Dealing with WinForms Combobox and name/value items.

I just read this article on aspalliance.com by Sandeep Archarya.

I think the article had 2 main points.  One was that databinding a combobox is not “bug free” because the act of manually databinding to a combobox causes the SelectedIndexChanged event to fire.  The second point was to show how to create a simple namevalue class to be added to the combobox items collection to get around the “problem” of combobox’s taking an object as the item in it’s list (as opposed to a name value pair).

I would point out the following:

First, I am not sure that I would call the SelectedIndexChanged event firing a bug.  When you manually databind a list, the first item become selected by default, and thus the selectedindex HAS changed, from -1 to 0.

Second, if you consider this a problem you can get around it a couple different ways.

1) Don’t use manual databinding.

In the designer, select a datasource or create a new one.  I created a simple employee object and created an object datasource for this employee.  This creates a EmployeeBindingSource object that I bind my employee list to.  Using this method, I didn’t experience the SelectedIndexChanged event firing on the databind.

Private list As New System.Collections.Generic.List(Of employee)
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    ‘*** create some fake employee objects
   For i As Integer = 70 To 80
      list.Add(New employee(i, Chr(i)))
   Next

    ‘*** this will populate our control (Combobox1)
   Me.EmployeeBindingSource.DataSource = list

End Sub

2) You can use manual databinding, and manually detach and attach the event handler for this event.

Private list As New System.Collections.Generic.List(Of employee)

Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    
    ‘*** create some fake employee objects
   For i As Integer = 70 To 80
      list.Add(New employee(i, Chr(i)))
   Next

    ‘*** remove the handler
    RemoveHandler ComboBox1.SelectedIndexChanged, AddressOf ComboBox1_SelectedIndexChanged
    ‘*** databind
    Me.ComboBox1.ValueMember = “id”
    Me.ComboBox1.DisplayMember = “name”
    Me.ComboBox1.DataSource = list
    ‘*** add the handler back
    AddHandler ComboBox1.SelectedIndexChanged, AddressOf ComboBox1_SelectedIndexChanged
End Sub

 

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