未引发 C# 事件

Question

So I am trying to learn events and I've done all that's needed to be done to Raise and listen to a simple event, but I am getting no feedback at all when I run the code. The event is simply ignored and only the Hello world is computed. I have two classes, one is a simple Car class, the other an Owner class.

In the car class, I create the event and Raise it according to how the documentation by microsoft says. In the owner class, I listen to it via calling function and then subscribing to it. Still, nothing happens. Please help, i'm about to give up on this.

//--------CAR CLASS-----//


using System;

namespace EventsTutorial

{
    public class Car
    {
        public event EventHandler<int> CarOnEvent;

        

        public Car(string name, string colour, int id)
        {
            Name = name;
            Colour = colour;
            IsOn = false;
            Id = id;
            TurnOn(id);
        }

        public string Name { get; set; }
        public string Colour { get; set; }
        public bool IsOn { get; private set; }
        public int Id { get; set; }

        protected virtual void TurnOn(int e)
        {
            EventHandler<int> handler = CarOnEvent;
            handler?.Invoke(this, e);
        }
    }
}

//-----------OWNER CLASS-------------
using System;

namespace EventsTutorial
{
    class MainClass
    {
        public static void Main(string[] args)
        {
            Console.WriteLine(" World!");

            Car mycar = new Car("Toyota", "Black", 1);
            mycar.CarOnEvent += Mycar_CarOnEvent;
            
        }

      

        private static void Mycar_CarOnEvent(object sender, int e)
        {
            Car var = (Car)sender;

            Console.WriteLine("The car {0}, is now on", var.Name);
        }
    }
}

Answer 1

You are calling TurnOn in the Car constructor, before anyone is attached to the event.

You must first attach to the event and then call TurnOn .

//New car constructor...
public Car(string name, string colour, int id)
{
    Name = name;
    Colour = colour;
    IsOn = false;
    Id = id;
}

//New TurnOn
protected virtual void TurnOn()
{
    EventHandler<int> handler = CarOnEvent;
    handler?.Invoke(this, this.Id);
}

//New main...
public static void Main(string[] args)
{
    Console.WriteLine(" World!");

    Car mycar = new Car("Toyota", "Black", 1);
    mycar.CarOnEvent += Mycar_CarOnEvent;
    myCar.TurnOn()
}