The State Pattern

The State Pattern


The State Pattern allows an object to alter its behaviour when its internal state changes.

This pattern promotes flexibility and adaptability in C# code by encapsulating behaviour within internal states.

Understanding the State Pattern

The State Pattern revolves around the concept of encapsulating behaviour within internal states.

An object can transition between different states, and each state defines a set of behaviours specific to that state.

This pattern decouples the object’s behaviour from its implementation, making it easier to manage and extend the object’s functionality.

Benefits of the State Pattern

The State Pattern offers several advantages, including:

  • Flexibility: It allows an object to change its behaviour dynamically based on its state.
  • Adaptability: It promotes adaptability by enabling the object to handle different scenarios without modifying its core code.
  • Encapsulation: It encapsulates behaviour within states, promoting code modularity and reducing coupling.
  • Testability: It enhances testability by isolating and testing each state independently.
  • Maintenance: It simplifies maintenance by making it easier to add new states without affecting existing code.

Types of State Patterns

The State Pattern encompasses several variations, each with its specific characteristics:

  • Finite State Machine (FSM): Represents a finite number of states and transitions between them.
  • Hierarchical State Machine: Allows for nested state hierarchies and complex behaviour.
  • Polymorphic State Machine: Allows for polymorphism in state implementations.
  • Hybrid State Machine: Combines aspects of different state machine types.

Implementing the State Pattern in C#

To illustrate the implementation of the State Pattern in C#, consider a simplified scenario of managing a vending machine:


The context represents the vending machine and holds its current state.

public class VendingMachine
    private State soldOutState;
    private State hasCoinState;
    private State selectingProductState;
    private State dispensingProductState;

    private State current;

    public VendingMachine()
        soldOutState = new SoldOutState(this);
        hasCoinState = new HasCoinState(this);
        selectingProductState = new SelectingProductState(this);
        dispensingProductState = new DispensingProductState(this);

        current = soldOutState;

    public void InsertCoin() => current.InsertCoin();

    public void SelectProduct(Product product) => current.SelectProduct(product);

    public void DispenseProduct() => current.DispenseProduct();

    public void ReleaseCoin() => current.ReleaseCoin();


Each state defines the behaviour associated with a specific state of the vending machine.

public abstract class State
    protected VendingMachine vendingMachine;

    public State(VendingMachine vendingMachine)
        this.vendingMachine = vendingMachine;

    public abstract void InsertCoin();
    public abstract void SelectProduct(Product product);
    public abstract void DispenseProduct();
    public abstract void ReleaseCoin();

This example demonstrates a basic implementation of the State Pattern in C# for managing a vending machine.

The state pattern can be extended to handle more complex vending machines and product scenarios.


The State Pattern is a valuable tool for managing the behaviour of an object across different internal states in C# code.

It promotes flexibility, adaptability, and testability by encapsulating behaviour within states.

By leveraging the State Pattern, developers can create more robust and maintainable applications that can handle changing conditions effectively.


Hi, my name is Stephen Finchett. I have been a software engineer for over 30 years and worked on complex, business critical, multi-user systems for all of my career. For the last 15 years, I have been concentrating on web based solutions using the Microsoft Stack including ASP.Net, C#, TypeScript, SQL Server and running everything at scale within Kubernetes.