Edit the display name of enumeration members in a PropertyGrid

Question

I have a property grid that I am using for users to be able to configure objects for any plugin that is written to be used in my application. I would like to be able to tell developers writing plugins to use the ComponentModel Attributes for their members like so:

[CategoryAttribute("On Screen Display Settings"),
 DescriptionAttribute("Whether or not to show the session timer."),
 DisplayName("Show Session Timer")]
 public bool ShowTimer
 {
    get;
    set;
 }

This works great. Now I would like for the members of an enumeration to be able to be edited as well. i.e.

public enum Resolution_ : byte
{
    DCIF,
    CIF,
    QCIF,
    [DisplayName("4CIF")]
    CIF4,
    [DisplayName("2CIF")]
    CIF2
}

So that they are displayed in the PropertyGrid's list like so:

 DCIF
 CIF
 QCIF
 CIF4
 CIF2

Along with any Descriptions and Display names they may have with them.

It seems that I can only do this with properties, events, and methods. Does anyone know how I can do this for an enumeration?

Answer 1

You will have to make an EnumConverter class and decorate your property with a TypeConverter attribute in order to do this.

See this Using PropertyGrid in .NET, it's a fun example:

Imagine that you want more than two items in list. The boolean type is not enough; you need to set Description attributes with a name for every element in enum.

enum DrinkDoses {
  [Description("Half of litre")]
  litre,
  [Description("One litre")]
  oneLitre,
  [Description("Two litres")]
  twoLitre,
  [Description("Three litres")]
  threeLitres,
  [Description("Four litres")]
  fourLitres,
  [Description("Death dose, five litres")]
  fiveLitres
}

In another class you need to utilize the type EnumConverter.

class DrinkDosesConverter : EnumConverter {
  private Type enumType;

  public DrinkDosesConverter(Type type) : base(type) {
    enumType = type;
  }

  public override bool CanConvertTo(ITypeDescriptorContext context, Type destType) {
    return destType == typeof(string);
  }

  public override object ConvertTo(ITypeDescriptorContext context, CultureInfo culture,
                                   object value, Type destType) {
    FieldInfo fi = enumType.GetField(Enum.GetName(enumType, value));
    DescriptionAttribute dna = (DescriptionAttribute)Attribute.GetCustomAttribute(fi, 
                                typeof(DescriptionAttribute)); 
    if (dna != null)
      return dna.Description;
    else
      return value.ToString();
  }

  public override bool CanConvertFrom(ITypeDescriptorContext context, Type srcType) {
    return srcType == typeof(string);
  } 

  public override object ConvertFrom(ITypeDescriptorContext context, CultureInfo culture,
                                     object value) {
    foreach (FieldInfo fi in enumType.GetFields()) {
      DescriptionAttribute dna = (DescriptionAttribute)Attribute.GetCustomAttribute(fi, 
                                  typeof(DescriptionAttribute)); 
      if ((dna != null) && ((string)value == dna.Description))
        return Enum.Parse(enumType, fi.Name);
    }
    return Enum.Parse(enumType, (string)value);
  }
}

Third, you need set the attribute TypeConverter for displaying the property.

class DrinkerDoses {
  DrinkDoses doses;
  [DisplayName("Doses")]
  [Description("Drinker doses")]
  [Category("Alcoholics drinking")]
  [TypeConverter(typeof(DrinkDosesConverter))]
  public DrinkDoses Doses {
    get { return doses; }
    set { doses = value; }
  }
  int dataInt; 
  public int DataInt {
    get { return dataInt; }
    set { dataInt = value; }
  }
}

Answer 2

You can attach a custom TypeConverter implementation to the property whose type is your enumeration and override the GetStandardValuesSupported and GetStandardValues to return a custom list of items to show in the drop-down list in the PropertyGrid. You can then override ConvertFrom/ConvertTo methods to handle converting values to/from your enumeration type.

You may also want to override GetStandardValuesExclusive and have it return "true" so the user can't type anything into the property value.

So, something like this:

public class MyTypeConverter : TypeConverter
{
  //Override GetStandardValuesExclusive, 
  //GetStandardValues and GetStandardValuesSupported
}

public class SomeClass
{
   [TypeConverter(typeof(MyTypeConverter))]
   public Resolution SomePropertry
   {
      ...
   }
}

In your implementation of GetStandardValues/ConvertFrom/ConvertTo you could then use Reflection to pull out the DisplayNameAttribute (or DescriptionAttribute, which may be more suited to this task) attributes of the various enum members to show that text instead of hard-coding the list of items to show.