Question

我正在使用数据库连接进行Windows窗体应用我想点击listbox1项目并对db表进行查询并根据该条目填充listbox2。

listbox1有团队 listbox2有这些团队的成员。

目前，只要有人选择了一个项目，这就是我在listbox1上使用的方法：

        string teamSelected = listBox1.GetItemText(listBox1.SelectedItem);
        conexion = new dbconnector();

        conexion.getMembersOfTeam(ref employeesM, teamSelected);
        this.listBox2.DisplayMember = "userID";
        this.listBox2.ValueMember = "userID"; //Field in the datatable which you want to be the value of the combobox
        this.listBox2.DataSource = employeesM.Tables["users_table"];

但是我收到此错误消息：

对象引用未设置为对象的实例。

触发的代码行是：

datasetMembers.Tables.Add(employeesM);

该方法的完整代码是：

public void getMembersOfTeam(ref DataSet datasetMembers, string teamDesired)
    {

        string query4 = "select * from users_table Where userTeam = '" + teamDesired + "'"; //added by fran to retrieve all the teams
        if (OpenConnection())
        {

            //retrieving all the teams using query3
            MySqlCommand cmd4 = new MySqlCommand(query4, connection);
            MySqlDataReader dataReader4 = cmd4.ExecuteReader();
            dataReader4.Read();

            if (dataReader4.HasRows)
            {
                //dataGridView1.Visible = true;

                DataTable employeesM = new DataTable();
                employeesM.Load(dataReader4);
                datasetMembers.Tables.Add(employeesM);

            }
            else
            {
                //dataGridView1.Visible = false;
            }


            dataReader4.Close();
            //end of retrieving teams

            CloseConnection();
        }
    }

如何将查询中的所有结果发送到合适的数据集并更新listbox1？

提前感谢您提供任何帮助，我想我已经分享了一切以澄清我的问题，如果您需要更多数据，请告诉我们谢谢！

Answer 1

The datasetMembers is null. You have to initialized it before calling the getMembersOfTeam method.

无法从其他列表框和数据库填充列表框

1 个答案: