VB.Net - Combobox 不显示数据

Question

Combobox2.text not showing the called data from the table. Any help will be appreciated!

Public Sub loadproductdata()

    Dim i As Integer

    str = "SELECT * FROM tbl_products INNER JOIN tbl_suppliers ON tbl_products.prod_supplier = tbl_suppliers.supp_ID WHERE prod_ID = '" & frm_ProductList.DataGridView1.SelectedRows(i).Cells(0).Value & "'"

    cmd = New MySqlCommand(str, con)
    con.Open()
    dr = cmd.ExecuteReader()

    If dr.Read() Then

        TextBox1.Text = (dr.Item("prod_code").ToString())
        TextBox2.Text = (dr.Item("prod_name").ToString())
        ComboBox1.Text = (dr.Item("prod_category").ToString())
        Label1.Text = (dr.Item("prod_supplier").ToString())
        ComboBox2.Text = (dr.Item("supp_name").ToString())
        TextBox3.Text = (dr.Item("prod_purchaseprice").ToString())
        TextBox4.Text = (dr.Item("prod_retailprice").ToString())
        TextBox5.Text = (dr.Item("prod_discount").ToString())
        ComboBox3.Text = (dr.Item("prod_unit").ToString())
        TextBox6.Text = (dr.Item("prod_stockqty").ToString())
        TextBox7.Text = (dr.Item("prod_reorderlvl").ToString())
        TextBox8.Text = (dr.Item("prod_description").ToString())
        TextBox9.Text = (dr.Item("prod_remarks").ToString())
   
    End If

    con.Close()

End Sub

Answer 1

When a combo box is in DropDownList mode, as yours appears to be, to set its current value to an item from its list you should set the SelectedValue property. You should also consider filling the control with some kind of object that can maintain the difference between a key and a value items, to support a different display value versus backing value (supplier "Microsoft" has ID "6")

While dr.Read()
    Dim kvp = new KeyValuePair(Of Integer, String) (0,"")
    kvp.Value= (dr.Item("supp_name").ToString())
    kvp.Key = DirectCast(dr.Item("supp_id"), Integer)

    ComboBox2.Items.Add(kvp)

Loop

Combobox2.DisplayMember = "Value"
Combobox2.ValueMember = "Key"

Now, if you set SelectedValue = 6 in your other query the combo shows "Microsoft"

ps; it's actually a lot easier if you just use a datatable for this:

Dim dt = new DataTable
Dim da as MySqlDataAdapter("SELECT * FROM...", "conn string here")
da.Fill(dt)
'rename your combobox2 to supplierComboBox
supplierComboBox.DataSource = dt
supplierComboBox.DisplayMember = "supp_name"
supplierComboBox.ValueMember = "supp_id"

And it gets easier still if you use strongly typed datasets everywhere instead of this intensely manual yanking data around - but that's out of scope of this question