I tried to bind the following Enum to a ComboBox
Public Enum PossibleActions
ActionRead
ActionWrite
ActionVerify
End Enum
I can't change the Enum itself, but I do not want to display these strings. My intention is just to cut the prefix 'Action' and display 'Read', 'Write' and 'Verify' in the ComboBox. Therefore I wrote a ValueConverter
Public Class PossibleActionsConverter
Implements IValueConverter
Public Function Convert(ByVal value As Object, ByVal targetType As System.Type, ByVal parameter As Object, ByVal culture As System.Globalization.CultureInfo) As Object Implements System.Windows.Data.IValueConverter.Convert
Dim actions() As PossibleActions
Dim strings() As String
actions = CType(value, PossibleActions())
ReDim strings(actions.GetUpperBound(0))
For i = 0 To actions.GetUpperBound(0)
strings(i) = actions(i).ToString.Substring(6)
Next
Return strings
End Function
Public Function ConvertBack(ByVal value As Object, ByVal targetType As System.Type, ByVal parameter As Object, ByVal culture As System.Globalization.CultureInfo) As Object Implements System.Windows.Data.IValueConverter.ConvertBack
Dim s As String
s = CStr(value)
Return [Enum].Parse(GetType(PossibleActions), "Action" & s)
End Function
End Class
My XAML looks like
xmlns:sys="clr-namespace:System;assembly=mscorlib"
xmlns:local="clr-namespace:StepEditor"
[...]
<Window.Resources>
<ObjectDataProvider x:Key="possibleActionsEnum" MethodName="GetValues"
ObjectType="{x:Type sys:Enum}">
<O开发者_Python百科bjectDataProvider.MethodParameters>
<x:TypeExtension Type="local:PossibleActions"></x:TypeExtension>
</ObjectDataProvider.MethodParameters>
</ObjectDataProvider>
<local:PossibleActionsConverter x:Key="possibleActionsConverter"></local:PossibleActionsConverter>
</Window.Resources>
[...]
Either:<ComboBox ItemsSource="{Binding Source={StaticResource possibleActionsEnum}, Converter={StaticResource possibleActionsConverter}}"
SelectedItem="{Binding SelectedAction}"></ComboBox>
Or:
<ComboBox ItemsSource="{Binding Source={StaticResource possibleActionsEnum}, Converter={StaticResource possibleActionsConverter}}"
SelectedItem="{Binding SelectedAction, Converter={StaticResource possibleActionsConverter}}"></ComboBox>
My problem is the binding of the selected item. It fails, but I can't figure out why.
The binding of SelectedItem is wrong, because you convert your Enum into Strings, but SelectedItems is a single string. If you want to stick on this architecture, write a converter that converts a single string back to your enum. The Convert and ConvertBack-methods of your existing converter are close to the solution. They can look like:
Public Function Convert(ByVal value As Object, ByVal targetType As System.Type, ByVal parameter As Object, ByVal culture As System.Globalization.CultureInfo) As Object Implements System.Windows.Data.IValueConverter.Convert
Dim action As PossibleActions
action = CType(value, PossibleActions)
Return action.ToString.Substring(6)
End Function
Public Function ConvertBack(ByVal value As Object, ByVal targetType As System.Type, ByVal parameter As Object, ByVal culture As System.Globalization.CultureInfo) As Object Implements System.Windows.Data.IValueConverter.ConvertBack
Dim s As String
s = CStr(value)
Return [Enum].Parse(GetType(PossibleActions), "Action" & s)
End Function
The best solution here iMHO is to use a data template, so you don't have to implement 2 converters as in the previous answer (one that converts a single enum, and another that converts an array). Using a datatemplete, the converter can be applied to each item of the drop down individually, so the converter that converts an array is no longer needed.
<ComboBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Converter={StaticResource possibleActionConverter}}" />
</DataTemplate>
</ComboBox.ItemTemplate>
with possibleActionConverter converting a single enum to string.
HTH
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