Timer1.Interval = 500
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Private Sub Timer1_Timer()
Timer1.Enabled = False
Dim ss As String
ss = Format(Now, "HH:mm:ss")
If ss = "12:00:00" Then
'执行备份语句
End If
Timer1.Enabled = True
End Sub
还有一个办法就是可以用SQL自身的功能，在SQL里面可以添加任务 ，设置周期为每天，时间为12点，到时候执行一下备份
Visual Basic .NET Visual Basic.NET是基于微软.NET Framework之上的面向对象的中间解释性语言，可以看作是Visual Basic在.Net Framework平台上的升级版本,增强了对面向对象的支持。但由于改动太大，导致VB.net对VB的向后兼容性不好，在业界引起不小的争议。 大多的VB.Net程序员使用Visual Studio .Net作为IDE（integrated development environment). SharpDevelop是另一种可用的开源的IDE。VB.Net需要在.Net Framework平台上才能执行。 VB.NET的主页 1 目前版本 2005年9月以来，存在三种不同版本的Visual Basic .NET. 1 Visual Basic .NET:是随vc#和ASP.NET一起在2002年发布的最初始的VB.net版本。C#被大力宣传为微软对付JAVA的王牌，受到媒体极力关注。然而VB.NET(有时被称为VB7)影响面不广，这导致VB社区之外很少人关注它。那些试用过此版VB.NET的人在层层幕布下发现一个强大却艰深的语言，而且还有不少弱点，比如它比VB6来有一个大了十倍的进行时(RunTime)，内存footprint也大大增加。 2 Visual Basic .NET 2003:是和.NET Framework 1.1一起发布的。新功能包括对.NET Compact Framework的支持和更好的VB升迁向导。并改进了运行状况，IDE稳定性(尤其是后台编译器)，以及运行时RunTime稳定性。另外，VB.NET 2003还有一个学院版Visual Studio .NET 2003 Academic Edition (VS03AE)，它是分发给各国某些学者免费使用的版本。 3 Visual Basic 2005:VB2005是VB.Net的重大转变，微软决意在其软件名称中去掉了.NET部份。在VB2005中，微软增加了许多新功能，以引用VB对于初学者来说的一些优点： A, Edit and Continue - 也许是从VB那里丢掉的最大的功能，允许代码的编辑和执行立即的执行恢复。 B, Design-time expression evaluation C, My伪命名空间，提供了访问.NET Framework特定域的不需大量编码的简单方式；还能动态产生类(显然的是My.Forms)；提供了改进的VB到VB.NET转换向导；Using 语法，简化了需要部署pattern to free resources的对象的使用；My编码，可隐藏由VB.NET IDE写的模板代码；数据源绑定，简化了数据库C/S开发 上述功能(尤其是My)增强了VB.Net成为快速开发应用平台的可能，并与C#进一步区别开来。参见： 使用My开发 通过My命名空间访问.NET Framework 和项目 Visual Basic 2005 通过增加新功能而填补了和其它所谓更强大的.NET语言的差距。 A, 增加了.NET 2.0语言功能包括：generics和Partial类(在一个文件里定义一个类的某部份然后再添加更多的定义，这个方法在整合用户编码和系统自动生成编码时尤其有用)。 B, XML注释，可以被NDoc等工具处理而自动生成文档 C, operator overloading D, 支持在其它语言中已经广泛使用的unsigned integer数据类型。 E, 支持在许多C衍生编程语言已提供的复合操作符如："+=", "-=" 4, IsNot专利：If Not X Is Y表达式被转换成If X IsNot Y。当微软为IsNot申请专利时招致了恶名(尤其来自Real公司)。 5, Visual Basic 2005 Express：作为VS产品线上的一部份,VB2005 Express是专为业余爱好者和新手定制的免费的VS Express系列的一员。Express版本目的定位在帮助人们学习一种语言，所以他们有和标准版一致的用户界面，只是少了一些高级功能。另外，VS 查看更多答案
记得采纳啊
Public Class SimpleCalculator
Inherits System.Windows.Forms.Form
#Region " Windows 窗体设计器生成的代码 "
Public Sub New()
MyBase.New()
'该调用是 Windows 窗体设计器所必需的。
InitializeComponent()
'在 InitializeComponent() 调用之后添加任何初始化
End Sub
'窗体重写处置以清理组件列表。
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Dispose()
End If
End If
MyBase.Dispose(disposing)
End Sub
'Windows 窗体设计器所必需的
Private components As System.ComponentModel.IContainer
'注意：以下过程是 Windows 窗体设计器所必需的
'可以使用 Windows 窗体设计器修改此过程。
'不要使用代码编辑器修改它。
Friend WithEvents Label1 As System.Windows.Forms.Label
Friend WithEvents TextBox1 As System.Windows.Forms.TextBox
Friend WithEvents Button1 As System.Windows.Forms.Button
Friend WithEvents Button2 As System.Windows.Forms.Button
Friend WithEvents Button3 As System.Windows.Forms.Button
Friend WithEvents Button4 As System.Windows.Forms.Button
Friend WithEvents Button5 As System.Windows.Forms.Button
Friend WithEvents Button6 As System.Windows.Forms.Button
Friend WithEvents Button7 As System.Windows.Forms.Button
Friend WithEvents Button8 As System.Windows.Forms.Button
Friend WithEvents Button9 As System.Windows.Forms.Button
