Binding the selected text of a RichTextBox to a property in the ViewModel

Question

Hi i am working with WPF and using the MVVM pattern. So my problem is that i am trying to bind the selected text of a RichTextBox to a property in my ViewModel but i can't bind the Selection property.

So how can i do it?

Binding the Selection property of the RichTextBox to a property in my ViewModel is the way that i think is better to apply effects and decorations to the text.

If anyone knows a better way to know in the ViewModel the selected text of the RichTextBox, let me know. I am starting to learn about FlowDocuments and working with the RichTextBox so it's why i am a bit lost.

Thanks in advance!

Answer 1

You could use a Behavior:

public class RichTextSelectionBehavior : Behavior<RichTextBox>
{
    protected override void OnAttached()
    {
        base.OnAttached();
        AssociatedObject.SelectionChanged += RichTextBoxSelectionChanged;
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();
        AssociatedObject.SelectionChanged -= RichTextBoxSelectionChanged;
    }

    void RichTextBoxSelectionChanged(object sender, System.Windows.RoutedEventArgs e)
    {
        SelectedText = AssociatedObject.Selection.Text;
    }

    public string SelectedText
    {
        get { return (string)GetValue(SelectedTextProperty); }
        set { SetValue(SelectedTextProperty, value); }
    }

    public static readonly DependencyProperty SelectedTextProperty =
        DependencyProperty.Register(
            "SelectedText",
            typeof(string),
            typeof(RichTextSelectionBehavior),
            new FrameworkPropertyMetadata(null, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, OnSelectedTextChanged));

    private static void OnSelectedTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        var behavior = d as RichTextSelectionBehavior;
        if (behavior == null)
            return;
        behavior.AssociatedObject.Selection.Text = behavior.SelectedText;
    }
}

XAML usage:

    <RichTextBox>
        <i:Interaction.Behaviors>
            <local:RichTextSelectionBehavior SelectedText="{Binding SelectedText}" />
        </i:Interaction.Behaviors>
    </RichTextBox>

(where SelectedText is a string property on your ViewModel)