Pass deviceObj between callbacks in app

I am able to make VISA-USB connection in one callback but want to maintain this connection and pass the device object between callback so that I can perform various commands on the connection. How do I do this? I tried adding it to the app property but i get an error.

        function ConnectButtonPushed(app, event)
            % Create a VISA-USB object.
            interfaceObj = instrfind('Type', 'visa-usb', 'RsrcName', 'USB0::0x0699::0x03A6::C041227::0::INSTR', 'Tag', '');
            
            % Create the VISA-USB object if it does not exist
            % otherwise use the object that was found.
            if isempty(interfaceObj)
                interfaceObj = visa('NI', 'USB0::0x0699::0x03A6::C041227::0::INSTR');
            else
                fclose(interfaceObj);
                interfaceObj = interfaceObj(1);
            end
            
            % Create a device object.
            deviceObj = icdevice('tektronix_tds2024.mdd', interfaceObj);
            
            % Connect device object to hardware.
            connect(deviceObj);
        end

[Maadhav Akula]

It would be helpful if you can share your error message.