Can you give an example of applying specific design patterns in software development?

The following design patterns are often used in Flutter development:

• MVVM (Model-View-ViewModel): separates presentation logic and business logic, making testing and maintenance easier. For example, the ViewModel contains state and logic, while the View only displays.

• Singleton: used to create a single instance of a class, for example, to manage application state or access a database.

• Builder: helps create complex widgets step-by-step, improving code readability.

Example of using Singleton to manage state:

class AppState {
  static final AppState _instance = AppState._internal();
  factory AppState() => _instance;
  AppState._internal();

  int counter = 0;
}

void main() {
  var state1 = AppState();
  var state2 = AppState();
  state1.counter++;
  print(state2.counter); // Will output 1, since state1 and state2 are the same instance
}