c＃“Enum”方法和“枚举”参数 [英] c# "Enum" on method and "enum" parameter

问题描述

我有一个扩展方法，以枚举为参数。

  public static T GetEntry< T>（此字典<枚举，字符串>字典，枚举键）
 {
 string val; 
 if（dictionary.TryGetValue（key，out val））
 {
 return（T）Convert.ChangeType（val，typeof（T））; 
} 
返回默认（T）; 
} 
  

但是当我尝试使用一个声明的枚举时，编译器不能找到扩展方法

 字典< CmdAttr，String>属性; 
 cmd.CommandText.Attributes.GetEntry< double>（CommandText.CmdAttr.X）; 
  

任何想法如何使这项工作除了将该字典声明为

 字典<枚举，字符串>属性
  

哪些工作有点失败，具有一个声明的枚举？

非常感谢

解决方案

你不能像你想要那样做，因为个人枚举不是枚举的子类。但是，虽然这段代码并不像你想要的那样漂亮，但它并不难看，它的工作原理如下：

  // MyTestEnum.cs 
 
枚举MyTestEnum 
 {
首先，
第二，
第三
} 
 
 // Extensions.cs 
 
 static class Extensions 
 {
 public static TResult GetEntry< TEnum，TResult>（此字典< TEnum，string>字典，TEnum键）
 {
 string value; 
 if（dictionary.TryGetValue（key，out value））
 {
 return（TResult）Convert.ChangeType（value，typeof（TResult））; 
} 
 return default（TResult）; 
} 
} 
 
 //最有可能的Program.cs 
 
 void Main（）
 {
 Dictionary< MyTestEnum，串GT; attributes = new Dictionary< MyTestEnum，string>（）; 
 attributes.Add（MyTestEnum.First，1.23）; 
 
 // ***这里是扩展方法的实际调用*** 
 var result = attributes.GetEntry< MyTestEnum，double>（MyTestEnum.First）; 
 
 Console.WriteLine（result）; 
} 
  

This is a difficult question to google!

I have an extension method that takes "Enum" as a parameter.

    public static T GetEntry<T>(this Dictionary<Enum, string> dictionary, Enum key)
    {
        string val;
        if (dictionary.TryGetValue(key, out val))
        {
            return (T)Convert.ChangeType(val, typeof(T));               
        }
        return default(T);
    }

but when I try to use it with a declared enum the compiler can't find the extension method

Dictionary<CmdAttr, String> Attributes;
cmd.CommandText.Attributes.GetEntry<double>(CommandText.CmdAttr.X);

Any idea how to make this work other than to declare the dictionary as

Dictionary<Enum, String> Attributes

which works but kind of defeats the point in having a declared enum?

Many Thanks

解决方案

You can't do it exactly like you want to, because individual enums are not subclasses of Enum. But although this code isn't as pretty as you'd like, it's hardly ugly, and it works as you'd like:

// MyTestEnum.cs

enum MyTestEnum
{
    First,
    Second,
    Third
}

// Extensions.cs

static class Extensions
{
    public static TResult GetEntry<TEnum, TResult>(this Dictionary<TEnum, string> dictionary, TEnum key)
    {
        string value;
        if (dictionary.TryGetValue(key, out value))
        {
            return (TResult)Convert.ChangeType(value, typeof(TResult));
        }
        return default(TResult);
    }
}

// most likely Program.cs

void Main()
{
    Dictionary<MyTestEnum, string> attributes = new Dictionary<MyTestEnum, string>();
    attributes.Add(MyTestEnum.First, "1.23");

    // *** here's the actual call to the extension method ***
    var result = attributes.GetEntry<MyTestEnum, double>(MyTestEnum.First);

    Console.WriteLine(result);
}

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