delete button c# dataGridView

Question

When selecting a line for deletion, these errors appear, what is the problem?

private void button3_Click(object sender, EventArgs e)
{
    con = new SqlConnection(@"Data Source=(LocalDB)\MSSQLLocalDB;AttachDbFilename=E:\desk\new\abusalem\abusalem\Database1.mdf;Integrated Security=True");
    cmd.Connection = con;
    cmd.CommandType = CommandType.Text;
    cmd.CommandText = "delete from datauser where id= "+dataGridView1.CurrentRow.Cells[0].Value;
    con.Open();
    cmd.ExecuteNonQuery();
    con.Close();
    filltable();
}

welcome to stackoverflow ibrahim. where is this cmd being created/initialized? is it a property of Page? — Bagus Tesa
– Bagus Tesa, Commented Jun 24, 2022 at 6:33
Does this answer your question? What is a NullReferenceException, and how do I fix it? — MDT
– MDT, Commented Jun 24, 2022 at 9:24

Karen Payne · Accepted Answer · 2022-06-24 07:53:43Z

Here is a conceptual path to follow. The example is setup for a DataTable, if not using a DataTable but not setting the DataGridView.DataSource consider what is shown below. There is no need to reload the DataGridView once a row has been removed.

Setup a BindingSource scoped form level, set the DataSource to what you are using to populate the DataGridView currently e.g. a Datatable then dataGridView1.DataSource = someBindingSource. Set the primary key column to hidden so it is not seen.

If no primary key than adjust dataGridView1.CurrentRow.Cells[0].Value the code below to accept that value.

To remove a row, in the button click event. Here I have Id as the key.

public class Operations
{
    private static string _connectionString =
        @"Data Source=(LocalDB)\MSSQLLocalDB;" + 
        @"AttachDbFilename=E:\desk\new\abusalem\abusalem\Database1.mdf;" + 
        "Integrated Security=True";

    public static bool Remove(int id)
    {
        using (var cn = new SqlConnection(_connectionString))
        {
            using (var cmd = new SqlCommand() {Connection = cn})
            {
                cmd.CommandText = "delete from datauser where id=@Id";
                cmd.Parameters.Add("@Id", SqlDbType.Int).Value = id;
                return cmd.ExecuteNonQuery() == 1;
            }
        }
    }
}

Form code

private BindingSource someBindingSource = new BindingSource();
private void RemoveButton_Click(object sender, EventArgs e)
{
    DataRow row = ((DataRowView)someBindingSource.Current).Row;
    if (Operations.Remove(row.Field<int>("id")))
    {
        someBindingSource.RemoveCurrent();
    }
}

In the future provide enough code so we have a idea what exactly is being done in regards to how the DataGridView gets loaded.

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