付款方式存在问题 [英] problem in sum payments method

问题描述

请有人帮助我

我有两个表，第一个是imprests表，第二个是payments_imprests

我有方法返回payment_imprests中的付款金额

please someone help me
I have two tables the first is imprests table and the second is payments_imprests
I have method that return payments values sum in payments_imprests

 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();
}

当我在imprests表中有imprest_ID并且我在imprests_payments表中有impres_ID的付款值时，此代码工作正常
但我的问题是当我在imprest_ID中获得imprest_ID时

但在imprests_payments表中找不到行，其中worker没有支付任何付款额

where以下错误正在上升

对象引用未设置为对象的实例。

我需要解决此问题的方法

this code is working perfectly when I have imprest_ID in imprests table and I have payments values for this impres_ID in imprests_payments table
but my problem is when I have imprest_ID in imprests tbale
but no rows is found in imprests_payments table where worker hasn't paid any payment value
where the following error is rising
Object reference not set to an instance of an object.
I need the solution for this problem

推荐答案

尝试：

Try:

private void button1_Click(object sender, EventArgs e)
       {
          if (GridViewImprestsPays.CurrentRow != null)
          {
          double val = ImprestsPaysMgr.PaymentsvalueSum(int.Parse(GridViewImprestsPays.CurrentRow.Cells["Imprest_ID"].Value.ToString()));
               textBox1.Text = val.ToString();
          }
          else
          {
               // CurrentRow is null: you can't get the value of the Imprest_ID cell
          }
}

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