Reference to an object is not updating the object

Question

Hi I am working with code that looks something like this .

class A
{
    Custom objA;

    public A()
    {
        //Assign some value to objA;
        B obj =          


        

Answer 1

It seems to me that this is the code that you're asking about in your question:

class A
{
    Custom objCustom;

    public A()
    {
        objCustom = new Custom();
        B objB = new B(objCustom);
        objB.Func();
    }
}

class B
{
    Custom objCustom;

    public B(Custom objCustom)
    {
        this.objCustom = objCustom;
    }

    public void Func()
    {
        this.objCustom = null;
    }
}

This compiles and has a fairly consistent naming convention.

The issue you have the with the Custom objCustom field in both class A and B is that even though they both reference the same instance before the call to .Func() you need to understand that the Custom objCustom field is just a reference to the object, and not the object itself. So when you call .Func() you are assigning a new reference to the Custom objCustom in objB, but you're not doing anything to the reference in objA. It still points to the original object.

Answer 2

In function Func you assign null to the field of B object (not A object) so after this function call field objB of B object is not pointing to any object of type Custom, but objA field of A object is still pointing to a single Custom object.

Here is example of code, where Func will change objA field of A object:

class A
{
    public Custom objA = new Custom();

    public A()
    {
        B obj = new B(this);
        B.Func(); // after this, objA field will be null
    }
}

class B
{
    А obj;

    public B(А obj)
    {
        this.obj = obj;
    }

    public void Func()
    {
        obj.objA = null;
    }
}

Also note:

1. When you create an A object, its objA field is null, so in constructor of A you actually calling B obj = new B(null);, so its objB field is null too.
2. After A object is constructed, object obj of type B will be disposed, since you don't hold a reference to it, so you not calling a Func function in your example.

Answer 3

Firstly, on line 5, you have a syntax error. You could do B obj = new B(objA) if you are trying to create a new instance of B. But I can only guess.

What it seems like you are trying to do is modify objA by having passed it into a new object of type B, storing it in a field, and then modifying the field. The problem is that what you are storing is a copy of a reference to objA. When you do this.objB = null, you are modifying the field objB to have a new reference (null), but you have not done anything to the field objA which is a member of the instance of class A.