Question

I have a custom UserControl in Silverlight which in all simplicity is composed of TextBlocks and TextBoxes. I have a hierarchy of class entities as follows:

• Person is an abstract super class that contains the properties Name and Age
• Man is a child of Person that adds the property FacialFeature
• Woman is a child of Person that adds the property LastMenstruated and HasHymen

So:

• a Person contains the properties Name and Age
• a Man contains the properties Name, Age and FacialFeature
• a Woman contains the properties Name, Age, LastMenstruated and HasHymen

What I want is for my UserControl to simply display the values of those properties like so:

if Person is of type Man:

Name : Mark
Age : 23
FacialFeature : Fully Shaved

or if Person is of type Woman:

Name : Jane
Age : 8
LastMenstruated : Never
HasHymen : Yes

Bear in mind this is a simplified example for the sake of my question.

What I want is for my UserControl to display different information and possibly display it differently depending on the run-time type of Person.

I have thought about creating the control in the code-behind using a switch statement that would switch on GetType(Person), but what I don’t like about this, is that the logic would be in the UserControl. I would like a solution that has the objects encapsulate their own display, so that if I add new types of Person, I don’t need to go back to the UserControl and add in a case for the new types, etc.

Answer 1

Taking your male/female split as an example you need to bind the Visibilty of the elements to the object being displayed through a converter that takes a parameter:

<TextBlock Visibility="{Binding SelectedPerson,
                        Converter={StaticResource GenderConverter},
                        ConverterParameter=Male)" />

Then in your converter:

public class GenderConverter: IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if ((value is Man && parameter == "Male") ||
             value is Woman && parameter == "Female"))
            return Visibility.Visible;
        else
            return Visibility.Collapsed;
    }

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

This means that you don’t have to add arbitrary UI properties to your classes to get them to display how you want them to.

I’m not 100% sure of the tests for the object type (I don’t have Silverlight 5 installed on this machine)

More information on the IValueConverter interface can be found on the MSDN.