Question

I’m attempting to bind a combo to a collection of objects:

    Dim t As New TradeOrderStatus()
    Dim ts As List(Of TradeOrderStatus) = t.GetStatuses

    With Me.cboTradeStatus
        .DataSource = ts
        .SelectedItem = Nothing
    End With

This works fine and I see the list of items in the combo. However when I try to set the SelectedItem of the combo to one of the items:

Me.cboTradeStatus.SelectedItem = Trade.TradeStatus

nothing happens. Trade.TradeStatus is an instance of the class TradeOrderStatus and all the necessart statuses are visible in the drop-down list. The SelectedItem remains as Nothing (or as the first item in the list if I omit the .SelectedItem = Nothing line from the binding code).

Debug.Print(CStr(Me.cboTradeStatus.Items.Contains(.TradeStatus)))

also returns false. Can anyone help?

Answer 1

Trade.TradeStatus is an instance of the class TradeOrderStatus

You mention it is a class; is it the same instance as one of those in the data-bound list? It needs to find an equality match. Alternatively, you can override Equals (and GetHashCode() – always keep the two in sync) to achieve the same thing.

---

(edit)

The simplest way to fix it is to bind to SelectedValue; with the “full” example (below), something like:

cbo.DisplayMember = cbo.ValueMember = "Name";    
...
btn.Click += delegate { cbo.SelectedValue = GetCurrentStatus().Name; };

(edit)

Here’s a C# example (sorry, my VB-fu is weak) of providing custom equality of the different statuses – note the “uncomment to fix”:

using System.Windows.Forms;
using System.Collections.Generic;

class MyStatus {
    public MyStatus(string name) { Name = name; }
    public string Name { get; private set; }
    public override string ToString() {return Name; }
    /* uncomment to fix
    public override bool Equals(object obj) {
        MyStatus other = obj as MyStatus;
        return other != null && other.Name == this.Name;
    }
    public override int GetHashCode() {return Name.GetHashCode(); }
    */
}
static class Program {
    static void Main() {
        ComboBox cbo = new ComboBox();
        cbo.DataSource = GetStatuses();
        Button btn = new Button();
        btn.Click += delegate { cbo.SelectedItem = GetCurrentStatus(); };
        btn.Text = "Set Status";
        btn.Dock = DockStyle.Bottom;
        Application.Run(new Form { Controls = { cbo, btn } });
    }
    static List<MyStatus> GetStatuses() {
        List<MyStatus> stats = new List<MyStatus>();
        stats.Add(new MyStatus("Open"));
        stats.Add(new MyStatus("Pending"));
        stats.Add(new MyStatus("Closed"));
        return stats;
    }
    static MyStatus GetCurrentStatus() {
        return new MyStatus("Closed");
    }
}