从数据库中填充Combobox

Question

我有一个组合框的错误

我的代码:

SqlConnection conn = new SqlConnection();
try
{
    conn = new SqlConnection(@"Data Source=SHARKAWY;Initial Catalog=Booking;Persist Security Info=True;User ID=sa;Password=123456");
    string query = "select FleetName, FleetID from fleets";
    SqlCommand cmd = new SqlCommand(query, conn);
    cmd.CommandText = query;
    conn.Open();
    SqlDataReader drd = cmd.ExecuteReader();
    while (drd.Read())
    {
         cmbTripName.Items.Add(drd["FleetName"].ToString());
         cmbTripName.ValueMember = drd["FleetID"].ToString();
         cmbTripName.DisplayMember = drd["FleetName"].ToString();
    }
}
catch
{
     MessageBox.Show("Error ");
}

数据在组合框中显示,但是当您更改选择值时,显示成员不会更改.

它现在正在工作,但是当我点击按钮显示数据时

private void button1_Click(object sender, EventArgs e)
{
    label1.Text = cmbTripName.DisplayMember;
    label2.Text = cmbTripName.ValueMember;
}

显示如下:

FleetName
FleetID

它不显示值

Answer 1

您必须完全重写代码.DisplayMember和ValueMember指向columnNames!此外,您应该使用using block- 所以在查询执行后连接被处理(和关闭).

我没有使用dataReader来访问值,而是选择了dataTable并将其作为dataSource绑定到comboBox上.

using (SqlConnection conn = new SqlConnection(@"Data Source=SHARKAWY;Initial Catalog=Booking;Persist Security Info=True;User ID=sa;Password=123456"))
{
    try
    {
        string query = "select FleetName, FleetID from fleets";
        SqlDataAdapter da = new SqlDataAdapter(query, conn);
        conn.Open();
        DataSet ds = new DataSet();
        da.Fill(ds, "Fleet");
        cmbTripName.DisplayMember =  "FleetName";
        cmbTripName.ValueMember = "FleetID";
        cmbTripName.DataSource = ds.Tables["Fleet"];
    }
    catch (Exception ex)
    {
        // write exception info to log or anything else
        MessageBox.Show("Error occured!");
    }               
}

使用的dataTable可能是一个慢一点比DataReader的,但我没有创建自己的类.如果您真的必须/想要使用DataReader,您可以选择@Nattrass方法.无论如何你应该写一个使用块!

编辑

如果你想获得组合框的当前值,试试这个

private void cmbTripName_SelectedIndexChanged(object sender, EventArgs e)
{
    if (cmbTripName.SelectedItem != null)
    {
        DataRowView drv = cmbTripName.SelectedItem as DataRowView;

        Debug.WriteLine("Item: " + drv.Row["FleetName"].ToString());
        Debug.WriteLine("Value: " + drv.Row["FleetID"].ToString());
        Debug.WriteLine("Value: " + cmbTripName.SelectedValue.ToString());
    }
}

Answer 2

要Combobox以您想要的方式使用,您可以将对象传递给cmbTripName.Items.Add方法.

该对象应具有FleetID和FleetName属性:

while (drd.Read())
{
    cmbTripName.Items.Add(new Fleet(drd["FleetID"].ToString(), drd["FleetName"].ToString()));
}
cmbTripName.ValueMember = "FleetId";
cmbTripName.DisplayMember = "FleetName";

该Fleet类别:

class Fleet
{
     public Fleet(string fleetId, string fleetName)
     {
           FleetId = fleetId;
           FleetName = fleetName
     }
     public string FleetId {get;set;}
     public string FleetName {get;set;}
}

或者,您可以Fleet通过使用匿名类型完全取消对类的需求...

while (drd.Read())
{
    cmbTripName.Items.Add(new {FleetId = drd["FleetID"].ToString(), FleetName = drd["FleetName"].ToString()});
}
cmbTripName.ValueMember = "FleetId";
cmbTripName.DisplayMember = "FleetName";