error : Connection Property has not been initialized

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 System.Data.OleDb;


namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        System.Data.OleDb.OleDbConnection con;
        DataSet ds1;
        System.Data.OleDb.OleDbDataAdapter da;

        int MaxRows = 0;
        int inc = 0;

        private void Form1_Load(object sender, EventArgs e)
        {
            con = new System.Data.OleDb.OleDbConnection();
            ds1 = new DataSet();

            con.ConnectionString="Provider=Microsoft.Jet.OLEDB.4.0;Data Source=D:/MyWorkers1.mdb";

            string sql = "SELECT * from tblWorkers";
            da = new System.Data.OleDb.OleDbDataAdapter(sql, con);

            con.Open();
            da.Fill(ds1, "MyWorkers1");
            NavigateRecords();
          开发者_JAVA技巧  MaxRows = ds1.Tables["MyWorkers1"].Rows.Count;
            //MaxRows = ds1.Tables["MyWorkers1"].Rows[inc];
            //MessageBox.Show("Database open");

            con.Close();
            //MessageBox.Show("Database close");

            con.Dispose();
        }

        private void NavigateRecords()
        {
            DataRow drow = ds1.Tables["MyWorkers1"].Rows[inc];
            textBox1.Text = drow.ItemArray.GetValue(0).ToString();
            textBox2.Text = drow.ItemArray.GetValue(1).ToString();
            textBox3.Text = drow.ItemArray.GetValue(2).ToString();
        }

        private void btnNext_Click(object sender, EventArgs e)
        {
            if (inc != MaxRows - 1)
            {
                inc++;
                NavigateRecords();
            }
            else
            {
                MessageBox.Show("No More Records");
            }
        }

        private void btnPrevious_Click(object sender, EventArgs e)
        {
            if (inc > 0)
            {
                inc--;
                NavigateRecords();
            }
            else
            {
                MessageBox.Show("First Record");
            }
        }

        private void btnFirst_Click(object sender, EventArgs e)
        {

            if (inc != 0)
            {
                inc = 0;
                NavigateRecords();
            }
        }

        private void btnLast_Click(object sender, EventArgs e)
        {
            if (inc != MaxRows - 1)
            {
                inc = MaxRows - 1;
                NavigateRecords();
            }
        }

        private void btnAddNew_Click(object sender, EventArgs e)
        {
            textBox1.Clear();
            textBox2.Clear();
            textBox3.Clear();
        }

        private void btnSave_Click(object sender, EventArgs e)
        {
            System.Data.OleDb.OleDbCommandBuilder cb;
            cb = new System.Data.OleDb.OleDbCommandBuilder(da);

            DataRow drow = ds1.Tables["MyWorkers1"].NewRow();

            drow[0] = textBox1.Text;
            drow[1] = textBox2.Text;
            drow[2] = textBox3.Text;

            ds1.Tables["MyWorkers1"].Rows.Add(drow);

            MaxRows = MaxRows + 1;
            inc = MaxRows - 1;

            da.Update(ds1, "MyWorkers1");

            MessageBox.Show("Record / Entry Added");
        }       

    }
}

When I run this it shows an error like "Invalid Operation - Exception Unhandled connection property has not been initialized."

What is wrong?

I'm not an expert, but try

con = new System.Data.OleDb.OleDbConnection(you_connection_string);

You can check if your ConnectionString is valid or not here : http://www.connectionstrings.com/

Notice that the Provider is different, regarding the .mdb version you are using (2007, 2000...)

By the way, would you like to try Source=D:\MyWorkers1.mdb instead of Source=D:/MyWorkers1 ? With a "\" instead of a "/".

I was working on the same example and figured that con.Dispose(); that is in the Form Load is not allowing da.Update(ds1, "MyWorkers1"); to update the record. So for the time being i have removed it, but it should better be moved to the Destroy/ Unload etc (i really don't know which is the correct event before closing the form)

The exception is very clear. The ConnectionString property has not been 'properly' set, when trying to call Open the SqlConnection object.

Have you tried creating one inside the web.config?