C# 中的选定索引值，带有数据库的组合框

Question

我是c#新手，我有一个问题。 我想从组合框中选择一个值，它应该在标签中显示它的年龄。

我所做的是这样的：

 public void FillCombo()
        {
           SqlDataAdapter adap = new SqlDataAdapter("Select * from customers",con);
            DataTable dt = new DataTable();
            adap.Fill(dt);
            comboBox1.DataSource = dt;
            comboBox1.DisplayMember = "name";
            comboBox1.ValueMember = "id";
        }
  private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            con.Open();
           SqlCommand cmd1 = new SqlCommand("Select * from customers where name=@name ", con);
            cmd1.Parameters.AddWithValue("@name",comboBox1.SelectedItem));
           int i= cmd1.ExecuteNonQuery();
            if (i > 0)
            {
               SqlDataReader sqlrdr = cmd1.ExecuteReader();
            while (sqlrdr.Read())
            {
                String age= sqlrdr["age"].ToString();
                label1.Text = age;
            }
            }
 else{
MessageBox.Show("no value");
}
con.Close();
    }

它不显示任何值消息，即使我在数据库中有值。我能做什么？

Answer 1

将数据源设置为数据表时，组合框中的每个项目都是 DataRowView。因此，您已经在组合框中获得了有关当前客户年龄的信息。无需再次调用数据库。

只需使用 SelectedItem 属性来检索有关年龄字段或数据源中存在的任何其他字段的信息

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
{
    DataRowView rv = l.SelectedItem as DataRowView;
    // For safety, always check for null. 
    // It is possible that SelectedIndexChanged 
    // will be called even when there is no selection in the combobox
    if(rv != null)
    {
        label1.Text = rv["age"].ToString();
        ....
    }
}

Answer 2

尝试获取索引，值和所选名称：

private void comboBox1_SelectedIndexChanged(object sender, EventArgs e)
    {
        ComboBox cmb = (ComboBox)sender;
        int selectedIndex = cmb.SelectedIndex;
        int selectedValue = (int)cmb.SelectedValue;
        ComboboxItem selectedName = (ComboboxItem)cmb.SelectedItem;
    }