מריה בוטוסוב

State Pattern - אחד הפאטרנים הכי חשובים שיש. דוגמה של כספומט:

בדרך כלל State Pattern מורכב משלושה חלקים:

1. Context  - ישות שמשתמש ניגש אליה:

public class ATM {
    public ATMState currentState = null;        
    public ATM() {
        currentState = new NoCardState(1000, this);
    }
    public void StartTheATM() {
        while (true) {
            Console.WriteLine(currentState.GetNextScreen());
        }
    }
}

2. State - זה Interface או Abstract class שמגדיר כל המצבים האפשריים של Context:

public abstract class ATMState {
    public ATM Atm { get; get; }
    public int DummyCashPresent { get;set; } = 1000;
    public abstract string GetNextScreen();
}

3. Concrete State - מצב של Context. לכל מצב יהיה class משלו.:

public class NoCardState : ATMState {
    public NoCardState(ATMState state):this(state.DummyCashPresent, state.Atm) {
    }
    public NoCardState(int amountRemaining, ATM atmBeingUsed) {
        this.Atm = atmBeingUsed;
        this.DummyCashPresent = amountRemaining;
    }
    public override string GetNextScreen() {            
        Console.WriteLine("Please enter your pin");
        string userInput = Console.ReadLine();
        if (userInput.Trim() == "1234") {
            UpdateState();
            return "Enter the amount to withdraw";
        }
        return "Invalid PIN";
    }
    private void UpdateState() {
        Atm.currentState = new CardValidatedState(this);
    }
}
 
public class CardValidatedState : ATMState {
    public CardValidatedState(ATMState state):this(state.DummyCashPresent, state.Atm){
    }
    public CardValidatedState(int amountRemaining, ATM atmBeingUsed) {
        this.Atm = atmBeingUsed;
        this.DummyCashPresent = amountRemaining;
    }
    public override string GetNextScreen() {
        string userInput = Console.ReadLine();
        int requestAmount;
        bool result = Int32.TryParse(userInput, out requestAmount);
        if (result == true) {
            if (this.DummyCashPresent < requestAmount) {
                return "Amount not present";
            }
            this.DummyCashPresent -= requestAmount;
            UpdateState();
 
            return $"Amount of {requestAmount} has been withdrawn. Press Enter to proceed";
        }
        return "Invalid amount";
    }
 
    private void UpdateState() {        
        Atm.currentState = new NoCashState(this);        
    }
}