Explain the 'Abstract Factory' pattern and how it is used in software design.

The "Abstract Factory" pattern is a creational design pattern that provides an interface for creating families of related or dependent objects without specifying their concrete classes.

The idea is to isolate client code from the specific implementations of the objects being created, allowing families of products to be changed without modifying the code that uses them.

Example of usage in Flutter: Suppose we have different themes with a set of widgets (buttons, input fields). The abstract factory creates an interface for creating these widgets, and concrete factories implement them for light and dark themes.

abstract class WidgetFactory {
  Button createButton();
  TextField createTextField();
}

class LightThemeFactory implements WidgetFactory {
  @override
  Button createButton() => LightButton();

  @override
  TextField createTextField() => LightTextField();
}

class DarkThemeFactory implements WidgetFactory {
  @override
  Button createButton() => DarkButton();

  @override
  TextField createTextField() => DarkTextField();
}

// Client code
void buildUI(WidgetFactory factory) {
  var button = factory.createButton();
  var textField = factory.createTextField();
  // Use button and textField
}

This approach simplifies support and extension of the code, making it easy to add new product families.