C# と VB.NET の質問掲示板

shuさんの案でコード書いてみました。
UserControlにToolTipとボタン3つがある前提です。

Public Class UserControl1

    Private _flag As Boolean = False

    Private Sub Button_MouseHover(sender As System.Object, e As System.EventArgs) _
        Handles Me.MouseHover, Button1.MouseHover, Button2.MouseHover, Button3.MouseHover

        If (Me._flag) Then Return

        Dim c As System.Windows.Forms.Control = DirectCast(sender, System.Windows.Forms.Control)
        Me.ToolTip1.SetToolTip(c, "Hello World")
        Me._flag = True

    End Sub

    Private Sub Button_MouseMove(sender As System.Object, e As System.Windows.Forms.MouseEventArgs) _
        Handles Me.MouseMove, Button1.MouseMove, Button2.MouseMove, Button3.MouseMove

        Me._flag = False

    End Sub

End Class