How do I have an enum bound combobox with custom string formatting for enum values?
In the post Enum ToString, a method is described to use the custom attribute DescriptionAttribute
like this:
Enum HowNice {
[Description("Really Nice")]
ReallyNice,
[Description("Kinda Nice")]
SortOfNice,
[Description("Not Nice At All")]
NotNice
}
And then, you call a function GetDescription
, using syntax like:
GetDescription<HowNice>(NotNice); // Returns "Not Nice At All"
But that doesn't really help me when I want to simply populate a ComboBox with the values of an enum, since I cannot force the ComboBox to call GetDescription
.
What I want has the following requirements:
- Reading
(HowNice)myComboBox.selectedItem
will return the selected value as the enum value. - The user should see the user-friendly display strings, and not just the name of the enumeration values. So instead of seeing "
NotNice
", the user would see "Not Nice At All
". - Hopefully, the solution will require minimal code changes to existing enumerations.
Obviously, I could implement a new class for each enum that I create, and override its ToString()
, but that's a lot of work for each enum, and I'd rather avoid that.
Any ideas?
Heck, I'll even throw in a hug as a bounty :-)
ComboBox
has everything you need: the FormattingEnabled
property, which you should set to true
, and Format
event, where you'll need to place desired formatting logic. Thus,
myComboBox.FormattingEnabled = true;
myComboBox.Format += delegate(object sender, ListControlConvertEventArgs e)
{
e.Value = GetDescription<HowNice>((HowNice)e.Value);
}
Don't! Enums are primitives and not UI objects - making them serve the UI in .ToString() would be quite bad from a design standpoint. You are trying to solve the wrong problem here: the real issue is that you do not want Enum.ToString() to show up in the combo box!
Now this is a very solveable problem indeed! You create a UI object to represent your combo box items:
sealed class NicenessComboBoxItem
{
public string Description { get { return ...; } }
public HowNice Value { get; private set; }
public NicenessComboBoxItem(HowNice howNice) { Value = howNice; }
}
And then just add instances of this class to your combo box's Items collection and set these properties:
comboBox.ValueMember = "Value";
comboBox.DisplayMember = "Description";
You could write an TypeConverter that reads specified attributes to look them up in your resources. Thus you would get multi-language support for display names without much hassle.
Look into the TypeConverter's ConvertFrom/ConvertTo methods, and use reflection to read attributes on your enum fields.
TypeConverter. I think this is what I was looking for. All hail Simon Svensson!
[TypeConverter(typeof(EnumToStringUsingDescription))]
Enum HowNice {
[Description("Really Nice")]
ReallyNice,
[Description("Kinda Nice")]
SortOfNice,
[Description("Not Nice At All")]
NotNice
}
All I need to change in my current enum is add this line before their declaration.
[TypeConverter(typeof(EnumToStringUsingDescription))]
Once I do that, any enum will get displayed using the DescriptionAttribute
of its fields.
Oh, and the TypeConverter
would be defined like this:
public class EnumToStringUsingDescription : TypeConverter
{
public override bool CanConvertFrom(ITypeDescriptorContext context, Type sourceType)
{
return (sourceType.Equals(typeof(Enum)));
}
public override bool CanConvertTo(ITypeDescriptorContext context, Type destinationType)
{
return (destinationType.Equals(typeof(String)));
}
public override object ConvertFrom(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value)
{
return base.ConvertFrom(context, culture, value);
}
public override object ConvertTo(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value, Type destinationType)
{
if (!destinationType.Equals(typeof(String)))
{
throw new ArgumentException("Can only convert to string.", "destinationType");
}
if (!value.GetType().BaseType.Equals(typeof(Enum)))
{
throw new ArgumentException("Can only convert an instance of enum.", "value");
}
string name = value.ToString();
object[] attrs =
value.GetType().GetField(name).GetCustomAttributes(typeof(DescriptionAttribute), false);
return (attrs.Length > 0) ? ((DescriptionAttribute)attrs[0]).Description : name;
}
}
This helps me with my ComboBox case, but obviously doesn't actually override the ToString()
. I guess I'll settle for this meanwhile...