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elapsed.Milliseconds 获取毫秒。
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每100毫秒，do中的代码执行一次，执行时间将大于100毫秒，这是产生误差的地方之一。invoke执行一个方法txt，必须等txt里面的代码运行完毕，方法才能返回，期间占用的时间全是“误差”。
无限循环，且没有退出机制，停不下来。
定时器中处理
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Timer1.Interval = 10 '10毫秒刷新一次
Timer1.Start() '开启定时器
End Sub
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
Label1.Text = Now
End Sub
不对。步骤如下：
添加一个label标签名字label1 用来显示时间
再添加一个timer控件 名字timer1 interval属性=1000 用来计时
窗体添加代码
Dim t As Date '用来记录时间
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As _
System.EventArgs) Handles Timer1.Tick
t = t.AddSeconds(1)
Label1.Text = "登录时间:" t.TimeOfDay.ToString
End Sub
不需要控件就可以，用多线程的方式实现，在窗体上放一个Label和一个button按钮，代码如下：
Imports System.Threading
Public Class Form1
Dim Start As Double
Dim td As Thread
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
Label1.Text = "00:00:00 000"
Button1.Text = "开始"
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
If Button1.Text = "开始" Then
Button1.Text = "结束"
Start = DateAndTime.Timer
td = New Thread(AddressOf fun1)
td.Start()
Else
Button1.Text = "开始"
td.Abort()
End If
End Sub
'定义一个线程
Private Sub fun1()
Dim elapsed As TimeSpan
Dim Dg_txt As New Dg(AddressOf txt)
Do
elapsed = TimeSpan.FromMilliseconds((DateAndTime.Timer - Start) * 1000)
Me.Invoke(Dg_txt, elapsed.ToString, Label1)
Thread.Sleep(100)
Loop
End Sub
'定义一个委托
Delegate Sub Dg(ByVal s As String, ByVal obj As Label)
Sub txt(ByVal s As String, ByVal obj As Label)
obj.Text = s
End Sub
End Class
给你个方法，在软件加载时就判断下当前系统时间（最好是判断远程服务器上的时间，因为当前运行系统的时间他可以手动），判断当前时间是否有超过最后期限。。
是我以前自己设计的用来测试自己点钞速度用的，希望是你需要的
以下是窗体的全部代码
Public Class Form1
Dim StartFlag As Boolean = False
Dim secon As Integer
Dim minut As Integer
'空格
Private Sub Form1_KeyUp(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyEventArgs) Handles Me.KeyUp
If e.KeyCode = Keys.Space Then
If StartFlag Then
StartFlag = False
Timer1.Enabled = False
If Val(Strings.Right(Label1.Text, 2)) 10 And Val(Strings.Right(Label1.Text, 2)) = 0 Then secon = 0 : minut = 0 : Label1.Text = "00:00" : Exit Sub
ListBox1.Items.Add(Label1.Text.ToString)
ListBox1.SelectedItem = ListBox1.Items.Count - 1
Label1.Focus()
Button1.Enabled = True
Label1.Text = "00:00"
secon = 0
minut = 0
Else
StartFlag = True
Timer1.Enabled = True
End If
End If
End Sub
'加载
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
ListBox1.Items.Clear()
Label1.Text = "00:00"
Button1.Enabled = False
secon = 0
minut = 0
Label1.Focus()
End Sub
'清空
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
Button1.Enabled = False
ListBox1.Items.Clear()
Label1.Focus()
End Sub
Private Sub Timer1_Tick(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Timer1.Tick
secon += 1
If secon = 60 Then
secon = 0
minut += 1
End If
Dim seconStr As String = secon
If seconStr.Length = 1 Then seconStr = "0" + seconStr
Dim minutStr As String = minut
If minutStr.Length = 1 Then minutStr = "0" + minutStr
Label1.Text = minutStr + ":" + seconStr
Label1.Focus()
End Sub
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Dim SeconSun As Integer
If ListBox1.Items.Count 0 Then
For i = 0 To ListBox1.Items.Count - 1
Dim TemStr As String = ListBox1.Items.Item(i).ToString
Dim TemInt1 As Integer = Val(Strings.Right(TemStr, 2))
Dim TemInt2 As Integer = Val(Strings.Left(TemStr, 2))
Debug.Print(TemInt1.ToString)
Debug.Print(TemInt2.ToString)
SeconSun += TemInt1 + TemInt2 * 60
Debug.Print(SeconSun.ToString)
Next
TextBox1.Text = (SeconSun / ListBox1.Items.Count).ToString + "秒"
End If
Label1.Focus()
End Sub
End Class