Friend WithEvents Button10 As System.Windows.Forms.Button
Friend WithEvents Button11 As System.Windows.Forms.Button
Friend WithEvents Button12 As System.Windows.Forms.Button
Friend WithEvents Button13 As System.Windows.Forms.Button
Friend WithEvents Button14 As System.Windows.Forms.Button
Friend WithEvents Button15 As System.Windows.Forms.Button
Friend WithEvents Button16 As System.Windows.Forms.Button
System.Diagnostics.DebuggerStepThrough() Private Sub InitializeComponent()
Me.Label1 = New System.Windows.Forms.Label
Me.TextBox1 = New System.Windows.Forms.TextBox
Me.Button1 = New System.Windows.Forms.Button
Me.Button2 = New System.Windows.Forms.Button
Me.Button3 = New System.Windows.Forms.Button
Me.Button4 = New System.Windows.Forms.Button
Me.Button5 = New System.Windows.Forms.Button
Me.Button6 = New System.Windows.Forms.Button
Me.Button7 = New System.Windows.Forms.Button
Me.Button8 = New System.Windows.Forms.Button
Me.Button9 = New System.Windows.Forms.Button
Me.Button10 = New System.Windows.Forms.Button
Me.Button11 = New System.Windows.Forms.Button
Me.Button12 = New System.Windows.Forms.Button
Me.Button13 = New System.Windows.Forms.Button
Me.Button14 = New System.Windows.Forms.Button
Me.Button15 = New System.Windows.Forms.Button
Me.Button16 = New System.Windows.Forms.Button
Me.SuspendLayout()
'
'Label1
'
Me.Label1.Location = New System.Drawing.Point(16, 16)
Me.Label1.Name = "Label1"
Me.Label1.Size = New System.Drawing.Size(48, 16)
Me.Label1.TabIndex = 0
Me.Label1.Text = "结果："
'
'TextBox1
'
Me.TextBox1.Location = New System.Drawing.Point(64, 8)
Me.TextBox1.Name = "TextBox1"
Me.TextBox1.Size = New System.Drawing.Size(120, 21)
Me.TextBox1.TabIndex = 1
Me.TextBox1.Text = ""
'
'Button1
'
Me.Button1.Location = New System.Drawing.Point(200, 8)
Me.Button1.Name = "Button1"
Me.Button1.Size = New System.Drawing.Size(56, 24)
Me.Button1.TabIndex = 2
Me.Button1.Text = "清空"
'
'Button2
'
Me.Button2.Location = New System.Drawing.Point(48, 56)
Me.Button2.Name = "Button2"
Me.Button2.Size = New System.Drawing.Size(24, 24)
Me.Button2.TabIndex = 3
Me.Button2.Text = "1"
'
'Button3
'
Me.Button3.Location = New System.Drawing.Point(88, 56)
Me.Button3.Name = "Button3"
Me.Button3.Size = New System.Drawing.Size(24, 24)
Me.Button3.TabIndex = 4
Me.Button3.Text = "2"
'
'Button4
'
Me.Button4.Location = New System.Drawing.Point(136, 56)
Me.Button4.Name = "Button4"
Me.Button4.Size = New System.Drawing.Size(24, 24)
Me.Button4.TabIndex = 5
Me.Button4.Text = "3"
'
'Button5
'
Me.Button5.Location = New System.Drawing.Point(48, 88)
Me.Button5.Name = "Button5"
Me.Button5.Size = New System.Drawing.Size(24, 24)
Me.Button5.TabIndex = 6
Me.Button5.Text = "4"
'
'Button6
'
Me.Button6.Location = New System.Drawing.Point(88, 88)
Me.Button6.Name = "Button6"
Me.Button6.Size = New System.Drawing.Size(24, 24)
Me.Button6.TabIndex = 7
Me.Button6.Text = "5"
'
'Button7
'
Me.Button7.Location = New System.Drawing.Point(136, 88)
Me.Button7.Name = "Button7"
Me.Button7.Size = New System.Drawing.Size(24, 24)
Me.Button7.TabIndex = 8
Me.Button7.Text = "6"
'
'Button8
'
Me.Button8.Location = New System.Drawing.Point(48, 120)
Me.Button8.Name = "Button8"
Me.Button8.Size = New System.Drawing.Size(24, 24)
