C# 如何在C语言中正确触发事件

我试图在单击按钮时触发事件。我点击按钮，什么也没发生

问题是，在OnEventA中，我总是将EventA设置为null：

编辑：

基于Henk Holterman的链接，我还测试了该代码：

public delegate void Eventhandler(object sender, Eventargs args);  

// your publishing class
class Foo  
{
    public event EventHandler Changed;    // the Event

    protected virtual void OnChanged()    // the Trigger method, called to raise the event
    {
        // make a copy to be more thread-safe
        EventHandler handler = Changed;   

        if (handler != null)
        {
            // invoke the subscribed event-handler(s)
            handler(this, EventArgs.Empty);  
        }
    }

    // an example of raising the event
    void SomeMethod()
    {
       if (...)        // on some condition
         OnChanged();  // raise the event
    }
}

---

我在单击按钮时调用OnChanged，但结果始终不变：EventA=null。

我通过以下方式解决了问题：

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.Windows.Forms;

namespace eventsC
{    

    public partial class Form1 : Form
    {

        public static event EventHandler<EventArgs> myEvent;

        protected void OnMyEvent()
        {
            if (myEvent != null)
                myEvent(this, EventArgs.Empty);
        }

        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            myEvent += Handler;

            //call all methods that have been added to the event
            myEvent(this, EventArgs.Empty);

        }

        private void button1_Click(object sender, EventArgs e)
        {
            OnMyEvent();
        }


        static void Handler(object sender, EventArgs args)
        {
            Console.WriteLine("Event Handled!");
        }

    }
}

---

我认为他们的回答是正确的，它没有任何订户

namespace TestConsoleApp
{
    public delegate void Eventhandler(object sender, EventArgs args);

    // your publishing class
    class Foo
    {
        public event EventHandler Changed;    // the Event

        protected virtual void OnChanged()    // the Trigger method, called to raise the event
        {
            // make a copy to be more thread-safe
            EventHandler handler = Changed;

            if (handler != null)
            {
                // invoke the subscribed event-handler(s)
                handler(this, EventArgs.Empty);
            }
        }

        // an example of raising the event
        public void SomeMethod()
        {

                OnChanged();  // raise the event
        }
    }

    public class Program
    {

        static void Main(string[] args)
        {
            Foo objFoo = new Foo();
            objFoo.Changed += ObjFoo_Changed;
            objFoo.SomeMethod();
            Console.ReadLine();
        }

        private static void ObjFoo_Changed(object sender, EventArgs e)
        {
            Console.WriteLine("Event fired and changed");
        }
    }
  }

---

您的活动有订户吗？我在@PeterBons上写了完整的图片：我需要在同一个解决方案中的另一个VB.NET项目中接收该活动。但由于EventA=null而从未到达。我可以像我展示的代码一样从同一个类触发事件吗？您没有提供足够的信息来回答问题-您的+=？Re行在哪里？如果我没有，那么您没有subcriber，在这种情况下，EventA应该为null。这似乎不能回答您的问题。您的问题似乎是关于使用不同班级的活动。是这样吗？重写OnMyEvent并在自己的类中处理事件是没有意义的。事件处理程序应该在订阅类中完成，而不是在Form1中

namespace TestConsoleApp
{
    public delegate void Eventhandler(object sender, EventArgs args);

    // your publishing class
    class Foo
    {
        public event EventHandler Changed;    // the Event

        protected virtual void OnChanged()    // the Trigger method, called to raise the event
        {
            // make a copy to be more thread-safe
            EventHandler handler = Changed;

            if (handler != null)
            {
                // invoke the subscribed event-handler(s)
                handler(this, EventArgs.Empty);
            }
        }

        // an example of raising the event
        public void SomeMethod()
        {

                OnChanged();  // raise the event
        }
    }

    public class Program
    {

        static void Main(string[] args)
        {
            Foo objFoo = new Foo();
            objFoo.Changed += ObjFoo_Changed;
            objFoo.SomeMethod();
            Console.ReadLine();
        }

        private static void ObjFoo_Changed(object sender, EventArgs e)
        {
            Console.WriteLine("Event fired and changed");
        }
    }
  }