WPF: Cancel a user selection in a databound ListBox?

Question

How do I cancel a user selection in a databound WPF ListBox? The source property is set correctly, but the ListBox selection is out of sync.

I have an MVVM app that

Answer 1

Bind ListBox's property: IsEnabled="{Binding Path=Valid, Mode=OneWay}" where Valid is the view-model property with the validation algoritm. Other solutions look too far-fetched in my eyes.

When the disabled appearance is not allowed, a style could help out, but probably the disabled style is ok because changing the selection is not allowed.

Maybe in .NET version 4.5 INotifyDataErrorInfo helps, I dont'know.

Answer 2

I came up against this recently, and came up with a solution that works well with my MVVM, without the need for and code behind.

I created a SelectedIndex property in my model and bound the listbox SelectedIndex to it.

On the View CurrentChanging event, I do my validation, if it fails, I simply use the code

e.cancel = true;

//UserView is my ICollectionView that's bound to the listbox, that is currently changing
SelectedIndex = UserView.CurrentPosition;  

//Use whatever similar notification method you use
NotifyPropertyChanged("SelectedIndex"); 

It seems to work perfectly ATM. There may be edge cases where it doesnt, but for now, it does exactly what I want.