为什么要使用“new DelegateType（Delegate）”？ [英] Why use "new DelegateType(Delegate)"?

问题描述

好的，假设你在某个类中定义一个委托。

  public delegate void StringDelegate（string s）; 
  

另一个类实现了一个方法：

  public static void StringWriter（string s）{...} 
  

在我正在阅读的编程C＃第4版中，他们使用新的关键字创建代表，例如：

  ClassDelegate.StringDelegate writer; 
 writer = new ClassDelegate.StringDelegate（DelegateImplementer.StringWriter）; 
 writer（Hello）; 
  

但是，我看到一个也可以这样调用委托方法

  ClassDelegate.StringDelegate writer; 
 writer = DelegateImplementer.StringWriter; 
 writer（Hello）; 
  

有什么区别？为什么要实例化并创建一个对象委托，当我只是简单地传递或引用方法委托的签名。

解决方案

这两个语句绝对没有区别。 writer = DelegateImplementer.StringWriter; 仍然创建一个委托对象;编译器将为您生成新的ClassDelegate.StringDelegate（） 。它只是一个更干净的语法是添加到C＃2.0

由于@Ben Voigt在答案中提到，只需要在C＃2.0中，编译器无法推断代表的类型，当使用< a href =http://msdn.microsoft.com/en-us/library/zyzhdc6b.aspx =noreferrer> Control.Invoke（）例如。

Ok, suppose you define a delegate in some class.

public delegate void StringDelegate (string s);

and another class implements a method :

public static void StringWriter (string s) {...}

In the book that I'm reading "Programming C#" 4th ed they create delegates using the new keyword, ex:

ClassDelegate.StringDelegate writer;
writer = new ClassDelegate.StringDelegate (DelegateImplementer.StringWriter);
writer("Hello");

However, I see one can also call the delegate method this way

ClassDelegate.StringDelegate writer;
writer = DelegateImplementer.StringWriter;
writer ("Hello");

What's the difference? Why do I want instantiate and create an object delegate when I can just simply pass or make reference to the signature of the method delegate.

解决方案

There is absolutely no difference between the two statements. writer = DelegateImplementer.StringWriter; still creates a delegate object; the compiler will generate the new ClassDelegate.StringDelegate () for you. It's just a cleaner syntax that was added in C# 2.0.

As @Ben Voigt mentioned in his answer is only required in C# 2.0 where the compiler can't deduce the type of the delegate, when using Control.Invoke() for example.

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