Me.Button8.TabIndex = 9
Me.Button8.Text = "7"
'
'Button9
'
Me.Button9.Location = New System.Drawing.Point(88, 120)
Me.Button9.Name = "Button9"
Me.Button9.Size = New System.Drawing.Size(24, 24)
Me.Button9.TabIndex = 10
Me.Button9.Text = "8"
'
'Button10
'
Me.Button10.Location = New System.Drawing.Point(136, 120)
Me.Button10.Name = "Button10"
Me.Button10.Size = New System.Drawing.Size(24, 24)
Me.Button10.TabIndex = 11
Me.Button10.Text = "9"
'
'Button11
'
Me.Button11.Location = New System.Drawing.Point(48, 152)
Me.Button11.Name = "Button11"
Me.Button11.Size = New System.Drawing.Size(24, 24)
Me.Button11.TabIndex = 12
Me.Button11.Text = "0"
'
'Button12
'
Me.Button12.Location = New System.Drawing.Point(176, 56)
Me.Button12.Name = "Button12"
Me.Button12.Size = New System.Drawing.Size(24, 24)
Me.Button12.TabIndex = 13
Me.Button12.Text = "+"
'
'Button13
'
Me.Button13.Location = New System.Drawing.Point(176, 88)
Me.Button13.Name = "Button13"
Me.Button13.Size = New System.Drawing.Size(24, 24)
Me.Button13.TabIndex = 14
Me.Button13.Text = "-"
'
'Button14
'
Me.Button14.Location = New System.Drawing.Point(176, 120)
Me.Button14.Name = "Button14"
Me.Button14.Size = New System.Drawing.Size(24, 24)
Me.Button14.TabIndex = 15
Me.Button14.Text = "*"
'
'Button15
'
Me.Button15.Location = New System.Drawing.Point(176, 152)
Me.Button15.Name = "Button15"
Me.Button15.Size = New System.Drawing.Size(24, 24)
Me.Button15.TabIndex = 16
Me.Button15.Text = "/"
'
'Button16
'
Me.Button16.Location = New System.Drawing.Point(88, 152)
Me.Button16.Name = "Button16"
Me.Button16.Size = New System.Drawing.Size(72, 24)
Me.Button16.TabIndex = 17
Me.Button16.Text = "计算"
'
'SimpleCalculator
'
Me.AutoScaleBaseSize = New System.Drawing.Size(6, 14)
Me.ClientSize = New System.Drawing.Size(264, 190)
Me.Controls.Add(Me.Button16)
Me.Controls.Add(Me.Button15)
Me.Controls.Add(Me.Button14)
Me.Controls.Add(Me.Button13)
Me.Controls.Add(Me.Button12)
Me.Controls.Add(Me.Button11)
Me.Controls.Add(Me.Button10)
Me.Controls.Add(Me.Button9)
Me.Controls.Add(Me.Button8)
Me.Controls.Add(Me.Button7)
Me.Controls.Add(Me.Button6)
Me.Controls.Add(Me.Button5)
Me.Controls.Add(Me.Button4)
Me.Controls.Add(Me.Button3)
Me.Controls.Add(Me.Button2)
Me.Controls.Add(Me.Button1)
Me.Controls.Add(Me.TextBox1)
Me.Controls.Add(Me.Label1)
Me.Name = "SimpleCalculator"
Me.Text = "简单计算器"
Me.ResumeLayout(False)
End Sub
#End Region
Private Sub TextBox1_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)
End Sub
Private Sub TextBox1_TabStopChanged(ByVal sender As System.Object, ByVal e As System.EventArgs)
End Sub
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
Dim btn As Button '按钮类型的变量
btn = sender '把产生该事件的按钮对象赋值给btn
TextBox1.Text = TextBox1.Text + btn.Text '把该按钮的Text属性值连接到TextBox1中
End Sub
Private Sub Button3_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button3.Click
Dim btn As Button
btn = sender
TextBox1.Text += btn.Text
End Sub
Private Sub Button4_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button4.Click
Dim btn As Button
btn = sender
TextBox1.Text += btn.Text
End Sub
Private Sub Button5_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button5.Click
Dim btn As Button
btn = sender
