In our WPF/MVVM application, we are binding to property of the Model directly because the Model is from legacy library (we added the support of INotifyPropertyChanged to the Model class). I.e., the code of ViewModel looks like

Public Class MyViewModel
    Inherits ViewModelBase

    Public Property Model As MyModel

End Class

And then the binding looks like this:

<TextBox Text="{Binding Model.Prop1}" />

Everyting worked fine until I have this requirement to have some properties in the ViewModel which depend on Model.Prop1. Specifically, I am binding the ItemSource of one ComboBox to a property of collection in the ViewModel, and this collection should be refreshed/recalculated whenever Model.Prop1 is changed. The code looks like this:

<ComboBox ItemsSource="{Binding MyCollection}" />

I have some options but they are not good in my opinion:

1. I can have Model class hold a reference of ViewModel. And in the setter of Prop1 in the Model I update the MyColleciton property of ViewModel. Of course it is not a good idea
2. Use EventAggregator for the communication between Model and ViewModel. Not efficient in my opinion plus I need to make big change in the Model class too.
3. Let ViewModel have one property Prop1 and bind to this. In the getter of it return Model.Prop1 and in the setter assign ModelProp1 = Value. This is my current solution but there is one problem: in our Model we have other property/attribute which are useful and we create a common Style based on this property/attribute. For example, when the Model.Prop1 is changed, another property called IsDirty in Model class is set to True and in the View we change the color. But if we use Prop1 from ViewModel, instead of from Model, we lose this common Style behavior like other properties.

So now I still want to use the binding to {Binding Model.Prop1} (not create a wrapper property in the ViewModel) but somehow notify other properties in the Model when it is changed. Can I do that?