Xamarin Quick Hit: Dimming a button to indicate it is disabled

I often have to dim a button to indicate that it is disabled, and I want to do that via data binding.

Thus, I want my button to look more or less like this:

 <Button x:Name="StartButton"
 Opacity="{Binding CanStart, 
    Converter={StaticResource CanStartOpacityConverter}}"
 Command="{Binding StartCommand}"
 FontAttributes="Bold"
 FontSize="16"
 HeightRequest="50"
 HorizontalOptions="Center"
 Text="{Binding StartText}"
 TextColor="White"
 VerticalOptions="Center"
 WidthRequest="116" />

The key line is the second, where the opacity is bound to a property, CanStart and converted by the CanStartOpacityConverter.

The CanStart is a standard boolean property.

The magic is in the converter.  For this, I wrote the following custom converter, which is designed to take in a bool and spit out a percentage:

   public class BoolToPercentConverter : IValueConverter
   {
      public double True { get; set; }

      public double False { get; set; }

      public object Convert(object value, Type targetType, 
object parameter, System.Globalization.CultureInfo culture)
      {
         if (value == null)
         {
            return False;
         }
         if (value.GetType() != typeof(bool))
         {
            return False;
         }
         return ((bool)value) ? True : False;
      }

      public object ConvertBack(object value, 
Type targetType, 
object parameter, 
System.Globalization.CultureInfo culture)
      {
         return value;
      }
   }

This allows me to create an instance of the converter, setting the percent value for True and False,

 <converters:BoolToPercentConverter 
             x:Key="CanStartOpacityConverter"
 True="1"
 False="0.4" />

Now, to dim the button, all I have to do is set CanStart to false and its opacity is set to 40%

Remember, this is only the UI, you still have to disable the button!