

class EnumFromString<T> {
  T get(String value) {
    return (reflectType(T) as ClassMirror).getField(#values).reflectee.firstWhere((e)=>e.toString().split('.')[1].toUpperCase()==value.toUpperCase());
  }
}

dynamic enumFromString(String value, t) {
  return (reflectType(t) as ClassMirror).getField(#values).reflectee.firstWhere((e)=>e.toString().split('.')[1].toUpperCase()==value.toUpperCase());
}

void main() {
  var converter = new EnumFromString<Visibility>();

  Visibility x = converter.get('COLLAPSED');
  print(x);

  Visibility y = enumFromString('HIDDEN', Visibility);
  print(y);
}

输出：

Visibility.COLLAPSED
Visibility.HIDDEN

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