CODESAMPLE

State - C#

State C_sharp

The State pattern allows an object to alter its behavior when its internal state changes. It encapsulates each state as a separate class, avoiding large conditional statements and promoting the Open/Closed Principle.

This C# example models a simple traffic light. Each color (Red, Yellow, Green) is a separate state class implementing a common TrafficLightState interface. The TrafficLightContext manages the current state. Transitions between states are handled within the state classes themselves, making the context unaware of specific state logic. The use of interfaces and abstract classes promotes loose coupling and extensibility - new states can be added without modifying existing ones. This is a clean and standard approach to state management in C#.

// Define the State interface
public interface ITrafficLightState
{
    void Handle(TrafficLightContext context);
}

// Concrete State: Red
public class RedState : ITrafficLightState
{
    public void Handle(TrafficLightContext context)
    {
        Console.WriteLine("Traffic Light: RED - Stop!");
        context.SetState(new YellowState()); // Transition to Yellow
    }
}

// Concrete State: Yellow
public class YellowState : ITrafficLightState
{
    public void Handle(TrafficLightContext context)
    {
        Console.WriteLine("Traffic Light: YELLOW - Caution!");
        context.SetState(new GreenState()); // Transition to Green
    }
}

// Concrete State: Green
public class GreenState : ITrafficLightState
{
    public void Handle(TrafficLightContext context)
    {
        Console.WriteLine("Traffic Light: GREEN - Go!");
        context.SetState(new RedState()); // Transition to Red
    }
}

// The Context
public class TrafficLightContext
{
    private ITrafficLightState _state;

    public TrafficLightContext()
    {
        _state = new RedState(); // Initial state
    }

    public void SetState(ITrafficLightState state)
    {
        _state = state;
    }

    public void Request()
    {
        _state.Handle(this);
    }
}

// Example Usage
public class Example
{
    public static void Main(string[] args)
    {
        TrafficLightContext trafficLight = new TrafficLightContext();
        for (int i = 0; i < 5; i++)
        {
            trafficLight.Request();
        }
    }
}