Add/Remove User Controls in VB.NET

A nice feature in the Visual.NET environment is the ability to create User Controls.

Below is the files for the Visual.NET Add/Remove project:

The AddRemoveControl.vb is the User Control code for the Add Remove control and the Form1.vb code shows you how to implement this control in a form.

To create a user control is fairly easy.  In the Project menu,  you choose User Control, and it will add a custom control to your existing project as a separate class. This example is a user control that has two list boxes that can transfer strings back and forth between them.  In essence,  you are 'adding'  and 'removing' strings from one list into another.

The Source List (Inside Barn) is initially populated through the user controls populate method (In AddRemoveControl.vb):

Public Sub PopulateSource(ByVal list() As String)
SourceListbox.Items.All = list
ControlLogic()
End Sub 'PopulateSource

The rest of the functionality of the Add/Remove Control is initiated by the Add, Remove buttons.  If the Add button is pressed,  items selected in the source list box are moved to the destination list box. The code for this is illustrated below:

Protected Sub AddButton_Click(ByVal sender As Object, ByVal e As System.EventArgs)
' copy selected strings in the source list to the destination list
Dim i As Integer
For i = 0 To SourceListbox.SelectedItems.Count - 1
DestinationListbox.Items.Add(SourceListbox.SelectedItems(i))
Next i
' remove selected strings from the source listfor(int j = SourceListbox.SelectedIndices.Count - 1; j >= 0; j --)
If (True) Then
SourceListbox.Items.Remove(SourceListbox.SelectedIndices(j))
End If
ControlLogic()
End Sub 'AddButton_Click

Also noteworthy in the User Control is the use of the ArrayList type as a property for extracting data from the lists in the control:

Private m_DestList As New ArrayList
Public ReadOnly Property DestinationList() As ArrayList
Get
m_DestList.Clear()
Dim i As Integer
For i = 0 To DestinationListbox.Items.Count - 1
m_DestList.Add(Me.DestinationListbox.Items(i))
Next i
Return m_DestList
End Get
End Property

The ArrayList is a C# dynamic collection that works much the same as the old MFC CObArray collections, but is a bit easier to use.
In the property shown above, the array list is cleared and repopulated from the destination list box.  We can see the use of this property for retrieving data from our control in the form method below.  This method is called in the form, when the result button is pushed.