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?

WPF data binding works with public properties only. Hence, the UserControl needs to have a public property that returns the `cbxServerDatabaseCollection` field value, or a property that directly returns the `SelectedItem` of its ComboBox. — Clemens, Feb 18 '16 at 13:43
Then you could simplify the code of your converter, using LINQ, by writing `return values.All(v => v != null);` — Clemens, Feb 18 '16 at 13:45
Thank you, Clemens! Setting up the public property that references the `cbxServerDatabaseCollection` worked exactly as intended. Is there a way to mark your comment as an answer? — Konstantin Strehlow, Feb 18 '16 at 14:03

score 1 · Accepted Answer · answered Feb 18 '16 at 14:29

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; }
}

IMultiValueConverter Binding from MainWindow through UserControl onto UIElement

1 Answers1