Question

edittted:

I already debug, I figure out that once I fill all the fields, autmatically generate a new row empty, and once it is stored in the dabase, it follow with the loop foreach, and automaticaly detect null reference this is an image, I hope you understand me img8.imageshack.us/i/error3xh.jpg

I need your help, I can’t control the exception,here is my method and the error say System.NullReferenceException: Object reference not set to an instance of an object”, how can I fix it, control the exeption, no more messages of this type?, no matter how its the structure : the error is the line ** if (combo3 == null || combo4 == null) **

private void btnCronograma_Click(object sender, EventArgs e)
{
  string connstring = @"Provider=Microsoft.ACE.OLEDB.12.0;Data Source=C:\\Users\\amaury\\Documents\\TEC\\Septimo Semestre\\Administracion de proyectos de ingenieria de softwaere\\nuevo4\\nuevo\\Office\\Office\\Policias.accdb";
  using (OleDbConnection conn = new OleDbConnection(connstring))
   {
    conn.Open();

    string sql = "INSERT INTO IndicadorProyecto (idProyecto, idMes, meta, real) VALUES(@idProyecto , @idMes , @meta, @real)";
    OleDbCommand cmd = new OleDbCommand(sql, conn);

  foreach (DataGridViewRow row in dataGridView8.Rows)
  {
    DataGridViewComboBoxCell combo3 = row.Cells["idProyecto"] as DataGridViewComboBoxCell;
    DataGridViewComboBoxCell combo4 = row.Cells["idMes"] as DataGridViewComboBoxCell;

    if (combo3 == null || combo4 == null)
    {
        MessageBox.Show("No se pudo convertir");
        continue;
    }

  int idProyecto = int.Parse(combo3.Value.ToString());
  int idMes = int.Parse(combo4.Value.ToString());
  int meta = int.Parse(row.Cells[3].Value.ToString());
  int real = int.Parse(row.Cells[4].Value.ToString());  

  cmd.Parameters.Clear();
  cmd.Parameters.AddWithValue("@idProyecto", idProyecto);
  cmd.Parameters.AddWithValue("@idMes", idMes);
  cmd.Parameters.AddWithValue("@meta", meta);
  cmd.Parameters.AddWithValue("@real", real);


  cmd.ExecuteNonQuery();
  }
}
}

this is the complete error

Consulte el final de este mensaje para
obtener más detalles sobre cómo
invocar a la depuración Just-In-Time
(JIT) en lugar de a este cuadro de
diálogo.

************** Texto de la excepción ************** System.NullReferenceException:
Referencia a objeto no establecida
como instancia de un objeto. en
Office.Form1.btnCronograma_Click(Object
sender, EventArgs e) en
C:\Users\amaury\Documents\TEC\Septimo
Semestre\Administracion de proyectos
de ingenieria de
softwaere\nuevo4\nuevo\Office\Office\Form1.cs:línea
726 en
System.Windows.Forms.Control.OnClick(EventArgs
e) en
System.Windows.Forms.Button.OnClick(EventArgs
e) en
System.Windows.Forms.Button.OnMouseUp(MouseEventArgs
mevent) en
System.Windows.Forms.Control.WmMouseUp(Message&
m, MouseButtons button, Int32 clicks)
en
System.Windows.Forms.Control.WndProc(Message&
m) en
System.Windows.Forms.ButtonBase.WndProc(Message&
m) en
System.Windows.Forms.Button.WndProc(Message&
m) en
System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message&
m) en
System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message&
m) en
System.Windows.Forms.NativeWindow.Callback(IntPtr
hWnd, Int32 msg, IntPtr wparam, IntPtr
lparam)

Answer 1

I think most likely cause is that row.Cells[3].Value or row.Cells[4].Value are null (since you have not given them a value) and .ToString() throws a null exception.

Change the code to:

int meta = int.Parse(row.Cells[3].Value == null ? "0" : row.Cells[3].Value.ToString());
int real = int.Parse(row.Cells[4].Value == null ? "0" : row.Cells[4].Value.ToString());