this is the xaml and c++ code I used:

XAML:

            <StackPanel>
              <TextBlock Text="{DynamicResource title}"/>
              <ComboBox
                SelectedIndex="{Binding SelectedItemIndex, Mode=TwoWay}">
                <ComboBoxItem Content="{DynamicResource ex1}"/>
                <ComboBoxItem Content="{DynamicResource ex2"/>
                <ComboBoxItem Content="{DynamicResource ex3}"/>
              </ComboBox>
            </StackPanel>

C++:

int ExampleViewModel::GetSelectedItemIndex() const {
return mItemIndex;
}

void ExampleViewModel::SetSelectedItemIndex(int index) {
mItemIndex = index;
OnPropertyChanged("SelectedItemIndex");
UpdateFilteredList();
}
...
NsProp("SelectedItemIndex", &ExampleViewModel::GetItemIndex,
&ExampleViewModel::SetItemIndex);