Why is a button enabled if the Command binding resolves to null?

Question

OK, the XAML is quite simple and uses MVVM to bind to an ICommand SomeCommand { get; } property on a view model:

Answer 1

It is enabled because that's the default state. Disabling it automatically would be an arbitrary measure that gives rise to other problems.

If you want to have a button without an associated command be disabled, bind the IsEnabled property to SomeCommand using an appropriate converter, e.g.:

[ValueConversion(typeof(object), typeof(bool))]
public class NullToBooleanConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return value !== null;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotSupportedException();
    }
}