C＃事件处理（相比于Java）

问题描述：

我目前有一个hardtime的理解和执行使用delagates在C＃中的事件。我习惯做事Java的方式：

I am currently having a hardtime understanding and implementing events in C# using delagates. I am used to the Java way of doing things:

定义为一个监听器类型的接口，包含大量的方法定义

定义适配器类的界面，使事情变得更容易，如果我不感兴趣，在听众中定义的所有事件

定义添加，删除和获取[]中引发的事件

定义保护消防方法来做，通过添加侦听器列表循环和调用正确的方法的脏活类的方法

Define an interface for a listener type which would contain a number of method definitions
Define adapter class for that interface to make things easier if I'm not interested in all the events defined in a listener
Define Add, Remove and Get[] methods in the class which raises the events
Define protected fire methods to do the dirty work of looping through the list of added listeners and calling the correct method

这我理解（和喜欢！） - 我知道我能做到这一点正是在C＃一样的，但似乎一个新的（更好？）系统是在放置的C＃。阅人无数的教程说明在C＃中使用委托和事件后，我仍然感到没有接近真正了解正在发生的事情：•

This I understand (and like!) - I know I could do this exactly the same in c#, but it seems that a new (better?) system is in place for c#. After reading countless tutorials explaining the use of delegates and events in c# I still am no closer to really understanding what is going on :S

总之，对于下面的方法我将如何实现事件系统在C＃中：

In short, for the following methods how would I implement the event system in c#:

void computerStarted(Computer computer);
void computerStopped(Computer computer);
void computerReset(Computer computer);
void computerError(Computer computer, Exception error);

^上面的方法都从我试图端口超过我曾经做了一个Java应用程序采取为C＃。

^ The above methods are taken from a Java application I once made which I'm trying to port over to c#.

很多很多的感谢！

答

您会创建四个事件和方法，以提高他们，一个新的基于EventArgs的类一起指示错误：

You'd create four events, and methods to raise them, along with a new EventArgs-based class to indicate the error:

public class ExceptionEventArgs : EventArgs
{
    private readonly Exception error;

    public ExceptionEventArgs(Exception error)
    {
         this.error = error;
    }

    public Error
    {
         get { return error; }
    }
}

public class Computer
{
    public event EventHandler Started = delegate{};
    public event EventHandler Stopped = delegate{};
    public event EventHandler Reset = delegate{};
    public event EventHandler<ExceptionEventArgs> Error = delegate{};

    protected void OnStarted()
    {
        Started(this, EventArgs.Empty);
    }

    protected void OnStopped()
    {
        Stopped(this, EventArgs.Empty);
    }

    protected void OnReset()
    {
        Reset(this, EventArgs.Empty);
    }

    protected void OnError(Exception e)
    {
        Error(this, new ExceptionEventArgs(e));
    }
}

班会，然后订阅使用一个方法事件或匿名函数：

Classes would then subscribe to the event using either a method or a an anonymous function:

someComputer.Started += StartEventHandler; // A method
someComputer.Stopped += delegate(object o, EventArgs e)
{ 
    Console.WriteLine("{0} has started", o);
};
someComputer.Reset += (o, e) => Console.WriteLine("{0} has been reset");

有几件事情需要注意上述：

A few things to note about the above:

的OnXXX方法保护，使派生类可以提高事件。这并不总是必要的 - 这样做，你认为合适

的委托{}每个事件的声明片只是一个。招避免做一个空检查。它的订阅无操作事件处理程序的每个事件

事件声明是的字段般的事件的。什么是真正被创造既是一个变量的和的事件。类在里面你看到变量;类的外部看到的事件。

The OnXXX methods are protected so that derived classes can raise the events. This isn't always necessary - do it as you see fit.
The delegate{} piece on each event declaration is just a trick to avoid having to do a null check. It's subscribing a no-op event handler to each event
The event declarations are field-like events. What's actually being created is both a variable and an event. Inside the class you see the variable; outside the class you see the event.

请参阅我的events/delegates 文章有关事件的更详细信息。

See my events/delegates article for much more detail on events.

C＃事件处理（相比于Java）

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