将参数传递给模板化类型的 C# 泛型 new() [英] Passing arguments to C# generic new() of templated type

问题描述

在添加到列表时，我试图通过其构造函数创建一个 T 类型的新对象.

I'm trying to create a new object of type T via its constructor when adding to the list.

我收到一个编译错误:错误信息是:

I'm getting a compile error: The error message is:

'T':创建变量实例时不能提供参数

'T': cannot provide arguments when creating an instance of a variable

但是我的类确实有一个构造函数参数！我怎样才能做到这一点?

But my classes do have a constructor argument! How can I make this work?

public static string GetAllItems<T>(...) where T : new()
{
   ...
   List<T> tabListItems = new List<T>();
   foreach (ListItem listItem in listCollection) 
   {
       tabListItems.Add(new T(listItem)); // error here.
   } 
   ...
}

推荐答案

为了在函数中创建泛型类型的实例，您必须使用new"标志对其进行约束.

In order to create an instance of a generic type in a function you must constrain it with the "new" flag.

public static string GetAllItems<T>(...) where T : new()

但是，这仅在您想调用没有参数的构造函数时才有效.不是这里的情况.相反，您必须提供另一个参数来允许基于参数创建对象.最简单的是函数.

However that will only work when you want to call the constructor which has no parameters. Not the case here. Instead you'll have to provide another parameter which allows for the creation of object based on parameters. The easiest is a function.

public static string GetAllItems<T>(..., Func<ListItem,T> del) {
  ...
  List<T> tabListItems = new List<T>();
  foreach (ListItem listItem in listCollection) 
  {
    tabListItems.Add(del(listItem));
  }
  ...
}

然后你可以这样称呼它

GetAllItems<Foo>(..., l => new Foo(l));

这篇关于将参数传递给模板化类型的 C# 泛型 new()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！