C＃事件处理（与Java相比） [英] C# event handling (compared to Java)

问题描述

我目前正在C＃中使用delagate进行硬体理解和实现活动。我习惯了Java的做事方式：

1. 定义一个监听器类型的接口，该接口将包含多个方法定义
2. 
   
3. 为该界面定义适配器类，如果我对所有在监听器中定义的事件不感兴趣，可以使事情变得更容易。


4. 定义添加，删除和获取引发事件的类中的[]方法


5. 定义受保护的fire方法来循环添加侦听器列表并调用正确的方法

这个我明白（和！！） - 我知道我可以在c＃中完全一样，但是似乎一个新的（更好的）系统是c＃的地方。阅读无数的教程，解释在c＃中使用代表和事件，我仍然没有更接近真正了解发生了什么：S

---

简而言之，对于以下方法，我将如何在c＃中实现事件系统：

  void computerStarted（Computer computer） ; 
 void computerStopped（Computer computer）; 
 void computerReset（Computer computer）; 
 void computerError（计算机计算机，异常错误）; 
  

^以上方法取自我曾经做过的Java应用程序，我试图移植到c＃。

很多谢谢！

解决方案

创建四个事件和方法来提高它们，以及一个新的基于EventArgs的类来指示错误：

  public class ExceptionEventArgs ：EventArgs 
 {
 private readonly异常错误; 
 
 public ExceptionEventArgs（异常错误）
 {
 this.error = error; 
} 
 
 public错误
 {
 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（）
 {
已停止（此为EventArgs.Empty）; 
} 
 
 protected void OnReset（）
 {
重置（this，EventArgs.Empty）; 
} 
 
 protected void OnError（异常e）
 {
错误（这是新的ExceptionEventArgs（e））; 
} 
} 
  

然后类可以使用方法订阅事件或一个匿名函数：

  someComputer.Started + = StartEventHandler; //方法
 someComputer.Stopped + = delegate（object o，EventArgs e）
 {
 Console.WriteLine（{0} has started，o）; 
}; 
 someComputer.Reset + =（o，e）=> Console.WriteLine（{0}已被重置）; 
  

需要注意的几件事情是：

• OnXXX方法受到保护，以便派生类可以引发事件。这并不总是必要的 - 按照你的看法做到这一点。


• 每个事件声明的委托{} 避免不必执行空检查的技巧。它正在为每个事件订阅一个无操作的事件处理程序。


• 事件声明是类似字段的事件。实际创建的是变量和事件。在课堂里你看到变量;

请参阅我的事件/代表文章更多的事件细节。

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

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

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

---

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);

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

Many many thanks!

解决方案

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));
    }
}

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");

A few things to note about the above:

• 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.

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

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