wpf mvvm with non dependency properties?

Question

I have a small (I hope) problem. I have a wpf project and I use MVVM, but I need to set the "SelectedText" property of the textbox. The "selectedText" is not a dependency property so, I can't use bindings... How can I solve this problem?

Answer 1

If you only need the value assignment from the VM to the control you could use an AttachedProperty like this.

public class AttachedProperties
{
    private static DependencyProperty SelectedTextProperty =
        DependencyProperty.RegisterAttached("SelectedText", typeof(string),
            typeof(AttachedProperties), new PropertyMetadata(default(string), OnSelectedTextChanged)));

     private static void OnSelectedTextChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
     {
         var txtBox = d as TextBox;
         if (txtBox == null)
             return;

         txtBox.SelectedText = e.NewValue.ToString();
     }

     public static string GetSelectedText(DependencyObject dp)
     {
         if (dp == null) throw new ArgumentNullException("dp");

         return (string)dp.GetValue(SelectedTextProperty);
     }

     public static void SetSelectedText(DependencyObject dp, object value)
     {
         if (dp == null) throw new ArgumentNullException("dp");

         dp.SetValue(SelectedTextProperty, value);
     }
}

And the usage

<!-- Pls note, that in the Binding the property 'SelectedText' on the VM is refered -->
<TextBox someNs:AttachedProperties.SelectedText="{Binding SelectedText}" />