INotifyPropertyChanged inside a Model when needing multiple instances of that class WPF

Question

I have a ListView and the ItemTemplate of the ListView contains a TextBox. The ItemSource of the ListView is an ObservableCollection of type T of which the Viewmodel has an instance of as Property. The View needs to bind itself to a particular Property of T. (with T existing out of multiple Properties)

        <ListView ItemSource={Binding SomeObservableCollectionOfTypeT}>
           <ListView.ItemTemplate>
              <DataTemplate>
                   <TextBox Text = {Binding T.Someproperty, UpdateSourceTrigger=PropertyChanged} />
              </DataTemplate>
           </ListView.ItemTemplate>
        </ListView>

At first I had T as an inner class inside the ViewModel (with T also implementing INotifyPropertyChanged) but I realised I needed this class in multiple ViewModels in an identical fashion. T would be the model here.

I'm inclined to avoid using INotifyPropertyChanged in the Model as I think it is desirable having the View bind to the Viewmodel exclusively. Is this the exact scenario where using INotifyPropertyChanged is valid in Models? How should I approach this situation in a typical situation like this, where you need to bind to Properties of a Type that is inside a collection in your ViewModel using the MVVM Design pattern?

Model wouldn't implement INPC if it was readonly, otherwise implement INPC interface on it. Why do you need scrollviewer? ListView can scroll content too. Then how do you propose to present Model if you don't want to bind it to view? — XAMlMAX, Sep 15 '20 at 13:52
Binding directly to model properties or adding to a model certain view model features is sort of *lazy* MVVM. Think of it as if you combine model + view model in a single class. Probably not good SRP-wise, but is easier if view model only acts like a simple wrapper. — Sinatr, Sep 15 '20 at 14:00
"Model wouldn't implement INPC if it was readonly, otherwise implement INPC interface on it." Thanks. Also I wouldn't know how to implement it otherwise. But i've heard people state that the View should bind exclusively to the Viewmodel. (I'll edit out the scrollviewer.) — Merlin, Sep 15 '20 at 14:04
"Binding directly to model properties or adding to a model certain view model features is sort of lazy MVVM.". How would you expose the properties of T in somecollection in this example without lazy mvvm? — Merlin, Sep 15 '20 at 14:07

score 0 · Accepted Answer · answered Sep 15 '20 at 14:31

I'm inclined to avoid using INotifyPropertyChanged in the Model as I think it is desirable having the View bind to the Viewmodel exclusively.

It depends on how you define a "model". If it's some kind of domain object that is used across several applications, you should not bind directly against it but instead create a wrapper view model class that does implement INotifyPropertyChanged.

Is this the exact scenario where using INotifyPropertyChanged is valid in Models?

Certainly as long as the "model" is not a domain object. Then you should replace it with a view model in your client application.

How should I approach this situation in a typical situation like this, where you need to bind to Properties of a Type that is inside a collection in your ViewModel using the MVVM Design pattern?

Create a "child" view model class that implements INotifyPropertyChanged and translate the current model objects to this type, for example by simply wrapping the properties.

INotifyPropertyChanged inside a Model when needing multiple instances of that class WPF

1 Answers1