Using converters with enums in wpf

Question

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I want to change the enum string value before I display it in a combo box. In this case I want "oranges to display as "Juicy oranges" etc.

XML

<Window x:Class="Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        xmlns:System="clr-namespace:System;assembly=mscorlib"
        xmlns:local="clr-namespace:FruitProject"
    
    Title="Window1" Height="300" Width="300">
    <Window.Resources>

        
        <local:EnumConverter x:Key="fruitImprover"></local:EnumConverter>
            <ObjectDataProvider MethodName="GetValues"
                        ObjectType="{x:Type System:Enum}"
                        x:Key="deliciousFruits">
            <ObjectDataProvider.MethodParameters>
                <x:Type TypeName="local:Window1+Fruit" />
            </ObjectDataProvider.MethodParameters>
        </ObjectDataProvider>
    </Window.Resources>
        
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="*"></ColumnDefinition>
            <ColumnDefinition Width="*"></ColumnDefinition>
            <ColumnDefinition Width="*"></ColumnDefinition>
        </Grid.ColumnDefinitions>
        <Grid.RowDefinitions>
            <RowDefinition Height="*"></RowDefinition>
            <RowDefinition Height=".25*"></RowDefinition>
            <RowDefinition Height="*"></RowDefinition>
        </Grid.RowDefinitions>
        
        <ComboBox Grid.Column="1" Grid.Row="1" ItemsSource="{Binding Source={StaticResource deliciousFruits}, Converter={StaticResource fruitImprover}}"></ComboBox>
        
    </Grid>
</Window>

The VB code behind window1 is

VB

Public Class Window1
    Public Enum Fruit
        Oranges
        Apples
        Plums
    End Enum
  
End Class

My converter class is:

VB

Public Class EnumConverter
    Implements IValueConverter

    Public Function Convert(value As Object, targetType As Type, parameter As Object, culture As Globalization.CultureInfo) As Object Implements IValueConverter.Convert

        Dim f As Window1.Fruit = CType(value, Window1.Fruit)
        Select Case f
            Case Window1.Fruit.Apples
                Return "Juicy apples"
            Case Window1.Fruit.Oranges
                Return "Sweet Oranges"
            Case Window1.Fruit.Plums
                Return "Purple Plums"
        End Select

    End Function

    Public Function ConvertBack(value As Object, targetType As Type, parameter As Object, culture As Globalization.CultureInfo) As Object Implements IValueConverter.ConvertBack
        Return 4
    End Function
End Class

I get the following error message when I try and convert value to a fruit enumeration.

Conversion from type 'Fruit()' to type 'Integer' is not valid.

Any ideas ?

Posted 9-Aug-13 22:25pm

Hummer463

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2 solutions

Solution 2

I would look at the following article: Using DescriptionAttribute for enumerations bound to a ComboBox[^]

Posted 10-Aug-13 8:42am

Clifford Nelson

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Pheonyx · Accepted Answer · 2013-08-10T01:28:00

Yes, don't do it like that (I never managed to get that approach to work0. There is a much better approach you can use which I think is more re-usable. Use the [Description()] Attribute on your enum like this:

VB

Public Enum Fruit
        <Description("Juicy Oranges")>
        Oranges
        <Description("Crunchy Apples")>
        Apples
        Plums
    End Enum

Then use a converter that retrieves description attributes from the bound object.

VB

Public Class EnumDescriptionConverter
	Implements IValueConverter
	Private Function GetEnumDescription(enumObj As [Enum]) As String
		Dim fieldInfo As FieldInfo = enumObj.[GetType]().GetField(enumObj.ToString())

		Dim attribArray As Object() = fieldInfo.GetCustomAttributes(False)

		If attribArray.Length = 0 Then
			Return enumObj.ToString()
		Else
			Dim attrib As DescriptionAttribute = TryCast(attribArray(0), DescriptionAttribute)
			Return attrib.Description
		End If
	End Function

	Private Function IValueConverter_Convert(value As Object, targetType As Type, parameter As Object, culture As CultureInfo) As Object Implements IValueConverter.Convert
		Dim myEnum As [Enum] = DirectCast(value, [Enum])
		Dim description As String = GetEnumDescription(myEnum)
		Return description
	End Function

	Private Function IValueConverter_ConvertBack(value As Object, targetType As Type, parameter As Object, culture As CultureInfo) As Object Implements IValueConverter.ConvertBack
		Return String.Empty
	End Function
End Class

Then in your combo box set the datasource to your dataprovider and set the DisplayMemberPath to the converter.

Combobox XAML:

XML

<combobox itemssource="{Binding Source={StaticResource deliciousFruits}}">
            <combobox.itemtemplate>
                <datatemplate>
                    <textblock text="{Binding Converter={StaticResource fruitImprover}}"></textblock>
                </datatemplate>
            </combobox.itemtemplate>
        </combobox>