problem in sum payments method

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please someone help me
I have method that return payments values sum for workers imprests

C#

public static double PaymentsvalueSum(int id)
        {
            string strconn = myproject.Properties.Settings.Default.SalariesConnectionString;
            OleDbConnection conn = new OleDbConnection(strconn);

            if (conn.State == ConnectionState.Closed)
            {
                conn.Open();
            }
             OleDbCommand command = new OleDbCommand("select SUM(Payment_Value)from  imprests_payments  WHERE Imprest_ID=@id;", conn);
            command.Parameters.Add(new OleDbParameter("@id", id));
            double sumvalue = (double)command.ExecuteScalar();
            try
            { }

            catch (Exception ex)
            {
                MessageBox.Show(ex.Message);
            }

            finally
            {
                conn.Close();
            }
            return sumvalue;
        }

when button_click event I write

 private void button1_Click(object sender, EventArgs e)
        {
           double val = ImprestsPaysMgr.PaymentsvalueSum(int.Parse(GridViewImprestsPays.CurrentRow.Cells["Imprest_ID"].Value.ToString()));
                textBox1.Text = val.ToString();
 }

this code is working perfectly when payments values in imprests_payments table is available but my problem is when no payments values is available in imprests_payments table
where the following error is rising
Object reference not set to an instance of an object.
I need the solution for this problem

Posted 27-Aug-13 0:12am

firaso

Updated 27-Aug-13 0:30am

Aarti Meswania

v4

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Comments

[no name] 27-Aug-13 6:32am

You are getting that error because you are assuming that your call to ExecuteScalar always returns something.

Marvin Ma 27-Aug-13 6:37am

You should check the payment values for null before calling your method.

2 solutions

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Aarti Meswania · Answer 1 · 2013-08-27T00:36:00

Solution 1

instead of,

C#

double sumvalue = (double)command.ExecuteScalar();

use

C#

double sumvalue = 0;
Double.TryParse(command.ExecuteScalar(),out sumvalue);

Happy Coding!
:)

Posted 27-Aug-13 0:36am

Aarti Meswania

CPallini · Answer 2 · 2013-08-27T01:09:00

When there is no result, the SqlCommand.ExecuteScalar method returns null (see SqlCommand.ExecuteScalar at MSDN[^]).
You may either test for it, e.g.

C#

object obj = command.ExecuteScalar();
if ( obj == null)
{
  // handle the no-result case, for instance set sumvalue=0
}
else
{
  sumvalue = (double) obj;
}

or follow the Aarti Meswania's suggestion and use Double.TryParse. instead