How Can I Easily Data Bind a RichTextBox's Document Property in WPF?

Simplifying WPF RichTextBox Data Binding

Data binding the Document property of a WPF RichTextBox is often considered challenging. While custom RichTextBox controls or proxy methods are sometimes suggested, a more elegant solution exists: using an attached dependency property.

The Attached Property Approach

This method leverages an attached dependency property, DocumentXaml, to seamlessly bind the RichTextBox's document to a string property within your data model. This allows for clean, intuitive binding, similar to binding other text controls:

<code class="language-xml"><TextBox Text="{Binding FirstName}"></TextBox>
<TextBox Text="{Binding LastName}"></TextBox>
<RichTextBox local:RichTextBoxHelper.DocumentXaml="{Binding Autobiography}"></RichTextBox></code>

Implementation Details

The RichTextBoxHelper class manages the attached property. When DocumentXaml is set, it parses the XAML or RTF string, creating a FlowDocument. Conversely, changes to the FlowDocument update the DocumentXaml property value. A simplified implementation might look like this:

<code class="language-csharp">public class RichTextBoxHelper : DependencyObject
{
    public static string GetDocumentXaml(DependencyObject obj) { /* ... Getter implementation ... */ }
    public static void SetDocumentXaml(DependencyObject obj, string value) { /* ... Setter implementation ... */ }
    public static readonly DependencyProperty DocumentXamlProperty =
        DependencyProperty.RegisterAttached("DocumentXaml", typeof(string), typeof(RichTextBoxHelper), 
                                            new PropertyMetadata(null, OnDocumentXamlChanged));

    private static void OnDocumentXamlChanged(DependencyObject d, DependencyPropertyChangedEventArgs e) { /* ... Handle changes ... */ }
}</code>

Beyond XAML: Handling RTF and XamlPackage

This technique isn't limited to XAML. You can adapt it to handle RTF or the more robust XamlPackage format. XamlPackage offers advantages like inline resource inclusion, making it a preferable choice over RTF for complex documents.

Conclusion

This attached property approach significantly simplifies RichTextBox data binding in WPF. It avoids cumbersome workarounds, providing a cleaner and more maintainable solution for integrating rich text editing capabilities into your data-bound applications.

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