ViewModel or Model: Where Should INotifyPropertyChanged Live in MVVM?

Where Should INotifyPropertyChanged Be Implemented in MVVM: ViewModel or Model?

When developing MVVM applications, the question arises whether the ViewModel or the Model should implement the INotifyPropertyChanged interface. While many examples show the Model implementing this interface, Josh Smith's CommandSink example takes a different approach by having the ViewModel implement it.

Rationale for Model INotifyPropertyChanged Implementation

Some argue that the Model should not implement INotifyPropertyChanged, as it is not UI-specific. However, this argument overlooks the fact that this interface merely notifies of changes, regardless of UI involvement. Therefore, it is suitable for other use cases, such as triggering non-UI logic.

Rationale for ViewModel INotifyPropertyChanged Implementation

Others support the ViewModel implementing INotifyPropertyChanged, as it simplifies data binding. It eliminates the need for intricate event handlers on the Model or propagating property changes from the ViewModel to the Model.

Is There a Standard Approach?

Despite these arguments, there is no definitive answer to this question. MVVM allows for flexibility in implementation. Consider the following factors when making your decision:

• Performance: In most cases where the Model is not receiving external updates, implementing INotifyPropertyChanged in the Model can create unnecessary performance overhead.
• Ease of Development: Implementing INotifyPropertyChanged in the ViewModel simplifies binding, especially when working with potentially stale data.
• Testability: Mocking the Model becomes easier when it does not implement INotifyPropertyChanged.

Conclusion

Ultimately, the decision depends on the specific requirements of your project. Weigh the pros and cons of each approach to determine the most appropriate solution. Avoid dogma and explore different implementations to find what works best for your application.

The above is the detailed content of ViewModel or Model: Where Should INotifyPropertyChanged Live in MVVM?. For more information, please follow other related articles on the PHP Chinese website!