Why this UWP ComboBox can be blank after initialization but works fine for selection?

Question

I have a ComboBox like this

Answer 1

I used x:Bind for the ItemResource and added ViewModel inside code behind, and solved this problem.

Answer 2

You ComboBox isn't blank, but it don't know how to render your MaxXXAgeMembers. You should use ItemTemplate to tell this to him. For Ex:

<ComboBox
    Grid.Column="1"
    Padding="5,0,0,0"
    SelectedValue="{Binding MaxXXAge, Mode=TwoWay, Converter={StaticResource MaxXXAgeToMaxXXAgeMemberConverter}}"
    ItemsSource="{Binding ElementName=SettingsXXScrollViewer, Path=DataContext.MaxXXAgeMemberGroup, Mode=OneWay}">
    <ComboBox.ItemTemplate>
        <DataTemplate>
            <TextBlock Text="{Binding Description}" /> 
        </DataTemplate>
    </ComboBox.ItemTemplate>
</ComboBox>

Answer 3

It's blank because you don't have anything selected in the first place. If I'm not mistaken, you have to either use SelectedItem to bind your selection or SelectedValue with SelectedValuePath.

I actually never use SelectedValue with SelectedValuePath myself, so after initializing collection of items which ComboBox.ItemSource will be binded to - for example ObservableCollection<Person> Persons {get; set;} - I also set selected item property Person SelectedPerson {get; set;} to one of the values from collection. Then I bind ComboBox.SelectedItem to this property, so on initialization it shows predefined selected value.

I guess you can achieve the same with SelectedValue and SelectedValuePath, but you have to use them together as described here.