Clear combobox in WPF - wpf

Question

I have a Combobox that I would like to clear whenever a checkbox is checked.
How would I go about doing that?
My combobox:
<ComboBox
DisplayMemberPath="KommuneNavn"
SelectedValuePath="KommuneNr"
ItemsSource="{Binding KommuneNavne}"
SelectedValue="{Binding kommuneNr, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}"
Margin="3"
IsEnabled="{Binding IsUdenlandskAdresse, Converter={StaticResource BooleanNotConverter}}"/>
My Checkbox that binds to a boolean property IsUdenlandskAdresse in my viewmodel:
<CheckBox Margin="3" IsChecked="{Binding IsUdenlandskAdresse, Mode=TwoWay}"/>
So when IsUdenlandskadresse is set to true, I would like the combobox to become blank.

Answer 1

If I understood what you are trying to do correctly, you want the ComoBox to be blank (or at least look blank) when it is disabled. The simplest way to do this is to change the Foreground (The color used for Text) to Transparent when the ComboBox is disabled with a style. That way you won't need any code-behind, can reuse that behavior on other ComboBoxes and you don't lose the selection if it gets re-enabled.
<Style TargetType="ComboBox">
<Style.Triggers>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Foreground" Value="Transparent"/>
</Trigger>
</Style.Triggers>
</Style>
Minimalistic Demo:
<ComboBox Height="Auto" IsEnabled="{Binding ElementName=cckEnabled, Path=IsChecked}">
<ComboBox.Style>
<Style TargetType="ComboBox">
<Style.Triggers>
<Trigger Property="IsEnabled" Value="False">
<Setter Property="Foreground" Value="Transparent"/>
</Trigger>
</Style.Triggers>
</Style>
</ComboBox.Style>
<ComboBoxItem>Entry 1</ComboBoxItem>
<ComboBoxItem>Entry 2</ComboBoxItem>
<ComboBoxItem>Entry 3</ComboBoxItem>
<ComboBoxItem>Entry 4</ComboBoxItem>
<ComboBoxItem>Entry 5</ComboBoxItem>
</ComboBox>
<CheckBox Name="cckEnabled" Content="Enabled"/>

Answer 2

To clear your ComboBox (remove all selectable items from ItemsSource):
public bool IsUdenlandskAdresse
{
get { return _isUdenLandskAdresse; }
set
{
SetProperty(ref _isUdenLandskAdresse, value);
// this will clear your collection if value=true
if(value)
KommuneNave.Clear();
}
}
If you want to unselect the SelectedItem:
public bool IsUdenlandskAdresse
{
get { return _isUdenLandskAdresse; }
set
{
SetProperty(ref _isUdenLandskAdresse, value);
// just set the SelectedItem BindingTarget to null
if(value)
kommunenr = null;
}
}