I have an ugly race condition with a WPF usercontrol, which is some kind of extended ComboBox: The UserControl mainly defines two bindable DependencyProperties, one is the selected item, another one is a list, from which the selected item can be chosen. Both are bindable, so the control may be initialized with or without a selected item and both properties can be changed via binding (on DataContext change), further the selection may change due to user interaction. The UserControl contains a ComboBox, whose ItemsSource and SelectedItem are synchronized with my list-property and SelectedItem of the UserControl - so far so good. The trouble now is, that if both properties are changed (quasi simultaneously) from outside when setting a new DataContext with both values set, it occasionally happens that the SelectedItem is set correctly but the list update causes the selection to be reset to null overwriting the previously set value -> corrupting my DataContext.
To make it short: I need to find a way to "lock" my SelectedItem during list update - but just observing the PropertyChanged-Events is not enough, since I receive them AFTER the updates, where the state to remember is already lost. Further I cannot identify, if the selection change was caused by the user or by (correctly) the binding or (not desired) indirectly by the other binding... I think I would need some BeforePropertyChanged or OnPropertyChanging event for my DependencyProperties - or another way to manage the ordering of simultanous updates of both properties.
Any suggestions welcome :)
Note that I talk of a list to select an item from, but actually it is some more complex structure that allows quick sorting and filtering, that is also the reason why I do not use an ItemsControl here, but I don't feel like that's relevant for the question.