C＃-为什么我不能投射List< MyObject>继承自List< MyObject>的类？ [英] C# - Why can I not cast a List<MyObject> to a class that inherits from List<MyObject>?

问题描述

我有一个对象，我将其称为MyObject。这是一个控制特定数据行的类。

I've got an object, which I'll call MyObject. It's a class that controls a particular data row.

然后我有了一个名为MyObjectCollection的集合类：

I've then got a collection class, called MyObjectCollection:

public class MyObjectCollection : List<MyObject> {}

为什么我不能执行以下操作：

Why can I not do the following:

List<MyObject> list = this.DoSomethingHere();
MyObjectCollection collection = (MyObjectCollection)list;

预先感谢。

编辑：错误是InvalidCastException

推荐答案

我的猜测是 DoSomethingHere 不返回 MyObjectCollection 的实例。

My guess is that DoSomethingHere doesn't return an instance of MyObjectCollection.

让我们在这里摆脱所有泛型等，因为它们不相关。这是我怀疑您要尝试执行的操作：

Let's get rid of all the generics etc here, as they're not relevant. Here's what I suspect you're trying to do:

public static object CreateAnObject()
{
    return new object();
}

object o = CreateAnObject();
string s = (string) o;

那会（在执行时）失败，这是很正确的。

That will fail (at execution time) and quite rightly so.

将其带回到您的代码中，除非 DoSomethingHere actually 返回 MyObjectCollection 在执行时，转换将失败。

To bring it back to your code, unless DoSomethingHere actually returns a MyObjectCollection at execution time, the cast will fail.

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