Public WithEvents textBox As TextBox
    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As _
      System.EventArgs) Handles Button1.Click
        For i As Integer = 1 To 10
            Dim newTextBox As New TextBox
            GroupBox1.Controls.Add(newTextBox)
            textBox = newTextBox
 
            With textBox
                .Location = New System.Drawing.Point(20, 30 * i)
                .Width = 200
                .Name = "TextBox" & i
                .BringToFront()
                .Text = .Name.ToString
                AddHandler textBox.MouseDown, AddressOf textBox_MouseDown
            End With
 
        Next
    End Sub
 
    Private Sub textBox_MouseDown(ByVal sender As Object, ByVal e As _
      System.Windows.Forms.MouseEventArgs) Handles textBox.MouseDown
        textBox.BackColor = Color.Blue
    End Sub