枚举类型判断存在

Enum.TryParse("thevalue", out TestEnum result);

这样判断 会存在说 如果 "thevalue" 为数字的 时候 仍然会被转化成功，即使它并没有在枚举中没初始化，以下是该方法的解释：

        //
        // Summary:
        //     Converts the string representation of the name or numeric value of one or more
        //     enumerated constants to an equivalent enumerated object. The return value indicates
        //     whether the conversion succeeded.
        //
        // Parameters:
        //   value:
        //     The case-sensitive string representation of the enumeration name or underlying
        //     value to convert.
        //
        //   result:
        //     When this method returns, result contains an object of type TEnum whose value
        //     is represented by value if the parse operation succeeds. If the parse operation
        //     fails, result contains the default value of the underlying type of TEnum. Note
16         //     that this value need not be a member of the TEnum enumeration. This parameter
17         //     is passed uninitialized.
        //
        // Type parameters:
        //   TEnum:
        //     The enumeration type to which to convert value.
        //
        // Returns:
        //     true if the value parameter was converted successfully; otherwise, false.
        //
        // Exceptions:
        //   T:System.ArgumentException:
        //     TEnum is not an enumeration type.
        public static bool TryParse<TEnum>(string? value, out TEnum result) where TEnum : struct;

所以这里推荐使用：IsDefined 方法去做存在判断。

        //
        // Summary:
        //     Returns a Boolean telling whether a given integral value, or its name as a string,
        //     exists in a specified enumeration.
        //
        // Parameters:
        //   enumType:
        //     An enumeration type.
        //
        //   value:
        //     The value or name of a constant in enumType.
        //
        // Returns:
        //     true if a constant in enumType has a value equal to value; otherwise, false.
        //
        // Exceptions:
        //   T:System.ArgumentNullException:
        //     enumType or value is null.
        //
        //   T:System.ArgumentException:
        //     enumType is not an Enum. -or- The type of value is an enumeration, but it is
        //     not an enumeration of type enumType. -or- The type of value is not an underlying
        //     type of enumType.
        //
        //   T:System.InvalidOperationException:
        //     value is not type System.SByte, System.Int16, System.Int32, System.Int64, System.Byte,
        //     System.UInt16, System.UInt32, or System.UInt64, or System.String.
        public static bool IsDefined(Type enumType, object value);