如何使用C#检查dataGridView中选定行中的单元格是否为空/空？

Question

I'm trying to write a code, which checks if a cell in selected row in dataGridView is empty/null before the cell will be updated with a value. The code, which I wrote, works but no matter if there is a value in cell in selected row or not, the data are not updated. I have tried with this code:

 if (dataGridView1.SelectedRows[0].Cells[1].Value == null)
            {
                try
                {
                    String ConnectionString = @"Data Source=.\SQLEXPRESS01;Initial Catalog=Vagtplan;Integrated Security=True";
                    SqlConnection myconnection = new SqlConnection(ConnectionString);
                    myconnection.Open();
                    DateTime primaryKey = Convert.ToDateTime(dataGridView1.SelectedRows[0].Cells[0].Value);
                    SqlCommand AddNumbeCommand = myconnection.CreateCommand();
                    AddNumbeCommand.CommandText = "UPDATE dbo.Vagter SET [ansatID] = @ansatID WHERE [Dato] = @dato";
                    AddNumbeCommand.Parameters.Add("@ansatID", SqlDbType.Int).Value = textBox1.Text;
                    AddNumbeCommand.Parameters.Add("@dato", SqlDbType.DateTime).Value = primaryKey;
                    AddNumbeCommand.ExecuteNonQuery();
                    myconnection.Close();
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message);
                }
                finally
                {
                    MessageBox.Show("The cell is updated.");
                }

            }
            else
            {
                MessageBox.Show("There is already a value in the cell.");
            }

As I mentioned befor, the actual result is that no matter if there is a value in cell in selected row or not, the data are not updated. The expected result is that when a user select in dataGrdView a row where cell under column ansatID already has a value, write a value in textBox1, and press on ''Tilføj ansatID til vagten'', the he get error:"There is already a value in the cell.". If he will select a row where cell under column ansatID is empty, write a value in textBox1, and press on ''Tilføj ansatID til vagten'', then the SQL query will be executed and he gets message "The cell is updated." This is also shown on following picture:

Answer 1

With this condition you can access that specific column in the selected row, you missed the OwningRow part and you need to compare to an empty string and null just in case:

(string)dataGridView1.SelectedCells[0].OwningRow.Cells[1].Value == "" ||
(string)dataGridView1.SelectedCells[0].OwningRow.Cells[1].Value == null

SelectedCells[0].OwningRow means the first selected row, Cells[1] means is the ansatID.

Gotta love winforms and its clarity.

Edit: As someone pointed out, you need to manually update the data in the datagrid in winforms, it is convinient to have a function like UpdateDatagrid() and call it every time you modify the DB.

Answer 2

您可以使用String.IsNullOrWhiteSpace((String)dataGridView1.SelectedCells[0].OwningRow.Cells[1].Value))