facade

Facade Structural Design Pattern

hides the complexities of the system by a class that provide a simple interface to a complex subsystem which contains lots of moving parts.

Sections

• Definitions
• What Problem Facade Solve
• Examples
  • Morning Facade Example
  • file converter example
  • Shape Maker Tutorial point Example
• Sources

Definitions

tutorialspoint

is a structural pattern.

this pattern adds an interface to existing system to hide its complexities.

and provides an interface to the client using which the client can access the system.

Wikipedia

a structural pattern

provides a simplified interface to a library, a framework, or any other complex set of classes.

Facade describe how to solve recurring design problems

to design flexible and reusable object-oriented software, that is, objects that are easier to implement, change, test, and reuse.

What Problem Facade Solve

• Imagine that you must make your code work with a broad set of objects that belong to a sophisticated library or framework.
• Ordinarily, you’d need to initialize all of those objects, keep track of dependencies, execute methods in the correct order, and so on.

As a result, the business logic of your classes would become tightly coupled to the implementation details of 3rd-party classes, making it hard to comprehend and maintain.

---

Solution

• A facade is a class that provides a simple interface to a complex subsystem which contains lots of moving parts.

• A facade might provide limited functionality in comparison to working with the subsystem directly.

• However, it includes only those features that clients really care about.

• Having a facade is handy when you need to integrate your app with a sophisticated library that has dozens of features, but you just need a tiny bit of its functionality.

Examples

Morning Facade Example

source: GOF scottt2 design-patterns-in-dart facade

all classes needed to be implemented

class Grinder {
  String _type;

  Grinder(this._type);
  void grind() => print("Grinding $_type!");
}

class Maker {
  String _type;

  Maker(this._type);
  void fill() => print("Filling the $_type maker!");
  void retrieve() => print("Retrieving the $_type!");
  void start() => print("Starting the $_type maker!");
}

class Imbiber {
  String _beverage;

  Imbiber(this._beverage);
  void drink() => print("Mmmmm...drinking $_beverage!");
}

facade class

class MorningFacade {
  final _coffeeDrinker = Imbiber("coffee");
  final _coffeeGrinder = Grinder("coffee beans");
  final _coffeeMaker = Maker("coffee");

  void prepareCoffee() {
    print("\r\nPreparing the coffee...");
    _coffeeGrinder.grind();
    _coffeeMaker
      ..fill()
      ..start();
    print("Coffee is brewing!\r\n");
  }

  void drinkCoffee() {
    print("\r\nMust...have...coffee...");
    _coffeeMaker.retrieve();
    _coffeeDrinker.drink();
    print("This is damn fine coffee!");
  }
}

main() to test

void main() {
  var typicalMorning = MorningFacade();

  print("Wake up! Grab a brush and put on a little makeup...");
  print("\r\nStumble to the kitchen...");

  typicalMorning.prepareCoffee();
  print("Oh my...that smells good...");

  typicalMorning.drinkCoffee();
  print("\r\nI'm ready to attack the day!");
}

file converter example

• Example in dart: file converter example

Shape Maker

• source: tutorialspoint.com/design_pattern/facade_pattern
• Example in dart: Shape Maker

Sources

• wikipedia.org Facade_pattern
• refactoring.guru design-patterns facade
• tutorialspoint - facade_pattern