什么是委托? [英] What is Delegate?

问题描述

我很困惑代表的实际角色是什么?

I am confused that what is the actual role of a delegate?

我在面试中多次被问到这个问题，但我认为面试官对我的回答并不满意.

I have been asked this question many times in my interviews, but I don't think that interviewers were satisfied with my answer.

谁能告诉我最好的定义，一句话，一个实际的例子?

Can anyone tell me the best definition, in one sentence, with a practical example?

推荐答案

我喜欢将委托视为指向函数的指针".这可以追溯到 C 天，但这个想法仍然成立.

I like to think of a delegate as "a pointer to a function". This goes back to C days, but the idea still holds.

这个想法是您需要能够调用一段代码，但您要调用的那段代码直到运行时才知道.因此，您为此目的使用代表".委托对于诸如事件处理程序之类的事情会派上用场，例如，您可以根据不同的事件做不同的事情.

The idea is that you need to be able to invoke a piece of code, but that piece of code you're going to invoke isn't known until runtime. So you use a "delegate" for that purpose. Delegates come in handy for things like event handlers, and such, where you do different things based on different events, for example.

这是参考C#你可以看看:

例如，在 C# 中，假设我们有一个我们想做的计算，我们想使用一种不同的计算方法，直到运行时我们才知道.所以我们可能有几个这样的计算方法:

In C#, for example, let's say we had a calculation we wanted to do and we wanted to use a different calculation method which we don't know until runtime. So we might have a couple calculation methods like this:

public static double CalcTotalMethod1(double amt)
{
    return amt * .014;
}

public static double CalcTotalMethod2(double amt)
{
    return amt * .056 + 42.43;
}

我们可以像这样声明一个委托签名:

We could declare a delegate signature like this:

public delegate double calcTotalDelegate(double amt);

然后我们可以声明一个将委托作为参数的方法，如下所示:

And then we could declare a method which takes the delegate as a parameter like this:

public static double CalcMyTotal(double amt, calcTotalDelegate calcTotal)
{
    return calcTotal(amt);
}

我们可以调用 CalcMyTotal 方法，传入我们想要使用的委托方法.

And we could call the CalcMyTotal method passing in the delegate method we wanted to use.

double tot1 = CalcMyTotal(100.34, CalcTotalMethod1);
double tot2 = CalcMyTotal(100.34, CalcTotalMethod2);
Console.WriteLine(tot1);
Console.WriteLine(tot2);

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