Model–View–Viewmodel (MVVM) Application

A Model–View–Viewmodel (MVVM) Application is a front-end application that follows an MVVM pattern (composed of a view layer and a modelview layer).

• Context:
  • It can range from being a Mobile MVVM App to being a Web MVVM App.
  • …
• Example(s):
  • an MVVM Data Entry App.
  • an MVVM e-Commerce App.
  • an MVVM Finanical App.
  • ...
• Counter-Example(s):
  • Model-View-Controller (MVC) App.
  • Model-View-Presenter (MVP) App.
• See: Separation of Concerns, Business Logic, Front End, Back End, Data Object, Mediator Pattern, Ember.js.

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References

2023

• chat
  • Q: describe how the business logic is handled in several examples of MVVM applications.
  • A: In Model-View-ViewModel (MVVM) architecture, the business logic is typically handled by the ViewModel. The ViewModel acts as a link between the View (which is responsible for displaying data to the user) and the Model (which contains the data and business logic).
    • A common example of MVVM in a business application is a data entry form. The View displays the form to the user, the ViewModel handles validation of the user's input and any necessary calculations, and the Model stores the final data.
    • Another example is a e-commerce application, the View displays the product details, the ViewModel handles the logic for adding the product to the cart, calculating the total cost and applying discounts, and the Model stores the final shopping cart data.
    • In a financial application, the View may display a list of transactions, the ViewModel may handle the logic for filtering and sorting the transactions, and the Model may store the financial data.

2023

• chat
  • Q: Write an essay on how to structure an MVVM application to support offline mode?
  • A: Structuring an MVVM application to support offline mode requires careful consideration of the data storage and synchronization strategies that will be used. The key to a successful offline mode implementation is to ensure that the application can continue to function seamlessly, regardless of the availability of network connectivity.

To begin, it is important to identify the data that needs to be available offline. This data should be stored locally, in a format that is easily accessible and queryable, such as a local database. The local storage should be implemented in a way that allows for easy synchronization with the server-side data store when a connection is re-established.

The ViewModel, which acts as the intermediary between the view and the model, should be responsible for managing the offline data storage and synchronization. It should provide the view with the necessary data and handle any updates to the data. The ViewModel should also monitor the network connectivity status, and switch between the local and remote data sources accordingly.

One strategy to handle the data synchronization is to use a "last write wins" approach, where the server-side data store is considered the source of truth, and any conflicting data is resolved in favor of the server-side data. This approach ensures that the data on the server is always up-to-date and minimizes the risk of data loss.

Another strategy is to use a "conflict resolution" approach, where the application presents the user with options to resolve any conflicts, such as choosing which version of the data to keep.

In addition, the application should also handle the scenarios where the user makes updates while offline, and prompt the user to save the changes locally or discard them when the network connection is re-established.

In conclusion, structuring an MVVM application to support offline mode requires careful consideration of the data storage and synchronization strategies. The key is to ensure that the application can continue to function seamlessly, regardless of the availability of network connectivity by identifying the data that needs to be available offline, implementing local storage, and handling the data synchronization and conflicts. The ViewModel should be responsible for managing the offline data storage and synchronization and switching between the local and remote data sources accordingly.

2022

• https://en.wikipedia.org/wiki/Model%E2%80%93view%E2%80%93viewmodel#Components_of_MVVM_pattern

  • Model

    Model refers either to a domain model, which represents real state content (an object-oriented approach), or to the data access layer, which represents content (a data-centric approach).^{[citation needed]}

    View

    As in the model–view–controller (MVC) and model–view–presenter (MVP) patterns, the view is the structure, layout, and appearance of what a user sees on the screen. It displays a representation of the model and receives the user's interaction with the view (mouse clicks, keyboard input, screen tap gestures, etc.), and it forwards the handling of these to the view model via the data binding (properties, event callbacks, etc.) that is defined to link the view and view model.

    View model

    The view model is an abstraction of the view exposing public properties and commands. Instead of the controller of the MVC pattern, or the presenter of the MVP pattern, MVVM has a binder, which automates communication between the view and its bound properties in the view model. The view model has been described as a state of the data in the model.

    The main difference between the view model and the Presenter in the MVP pattern is that the presenter has a reference to a view, whereas the view model does not. Instead, a view directly binds to properties on the view model to send and receive updates. To function efficiently, this requires a binding technology or generating boilerplate code to do the binding.

    Binder

    Declarative data and command-binding are implicit in the MVVM pattern. In the Microsoft solution stack, the binder is a markup language called XAML. The binder frees the developer from being obliged to write boiler-plate logic to synchronize the view model and view. When implemented outside of the Microsoft stack, the presence of a declarative data binding technology is what makes this pattern possible, and without a binder, one would typically use MVP or MVC instead and have to write more boilerplate (or generate it with some other tool).

20xx

• .
  • QUOTE:

    The Model View ViewModel (MVVM) architectural pattern. In MVVM, the View layer is concerned only about the graphical user interface, while the Model layer only about the business logic. All communication between them is realized by the ViewModel layer. 

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