AutoCompleteBox Don't SelectedItem on Down/Up Key - mvvm

Question

I use AutoCompleteBox in MVVM and i want to execute something only if the user click on the Item or if the user press Enter.
But now when I use the down\Up Key on the keyboard the selectedItem property changes...
My controls :
<Controls:AutoCompleteBox ItemsSource="{Binding IndicationDtos, Mode=TwoWay}"
Width="100" SelectedItem="{Binding IndicationSelected, Mode=TwoWay}"
ValueMemberPath="Diagnosis" Text="{Binding Criteria, Mode=TwoWay}" MinimumPopulateDelay="250"/>
What can I do to make the property "SelectedItem" is assigned only on Enter or click?
If you have any question...
thanks a lot

Answer 1

In your SelectedItem binding, you can use:
SelectedItem="{Binding IndicationSelected, Mode=TwoWay, UpdateSourceTrigger=LostFocus}"
That way selected item only changes when you focus on something else

Answer 2

I found solution i created new class.
Like this :
public class AutoCompleteBoxEx : AutoCompleteBox
{
public static readonly DependencyProperty SelectionBoxItemProperty =
DependencyProperty.Register(
"SelectionBoxItem",
typeof(object),
typeof(AutoCompleteBox),
new PropertyMetadata(OnSelectionBoxItemPropertyChanged));
public object SelectionBoxItem
{
get
{
return GetValue(SelectionBoxItemProperty);
}
set
{
SetValue(SelectionBoxItemProperty, value);
}
}
protected override void OnDropDownClosing(RoutedPropertyChangingEventArgs<bool> e)
{
base.OnDropDownClosing(e);
SelectionBoxItem = SelectionAdapter.SelectedItem;
}
private static void OnSelectionBoxItemPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
{
}
}