WPF TextBox referenced from presentationmodel gets unsync? - wpf

Question

I have a textbox on my wpfgrid that I need to perform some tekst inserting and such on. To do this, the textbox is referenced into the presentationmodel from the view, ReferenceToTextBox (we do MVP with Prism). Also, the textbox in the view TextDescription is bound to the Description-property on the model.
We also have a dropdown-list containing some predefined text-blobs (adresses, VAT-numbers and such). When you choose one of these, they should be inserted into the textbox at the carets current position. Since you can't bind on CaretIndex, the above mentioned workaround is made. The dropdown-list is bound on SelectedItem to a property on the model, so when the SelectedItem changes, the property changes, and in the setter on the property a method is called to insert the text of the selected-item into the ReferenceToTextBox "virtual" textbox in the model (which should be just a reference to the textbox in the view).
However, if I delete all the text from the textbox in the view and add a new predefined text-blob. The ReferenceToTextBox.Text property still contains all the text that I deleted. It seems like the ReferenceToTextBox is no longer just a reference, but a whole own textbox. Which makes it even weirder when updates to ReferenceToTextBox.Text actually updates the "visual" textbox on the view.
What is actually happening here?

Answer 1

Not a direct answer to your question, but what about a derived TextBox class that actually allows binding to its CaretIndex property:
public class TextBoxEx : TextBox
{
public static readonly DependencyProperty CaretIndexProperty = DependencyProperty.Register(
"CaretIndex", typeof(int), typeof(TextBoxEx),
new FrameworkPropertyMetadata(0, FrameworkPropertyMetadataOptions.BindsTwoWayByDefault, CaretIndexChanged));
public new int CaretIndex
{
get { return (int)GetValue(CaretIndexProperty); }
set { SetValue(CaretIndexProperty, value); }
}
protected override void OnTextChanged(TextChangedEventArgs e)
{
base.OnTextChanged(e);
CaretIndex = base.CaretIndex;
}
protected override void OnKeyDown(KeyEventArgs e)
{
base.OnKeyDown(e);
CaretIndex = base.CaretIndex;
}
protected override void OnKeyUp(KeyEventArgs e)
{
base.OnKeyUp(e);
CaretIndex = base.CaretIndex;
}
protected override void OnMouseDown(MouseButtonEventArgs e)
{
base.OnMouseDown(e);
CaretIndex = base.CaretIndex;
}
protected override void OnMouseUp(MouseButtonEventArgs e)
{
base.OnMouseUp(e);
CaretIndex = base.CaretIndex;
}
private static void CaretIndexChanged(DependencyObject obj, DependencyPropertyChangedEventArgs e)
{
if (obj is TextBox)
{
((TextBox)obj).CaretIndex = (int)e.NewValue;
}
}
}