ListBox DataTemplate for dynamically loaded type

Question

I have a sample MVVM WPF application and I'm having problems creating DataTemplates for my dynamically loaded model. Let me try explain:

I have the following simplified classes as part of my Model, which I'm loading dynamically

public class Relationship
{
    public string Category { get; set; }
    public ParticipantsType Participants { get; set; }
}

public class ParticipantsType
{
    public ObservableCollection<ParticipantType> Participant { get; set; }
}

public class ParticipantType
{

}

public class EmployeeParticipant : ParticipantType
{
    public EmployeeIdentityType Employee { get; set; }
}

public class DepartmentParticipant : ParticipantType
{
    public DepartmentIdentityType Department { get; set; }
}

public class EmployeeIdentityType
{
    public string ID { get; set; }
}

public class DepartmentIdentityType
{
    public string ID { get; set; }
}

Here is how my View Model looks like. I created a generic object Model property to expose my Model:

    public class MainViewModel : ViewModelBase<MainViewModel>
{
    public MainViewModel()
    {
        SetMockModel();
    }

    private void SetMockModel()
    {
        Relationship rel = new Relationship();
        rel.Category = "213";
        EmployeeParticipant emp = new EmployeeParticipant();
        emp.Employee = new EmployeeIdentityType();
        emp.Employee.ID = "222";
        DepartmentParticipant dep = new DepartmentParticipant();            
        dep.Department = new DepartmentIdentityType();
        dep.Department.ID = "444";
        rel.Participants = new ParticipantsType() { Participant = new ObservableCollection<ParticipantType>() };
        rel.Participants.Participant.Add(emp);
        rel.Participants.Participant.Add(dep);            
        Model = rel;
    }

    private object _Model;
    public object Model
    {
        get { return _Model; }
        set
        {
            _Model = value;
            NotifyPropertyChanged(m => m.Model);
        }
    }
}

Then I tried creating a ListBox to display specifically the Participants Collection:

<ListBox ItemsSource="{Binding Path=Model.Participants.Participant}">
<ListBox.ItemTemplate>
    <DataTemplate>
        <StackPanel>
            <Expander Header="IdentityFields">
            <!-- WHAT TO PUT HERE IF PARTICIPANTS HAVE DIFFERENT PROPERTY NAMES -->
            </Expander>
        </StackPanel>
    </DataTemplate>
</ListBox.ItemTemplate>

The problem is:

1. I don't know how to create a template that can handle both type of ParticipantTypes, in this case I could have EmployeeParticipant or DepartmentParticipant so depending on that, the data binding Path would be set to Employee or Department properties accordingly
2. I though about creating a DataTemplate for each type (e.g. x:Type EmployeeParticipant) but the problem is that my classes in my model are loaded dynamically at runtime so VisualStudio will complain that those types don't exist in the current solution.

How could I represent this data in a ListBox then if my concrete types are not known at compile time, but only at runtime?

EDIT: Added my test ViewModel class

Answer 1

You can still create a DataTemplate for each type but instead of using DataType declarations to have them automatically resolve you can create a DataTemplateSelector with a property for each template (assigned from StaticResource in XAML) that can cast the incoming data item to the base class and check properties or otherwise determine which template to use at runtime. Assign that selector to ListBox.ItemTemplateSelector and you'll get similar behavior to what DataType would give you.

Answer 2

That's not a good view-model. Your view-model should be view-centric, not business-centric. So make a class that can handle all four cases from a visual perspective, then bridge your business classes over to that view-model.

---

EDIT:

Working off your code:

<ListBox ItemsSource="{Binding Path=Model.Participants}">
<ListBox.ItemTemplate>
    <DataTemplate>
        <StackPanel>
            <Expander Header="IdentityFields">
                <TextBlock Text={Binding Id} />
                <TextBlock Text={Binding Name} />
            </Expander>
        </StackPanel>
    </DataTemplate>
</ListBox.ItemTemplate>
</ListBox>

I changed the binding, I assume that was a mistake?

I would create a ViewModel for Participant:

public class Participant_VM : ViewModelBase
{

    private string _name = string.Empty;
    public string Name
    {
        get
        {
            return _name ;
        }

        set
        {
            if (_name == value)
            {
                return;
            }
            _name = value;
            RaisePropertyChanged(() => Name);
        }

    private string _id= string.Empty;
    public string Id
    {
        get
        {
            return _id;
        }

        set
        {
            if (_id== value)
            {
                return;
            }
            _id = value;
            RaisePropertyChanged(() => Id);
        }

    }
}

Answer 3

Modify the ListBox as follows.

        <ListBox ItemsSource="{Binding Model.Participants.Participant}">
            <ListBox.Resources>
                <DataTemplate DataType="{x:Type loc:DepartmentParticipant}">
                    <Grid>
                        <TextBlock Text="{Binding Department.ID}"/>
                    </Grid>
                </DataTemplate>
                <DataTemplate DataType="{x:Type loc:EmployeeParticipant}">
                    <Grid>
                        <TextBlock Text="{Binding Employee.ID}"/>
                    </Grid>
                </DataTemplate>
            </ListBox.Resources>
            <ListBox.ItemTemplate>
                <DataTemplate>
                    <StackPanel>
                        <Expander Header="IdentityFields">
                            <!-- WHAT TO PUT HERE IF PARTICIPANTS HAVE DIFFERENT PROPERTY NAMES -->
                            <ContentPresenter Content="{Binding }"/>
                        </Expander>
                    </StackPanel>
                </DataTemplate>
            </ListBox.ItemTemplate>
        </ListBox>

Edit: loc refers to the namespace in which the DepartmentParticipant and EmployeeParticipant are present. Hope you are familiar with adding namespaces.