I’ve got a WPF app who’s menu is using the commanding capabilities. Everything is wired up just fine and when I click the buttons in the menu, the commands run. However I’m having trouble getting the button’s IsEnabled status to respect the CanExecute part of my commands.
One challenge is the commands need to see what you’re doing in the UI. For instance, one command should only be available when certain items in a ListBox are selected so I need to get a reference to the ListBox… but since the command is exposed in my view model (MVVM pattern), it doesn’t have access to the UI (BTW, the menu is in one user control [parent=mainwindow] while the ListBox is in another user control [parent=mainwindow]).
In addition, even when I hard code the command’s CanExecute method to return false, the Enabled property of the button doesn’t change… the command won’t fire, but it won’t change… frustrating. I assume I need to modify/raise the CanExecuteChanged event, but I’m not sure when I should be doing that (can’t find a good sample).
Feedback?
Try the Messenger class from MVVMLight. It helps in communicating between ViewModels.
And give this a try:
Have a SelectedItem property in your ListBox’s ViewModel. Broadcast messages while the property changes. Register for this message in the menu’s ViewModel. Use the SelectedItem property in your CanExecute method for your logic.