I like for all objects that I'm binding to be defined in my ViewModel
, so I try to avoid using <ObjectDataProvider>
in the xaml when possible.
My solution uses no data defined in the View and no code-behind. Only a DataBinding, a reusable ValueConverter, a method to get a collection of descriptions for any Enum type, and a single property in the ViewModel to bind to.
When I want to bind an Enum
to a ComboBox
the text I want to display never matches the values of the Enum
, so I use the [Description()]
attribute to give it the text that I actually want to see in the ComboBox
. If I had an enum of days of the week, it would look something like this:
public enum DayOfWeek
{
// add an optional blank value for default/no selection
[Description("")]
NOT_SET = 0,
[Description("Sunday")]
SUNDAY,
[Description("Monday")]
MONDAY,
...
}
First I created helper class with a couple methods to deal with enums. One method gets a description for a specific value, the other method gets all values and their descriptions for a type.
public static class EnumHelper
{
public static string Description(this Enum value)
{
var attributes = value.GetType().GetField(value.ToString()).GetCustomAttributes(typeof(DescriptionAttribute), false);
if (attributes.Any())
return (attributes.First() as DescriptionAttribute).Description;
// If no description is found, the least we can do is replace underscores with spaces
// You can add your own custom default formatting logic here
TextInfo ti = CultureInfo.CurrentCulture.TextInfo;
return ti.ToTitleCase(ti.ToLower(value.ToString().Replace("_", " ")));
}
public static IEnumerable<ValueDescription> GetAllValuesAndDescriptions(Type t)
{
if (!t.IsEnum)
throw new ArgumentException($"{nameof(t)} must be an enum type");
return Enum.GetValues(t).Cast<Enum>().Select((e) => new ValueDescription() { Value = e, Description = e.Description() }).ToList();
}
}
Next, we create a ValueConverter
. Inheriting from MarkupExtension
makes it easier to use in XAML so we don't have to declare it as a resource.
[ValueConversion(typeof(Enum), typeof(IEnumerable<ValueDescription>))]
public class EnumToCollectionConverter : MarkupExtension, IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
return EnumHelper.GetAllValuesAndDescriptions(value.GetType());
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
return null;
}
public override object ProvideValue(IServiceProvider serviceProvider)
{
return this;
}
}
My ViewModel
only needs 1 property that my View
can bind to for both the SelectedValue
and ItemsSource
of the combobox:
private DayOfWeek dayOfWeek;
public DayOfWeek SelectedDay
{
get { return dayOfWeek; }
set
{
if (dayOfWeek != value)
{
dayOfWeek = value;
OnPropertyChanged(nameof(SelectedDay));
}
}
}
And finally to bind the ComboBox
view (using the ValueConverter
in the ItemsSource
binding)...
<ComboBox ItemsSource="{Binding Path=SelectedDay, Converter={x:EnumToCollectionConverter}, Mode=OneTime}"
SelectedValuePath="Value"
DisplayMemberPath="Description"
SelectedValue="{Binding Path=SelectedDay}" />
To implement this solution you only need to copy my EnumHelper
class and EnumToCollectionConverter
class. They will work with any enums. Also, I didn't include it here, but the ValueDescription
class is just a simple class with 2 public object properties, one called Value
, one called Description
. You can create that yourself or you can change the code to use a Tuple<object, object>
or KeyValuePair<object, object>