falling back from a binding converter

[trebahl]

Inside an IValueConverter.Convert used in a binding, I would like to say, in specific cases "abandon the binding, try the lower precedence sources of value". Is it possible?

[miloush]

You can return Binding.DoNothing to cancel the value transfer, but there isn't a way to say "pretend I don't exist". What is the scenario?

[miloush]

Also note that converters do not need to be used inside bindings or DPs.

[trebahl]

Thanks, I also found DependencyProperty.UnsetValue where the documentation states more explicitly that it will fall back to other sources of value, but it doesn't seem to be working for me.

One of my scenarios is to selectively emphasize some items while keeping default display for others. That is is probably intended to be handled with a style selector or triggers, but neither of these solutions are good for me:

• style selectors force you to bundle everything in one style, so I would have to define one style per possible combination of properties I want to set
• triggers are a pain in a programmatic context.

I wrote a class like:

class StyleWrapper
{
    public readonly Style Style = new();
    public void Add(DependencyProperty p, Func<object, object> f)
    {
     // add to Style a binding for p with a converter calling f
    }
}

with which I can easily define styles:

var s = new StyleWrapper();
s.Add(FrameworkElement.BackgroundProperty, o => ... ? SolidBrushes.Red  : DependencyProperty.UnsetValue);
s.Add(FrameworkElement.ToolTipProperty, o => new ToolTip() { Content = ... }  );
// assign s.Style somewhere

[miloush]

Have you tried writing your StyleSelector? You could generate/adjust the returned Style on the fly.

[trebahl]

Seeing as the constructor of Style registers a global index, I'm reluctant to define style objects on the fly.