Generic method and passing any enum as parameter

Question

All,

I'm trying to sort out my last bits in a Enum-framework.

My goal: I want to send any enum type and convert it to a List and bind it to a drop down list. i will use an ObjectDataSource as DataSource for the given drop down list. I want to create a composite control that only takes one parameter; enum type. The composite control will sort out databinding and all other bits and bops.

Now, the only problem I have is to convert the generic method to be compatible with the ObjectDataSource.

Here is the code for my current method that i need to use on my ObjectDataSource. So, this method is working fine and returns a list of items for the Enum type WeekDays. However, I need the same functionality, but I need to replace WeekDays with any type of enum.

Code:

public class DropDownData
{

    public EnumDataItemList GetList()
    {
        EnumDataItemList items = new EnumDataItemList();

        foreach (int value in Enum.GetValues(WeekDays))
        {
            EnumDataItem item = new EnumDataItem();

            WeekDays d = (WeekDays)value;

            //Set display text
            if (!string.IsNullOrEmpty(DataHandlers.GetAttributeValue<DisplayTextAttribute, string>(d)))
            {
                //Translation logic goes here
                item.Text = DataHandlers.GetAttributeValue<DisplayTextAttribute, string>(d);
            }
            else
            {
                //Translation logic goes here
                item.Text = Enum.GetName(typeof(WeekDays), value);  
            }

            item.Value = value; //Actual value
            item.ToolTip = DataHandlers.GetAttributeValue<ToolTipAttribute, string>(d);
            item.Description = DataHandlers.GetAttributeValue<Lia.Library.Enums.CustomAttributes.DescriptionAttribute, string>(d);
            item.HelpText = DataHandlers.GetAttributeValue<HelpTextAttribute, string>(d);
            item.ExcludeOnBinding = DataHandlers.GetAttributeValue<ExcludeOnBinding, bool>(d);

            if (!item.ExcludeOnBinding)
            {
                items.Add(item);                    
            }
        }
        return items;
    }

}

public class EnumDataItemList : List<EnumDataItem>
{

}

As far as I know, I can't use a generic method with ObjectDataSOurce, but Generic Class is fine. I just can't get it to work with a generic class and all help is much appreciated. When all is working, I'll be happy to share the complete solution.

I'm using Framework 2.0.

Answer 1

I seem to have gone at this problem a little differently and came up with something fairly terse that appears to work for me. I cannot claim this as original work since I don't remember if I found it and copied it, or if I put it together from bits and pieces I found, with some original work of my own. I put an extension method on enums that gives me a ToDisplayText function for getting my custom enum attribute of the same name.

    this.ddlBlah.DataSource =
      Enum.GetValues(typeof(MyEnum)).Cast<MyEnum>()
      .ToDictionary(x => x, x => x.ToDisplayText());
    this.ddlBlahs.DataValueField = "key";
    this.ddlBlah.DataTextField = "value";
    this.ddlBlah.DataBind();


public static string ToDisplayText(this Enum Value)
{
  try
  {
    Type type = Value.GetType();
    MemberInfo[] memInfo = type.GetMember(Value.ToString());

    if (memInfo != null && memInfo.Length > 0)
    {
      object[] attrs = memInfo[0].GetCustomAttributes(
                                    typeof(DisplayText),
                                    false);
      if (attrs != null && attrs.Length > 0)
        return ((DisplayText)attrs[0]).DisplayedText;
    }
  }
  catch (Exception ex)
  {
    throw new Exception("Your favorite error handling here");
  }
  return Value.ToString();

  // End of ToDisplayText()
}


[System.AttributeUsage(System.AttributeTargets.Field)]
public class DisplayText : System.Attribute
{
  public string DisplayedText;

  public DisplayText(string displayText)
  {
    DisplayedText = displayText;
  }

  // End of DisplayText class definition
}

Answer 2

This should help you. (Will throw Exception if T is not an enum type.)

public static EnumDataItemList GetList<T>() where T : struct
{
    EnumDataItemList items = new EnumDataItemList();
    foreach (int e in Enum.GetValues(typeof(T)))
    {
       EnumDataItem item = new EnumDataItem();
       item.Text = Enum.GetName(typeof(T), e);
       item.Value = e;
    }
  //Rest of code goes here
}

Usage:

EnumDataItemList days = GetList<WeekDays>();

if you don't want to use a generic method, you can change it to:

public static EnumDataItemList GetList(Type t)
{
        EnumDataItemList items = new EnumDataItemList();
        foreach (int e in Enum.GetValues(t))
        {
           EnumDataItem item = new EnumDataItem();
           item.Text = Enum.GetName(t, e);
           item.Value = e;
        }
      //Rest of code goes here
}

Answer 3

Alternative to Magnus', but the idea is pretty much exactly the same (just didn't want to throw it out after being beat to it ;-) ) - just iterates over the enum value rather than int. Same usage:

public static class DropDownData
{
    // struct, IComparable, IFormattable, IConvertible is as close as we'll 
    // get to an Enum constraint. We don't actually use the constraint for 
    // anything except rudimentary compile-time type checking, though, so 
    // you may leave them out.
    public static EnumDataItemList GetList<T>() 
            where T : struct, IComparable, IFormattable, IConvertible
    {
        // Just to make the intent explicit. Enum.GetValues will do the
        // type check, if this is left out:
        if (!typeof(T).IsEnum)
        {
            throw new ArgumentException("Type must be an enumeration");
        }

        EnumDataItemList items = new EnumDataItemList();

        foreach (Enum e in Enum.GetValues(typeof(T)))
        {
            EnumDataItem items = new EnumDataItem();

            // Note: This assumes the enum's underlying type is
            // assignable to Int32 (for example, not a long):
            int value = Convert.ToInt32(e);

            // The same attribute retrieval code as in the 
            // WeekDays example, including:
            item.Text = e.ToString(); // e is Enum here, no need for GetName
        }
    }
}