Extension to add strings to a VB.NET ListBox for output or console logging.

AddLogLine.vb

'Usage: ListBox1.AddLogLine("Log this!")
Imports System.Runtime.CompilerServices

Module FormExtensions
    Delegate Sub UpdateLog(lb As ListBox, line As String)

    <Extension()>
    Public Sub AddLogLine(lb As ListBox, line As String)
        If (lb.InvokeRequired) Then 'Invoke from the GUI thread if called from a different one
            lb.Invoke(New UpdateLog(AddressOf AddLogLine), lb, line)
        Else
            lb.Items.Add(line) 'Add the given line
            If lb.Items.Count > 100 Then 'Remove old lines once the line limit is exceeded
                lb.Items.RemoveAt(0)
            End If
            lb.SelectedIndex = lb.Items.Count - 1 'Ensure the latest line is shown
            lb.ClearSelected()
        End If
    End Sub
End Module

'The following may also be useful to allow Ctrl + C copying from the listbox
'- First set ListBox1.SelectionMode = SelectionMode.MultiExtended

'    Private Sub ListBox1_KeyDown(sender As Object, e As System.Windows.Forms.KeyEventArgs) _
'        Handles ListBox1.KeyDown
'
'        If e.Control AndAlso e.KeyCode = Keys.C Then 'Detect Ctrl + C shortcut key combo
'            Dim Buffer As New System.Text.StringBuilder 'Create a string by concatenating all selected list items
'            For Each item As Object In ListBox1.SelectedItems
'                Buffer.AppendLine(item.ToString)
'            Next
'            If Buffer.Length > 0 Then
'                Clipboard.SetText(Buffer.ToString) 'Save the created string to the users clipboard
'            End If
'        End If
'    End Sub