The various part identifier "System.Data.Datarowview" cannot be associated

Question

Try {

                if (cmbFavorecido.SelectedValue != null )
                {

                    txtID.Text = cmbFavorecido.SelectedValue.ToString();

                    cn = conexao.ConectarSqlServer();
                    cn.Open();
                    SqlCommand cmd = new SqlCommand("select CNPJ_FORNECEDOR FROM FORNECEDOR WHERE ID_FORNECEDOR =  " + txtID.Text, cn);
                    SqlDataAdapter ad = new SqlDataAdapter(cmd);

                    DataSet ds = new DataSet();
                    ad.Fill(ds, "TbFornecedor");
                    txtCnpj.Text = ds.Tables["TbFornecedor"].Rows[0].ItemArray[0].ToString();

                }

Answer 1

Try to do it this way.

 if (cmbFavorecido.SelectedValue != null)
            {
                SqlConnection conn = new SqlConnection();
                conn.ConnectionString = myConnString;
                try
                {
                    String txtID = cmbFavorecido.SelectedValue.ToString();
                    txtID.Text = txtID;

                    //cn = conexao.ConectarSqlServer();
                    //cn.Open();

                    SqlCommand cmd = new SqlCommand();
                    cmd.Connection = conn;
                    cmd.CommandType = CommandType.Text;
                    cmd.CommandText = "select CNPJ_FORNECEDOR FROM FORNECEDOR WHERE ID_FORNECEDOR = @txtID";
                    cmd.Parameters.AddWithValue("@txtID", txtID);

                    SqlDataAdapter da = new SqlDataAdapter();
                    DataTable dt = new DataTable();

                    da.SelectCommand = cmd;
                    conn.Open();
                    da.Fill(dt);

                    txtCnpj.Text = dt.Rows[0][0];

                }
                catch (SqlException sqle)
                {
                    // MessageBox.Show("Falha ao efetuar a conexão. Erro: " + sqle);
                }
                finally
                {
                    conn.Close();
                }
            }

The one important thing in your code that you need to be careful of, which is passing parameters. The way you’re doing you run the risk of someone using SQL injection, so user always Parameters.AddWithValue("@txtID", txtID); to pass parameters.

Thus the types of the parameters are appropriate to the types of the columns and the SQL statement is on account of ADO.NET. In addition, a good practice is to carry out validations.