How to get variable in callback function out

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C#

sorry for the question title.
i have problem when using a OPC API.

this API declare a delegate ReadCompleteEventHandler Internally,
somehow in subscription.Read(), it pass ItemValueResult[] into the Mydelegate.

ItemValueResult[] is what i need. I can use it inside ReadCompleteCallback.
however, I am making it into a window form, another class, then trouble comes.

class tester
    {
        public  void Work()
        {
            ReadCompleteEventHandler Mydelegate = new ReadCompleteEventHandler(ReadCompleteCallback);

            subscription.Read(subscription.Items, 123, Mydelegate, out req);
           
        }

static  void ReadCompleteCallback(object nn,ItemValueResult[] mm)
        {
            MessageBox.Show(mm); //mm can only use in my Tester Class
        
        }
    }

What I have tried:

in tester Class:

public  ItemValueResult[] resultinTesterClass;
       static  void ReadCompleteCallback(object nn,ItemValueResult[]mm)
       {
           MessageBox.Show(mm);
         resultinTesterClass = mm;

       }

where in the form1:

public ItemValueResult[] resultinFormClass
        private void ButtonRead_Click(object sender, EventArgs e)
        {
            obj.Work();
            resultinFormClass=obj.resultinTesterClass;
        }

I think it is too indirect and somethime resultinFormClass return null.
Any conventional way to solve.
thank you!