I want minus to cells date from each other

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so that if it is more than 2, the text color of two cells will change

but error

System.InvalidOperationException: 'Invalid attempt to read when no data is present.'

What I have tried:

<pre>SqlDataAdapter sda = new SqlDataAdapter("select Entry_Date,Received_Date from tblSaleServices", con);
            DataTable dt = new DataTable();
            sda.Fill(dt);
            dataGridView1.DataSource = dt;

con.Open();
            Query = "select Entry_Date,Received_Date from tblSaleServices";
            SqlCommand cmd = new SqlCommand(Query, con);
            SqlDataReader sdr = cmd.ExecuteReader();

            DateTime entry = Convert.ToDateTime(sdr["Entry_Date"]);
            DateTime received = Convert.ToDateTime(sdr["Received_Date"]);

            TimeSpan value = received.Subtract(entry);
            int val = Convert.ToInt32(value);

            if (val > 2)
            {
                dataGridView1.DefaultCellStyle.ForeColor = Color.Red;
            }
            con.Close();

Posted 28-Jul-22 23:37pm

SaeedZer0

Updated 28-Jul-22 23:52pm

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Chris Copeland · Accepted Answer · 2022-07-28T23:52:00

The SqlDataReader is a reader class, which implies you need to actually run read operations on it before you can access any of the data returned from the SQL. That's exactly what your exception is telling you, you're attempting to read when there's nothing there to read yet.

Make sure you call sdr.Read() and check the result of this method (a boolean) before you try and access the data:

C#

// If you're only expecting one row:
if (sdr.Read()) {
  
}

// If you're expecting multiple rows:
while (sdr.Read()) {

}