Question

I have a custom DepenencyProperty which determines a UserControl’s visibility. It is usually bound to a boolean value, however I would like to set it False when the Escape key is hit.

The problem is, I don’t want to overwrite the binding, I want to update the bindings source value. How can I do this in code behind?

For example, with this XAML

<local:MyControl IsVisibile="{Binding IsControlVisible}" />

I want to update the value of IsControlVisible to false, not MyControl.IsVisible

Answer 1

This should be possible via BindingExpressions, try something like this:

private void MyControl_KeyDown(object sender, KeyEventArgs e)
{
    if (e.Key == Key.Escape)
    {
        var source = sender as FrameworkElement;
        var expression = source.GetBindingExpression(UIElement.IsVisibleProperty);
        (expression.DataItem as MyDataItem).IsControlVisible = false;
    }
}

(If you do not reuse the UIElement.IsVisibleProperty you need to specify it via MyControl.IsVisibleProperty of course)

---

Here is a reflection-using method:

var source = sender as FrameworkElement;
var expression = source.GetBindingExpression(UIElement.IsVisibleProperty);
var dataType = expression.DataItem.GetType();
dataType.GetProperties().Single(x => x.Name == expression.ParentBinding.Path.Path)
        .SetValue(expression.DataItem, false, null);