I'd like to be able to say
<DataTrigger Binding="{Binding SomeIntValue}"
Value="{x:Static local:MyEnum.SomeValue}">
and to have it resolve as True if the int value is equal to (int)MyEnum.Value
I know I could make a Converter that returns (MyEnum)intValue, however then I'd have to make a converter for every Enum type I use in my DataTriggers.
Is there a generic way to create a converter that would give me this kind of functionality?
It is possible to create a converter between enum values and their underlying integral types in a reusable way -- that is, you don't need to define a new converter for each enum types. There's enough information provided to Convert and ConvertBack for this.
public sealed class BidirectionalEnumAndNumberConverter : IValueConverter
{
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (value == null)
return null;
if (targetType.IsEnum)
{
// convert int to enum
return Enum.ToObject(targetType, value);
}
if (value.GetType().IsEnum)
{
// convert enum to int
return System.Convert.ChangeType(
value,
Enum.GetUnderlyingType(value.GetType()));
}
return null;
}
public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
{
// perform the same conversion in both directions
return Convert(value, targetType, parameter, culture);
}
}
When invoked, this converter flips the value's type between int/enum value based purely on the value and targetType values. There are no hard-coded enum types.
I think I figured it out
I just needed to set my ConverterParameter instead of the Value equal to the Enum I am looking for, and evaluate for True/False
<DataTrigger Value="True"
Binding="{Binding SomeIntValue,
Converter={StaticResource IsIntEqualEnumConverter},
ConverterParameter={x:Static local:MyEnum.SomeValue}}">
Converter
public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
{
if (parameter == null || value == null) return false;
if (parameter.GetType().IsEnum && value is int)
{
return (int)parameter == (int)value;
}
return false;
}
You could also go the other way around and convert the enum to int for the Value using a custom Markup Extension.
Example
<DataTrigger Binding="{Binding Path=MyNumber}"
Value="{Markup:EnumToInt {x:Static Visibility.Visible}}">
EnumToIntExtension
public class EnumToIntExtension : MarkupExtension
{
public object EnumValue
{
get;
set;
}
public EnumToIntExtension(object enumValue)
{
this.EnumValue = enumValue;
}
public override object ProvideValue(IServiceProvider provider)
{
if (EnumValue != null && EnumValue is Enum)
{
return System.Convert.ToInt32(EnumValue);
}
return -1;
}
}
We've wanted to do this a few times in the past as well, so we built several extension methods (on int, long, etc) to help us out. The core of all of these is implemented in a single static generic TryAsEnum method:
/// <summary>
/// Helper method to try to convert a value to an enumeration value.
///
/// If <paramref name="value"/> is not convertable to <typeparam name="TEnum"/>, an exception will be thrown
/// as documented by Convert.ChangeType.
/// </summary>
/// <param name="value">The value to convert to the enumeration type.</param>
/// <param name="outEnum">The enumeration type value.</param>
/// <returns>true if value was successfully converted; false otherwise.</returns>
/// <exception cref="InvalidOperationException">Thrown if <typeparamref name="TEnum"/> is not an enum type. (Because we can't specify a generic constraint that T is an Enum.)</exception>
public static bool TryAsEnum<TValue, TEnum>( TValue value, out TEnum outEnum ) where TEnum : struct
{
var enumType = typeof( TEnum );
if ( !enumType.IsEnum )
{
throw new InvalidOperationException( string.Format( "{0} is not an enum type.", enumType.Name ) );
}
var valueAsUnderlyingType = Convert.ChangeType( value, Enum.GetUnderlyingType( enumType ) );
if ( Enum.IsDefined( enumType, valueAsUnderlyingType ) )
{
outEnum = (TEnum) Enum.ToObject( enumType, valueAsUnderlyingType );
return true;
}
// IsDefined returns false if the value is multiple composed flags, so detect and handle that case
if( enumType.GetCustomAttributes( typeof( FlagsAttribute ), inherit: true ).Any() )
{
// Flags attribute set on the enum. Get the enum value.
var enumValue = (TEnum)Enum.ToObject( enumType, valueAsUnderlyingType );
// If a value outside the actual enum range is set, then ToString will result in a numeric representation (rather than a string one).
// So if a number CANNOT be parsed from the ToString result, we know that only defined values have been set.
decimal parseResult;
if( !decimal.TryParse( enumValue.ToString(), out parseResult ) )
{
outEnum = enumValue;
return true;
}
}
outEnum = default( TEnum );
return false;
}
This implementation handles Enums with any underlying type, as well as enums defined with the [Flags] attribute.
You could do a ToString() on the int value and then pass that into the static Enum.Parse or Enum.TryParse method which takes the enum type you care about and returns the appropriate value.
This isn't a perfect solution though because it won't work with integers that represent the binary ORing of multiple enum values
