System.NullReferenceException - Object reference not set to an instance of an object. Causes in C#

Question

Good day.

I'm new to C# and trying to call functions from a DLL (C++ ObjGen). I'm getting this message and can't figure out why. Here's the code:

object[] objID = new object[] { ID };

ObjGen.Invoke(InvokeEnum.Query_State, objID);

Dll code

///////////////////////

INVOKE_FUNC_IMPLEMENT(Query_State, CUtil::GetState)

///////////////////////

bool CUtil::GetState(InvokeEnum methodID, SAFEARRAY * psa)
{
    UNIT_ID UID = (UNIT_ID)PARAM_LONG(0);

    CUtil::Instance()->NotifyUpdateState(UID);
    for(int slot = 0; slot < SLOT_ID_MAX; slot++)
        g_CManager.m_PJAssociArray[UID][slot] = 0;

    return true;
}

There is a loop called the top Invoke function. When objID = 1 Or 2 Or 3, the function worked very well. But when objID = 4. the function exception.

What could be the reason? Issue in C# or Dll file?

Is there something error in the Instance() OR NotifyUpdateState() ? i can't do the judgement.

thank you.

Answer 1

You are creating an array of objects in which an object of ID is one element in that array. And you are passing it into a method, the said array objID

Can you include a code sample of what you are trying to achieve?

It is not very clear.

What is ID? Has ID been instantiated with the new ? What is ObjGen?

Do you have the function 4 in your dll, if not that explains why you got a null reference exception. Double check your DLL and make sure you are calling the function 4.

Hope this helps you in giving you hints? Best regards, Tom.