将字符串转换回枚举

Question

有更干净,更聪明的方法吗？

我正在使用数据库来获取数据以填充对象并将数据库字符串值转换回其枚举(我们可以假设数据库中的所有值都是匹配枚举中的值)

有问题的行是下面的行设置EventLog.ActionType ...我开始质疑我的方法的原因是因为在等号之后,VS2010一直试图通过放置这个来覆盖我正在键入的内容:"= EventActionType("

using (..<snip>..)
{
  while (reader.Read())
  {
     // <snip>
     eventLog.ActionType = (EventActionType)Enum.Parse(typeof(EventActionType), reader[3].ToString());

...etc...

Answer 1

据我所知,这是最好的方法.我已经设置了一个实用程序类来使用使这看起来更干净的方法来包装此功能.

    /// <summary>
    /// Convenience method to parse a string as an enum type
    /// </summary>
    public static T ParseEnum<T>(this string enumValue)
        where T : struct, IConvertible
    {
        return EnumUtil<T>.Parse(enumValue);
    }

/// <summary>
/// Utility methods for enum values. This static type will fail to initialize 
/// (throwing a <see cref="TypeInitializationException"/>) if
/// you try to provide a value that is not an enum.
/// </summary>
/// <typeparam name="T">An enum type. </typeparam>
public static class EnumUtil<T>
    where T : struct, IConvertible // Try to get as much of a static check as we can.
{
    // The .NET framework doesn't provide a compile-checked
    // way to ensure that a type is an enum, so we have to check when the type
    // is statically invoked.
    static EnumUtil()
    {
        // Throw Exception on static initialization if the given type isn't an enum.
        Require.That(typeof (T).IsEnum, () => typeof(T).FullName + " is not an enum type.");
    }

    public static T Parse(string enumValue)
    {
        var parsedValue = (T)System.Enum.Parse(typeof (T), enumValue);
        //Require that the parsed value is defined
        Require.That(parsedValue.IsDefined(), 
            () => new ArgumentException(string.Format("{0} is not a defined value for enum type {1}", 
                enumValue, typeof(T).FullName)));
        return parsedValue;
    }

    public static bool IsDefined(T enumValue)
    {
        return System.Enum.IsDefined(typeof (T), enumValue);
    }

}

使用这些实用方法,您可以说:

 eventLog.ActionType = reader[3].ToString().ParseEnum<EventActionType>();

Answer 2

您可以使用扩展方法为您的代码提供一些语法糖.你甚至可以使这个扩展方法泛化.

这是我正在谈论的那种代码:http://geekswithblogs.net/sdorman/archive/2007/09/25/Generic-Enum-Parsing-with-Extension-Methods.aspx

  public static T EnumParse<T>(this string value)
  {
      return EnumHelper.EnumParse<T>(value, false);
  }


  public static T EnumParse<T>(this string value, bool ignoreCase)
  {

      if (value == null)
      {
          throw new ArgumentNullException("value");
      }
      value = value.Trim();

      if (value.Length == 0)
      {

          throw new ArgumentException("Must specify valid information for parsing in the string.", "value");
      }

      Type t = typeof(T);

      if (!t.IsEnum)
      {

          throw new ArgumentException("Type provided must be an Enum.", "T");
      }

      T enumType = (T)Enum.Parse(t, value, ignoreCase);
      return enumType;
  }


  SimpleEnum enumVal = Enum.Parse<SimpleEnum>(stringValue);