OneWay binding for ToggleButton's IsChecked property in WPF

Question

I have a ToggleButton with its IsChecked property bound to a property using a OneWay binding.

<ToggleButton
    Command="{Binding Path=SomeCommand}"
    IsChecked="{Binding Path=SomeProperty, Mode=OneWay}" />

The SomeCommand toggles the boolean SomeProperty value, and a PropertyChanged event is raised for SomeProperty.

If I change SomeProperty in my viewmodel the ToggleButton depresses correctly. However if I click the ToggleButton the binding seems to get lost and the button no longer gets checked according to the value of SomeProperty. Any ideas on how to fix this problem?

Answer 1

This is by design when using oneway data binding. Add the attached property PresentationTraceSources.TraceLevel=High to your binding and you will see when it gets disconnected. This link describes the problem as well (without offering any solution): Debugging Data Binding in WPF

The way I normally solve it is to use a command for user interaction and code behind to change the control appearance because of some changed properties.

Answer 2

I think what the problem boils down to is a conflict between the command and the IsChecked binding. My solution was to change my viewmodel to expose a bool? and bind that to the IsChecked property. I did not bind a command to the ToggleButton. Elsewhere in my code where I want to toggle the property I use SomeCommand.