请解释 .NET 代表

问题描述

所以我阅读了 MSDN 和 Stack Overflow.我了解操作代表的一般作用，但无论我做了多少示例，它都不会点击.一般来说，代表的想法也是如此.所以这是我的问题.当你有这样的功能时:

So I read MSDN and Stack Overflow. I understand what the Action Delegate does in general but it is not clicking no matter how many examples I do. In general, the same goes for the idea of delegates. So here is my question. When you have a function like this:

public GetCustomers(Action<IEnumerable<Customer>,Exception> callBack)
{
}

这是什么，我应该传递给它什么?

What is this, and what should I pass to it?

推荐答案

它需要一个接受 IEnumerable 和 Exception 并返回 void 的函数.

it expects a function that takes IEnumerable and Exception and returns void.

void SendExceptionToCustomers(IEnumerable<Customer> customers, Exception ex) {
   foreach(var customer in customers)
      customer.SendMessage(ex.Message);
}

GetCustomers(SendExceptionToCustomers);

顺便说一句，GetCustomers 对这个函数来说似乎是一个糟糕的名字——它要求一个动作，所以它更像是 DoSomethingToCustomers

btw, GetCustomers seems like a terrible name for this function -- it's asking for an action, so its more like DoSomethingToCustomers

编辑回应评论

好吧 有道理，那么现在为什么还要费心使用 GetCustomer 函数呢?如果我只是将它重命名为 GetCustomer，我不能对你的函数做同样的事情吗?

Ok Makes sense, So now why even bother with having a GetCustomer Function? Can't I do that same thing with your function if i Just rename it GetCustomer?

好吧，这里发生的是调用者可以指定一些操作.假设 GetCustomers 是这样实现的:

Well, what's happening here is the caller can specify some action. Suppose GetCustomers is implemented like this:

public void GetCustomers(Action<Enumerable<Customer>, Exception> handleError) {
    Customer[] customerlist =  GetCustomersFromDatabase();
    try {
        foreach(var c in customerList) 
            c.ProcessSomething()
    } catch (Exception e) {
        handleError(customerList, e);
    }
}

然后你可以从命令行程序的某个地方调用 Getcustomers，然后传递它

then you could call Getcustomers from somewhere on a commandline program, and pass it

GetCustomers((list, exception) => { 
    Console.WriteLine("Encountered error processing the following customers");
    foreach(var customer in list) Console.WriteLine(customer.Name);
    Console.WriteLine(exception.Message);
}); 

例如，您可以从远程应用程序调用 GetCustomers 并传递它

while you could call GetCustomers from a remote application, for example, and pass it

Getcustomers((list, exception) => { 
    // code that emails me the exception message and customer list
})

<小时>此外，Slak 的评论提出了委托参数的另一个原因——GetCustomers 确实检索了客户，但是是异步的.每当它完成检索客户时，如果发生异常，它会使用客户列表或异常调用您提供给它的函数.

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