如何在 C# 中调度事件 [英] How to dispatch events in C#

问题描述

我希望创建自己的事件并调度它们.我以前在 C# 中没有这样做过，只有在 Flex 中.我想肯定有很多不同之处.

I wish to create own events and dispatch them. I never done this before in C#, only in Flex.. I guess there must be a lot of differencies.

谁能给我举个好例子?

推荐答案

有一个在所有库类中都使用的模式.也推荐用于您自己的类，尤其是框架/库代码.但是当你偏离或跳过几步时，没有人会阻止你.

There is a pattern that is used in all library classes. It is recommended for your own classes too, especially for framework/library code. But nobody will stop you when you deviate or skip a few steps.

这是一个基于最简单的事件委托System.Eventhandler的示意图.

Here is a schematic based on the simplest event-delegate, 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
    }
}

<小时>

当你有信息要传递时:

---

And when you have information to pass along:

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;
       ...
   }
}

<小时>

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. 无需复制，同时保持线程-安全:

Starting with C# 6 the calling code in the 'Trigger' method has become a lot easier, the null test can be shortened with the null-conditional operator ?. without making a copy while keeping thread-safety:

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

这篇关于如何在 C# 中调度事件的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！