TextBox1.Text += btn.Text
End Sub
Private Sub Button6_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button6.Click
Dim btn As Button
btn = sender
TextBox1.Text += btn.Text
End Sub
Private Sub Button7_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button7.Click
Dim btn As Button
btn = sender
TextBox1.Text += btn.Text
End Sub
Private Sub Button8_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button8.Click
Dim btn As Button
btn = sender
TextBox1.Text += btn.Text
End Sub
Private Sub Button9_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button9.Click
Dim btn As Button
btn = sender
TextBox1.Text += btn.Text
End Sub
Private Sub Button10_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button10.Click
Dim btn As Button
btn = sender
TextBox1.Text += btn.Text
End Sub
Private Sub Button11_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button11.Click
Dim btn As Button
btn = sender
TextBox1.Text += btn.Text
End Sub
Private Sub Button12_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button12.Click
Dim btn As Button
btn = sender
'在文本框的Text属性后连接一个空格、本按钮的Text属性值和一个空格
TextBox1.Text = TextBox1.Text + " " + btn.Text + " "
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
TextBox1.Text = "" '清空文本框
End Sub
Private Sub Button13_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button13.Click
Dim btn As Button
btn = sender
TextBox1.Text = TextBox1.Text + " " + btn.Text + " "
End Sub
Private Sub Button14_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button14.Click
Dim btn As Button
btn = sender
TextBox1.Text = TextBox1.Text + " " + btn.Text + " "
End Sub
Private Sub Button15_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button15.Click
Dim btn As Button
btn = sender
TextBox1.Text = TextBox1.Text + " " + btn.Text + " "
End Sub
Private Sub Button16_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button16.Click
'发生错误转移到标号“ErrorPro”指定的行去执行错误处理程序
On Error GoTo ErrorPro
Dim r As Decimal '保存计算结果的变量
Dim t As String = TextBox1.Text '用于保存文本框中的算术表达式
Dim space As Integer = t.IndexOf(" ") '搜索空格位置,如果没有空格，返回值为0
'字符串的取子符方法，第二个参数小于0，则将产生错误号为5的异常，即过程参数不正确
Dim s1 As String = t.Substring(0, space) '通过取子串方法获得第一个运算数
Dim op As String = t.Substring(space + 1, 1) '通过取子串方法获得运算符
Dim s2 As String = t.Substring(space + 3) '通过取子串方法获得第二个运算数
Dim arg1, arg2 As Integer
arg1 = Val(s1) : arg2 = Val(s2)
Select Case op
Case "+" : r = arg1 + arg2
Case "-" : r = arg1 - arg2
Case "*" : r = arg1 * arg2
Case "/" : r = arg1 / arg2
Case Else
MsgBox("输入的运算符有误！")
Exit Sub
End Select
TextBox1.Text = CStr(r) '显示结果
Exit Sub '退出过程
ErrorPro: '错误处理程序块
Select Case Err.Number
Case 6 '除数为零时，或运算溢出时的错误号
MsgBox("算术运算溢出！", , "溢出提示")
TextBox1.Focus()
Exit Sub
Case 5 ' Substring过程的参数不符合要求的错误号
MsgBox("必须输入运算符和第二个运算数！", , "运算数少")
Exit Sub
Case Else
'其它情况显示错误号和错误原因
MsgBox("错误号为" Err.Number Chr(10) Chr(13) "错误原因：" Err.Description)
Exit Sub
End Select
End Sub
End Class
一、带窗体的dll创建
1、先新建 类库（testdll），在项目中添加两个窗体form1(主窗体)、form2,为了与后面的调用区分分别命名为fm1,fm2；并在fm1窗体中添加一个按钮用来调用fm2如下图
2、在fm1窗体代码中先引用fm2, 按钮代码调用fm2.如图
3、生成dll,(class1.vb中不需要写任何代码）
二、调用dll
1、新建 一个windows应用程序并添加一个按钮用来调用dll中的窗体，选 择 “项目”－“添加引用”，选择刚才创建的testdll
2、窗体代码中先引用testdll,再定义一个testdll中的fm1对象，最后执行对象的show方法
3、运行结果如下：
