Starting with Catel 3.1, it is possible to determine the view model type of a view dynamically at runtime. This sounds complex, but let's bring up a user scenario which a user came up with:

“I have a shape view and a ShapeBaseViewModel. Then, I have models such as Rectangle, Circle, etc, and each model has its own view model (RectangleViewModel, CircleViewModel, etc). How can I solve this issue using Catel?”

This case proves that it should be at least possible to determine the type of the view model of a view, based on the DataContext of a view.

How to dynamically determine the view model type using a UserControl

Determining the view model dynamically when using the UserControl is extremely easy. You can override the GetViewModelType(object) method like this:

protected override Type GetViewModelType(object dataContext)
{
    if (dataContext is Rectangle)
    {
        return typeof (RectangleViewModel);
    }

    if (dataContext is Circle)
    {
        return typeof (CircleViewModel);
    }

    return null;
}

When the method returns null, it will fall back on the earlier determined view model type.

How to dynamically determine the view model using a behavior

Determining the view model dynamically when using behaviors must be done via the DetermineViewModelType event like this:

mvvmBehavior.DetermineViewModelType += (sender, e) =>
{
    if (e.DataContext is Rectangle)
    {
        e.ViewModelType = typeof (RectangleViewModel);
    }

    if (e.DataContext is Circle)
    {
        e.ViewModelType = typeof(CircleViewModel);
    }
};

There is no need to set the e.ViewModelType to null because that is the default value.