How can I convert a control that is already bound to multibinding

Question

Let's say I have a FrameworkElement that is already bound to a converter in the XAML. Programmatically, I wish to append a binding to the existing binding at runtime - for instance in the control's loaded event, effectively making it a multibinding.

How does one go about acquiring the existing binding on (for example) the Visibility property.

Answer 1

You might do something like this:

var oldBinding = BindingOperations.GetBinding(element, UIElement.VisibilityProperty);

var newBinding = new MultiBinding { Converter = ... };

var firstBinding = new Binding
{
    Path = oldBinding.Path,
    Source = oldBinding.Source // or RelativeSource or ElementName
};

var secondBinding = new Binding
{
    ...
};

newBinding.Bindings.Add(firstBinding);
newBinding.Bindings.Add(secondBinding);

BindingOperations.SetBinding(element, UIElement.VisibilityProperty, newBinding);