C# 存放不同的子类同时调用

Question

Actually all these classes are defined in the 3rd lib, so I can't change them.

=====================

I'm learning C# and I met a problem. Suppose I have a parent class and two child classes:

class ParentClass
{
    ....
};

class ChildA : ParentClass
{
    public string name;
};

class ChildB : ParentClass
{
    public string name;
};

Both class ChildA and ChildB have property name , but ParentClass doesn't. Now I need to store ChildA and ChildB in a dictionary, so I write Dictionary<string, ParentClass> .

But I can't get name because ParentClass doesn't have this property:

foreach (ParentClass pc in dict.Values) 
{
    // it works, but too verbose as I may have ChildC, ChildD...
    if (pc is ChildA ca) 
    {
        ca.name
    }
    if (pc is ChildB cb) 
    {
        cb.name
    }

    // how can I get the name property at same time?
}

how can I handle this?

Answer 1

The short version is "no". There are things that you could do if you have access to the types - for example, you could implement a common interface ( interface IHazName { public string Name {get;} } ) - but you can't do that here since you don't control the types.

A lazy way could be to abuse dynamic :

dynamic hack = pc;
hack.name = "yolo";

but... please don't! Your is approach (or perhaps a switch expression) is about as good as you can get. Note that if you need to talk to this member in a lot of places, you could move that shared logic to an extension method:

static class SomeUtilsType {
    public static string GetName(this ParentClass obj) => obj switch {
        ChildA ca => ca.name,
        ChildB cb => cb.name,
        _ => throw new ArgumentException("Unexpected object type", nameof(obj)),
    };
}
...
foreach (ParentClass pc in dict.Values) 
{
    Console.WriteLine(pc.GetName());
}

(or a similar set method) - then at least you don't need to repeat yourself.

Answer 2

One way to do this is to use reflection on the type to determine if it has a "name" property (or field, as you've shown):

public static string GetName(ParentClass parent)
{
    return parent.GetType().GetProperty("name")?.GetValue(parent, null).ToString()
        ?? parent.GetType().GetField("name")?.GetValue(parent).ToString();
}

Example usage:

static void Main(string[] args)
{
    ParentClass parent = new ParentClass();
    ChildA child = new ChildA { name = "ChildName" };

    Console.WriteLine($"Parent name: {GetName(parent)}");
    Console.WriteLine($"Child name: {GetName(child)}");

    Console.Write("\n\nDone. Press any key to exit...");
    Console.ReadKey();
}

Output

Parent name:
Child name: ChildName


Done. Press any key to exit...