Question

imagine the following simple Models (example for simplicity reasons; in fact, we have MVVM here but it doesn’t matter):

public class User {
  public string Username { get; set; }
}

public class StackOverflowUser : User {
  public int Reputation { get; set; }
}

Now we have a Silverlight UserControl which contains the following Controls (again, this is just an example, stripped down to the core):

<Grid>
    <TextBlock Text="Username:" />
    <TextBlock Text="{Binding Path=Username}" />

    <TextBlock Text="Reputation:" />
    <TextBlock Text="{Binding Path=Reputation}" />
</Grid>

Now I’d like this UserControl to be compatible with both Models, User and StackOverflowUser. I might set the UserControl’s DataContext to either a User or StackOverflowUser Type:

this.DataContext = new User { Username = "john.doe" };

If set to StackOverflowUser, everything works fine. If set to User, I’m getting a “BindingExpression Path error”, because the Property Reputation is missing in the User Model. Which I understand completely.

Is there any way to 1) avoid this
exception and 2) control the
visibility of the controls, collapse
when bound property is not available?

Of course, we prefer an elegant solution, where the problem is solved by tuning the Binding Expression and/or using Converters etc. and avoid tons of code behind if possible.

Thanks in advance for your help and suggestions,
best regards,

Thomas

Answer 1

I finally got my problem solved. A co-worker finally implemented a solution including a workaround for WPFs DataTemplates DataType attribute (or generally, a DataTemplateSelector). It’s not very pretty (i guess, no workaround is) but it works. Unfortunately, i cannot post any code snippets because its closed-source. But i found some links afterwards, providing a pretty similar solution, like this one: Silverlight: a port of the DataTemplateSelector. If you have a similar problem, this will help you as well. Here or there are more thoughts on this subject.

The actual solution is following Ozan’s hints. Unfortunately, his solution is not working so I don’t want to mark his comment as the accepted answer but I give at least an upvote.

Thanks!

best regards,

Thomas