Structural Design Pattern – Facade

Facade Design Pattern:

Façade pattern simplifies the interaction between complex subsystems, by providing a single interface for interacting with those subsystems. As a result the client has to interact with the single subsystem instead of interacting with those individual subsystems. In other words façade is a way to hiding a complex system inside a simpler interface. It has the following parts:

-          Facade – It is the class which actually provides a simplified interface to the complex subsystem.

-          Complex Subsystems – These are the complex subsystems which is required by the client and which is accessible indirectly from the Façade class.

Let’s look at an example.

1. Complex Subsystem – Contains of the classes which are independent and complex in nature. The client needs access to the all these functionality for a common task/activitity. Without façade the client would need to have knowledge about all functionalities of each of these classes.

public class Class1

    {

        public void Method1()

        {

            Console.WriteLine(“Class1.Method1()”);

        }

    }

    public class Class2

    {

        public void Method2()

        {

            Console.WriteLine(“Class2.Method2()”);

        }

    }

    public class Class3

    {

        public void Method3()

        {

            Console.WriteLine(“Class3.Method3()”);

        }

    }

2. Facade – You can see how the façade class hides all the complexities of the subsystems(class1, class2 and class3) and makes it accessible to the client through a simplified interface i.e. through MainMethod().

public class FacadePattern

    {

        Class1 c1;

        Class2 c2;

        Class3 c3;

        public FacadePattern()

        {

            c1 = new Class1();

            c2 = new Class2();

            c3 = new Class3();

        }

        public void MainMethod()

        {

            Console.WriteLine(“All methods…”);

            c1.Method1();

            c2.Method2();

            c3.Method3();

        }

    }

3. Client – Shows how the façade will be invoked

public static void Main()

        {

            FacadePattern fp = new FacadePattern();

            fp.MainMethod();

      }