如何：时间在和超时状态上vb.net

Question

'公用Sub updateTextBox（）

s = s + SerialPort1.ReadExisting() 

    If Len(s) > 12 Then 
     Try 

      txtReceived.Text = Microsoft.VisualBasic.Mid(s, 1, 12) 

      strSql = "SELECT * FROM stud WHERE tag = '" & txtReceived.Text & "';" 
      command.CommandText = strSql 
      command.Connection = SQLConnection 
      datapter.SelectCommand = command 
      datardr = command.ExecuteReader 
      Dim img() As Byte 
      If datardr.HasRows Then 
       datardr.Read() 
       img = datardr("picture") 
       Dim ms As New MemoryStream(img) 
       txtFname.Text = datardr("fname").ToString 
       txtLname.Text = datardr("lname").ToString 
       PictureBox1.Image = Image.FromStream(ms) 
       SQLConnection.Close() 
      End If 

      SQLConnection.Open() 
     Catch ex As Exception 
     End Try 
     Try 

      Dim i As Integer 
      Dim newtag As Boolean = True 
      Dim stringfix As String 
      Dim string1 As String 
      Dim string2 As String 

      For i = 0 To (grid.Rows.Count - 1) 
       stringfix = grid.Rows.Item(i).Cells(0).Value 
       string1 = Microsoft.VisualBasic.Mid(stringfix, 1, 10) 
       string2 = Microsoft.VisualBasic.Mid(stringfix, 2, 10) 
       If string1 = string2 Then 
        newtag = False 
        Exit For 
       Else 
        newtag = True 
       End If 
      Next 
      If newtag = True Then 
       Dim dr As Integer 
       dr = grid.Rows.Add() 
       grid.Rows.Item(dr).Cells.Item(0).Value = Microsoft.VisualBasic.Mid(s, 1, 12) 
       grid.Rows.Item(dr).Cells(1).Value = txtFname.Text 
       grid.Rows.Item(dr).Cells(2).Value = txtLname.Text 
       grid.Rows.Item(dr).Cells.Item(3).Value = txtDate.Text + " " + txtTime.Text 
       grid.Rows.Item(dr).Cells.Item(4).Value = "TIME IN" 
      ElseIf newtag = False Then 
       grid.Rows.Item(i).Cells.Item(3).Value = txtDate.Text + " " + txtTime.Text 
       grid.Rows.Item(i).Selected = True 

      End If 


     Catch ex As Exception 
     End Try 
     Dim timeOut As DateTimeOffset = Now.AddMilliseconds(1500) 

     Do 
      Application.DoEvents() 

     Loop Until Now > timeOut 

     s = SerialPort1.ReadExisting() 
     SerialPort1.DiscardOutBuffer() 
     s = String.Empty 
     SerialPort1.DtrEnable = True 
     txtReceived.Text = "" 
     txtFname.Text = "" 
     txtLname.Text = "" 
     PictureBox1.Image = Nothing 

    End If 
End Sub` 

美好的一天！我一直在为我们的论文研究一所学校的基于RFID的日常时间记录。我的问题是如何设置学生的“状态”，当他/她第一次点击RFID卡时，它应该是status = Time-In，当他/她第二次点击它时，状态应该是超时。每个学生每天有一次Time-In和一次Time-out限制。任何想法如何做到这一点？希望你们能得到我指出的内容。

Answer 1

有很多方法可以做到这一点，它几乎太宽泛。一种简单的方法是将两列添加到您的数据库中，并分别在RFID扫描或扫描时递增。然后，当你从你的数据库中选择你可以引用这些列，如果两者都> 1，那么这样的事情。

另一种方法是使用所有学生TAG的数组。你可以在本地跟踪计数器，而不是在数据库中。扫描标签后，所以，正确的...

If inCounter(tag) > 1 or outCounter(tag) > 1 Then 
    msgbox("User has reached the quota.") 
Else 
    inCounter(tag) += 1 
    outCounter(tag) += 1 
End If 

那么你就需要实现每天重置这些计数器一个DateTime类。