優雅地解析C＃枚舉

Question

有沒有人有解析枚舉更優雅的解決方案？以下對我來說似乎是一團糟。

UserType userType = (UserType)Enum.Parse(typeof(UserType), iUserType.ToString()); 

Answer 1

我經常做一個通用的幫手吧：

public static T ParseEnum<T>(string value) where T:struct 
{ 
    return (T)Enum.Parse(typeof(T), value); 
} 

可以結合起來，與Jon Skeet'sUnstrained Melody（或任何其他職位IL處理器），以獲得在枚舉適當類型的約束，但是可選的。

然後你可以使用它像這樣：

var enumValue = ParseEnum<UserType>(iUserType.ToString()); 

---

.NET框架4.0還帶有Enum.TryParse這也提供了類似的語法，並提供一種方法來處理，如果解析失敗。例如：

UserType userType; 
if (Enum.TryParse<UserType>(iUserType.ToString(), out userType)) 
{ 
    //Yay! Parse succeeded. The userType variable has the value. 
} 
else 
{ 
    //Oh noes! The parse failed! 
} 

Answer 2

您可以創建這樣

public static class EnumExtensions 
{ 
    public static T ToEnum<T>(this string s) 
    { 
     return (T)Enum.Parse(typeof(T), s); 
    } 
} 

的extesion方法，然後在代碼中，你可以使用這種方式（MyEnum包含值A和B）：

string s = "B"; 
MyEnum e = s.ToEnum<MyEnum>(); 

Answer 3

以下是基於@vcsjones版本和反饋的擴展方法，以及來自@Mones示例：

public enum TestEnum 
{ 
    None, 
    A, 
    B, 
}; 

void Main() 
{ 
    var testValues = new List<object>(); 
    testValues.AddRange(Enumerable.Range(-2, 6).Select(i => (object)i)); 
    testValues.AddRange(new List<string>() { String.Empty, "A", "B", "C", null }); 

    foreach (var testValue in testValues) 
    { 
     Console.WriteLine($"Testing value {testValue ?? String.Empty}:"); 
     TestEnum output; 
     var enumValues = Enum.GetNames(typeof(TestEnum)).ToList(); 
     try 
     { 
      if (TestEnum.TryParse(testValue.ToString(), out output)) 
      { 
       Console.WriteLine($"Succeeded with TryParse on {testValue} to {output}"); 
      } 
      else 
      { 
       Console.WriteLine($"Failed to TryParse on {testValue}"); 
      } 
     } 
     catch (Exception ex) 
     { 
      Console.WriteLine($"Test harness caught an exception: {ex.ToString()}"); 
     } 

     var toEnumOutput = (testValue ?? String.Empty).ToString().Parse<TestEnum>(); 
     Console.WriteLine($"Parse<TEnum> returned {toEnumOutput}"); 

     Console.WriteLine(); 
     Console.WriteLine(); 
    } 

} 


public static class EnumExtensions 
{ 
    public static TEnum Parse<TEnum>(this string value) where TEnum : struct 
    { 
     TEnum output = default(TEnum); 
     var enumValues = Enum.GetNames(typeof(TEnum)).ToList(); 

     if (Enum.TryParse<TEnum>(value, true, out output)) 
      if (Enum.IsDefined(typeof(TEnum), value) || value.ToString().Contains(",") || enumValues.Contains(output.ToString())) 
      { 
       Console.WriteLine($"Converted '{value}' to {output}."); 
       return output; 
      } 
      else 
      { 
       Console.WriteLine($"{value} is not an underlying value of the enumeration."); 
      } 
     else 
     { 
      Console.WriteLine($"{value} is not a member of the enumeration."); 
     } 
     return default(TEnum); 
    } 
} 

個

測試工具給出了這樣的輸出：

Testing value -2: 
Succeeded with TryParse on -2 to -2 
-2 is not an underlying value of the enumeration. 
Parse<TEnum> returned None 


Testing value -1: 
Succeeded with TryParse on -1 to -1 
-1 is not an underlying value of the enumeration. 
Parse<TEnum> returned None 


Testing value 0: 
Succeeded with TryParse on 0 to None 
Converted '0' to None. 
Parse<TEnum> returned None 


Testing value 1: 
Succeeded with TryParse on 1 to A 
Converted '1' to A. 
Parse<TEnum> returned A 


Testing value 2: 
Succeeded with TryParse on 2 to B 
Converted '2' to B. 
Parse<TEnum> returned B 


Testing value 3: 
Succeeded with TryParse on 3 to 3 
3 is not an underlying value of the enumeration. 
Parse<TEnum> returned None 


Testing value : 
Failed to TryParse on 
is not a member of the enumeration. 
Parse<TEnum> returned None 


Testing value A: 
Succeeded with TryParse on A to A 
Converted 'A' to A. 
Parse<TEnum> returned A 


Testing value B: 
Succeeded with TryParse on B to B 
Converted 'B' to B. 
Parse<TEnum> returned B 


Testing value C: 
Failed to TryParse on C 
C is not a member of the enumeration. 
Parse<TEnum> returned None 


Testing value : 
Test harness caught an exception: System.NullReferenceException: Object reference not set to an instance of an object. 
    at UserQuery.Main() in C:\Users\Colin\AppData\Local\Temp\3\LINQPad5\_zhvrhwll\query_ludjga.cs:line 49 
is not a member of the enumeration. 
Parse<TEnum> returned None 

參考文獻：

• .NET Programming Guide: Constraints on Type Parameters
• Sriram Sakthivel's mention of where TEnum: struct
• MSDN: Enum.TryParse Method (String, Boolean, TEnum)

Answer 4

哦我碰到泰勒·布林克利的來到圖書館做這個和更多！

這另一個StackOverflow答案Generic version of Enum.Parse in C#導致Jon Skeet的Unconstrained Melody圖書館網站，其中指示我們改爲Enums.NET。哇。