c# - 任何人都知道一种快速获取枚举值自定义属性的方法吗？

Question

这可能最好用一个例子来说明。我有一个带有属性的枚举:

public enum MyEnum {

    [CustomInfo("This is a custom attrib")]
    None = 0,

    [CustomInfo("This is another attrib")]
    ValueA,

    [CustomInfo("This has an extra flag", AllowSomething = true)]
    ValueB,
}

我想从实例中获取这些属性:

public CustomInfoAttribute GetInfo( MyEnum enumInput ) {

    Type typeOfEnum = enumInput.GetType(); //this will be typeof( MyEnum )

    //here is the problem, GetField takes a string
    // the .ToString() on enums is very slow
    FieldInfo fi = typeOfEnum.GetField( enumInput.ToString() );

    //get the attribute from the field
    return fi.GetCustomAttributes( typeof( CustomInfoAttribute  ), false ).
        FirstOrDefault()        //Linq method to get first or null
        as CustomInfoAttribute; //use as operator to convert
}

因为这是使用反射，所以我预计会有些慢，但是当我已经有了它的实例时，将枚举值转换为字符串(反射(reflect)名称)似乎很麻烦。

有没有人有更好的方法？

Answer 1

这可能是最简单的方法。

一种更快的方法是使用动态方法和 ILGenerator 静态发出 IL 代码。虽然我只将它用于 GetPropertyInfo，但不明白为什么您也不能发出 CustomAttributeInfo。

例如从属性发出 getter 的代码

public delegate object FastPropertyGetHandler(object target);    

private static void EmitBoxIfNeeded(ILGenerator ilGenerator, System.Type type)
{
    if (type.IsValueType)
    {
        ilGenerator.Emit(OpCodes.Box, type);
    }
}

public static FastPropertyGetHandler GetPropertyGetter(PropertyInfo propInfo)
{
    // generates a dynamic method to generate a FastPropertyGetHandler delegate
    DynamicMethod dynamicMethod =
        new DynamicMethod(
            string.Empty, 
            typeof (object), 
            new Type[] { typeof (object) },
            propInfo.DeclaringType.Module);

    ILGenerator ilGenerator = dynamicMethod.GetILGenerator();
    // loads the object into the stack
    ilGenerator.Emit(OpCodes.Ldarg_0);
    // calls the getter
    ilGenerator.EmitCall(OpCodes.Callvirt, propInfo.GetGetMethod(), null);
    // creates code for handling the return value
    EmitBoxIfNeeded(ilGenerator, propInfo.PropertyType);
    // returns the value to the caller
    ilGenerator.Emit(OpCodes.Ret);
    // converts the DynamicMethod to a FastPropertyGetHandler delegate
    // to get the property
    FastPropertyGetHandler getter =
        (FastPropertyGetHandler) 
        dynamicMethod.CreateDelegate(typeof(FastPropertyGetHandler));


    return getter;
}