是否可以创建一个只能作为另一个类的成员实例但仍可以通过VB.NET公开访问的类？

Question

I have a custom applicationdata class in this I would like to categorize its data through member subclasses eg a userdata class. However the userdata class should not be able to be instantiated other places than in the applicationdata class, but still be accessible through the applicationdata class. Is this possible.

To illustrate I want to be able to access the class like this: ApplicationData.UserData.SomeProperty

However outside the ApplicationData class it should not be possible to instance like this: Dim ud as new UserData

Answer 1

public class ApplicationData
{
    private UserData user = new UserData();

    public UserData User
    {
        get
        {
            return user;
        }
    }

    public class UserData
    {
        internal UserData()
        {
        }
    }
}

It's not exactly what you describe, in that it's still possible to create a UserData instance outside of your ApplicationData class - but only within the same assembly. Note also that you have to name the class (UserData) differently from the property you're exposing (User).

Rather than nest the class like this, the approach I would take instead would be to have a public IUserData interface, and an internal UserData class. Your ApplicationData class can then expose a UserData property of type IUserData.

Answer 2

我将解决此问题的方法如下：编写公共接口IUserData使UserData实现接口IUserData并将该类设为私有ApplicationData将通过名为IUserData类型的UserData属性公开该类。

Answer 3

You can define user data as a abstract class so that it can only be inherited, can not be instanced. For more information see this link

Now if UserData and ApplicationData reside in the same assembly, you can user 'internal' keyword. When you use internal keyword to the class, that class in only accessible in the same assembly. The classes which are outside the assembly can not access it. For more information see this link.

Cheerss!

Answer 4

Just use an internal constructor.

No one outside the assembly will be able to create instances.