创建泛型类型的实例？ [英] Create instance of generic type?

问题描述

如果 BaseFruit 有一个接受 INT重量构造函数，我可以实例化一个水果在通用这样的方法？

If BaseFruit has a constructor that accepts an int weight, can I instantiate a piece of fruit in a generic method like this?

public void AddFruit<T>()where T: BaseFruit{
    BaseFruit fruit = new T(weight); /*new Apple(150);*/
    fruit.Enlist(fruitManager);
}

这是例子后面添加注释。看来我只能这样做，如果我给 BaseFruit 参数的构造函数，然后通过成员变量填写的一切。在我真正的code（不是水果），这是非常不现实的。

An example is added behind comments. It seems I can only do this if I give BaseFruit a parameterless constructor and then fill in everything through member variables. In my real code (not about fruit) this is rather impractical.

- 更新 -
因此，似乎它不能被限制以任何方式解决然后。从答案有三个候选方案：

-Update-
So it seems it can't be solved by constraints in any way then. From the answers there are three candidate solutions:

• 在工厂模式
• 反射
• 激活

我倾向于认为反思是最干净的，但我不能在另外两个之间的决定。

I tend to think reflection is the least clean one, but I can't decide between the other two.

推荐答案

此外一个简单的例子：

return (T)Activator.CreateInstance(typeof(T), new object[] { weight });

请注意，使用T上的新的（）约束只是让编译器检查一个公共的无参数的构造函数在编译的时候，实际的code用来创建类型为Activator类。

Note that using the new() constraint on T is only to make the compiler check for a public parameterless constructor at compile time, the actual code used to create the type is the Activator class.

您需要确保自己有关的具体构造存在，而这种需求可能是一个code气味（或者更确切地说，你应该只是尽量避免在C＃中的当前版本）。

You will need to ensure yourself regarding the specific constructor existing, and this kind of requirement may be a code smell (or rather something you should just try to avoid in the current version on c#).

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