c# - 如何在 C# 中调度事件

Question

我希望创建自己的事件并发送它们。我以前从未在 C# 中这样做过，只是在 Flex 中。我想肯定有很多不同之处。

谁能给我一个很好的例子？

Answer 1

所有库类中都使用了一种模式。也推荐用于您自己的类，尤其是对于框架/库代码。但是，当您偏离或跳过几步时，没有人会阻止您。

这是基于最简单的事件委托的示意图，System.Eventhandler.

// The delegate type. This one is already defined in the library, in the System namespace
// the `void (object, EventArgs)` signature is also the recommended pattern
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
    }
}

以及如何使用它：

// your subscribing class
class Bar
{       
    public Bar()
    {
        Foo f = new Foo();
        f.Changed += Foo_Changed;    // Subscribe, using the short notation
    }

    // the handler must conform to the signature
    void Foo_Changed(object sender, EventArgs args)  // the Handler (reacts)
    {
        // the things Bar has to do when Foo changes
    }
}

---

当您有信息要传递时：

class MyEventArgs : EventArgs    // guideline: derive from EventArgs
{
    public string Info { get; set; }
}

class Foo  
{
    public event EventHandler<MyEventArgs> Changed;    // the Event
    ...
    protected virtual void OnChanged(string info)      // the Trigger
    {
        EventHandler handler = Changed;   // make a copy to be more thread-safe
        if (handler != null)
        {
           var args = new MyEventArgs(){Info = info};  // this part will vary
           handler(this, args);  
        }
    }
}

class Bar
{       
   void Foo_Changed(object sender, MyEventArgs args)  // the Handler
   {
       string s = args.Info;
       ...
   }
}

---

更新

从 C# 6 开始，'Trigger' 方法中的调用代码变得更加容易，可以使用空条件运算符缩短空测试，?.而无需复制，同时保持线程安全：

protected virtual void OnChanged(string info)   // the Trigger
{
    var args = new MyEventArgs{Info = info};    // this part will vary
    Changed?.Invoke(this, args);
}

Answer 2

C# 中的事件使用委托。

public static event EventHandler<EventArgs> myEvent;

static void Main()
{
   //add method to be called
   myEvent += Handler;

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

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

Answer 3

使用典型的 .NET 事件模式，并假设您的事件中不需要任何特殊参数。您的典型事件和调度模式如下所示。

public class MyClassWithEvents
    {
        public event EventHandler MyEvent;

        protected void OnMyEvent(object sender, EventArgs eventArgs)
        {
            if (MyEvent != null)
            {
                MyEvent(sender, eventArgs);
            }
        }

        public void TriggerMyEvent()
        {
            OnMyEvent(sender, eventArgs);
        }
    }

将一些东西绑定到事件中可以很简单：

public class Program
{
    public static void Main(string[] args)
    {
        MyClassWithEvents obj = new MyClassWithEvents();

        obj.MyEvent += obj_myEvent;
    }

    private static void obj_myEvent(object sender, EventArgs e)
    {
        //Code called when my event is dispatched.
    }
}

看看这个 MSDN 页面上的链接

Answer 4

查看“代表”。

• 定义委托
• 使用委托类型作为字段/属性（添加“事件”关键字）
• 您现在正在公开用户可以使用“+= MyEventMethod;”挂钩的事件

希望这可以帮助，