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Why do we need model view ViewModel pattern MVVM pattern?
MVVM combines the advantages of separation of concerns provided by MVP, while leveraging the advantages of data bindings. The result is a pattern where the model drives as many of the operations as possible, minimizing the logic in the view.
What are the benefits of MVVM design pattern?
As a separation pattern MVVM aims to provide 3 specific benefits:
- #1 Collaborative working.
- #2 Code reuse.
- #3 Ease of testing.
- bonus #4 Bindings make UI updates easier to handle.
- bonus #5 Ease of maintainability.
What should be in the ViewModel?
The simplest kind of viewmodel to understand is one that directly represents a control or a screen in a 1:1 relationship, as in “screen XYZ has a textbox, a listbox, and three buttons, so the viewmodel needs a string, a collection, and three commands.” Another kind of object that fits in the viewmodel layer is a …
When to use view model and ViewModel in MVVM?
Rule Number Four: View can call view-model whenever it needs something. ViewModel can provide helper methods for the view. Note that whether ViewModel updates the calculated values in LiveData or do it in helper method It’s the ViewModel that handles the logic and that’s what’s matter!!
How to alert ViewModel of changes in model?
In your example the models are being updated “on their own” and these changes of course need to somehow propagate to the views. Since the views can only directly access the viewmodels, it means the model must communicate these changes to the corresponding viewmodel.
Why does the ViewModel always ask for properties?
The ViewModel always asks the Model for properties. In Rachel’s example, she does have the model implement INotifyPropertyChanged, and raises events from the model, but they are for consumption by the view itself (see her article/code for more detail on why she does this).
How is my ViewModel passed to the view?
Accordingly, my ViewModel knows nothing about the View that uses it. The ViewModel is passed to the View by App.xaml.cs as a part of the application bootstrap process: The view model is instantiated and set as the DataContext of the main window, which serves as the demo application’s View.