Unity C＃：自定义对象为空，但是我可以访问其属性

Question

I found a way to get around this issue in the code, but I would like to understand why this is happening because I want to learn C# well. I´ve searched a lot and could simplify the problem, here's the simplified code:

/*MyCustomComponent.cs, this is attached to a game object in the scene*/
using UnityEngine;
using System.Collections;
using System.Collections.Generic;

public class MyCustomComponent : MonoBehaviour {
    void Start () {
        Test testInstance = new Test();
        Debug.Log (testInstance);
        Debug.Log (testInstance == null);
        Debug.Log (testInstance.Equals(null)); //Also tried the same with Equals()
        Debug.Log (testInstance.value);
    }
}

/*Test.cs*/
using UnityEngine;
using System.Collections;

public class Test : Object {
    public int value = 7;
    public Test(){

    }
}

Console Output:

null
true
7

Why is this happening? How can be possible an Object is null but returns a property value?

Answer 1

Because Unity.Object works in a very peculiar way, basically it contains data regarding the managed object while pointing to the native object (crudely speaking).

Let's make an example: you create a new object inheriting from MonoBehaviour . Now you have two objects, one on the native side and one on the managed side. You can access the instanceID propriety of the managed object thanks to the fact that MonoBehaviour inherits from Unity.Object . Basically, the latter is used to show all the relative data of the object in the Inspector.

Now, you want to Destroy this game object by calling the same named method. The native object is actually destroyed, but the managed object is not, since all managed objects can only be destroyed by the garbage collector. It's at this point that Unity.Object becomes null : it's a trick of the Unity engine uses in order to avoid that you try to access a native object which doesn't exist anymore. Eventually, when the GC is called, this Unity.Object will be destroyed too.

And this is why you should never create an Unity object which inherits directly from Unity.Object , but only from MonoBehaviour or ScriptableObject .