组合框显示system.data.datarowview

Question

我在winform中有一个组合框，它通过在MySQL中调用存储过程来获取数据。

我的存储过程：

CREATE PROCEDURE `GetCourses`()
BEGIN
SELECT course_name FROM my_db.courses where group_id=1;
END

现在，将课程名称与Combobox（ComboBox2）绑定，如下所示-在选择另一个Combobox（ComboBox1）时：

private void Form_Load(object sender, EventArgs e)
{
  var connectionString = ConfigurationManager.ConnectionStrings["ConnectionString"].ConnectionString;
  conn = new MySqlConnection(connectionString);
  conn.Open();
  MySqlCommand cmd1 = new MySqlCommand();
  cmd1.Connection = conn;
  cmd1.CommandType = CommandType.StoredProcedure;
  cmd1.CommandText = "GetCourses";
  DataTable dt1 = new DataTable();
  MySqlDataAdapter adp1 = new MySqlDataAdapter(cmd1);
  adp1.Fill(dt1);
}

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
  if (comboBox1.SelectedIndex == 3)
  {
    comboBox2.ValueMember = "course_name";
    comboBox2.DisplayMember = "course_name";
    comboBox2.DataSource = dt1;
  }
}

但是，当我运行表单时，组合框填充为“ system.data.datarowview”值

谁能帮我这个忙。

注意：我不想通过使用'MySqlDataReader'实现

提前致谢。

Answer 1

只需通过下面两行代码即可解决。

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
  if (comboBox1.SelectedIndex == 3)
  {
    foreach (DataRow row in dt1.Rows)
      comboBox2.Items.Add(row["course_name"]);
  }
}    

Answer 2

您可以将数据投影到具有命名字段的集合中，以防止datarow对象的默认ToString（）ing：

 if (comboBox1.SelectedIndex == 3)
  {
    comboBox2.ValueMember = "course_name_value";
    comboBox2.DisplayMember = "course_name";
    comboBox2.DataSource = dt1.AsEnumerable().Select 
       (n => new { course_name = n["course_name"], course_name_value = n["course_name"]}).ToList();
  }

编辑

我认为您应该将这些行放在Load事件中。 您不需要多次设置它们，这可能是组合框显示获取对象的ToString（）结果而不是单个属性的原因。

comboBox2.ValueMember = "course_name";
comboBox2.DisplayMember = "course_name";

Answer 3

我运行了一个模拟测试，我认为它是在完成selectedIndex更改事件之前（在完成OnLoad事件时）处置您的数据集。 尝试让您的SelectedIndexChanged事件引发一个函数来填充第二个框。 PS，别介意我使用SQLite数据库进行测试。

Private Sub ComboBox1_SelectedIndexChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ComboBox1.SelectedIndexChanged
        If (ComboBox1.SelectedIndex = 3) Then            
            Select3()    
        End If
    End Sub

    Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load    
        Dim range() As String = {"0", "1", "2", "3 - Fire Combo2", "4", "5", "6"}
        ComboBox1.Items.AddRange(range)            
    End Sub

    Private Sub Select3()
        Dim connectionString As String = MyStandAloneDB.DBConnStr
        Dim conn As New System.Data.SQLite.SQLiteConnection(connectionString)
        conn.Open()
        Dim cmd1 As New System.Data.SQLite.SQLiteCommand
        cmd1.Connection = conn
        cmd1.CommandType = CommandType.Text
        cmd1.CommandText = "SELECT * FROM Foo"
        Dim dt1 As New DataTable()
        Dim adp1 As New System.Data.SQLite.SQLiteDataAdapter(cmd1)
        adp1.Fill(dt1)
        ComboBox2.DataSource = dt1
        ComboBox2.ValueMember = dt1.Columns(1).ToString
        ComboBox2.DisplayMember = dt1.Columns(0).ToString
    End Sub