https://medium.com/flawless-app-stories/how-to-use-a-model-view-viewmodel-architecture-for-ios-46963c67be1b
In general, the ViewModel receives the user interaction from the View, fetches data from the Model, then process the data to a set of ready-to-display properties. The View updates itself after observing the change of the ViewModel. That’s the whole story of the MVVM.