Explain the concept of the Model-View-Model (MVVM) pattern and its role in application architecture.

MVVM (Model-View-ViewModel) is an architectural pattern that divides the application logic into three components:

• Model — responsible for data and business logic, such as retrieving and storing information.
• View — displays the UI and interacts with the user.
• ViewModel — acts as an intermediary between Model and View, containing presentation logic and state, transforming data from Model into a format suitable for the View.

The role of MVVM in application structure:

• Ensures separation of concerns, which simplifies maintenance and testing.
• ViewModel is independent of UI, allowing logic reuse.
• The View subscribes to changes in the ViewModel and updates automatically.

Example in Flutter:

class CounterViewModel extends ChangeNotifier {
  int _count = 0;
  int get count => _count;

  void increment() {
    _count++;
    notifyListeners();
  }
}

// View subscribes to changes in ViewModel and displays count

Thus, MVVM helps organize code so that the UI is as simple as possible, and business logic is centralized and independent of the presentation.