IMultiValueConverter Binding from MainWindow through UserControl onto UIElement

Question

Project Type: .NET 4.0 WPF Desktop Application

Greetings.

I'm currently working on a solution to utilize IMultiValueConverters in a WPF application to bind the SelectedItem properties of two ComboBoxes to the IsEnabled property of a button. The ComboBoxes are placed in separate UserControls which are nested within the MainWindow along with the Button itself.

Visualized Layout

MainWindow.xaml

<Window>
    <Window.Resources>
        <local:MultiNullToBoolConverter x:Key="MultiNullToBoolConverter" />
    </Window.Resources>
    <Grid>
        <local:ucDatabaseSelection x:Name="ucSourceDatabase" />
        <local:ucDatabaseSelection x:Name="ucTargetDatabase" />
        <Button x:Name="btnContinue">
            <Button.IsEnabled>
                <MultiBinding Converter="{StaticResource MultiNullToBoolConverter}">
                    <Binding ElementName="ucSourceDatabase" Path="cbxServerDatabaseCollection.SelectedItem" />
                    <Binding ElementName="ucTargetDatabase" Path="cbxServerDatabaseCollection.SelectedItem" />
                </MultiBinding>
            </Button.IsEnabled>
        </Button>
    </Grid>
</Window>

ucDatabaseSelection.xaml

<UserControl>
    <ComboBox x:Name="cbxServerDatabaseCollection">
        <ComboBoxItem Content="Server A" />
        <ComboBoxItem Content="Server B" />
    </ComboBox>
</UserControl>

MultiNullToBoolConverter.cs

/// <summary>
/// Converts two objects (values[0] and values[1]) to boolean
/// </summary>
/// <returns>TRUE if both objects are not null; FALSE if at least one object is null</returns>
public object Convert(object[] values, Type targetType, object parameter, CultureInfo culture)
{
    if (values[0] != null && values[1] != null) return true;
    else return false;
}

The IsEnabled property of the Button should only be true, when the SelectedItem properties of both ComboBoxes are not null.

The Issue I have now is that I can't get the Binding to work from the MainWindow Button through the UserControls and onto the ComboBoxes. Am I missing UpdateTriggers here or is it simply not possible to bind it directly without using DependencyProperties in the UserControl class?

Answer 1

WPF data binding works with public properties only. Hence, the UserControl needs to have a public property that returns the cbxServerDatabaseCollection field value, e.g:

public ComboBox CbxServerDatabaseCollection
{
    get { return cbxServerDatabaseCollection; }
}