由于以前用VB6.0做过系统，编辑的时候第一个想的是unload方法，但是实际不是这样的，VB.net 中根本就没有unload方法，但是看到了frmclosing方法，接着我就写了程序：

    Private Sub Frmmain_FormClosing(ByVal sender As Object,ByVal e As System.Windows.Forms.FormClosingEventArgs) Handles Me.FormClosing

        If MsgBox("你真的要退出吗?",vbOKCancel,"提示") = vbCancel Then
            e.Cancel = True
        Else
            Dim BOffwork As New BllOffwork
            Dim EOnwork As New Onwork
            Dim EWorkRecord As New WorkRecord
            Dim strUserName As String = FrmLogin.strUserName

            Try
                EOnwork = BOffwork.InquireOnwork(strUserName)
                EWorkRecord.EUserName = strUserName
                EWorkRecord.EOnworkTime = EOnwork.EOnworkTime
                EWorkRecord.EOffworkTime = Now
                BOffwork.Offwork(strUserName,EWorkRecord)
                Me.Close()
            Catch ex As Exception
                MsgBox(ex.Message)
            End Try
        End If
    End Sub

结果发现：如果选择不退出，程序要执行两遍，弹出两次“询问是否退出”的窗口，如果选择确定退出，会一直弹出“询问是否退出”窗口。调试了一下发现me.close()导致程序再次执行，但是如果删掉的话，整个程序就不能退出，以至成为死循环。

后来查了一下资料，知道了窗口的关闭有两个方法：formclosing() formclosed() 遂改动如下：

    Private Sub Frmmain_FormClosed(ByVal sender As Object,ByVal e As System.Windows.Forms.FormClosedEventArgs) Handles Me.FormClosed
        Dim BOffwork As New BllOffwork
        Dim EOnwork As New Onwork
        Dim EWorkRecord As New WorkRecord
        Dim strUserName As String = FrmLogin.strUserName

        Try
            EOnwork = BOffwork.InquireOnwork(strUserName)
            EWorkRecord.EUserName = strUserName
            EWorkRecord.EOnworkTime = EOnwork.EOnworkTime
            EWorkRecord.EOffworkTime = Now
            BOffwork.Offwork(strUserName,EWorkRecord)
            Me.Close()
        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub
  

    Private Sub Frmmain_FormClosing(ByVal sender As Object,"提示") = vbCancel Then
            e.Cancel = True
        End If
    End Sub

结果：点击确定退出时，还是会发生死循环，当然还是me.close()惹的祸，调试一遍恍然大悟，这两个方法有什么区别呢？formclosing() 是窗口的正在关闭事件，而formclosed() 却是窗口已经关闭的事件，窗口都已经关闭了还要me.close()做甚呢？ 所以正确写法如下：

    Private Sub Frmmain_FormClosed(ByVal sender As Object,EWorkRecord)

        Catch ex As Exception
            MsgBox(ex.Message)
        End Try
    End Sub
  

    Private Sub Frmmain_FormClosing(ByVal sender As Object,"提示") = vbCancel Then
            e.Cancel = True
        End If
    End Sub