Question

I builded a RibbonGroupBox like this in a C# file:

public class TextControl : RibbonGroupBox
{
    public TextControl()
    {
        const double widthOfComboBoxes = 150;

        Binding fontsBinding = new Binding();
        fontsBinding.Source = (TextControlVM)DataContext;
        fontsBinding.Path = new System.Windows.PropertyPath("Fonts");
        fontsBinding.Mode = BindingMode.TwoWay;

        Binding fontSizeBinding = new Binding();
        fontSizeBinding.Source = (TextControlVM)DataContext;
        fontSizeBinding.Path = new System.Windows.PropertyPath("FontSize");
        fontSizeBinding.Mode = BindingMode.TwoWay;

        /* Combobox for the fonts (Arial, etc.) */
        Fluent.ComboBox fontCombo = new Fluent.ComboBox();
        fontCombo.SetBinding(Fluent.ComboBox.ItemsSourceProperty, fontsBinding);
        fontCombo.SelectedItem = ((TextControlVM)DataContext).DefaultFont;
        fontCombo.Width = widthOfComboBoxes;
        this.AddChild(fontCombo);

        /* Combobox for the fontsizes */
        Fluent.ComboBox fontSizeCombo = new Fluent.ComboBox();
        fontSizeCombo.SetBinding(Fluent.ComboBox.ItemsSourceProperty, fontSizeBinding);
        fontSizeCombo.SelectedItem = ((TextControlVM)DataContext).DefaultFontSize;
        fontSizeCombo.Width = widthOfComboBoxes;
        this.AddChild(fontSizeCombo);
    }
}

I furthermore have a viewmodel (TextControlVM) that contains Properties for Fonts, FontSize, DefaultFont and DefaultFontSize.

When I now use this in another module like this, the DataContext in the above example is null:

<Fluent:RibbonTabItem Header="Export">
    <TextControl DataContext="{Binding DataContext.TextControl}"/>
</Fluent:RibbonTabItem>

When I build the RibbonGroupBox with XAML code everything works fine, so I want to do what XAML automatically does. How can I do that?

Background: I want to use the RibbonGroupBox in several modules. That is why I build it with C#-Code, so that I can access it dynamically. The DataContext will change dependend on the call.

Answer 1

The DataContext is implied in a binding automatically, so you are essentially binding to RibbonTabItem.DataContext.DataContext.TextControl, which doesn’t exist

To bind to RibbonTabItem.DataContext.TextControl, simply leave the extra DataContext out of the binding

<Fluent:RibbonTabItem Header="Export">
    <TextControl DataContext="{Binding TextControl}"/>
</Fluent:RibbonTabItem>