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Spyros Ponaris
Spyros Ponaris

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Understanding the State Pattern

<h1>Understanding the State Pattern</h1>



<h2>Introduction</h2>
<p>The State Pattern is a behavioral design pattern that allows an object to change its behavior when its internal state changes. This pattern is particularly useful when an object must exhibit different behavior based on its current state, eliminating complex conditional logic.</p>



<h2>Key Concepts</h2>
<ul>
    <li>
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State: Represents a state of the context. This is an interface or an abstract class.

  • ConcreteState: Implements the behavior associated with a particular state.

  • Context: Maintains a reference to the current state and allows its behavior to change dynamically.

  • <h2>Code Example from the Repository</h2>
    <p>The <a href="https://github.com/stevsharp/StatePattern">StatePattern</a> repository demonstrates the State Pattern with a practical example. Below is a simplified breakdown:</p>
    
    <h3>1. State Interface</h3>
    <pre><code>public interface IState
    
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    {
    void Handle(Context context);
    }

    <h3>2. Concrete States</h3>
    <pre><code>public class StartState : IState
    
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    {
    public void Handle(Context context)
    {
    Console.WriteLine("State changed to StartState.");
    context.SetState(this);
    }
    }

    public class StopState : IState
    {
    public void Handle(Context context)
    {
    Console.WriteLine("State changed to StopState.");
    context.SetState(this);
    }
    }

    <h3>3. Context</h3>
    <pre><code>public class Context
    
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    {
    private IState _state;

    public void SetState(IState state)
    {
        _state = state;
    }
    
    public void Request()
    {
        _state?.Handle(this);
    }
    
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    }

    <h3>4. Main Program</h3>
    <pre><code>class Program
    
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    {
    static void Main(string[] args)
    {
    Context context = new Context();

        StartState startState = new StartState();
        startState.Handle(context);
    
        StopState stopState = new StopState();
        stopState.Handle(context);
    }
    
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    }

    <h2>Benefits of the State Pattern</h2>
    <ul>
        <li>
    
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    Improved Code Organization: Encapsulates state-specific behavior, reducing conditional logic.

  • Flexibility: Makes it easy to add new states without altering the context or existing states.

  • Maintainability: Separates concerns, improving the clarity and testability of the code.

  • <h2>Use Cases</h2>
    <ul>
        <li>Workflow systems where the behavior depends on the current step.</li>
        <li>Game development to manage player states (e.g., idle, running, jumping).</li>
        <li>UI components that behave differently based on their states (e.g., enabled, disabled).</li>
    </ul>
    
    
    
    <h2>References</h2>
    <ul>
        <li>
    
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    State Pattern Repository - GitHub

  • State Pattern - Refactoring Guru

  • State Pattern - Wikipedia

  • State Design Pattern in C# - Dot Net Tutorials

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