Undefined object reference for an instance of a Visual Studio object

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I have a problem with the id variable of my dataGridView, it is giving the following error: "Object reference not defined for an instance of a Visual Studio object". I am using Windows Form, Mysql and Datagridview. Follow the code:

//Declarando variaveis globais
    int id;
    private MySqlConnection cone = new MySqlConnection();
    private MySqlCommand comandoSql = new MySqlCommand();
    private MySqlDataReader dados;
    public frmGerenciarClientes()
    {
        InitializeComponent();
        //Mapeando evento de seleção de celulas da tabela
        //dgvClientes.CellMouseUp += dgvClientes_CellMouseUp;
    }
    private void dgvClientes_CellClick(object sender, DataGridViewCellEventArgs e)
    {
        id = Convert.ToInt32(dgvClientes.Rows[e.RowIndex].Cells["cod_cli"].Value.ToString());
        MySqlCommand cmd = cone.CreateCommand();
        cmd.CommandType = CommandType.Text;
        cmd.CommandText = "select * from clientes where cod_cli=" + id + "";
        cmd.ExecuteNonQuery();
        DataTable dt = new DataTable();
        MySqlDataAdapter da = new MySqlDataAdapter(cmd);
        da.Fill(dt);
        foreach (DataRow dr in dt.Rows)
        {
            txtIdALT.Text = dr["cod_cli"].ToString();
            txtNome1.Text = dr["nome_cli"].ToString();
            txtEndereco.Text = dr["end_cli"].ToString();
            txtNum.Text = dr["endnum_cli"].ToString();
            txtBairro.Text = dr["bairro_cli"].ToString();
            txtCidade.Text = dr["cid_cli"].ToString();
            mtxtCel.Text = dr["cel_cli"].ToString();
            mtxtTel.Text = dr["tel_cli"].ToString();
            txtEmail.Text = dr["email_cli"].ToString();

        }
    }
c# mysql winforms

  • Are you sure it’s the id? This error happens when you try to access a property/method of a null object, but id is an int (have no null).

  • Then, the error occurred on the line: id = Convert.ToInt32(dgvClientes.Rows[e.RowIndex].Cells["cod_cli"].Value.ToString());

  • Certainly your . Cells["cod_cli"] this NULL, when you try to access your Value will happen this error. what you can do is check with a breakpoint which value you passed on that line.

1 answer

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As commented, this error happens when trying to access a property/method of a null object. As the exception is occurring on the line 

id = Convert.ToInt32(dgvClientes.Rows[e.RowIndex].Cells["cod_cli"‌​].Value.ToString());

Check which of the components of this expression is null:

  • See if dgvClientes is void; otherwise
  • See if the expression dgvClientes.Rows[e.RowIndex] returns null; otherwise
  • See if the expression dgvClientes.Rows[e.RowIndex].Cells["cod_cli"‌​] returns null. Otherwise
  • See if the expression dgvClientes.Rows[e.RowIndex].Cells["cod_cli"‌​].Value returns null.

If it’s none of them then we haven’t found the real problem yet.

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