问题
I have a DocumentListView.Xaml with a ListBox and 3 Buttons.
Behind that UserControl sits a DocumentListViewModel with 3 Buttons and their Command Property bound to 3 RelayCommands.
I have 3 Controller like AdministrationController, BillingController, ReportController.
Every Controller has ObservableCollections like Customer 1 : N Order 1: N Document same for the other Controller.
In one Controller I have a special binding situation. When my DocumentListViewModel is not initialized by its parent ViewModel like OrderViewModel (because no orders are loaded/exist) then my UserControl has 3 buttons which are ENABLED. Ok the user can press the 3 buttons and nothing happens but still its very confusing and above all the consistency in my user interface is gone.
How can I set the Command of a Button as default to "Disabled" ?
Setting the Buttons IsEnabled property to false does not help because the button will stay forever in the disabled state. No CanExecute TRUE will set it to IsEnabled = true.
AND I do not want to introduce another property IsButtonEnabled... that stupid because then I have both worlds winforms and wpf behind my buttons logic... ICommand should be enough.
回答1:
Or you can use a Style for the button to disable:
<Style TargetType="{x:Type Button}" x:Key="DisablerButton">
<Style.Triggers>
<Trigger Property="Command" Value="{x:Null}">
<Setter Property="IsEnabled" Value="False" />
</Trigger>
</Style.Triggers>
</Style>
回答2:
This is an interesting situation. Honestly I've never run into the case where the UI was loaded and interactive but the ViewModel was not yet bound.
However, ignoring that for a moment, you could potentially use a FallbackValue on your binding to bind to a globally available NullCommand or something that always returns false for its CanExecute method.
<Button Command="{Binding SaveCommand, FallbackValue={StaticResource NullCommand}}" />
来源：https://stackoverflow.com/questions/4423746/wpf-mvvm-disable-a-buttons-state-when-the-viewmodel-behind-the-usercontrol-is