setting c# wpf combobox background color with multibinding

Question

I trying to make my combo box selected value background color based on it self's value and other combo box value, but when debugging in a converter i find that values[0] gets dependency.not set value. so i tried to use Relative Source = self , but then i get this error: "Object reference not set to an instance of an object"

<ComboBox.Background>
    <MultiBinding Converter="{converters:BoolToColorConverter}">
        <Binding RelativeSource="{RelativeSource Mode=Self}" Path="SelectedValue"/>
        <Binding ElementName="cbStdPlate"
            Path="SelectedIndex" />
    </MultiBinding>
</ComboBox.Background>

Anyone could give me a hint ?

Answer 1

Check how you are handling your Converter property. I had reproduced your error and doing it like this worked:

 <Window.Resources>
        <local:Converter x:Key="BoolToColorConverter"/>
 </Window.Resources>

You can replace Window with the Control you are using. And in the Background Multibinding property you call the converter like this:

<ComboBox.Background>
   <MultiBinding Converter="{StaticResource BoolToColorConverter}">
      <Binding RelativeSource="{RelativeSource Mode=Self}" Path="SelectedValue"/>
      <Binding ElementName="cbStdPlate"
         Path="SelectedIndex" />
   </MultiBinding>
</ComboBox.Background>

With this if you debug the values[] property of your converter, you will see the selected value as the first position.