裏で重い処理をしておく - VB.net

Form1.vb

Public Class Form1
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Dim form2 As Form2 = New Form2
        form2.Show()
    End Sub
End Class

Form2.vb

Public Class Form2
    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
        Button1.Enabled = False

        ' 進捗報告ができるようにする
        BackgroundWorker1.WorkerReportsProgress = True

        ' 処理開始
        BackgroundWorker1.RunWorkerAsync()
    End Sub

    Private Sub BackgroundWorker1_DoWork(sender As Object, e As System.ComponentModel.DoWorkEventArgs) Handles BackgroundWorker1.DoWork

        ' 3秒
        For I As Integer = 1 To 100
            '30mSecスリープさせる
            System.Threading.Thread.Sleep(30)

            'ProgressChangedイベントを発生させる
            BackgroundWorker1.ReportProgress(I)
        Next

        MsgBox("終了！")
    End Sub

    ' 進捗状況を更新する
    Private Sub BackgroundWorker1_ProgressChanged(sender As System.Object, e As System.ComponentModel.ProgressChangedEventArgs) Handles BackgroundWorker1.ProgressChanged
        'プログレスバーを進捗させる
        ProgressBar1.Value = e.ProgressPercentage
    End Sub

    ' バックグラウンド処理完了時の処理
    Private Sub BackgroundWorker1_RunWorkerCompleted(sender As System.Object, e As System.ComponentModel.RunWorkerCompletedEventArgs) Handles BackgroundWorker1.RunWorkerCompleted
        'バックグラウンド処理が完了したので[START]ボタンを有効にする
        Button1.Enabled = True
    End Sub
End Class

Form2を閉じても「終了！」というメッセージボックスが出てくるため、処理は続いていると考えられる