什么是委托呢？ [英] What are delegates for?
问题描述
可能重复：
什么是代表的优势是什么？
我创建了一个示例应用程序。我真的发现很难理解为什么要使用委托，因为没有代表我们就可以实现一切。
I have created a sample application. I am really finding it difficult to understand why to use delegates because without delegates we can achieve everything .
class Program
{
public delegate double Integrand(double x);
static double MyFunc1(double x) { return x + 10; }
static double MyFunc2(double x) { return x + 20; }
public static double Gauss3DelMethod(Integrand f)
{
double a = f(1);
return a;
}
public static double Gauss3SimpleMethod(double x)
{
double a = x;
return a;
}
static void Main(string[] args)
{
//with delegates
double res = Gauss3DelMethod(MyFunc1);
double res1 = Gauss3DelMethod(MyFunc2);
//without delegates
double res2 = Gauss3SimpleMethod(MyFunc1(1));
double res3 = Gauss3SimpleMethod(MyFunc2(1));
int i = 0;
}
}
那么，我为什么要使用委托？
So, why should I use delegates?
推荐答案
在你的特殊的例子，也许是的没有的重要。 （目前还不清楚它正试图实现的。）
In your particular example, maybe it's not important. (It's not clear what it's trying to achieve.)
但是，假设你想使该方法的几个不同的输入执行相同的 MyFunc1 或 MyFunc2 。例如，假设您正在执行的牛顿迭代法，工作在普通的功能。在这种情况下，你不能调用函数的一次的，并传递到方法 - 你想传递的的实际功能的进入方法，这样的方法可以调用它与任何输入需要
But suppose you wanted to make the method execute the same MyFunc1 or MyFunc2 for several different inputs. For example, suppose you were implementing the Newton-Raphson method, to operate over a general function. In that situation, you couldn't call the function once and pass that into the method - you want to pass the actual function into the method, so that the method can call it with whatever inputs it needs.
有一个类似的例子是排序。例如，使用LINQ可以写这样的：
A similar example is sorting. For example, using LINQ you can write something like:
var sorted = people.OrderBy(x => x.Age).ToList();
目前，我们正在传递一个函数来预测每个源元素的排序键。我们没有执行该功能我们自己 - 排序依据会为我们做（懒洋洋）
There we're passing a function to project each source element to the ordering key. We don't have to execute that function ourselves - OrderBy will do it for us (lazily).
当然，所有这一切都可以用单一方法接口做得太 - 代表和单方法接口有很多共同点。不过，代表们有过单方法接口具有以下优点：
Of course, all of this can be done with single-method interfaces too - delegates and single-method interfaces have a lot in common. However, delegates have the following benefits over single-method interfaces:
- 委托是多播 - 它们可以组合/删除，通常为求的事件的
- 您可以异步的BeginInvoke / EndInvoke会执行它们
- 您可以用匿名方法和lambda EX pressions构建它们
- 您可以经由前pression树数据使用lambda EX presions重新present逻辑;然后这些可被编译为代表
- 您可以用适当的签名的任何方法构建一个委托 - 因此，例如一个类可以有多个方法实施相同的委托类型，而不能在一个班
- 同样下放的实施方法可以是私有的，而接口的方法必须是公共的（或有点公开通过显式接口实现）
- Delegates are multi-cast - they can be combined/removed, usually for the sake of events
- You can execute them asynchronously with BeginInvoke/EndInvoke
- You can build them with anonymous methods and lambda expressions
- You can represent logic as data via expression trees using lambda expresions; these can then be compiled into delegates
- You can build a delegate from any method with the appropriate signature - so for example a single class can have multiple methods "implementing" the same delegate type, whereas you can't implement an interface multiple times in one class
- Likewise delegate implementation methods can be private, whereas interface methods have to be public (or somewhat-public via explicit interface implementation)
所有这些可能已经解决不同使用单方法接口，当然，但代表是一个方便的替代。
All of these could have been addressed differently using single-method interfaces, of course, but delegates are a handy alternative.
结论：委托是非常有用的。仅仅因为你已经写了一些琐碎的code这并不特别需要它们并不意味着他们是没有用的。我强烈建议你看看LINQ，事件处理程序和第三方物流，所有这些都使用委托严重。
In conclusion: delegates are very useful. Just because you've written some trivial code which doesn't particularly require them doesn't mean they're not useful. I would strongly suggest you look into LINQ, event handlers and the TPL, all of which use delegates heavily.
这篇关于什么是委托呢？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！
