Read synchronously from opc server

Question

I can not read items synchronously from OPC server. My code always gives this error:

Object reference not set to an instance of an object. I created my object with new method but it doesn't work.

I'm using VS2010 and Interop.OPCAutomation.

Code:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using OPCAutomation;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        OPCServer oServer;
        OPCGroup oGroup;
        Array handles = new Array[2];

        public int temp1;
        public int temp2;

        public Form1()
        {
            InitializeComponent();
        }

        public void set_opc()
        {
            //add server - reference the kepserver that should already be setup
            oServer = new OPCServer();
            oServer.Connect("Kepware.KEPServerEX.V5", null);
            oServer.OPCGroups.DefaultGroupIsActive = true;
            oServer.OPCGroups.DefaultGroupDeadband = 0f; //the percentage change required before a change is reported, used to filter noise
            oServer.OPCGroups.DefaultGroupUpdateRate = 10; //the rate is ms before item is updated

            //set up group - this is an arbitrary container to place OPC items
            oGroup = oServer.OPCGroups.Add("g1");
            oGroup.IsSubscribed = false; //dont need to be subscribed to data change events
            oGroup.OPCItems.DefaultIsActive = false; //the item does not need to be active, it will only be refreshed with the latest value after we synch read

            //add group items - items can capture the values of registers from the device, the item is setup within the kepserver
            int[] h = new int[3];

            //index starts at 1
            h[1] = oGroup.OPCItems.AddItem("Channel1.s7-300.sayi0", 1).ServerHandle; //the handle is a server generated value that we use to reference the item for further operations
            h[2] = oGroup.OPCItems.AddItem("Channel1.s7-300.sayi1", 2).ServerHandle;
            handles = (Array)h;
        }

        public void synch_read() //reads device
        {
            System.Array values; //opc server will store the values in this array
            System.Array errors; //opc server will store any errors in this array
            object qualities = new object(); //opc server will store the quality of the item 
            object timestamps = new object(); //store the timestamp of the read

            //read directly from device
            oGroup.SyncRead((short)OPCAutomation.OPCDataSource.OPCDevice, 2, ref handles, out values, out errors, out qualities, out timestamps);

            temp1 = (int)values.GetValue(1);
            temp2 = (int)values.GetValue(2);
        }

        private void button1_Click(object sender, EventArgs e)
        {
            synch_read();
            textBox1.Text = temp1.ToString();
            textBox2.Text = temp2.ToString();
        }
    }
}

Answer 1

You have to call

set_opc();

before you call

synch_read();

unless both oGroup and oServer wont be initialized. As a result a exception was thrown.