C#复合赋值（例如+；=，-=，等等）“；“例外情况”；

我正在读一本关于C#的书，它是关于复合赋值的（例如+=，-=，*=，/=，=）：

这个规则的一个微妙的例外是事件，我们在第4章中描述了这一点：这里的+=和-=操作符被特别处理，并映射到事件的add和removed访问器

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有人能用通俗易懂的英语解释一下这意味着什么吗？我还没讲到第4章。

它只是意味着+=将事件方法附加到例如控件上，而不是加法（例如算术加法）

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看到差异了吗？

通常，

+=

会将右侧的表达式/变量添加到左侧的表达式/变量，并将结果分配到左侧

// if a = 4, after this statement, a would be 5
a += 1;

但如果表达式的左侧带有

+=

是一个事件，则情况并非如此，而是右侧的事件处理程序，它被添加到该事件的事件处理程序列表中

// whereas on the below statement someEventHandler is added to the collection of event handlers for the 'OnSomeEvent' event
self.OnSomeEvent += someEventHandler

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C#中有委托的概念，它可以指向一个方法。您可以将事件想象为一种特殊类型的代理。您可以

向事件添加

（或

删除

）许多方法。它允许您在特定事件发生时执行指定的方法

一个简单的示例，当您删除一个文件时，该文件在控制台和MessageBox上都显示删除结果

// This is the delegate. Any instance with DeletedEventHandler type 
// can point a method which returns voids and accepts parameters (object,bool)
public delegate void DeletedEventHandler(object sender, bool deleted);

public class FileDeleter
{   
     private DeletedEventHandler onDelete;

     public event DeletedEventHandler OnDelete
     {
         // The add and remove accessors
         add { onDelete += value; }
         remove { onDelete -= value; }
     }

     public void Delete(string filePath)
     {
         try
         {
             File.Delete(filePath);
             RaiseOnDelete(true);
         }
         catch
         {
             RaiseOnDelete(false);
         }
     }

     private void RaiseOnDelete(bool deleted) 
     {
         if (onDelete != null)
             onDelete(this, deleted); // all methods added executes here
     }
}


public void TestMethod()
{
    FileDeleter deleter = new FileDeleter();
    // Note that both ShowDeleteInfoWindows and ShowDeleteInfoConsole are in form of void(object,bool) which is compatible with DeletedEventHandler 
    deleter.OnDelete += new DeletedEventHandler(DeletedOnConsole);
    deleter.OnDelete += new DeletedEventHandler(ShowDeleteInfoWindows);
    deleter.Delete(@"C:\test.txt");
}

private void ShowDeleteInfoConsole(object deleter, bool isDeleted)
{
    Console.WriteLine(isDeleted);
}

private void ShowDeleteInfoWindows(object deleter, bool isDeleted)
{
    MessageBox.Show(isDeleted.ToString());
}

---

这就是它所说的。例如，这些操作符的行为很特殊-它们分别调用

add

和

remove

方法。您可以随时跳到第4章，看一眼，然后返回到您停止的地方。编辑：等一下，上面写着“我们在第四章中描述的”，用过去时态。这不意味着你在后面的章节吗？你是跳过了第四章，还是这本书的时态弄混了？ಠ_ಠ@正在发生的“事件”是什么？好的，我现在投我的-1。请阅读提供的链接。迈克尔：啊，这就解释了。这就是说，只要这本书没有在上下文中向我解释新概念，或者它指向相关章节，我就会按照我在评论中所说的去做。编程书籍是一种你不必从头到尾阅读的书籍——你可以随时在章节之间跳跃：）哦，好的。：）当LHS是一个事件时，它是一个重载运算符，具有新的含义。知道了。谢谢！：）

// This is the delegate. Any instance with DeletedEventHandler type 
// can point a method which returns voids and accepts parameters (object,bool)
public delegate void DeletedEventHandler(object sender, bool deleted);

public class FileDeleter
{   
     private DeletedEventHandler onDelete;

     public event DeletedEventHandler OnDelete
     {
         // The add and remove accessors
         add { onDelete += value; }
         remove { onDelete -= value; }
     }

     public void Delete(string filePath)
     {
         try
         {
             File.Delete(filePath);
             RaiseOnDelete(true);
         }
         catch
         {
             RaiseOnDelete(false);
         }
     }

     private void RaiseOnDelete(bool deleted) 
     {
         if (onDelete != null)
             onDelete(this, deleted); // all methods added executes here
     }
}


public void TestMethod()
{
    FileDeleter deleter = new FileDeleter();
    // Note that both ShowDeleteInfoWindows and ShowDeleteInfoConsole are in form of void(object,bool) which is compatible with DeletedEventHandler 
    deleter.OnDelete += new DeletedEventHandler(DeletedOnConsole);
    deleter.OnDelete += new DeletedEventHandler(ShowDeleteInfoWindows);
    deleter.Delete(@"C:\test.txt");
}

private void ShowDeleteInfoConsole(object deleter, bool isDeleted)
{
    Console.WriteLine(isDeleted);
}

private void ShowDeleteInfoWindows(object deleter, bool isDeleted)
{
    MessageBox.Show(isDeleted.ToString());
}