具有静态实例创建的Unity3D C＃抽象类无法正常工作

Question

Hello I am working on a objectpooling class has T "ObjectPooling". And made a child class. So I want to make automatic singleton for this class. So if I use "instance" it should check if m_instance is null. If yes "spawn" the script and assign m_instance.

public abstract class ObjectPooling<T> : MonoBehaviour
{

    public static float start = 30;
    public static bool extendable = true;

    public List<T> objects = new List<T>();

    public abstract T getNext();
    public abstract void Add(T obj);

    static T m_instance;
    public static T instance
    {
        get
        {
            return m_instance ?? (m_instance = CreateInstance());
        }
    }

    protected static T CreateInstance()
    {

        GameObject g = new GameObject("ObjectPooling");
        var c = g.AddComponent<T>();
        return c;
    }
}

The problem is at the last lines in the CreateInstance(). It says

An implicitly typed local variable declaration cannot be initialized with `UnityEngine.GameObject.AddComponent(System.Type)'

I am not sure what can I do here now. I tried with ObjectPooling before but thats gives no error but also is not working.

So my goal is that the child has also singleton. I did it currently manually but want I want to later should be like this (ofc the base class should do it instead of child class but still check it).

public class BulletPooling : ObjectPooling<BulletBase>  
{
    public override void Add(BulletBase obj)
    {
        if(extendable)
            objects.Add(obj);
    }

    public override BulletBase getNext()
    {

        for(int i = 0; i < objects.Count; i++)
        {
            var bs = objects[i];
            if (!bs.gameObject.activeInHierarchy)
                return bs;
        }


        return null;
    }

    // this part
    static BulletPooling m_instance;
    public static BulletPooling instance
    {
        get
        {
            return m_instance ?? (m_instance = CreateInstance());
        }
    }

    protected static BulletPooling CreateInstance()
    {

        GameObject g = new GameObject("ObjectPooling");
        var c = g.AddComponent<BulletPooling>();
        return c;
    }
}

You can see here I am working with new Childclass which has T = BulletBase

Answer 1

This is because GameObject.AddComponent requires an object of a specific type, rather than "any type". In your ObjectPooling class, you only specify that it can be an object of any type, and the compiler cannot infer which types you are using beforehand.

AddComponent is kind of a nasty function, since you can also pass it a string, which should be the name of a script class.

You could specify the type that T must adhere to as UnityEngine.Component to get around this. that would look like this :

public abstract class ObjectPooling<T>: MonoBehaviour where T : UnityEngine.Component 
{

    public static float start = 30;
    public static bool extendable = true;

    public List<T> objects = new List<T>();

    public abstract T getNext();
    public abstract void Add(T obj);

    static T m_instance;
    public static T instance
    {
        get
        {
            return m_instance ?? (m_instance = CreateInstance());
        }
    }

    protected static T CreateInstance()
    {

        GameObject g = new GameObject("ObjectPooling");
        //this is where your compiler could not tell if T was the correct type by the way...
        var c = g.AddComponent<T>(); 
        return c;
    }
}

but that might break the functionality of adding scripts as game components using a string with their name. (though i think in your case, it won't be a problem)