C# と VB.NET の質問掲示板

VB.NETですがサンプルです。
C#2008なら似たようなことは出来ると思います。

    Private m_act As Action = Nothing

    Private Sub Button1_Click(sender As System.Object, e As System.EventArgs) Handles Button1.Click
        If m_act IsNot Nothing Then
            m_act()
        End If
        m_act = Nothing
        Label1.Text = "Button1_Click"
    End Sub

    Private Sub TextBox1_Enter(sender As Object, e As System.EventArgs) Handles TextBox1.Enter
        If m_act IsNot Nothing Then
            m_act()
        End If
        m_act = Nothing
        Label1.Text = ""
    End Sub

    Private Sub TextBox2_Enter(sender As Object, e As System.EventArgs) Handles TextBox2.Enter
        If m_act IsNot Nothing Then
            m_act()
        End If
        m_act = Nothing
        Label1.Text = ""
    End Sub

    Private Sub TextBox1_Validating(sender As Object, e As System.ComponentModel.CancelEventArgs) Handles TextBox1.Validating
        If TextBox1.Text = "1" Then
            MessageBox.Show("TextBox1_Validating Cancel", "TextBox1_Validating")
            e.Cancel = True
        Else
            m_act = Sub()
                        MessageBox.Show("TextBox1_Validating Accepted", "TextBox1_Validating")
                    End Sub
        End If
    End Sub