How to change the class of an object dynamically in C#?

Question

Suppose I have a base class named Visitor, and it has 2 subclass Subscriber and NonSubscriber.

At first a visitor is start off from a NonSubscriber, i.e.

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Answer 1

Adding to the other answers and your comment, you indeed can use the state pattern for your purpose, it would go something like this:

public class MyProgram
{
    public void Run()
    {
        Visitor v = new Visitor("Mary");

        Debug.Assert(v.SubscriptionLinkText == "Join now");

        v.IsSubscribed = true;
        Debug.Assert(v.SubscriptionLinkText == "Today's special");

        v.IsSubscribed = false;
        Debug.Assert(v.SubscriptionLinkText == "Join now");
    }
}

public class Visitor
{
    public string Name { get; set; }

    private bool _isSubscribed;
    public bool IsSubscribed
    {
        get { return this._isSubscribed; }

        set
        {
            if (value != this._isSubscribed)
            {
                this._isSubscribed = value;
                this.OnSubscriptionChanged();
            }
        }
    }

    private SubscriptionBase _subscription;

    public string SubscriptionLinkText
    {
        get { return this._subscription.LinkText; }
    }

    public Visitor(string name)
    {
        this.Name = name;
        this._isSubscribed = false;
        this.OnSubscriptionChanged();
    }

    private void OnSubscriptionChanged()
    {
        // Consider also defining an event and raising it here

        this._subscription =
            SubscriptionBase.GetSubscription(this.IsSubscribed);
    }
}

abstract public class SubscriptionBase
{
    // Factory method to get instance
    static public SubscriptionBase GetSubscription(bool isSubscribed)
    {
        return isSubscribed ?
                new Subscription() as SubscriptionBase
                : new NoSubscription() as SubscriptionBase;
    }

    abstract public string LinkText { get; }
}

public class Subscription : SubscriptionBase
{
    public override string LinkText
    {
        get { return "Today's Special"; }
    }
}

public class NoSubscription : SubscriptionBase
{
    public override string LinkText
    {
        get { return "Join now"; }
    }
}