多用戶登錄表單

Question

我按照this guide，結果發現，如果我的用戶名和密碼都錯了，它會拋出一個運行時錯誤：

"6" Overflow error.

不過，我已經使用下面的代碼嘗試：

ElseIf Username <> u And Password <> p Then 
    MsgBox "Username & Password not matched", vbCritical + vbOKCancel 
Exit Do 

我試過使用此代碼，但即使我的用戶名和密碼匹配它仍然會拋出下面的MsgBox。

這裏

Private Sub LoginButton_Click() 
    Application.ScreenUpdating = False 
    Dim Username As String 
    Dim Password As String 
    Dim i As Integer 
    Dim j As Integer 
    Dim u As String 
    Dim p As String 
    If Trim(TextBox1.Text) = "" And Trim(TextBox2.Text) = "" Then 
    MsgBox "Enter username and password.", vbOKOnly 
    ElseIf Trim(TextBox1.Text) = "" Then 
    MsgBox "Enter the username ", vbOKOnly 
    ElseIf Trim(TextBox2.Text) = "" Then 
    MsgBox "Enter the Password ", vbOKOnly 
    Else 
    Username = Trim(TextBox1.Text) 
    Password = Trim(TextBox2.Text) 
    i = 1 
    Do While Cells(1, 1).Value <> "" 
    j = 1 
    u = Cells(i, j).Value 
    j = j + 1 
    p = Cells(i, j).Value 
If Username = u And Password = p And Cells(i, 3).Value = "fail" Then 
    MsgBox "Your Account temporarily locked", vbCritical 
Exit Do 

ElseIf Username = u And Password = p Then 
    Call clr 
    'LoginFlag = True 
    Unload Me 
    MsgBox ("Welcome " + u + ", :)") 
Exit Do 

ElseIf Username <> u And Password = p Then 
    MsgBox "Username not matched", vbCritical + vbOKCancel 
Exit Do 
ElseIf Username = u And Password <> p Then 
If Cells(i, 3).Value = "fail" Then 
    MsgBox "Your account is blocked", vbCritical + vbOKCancel 
Exit Do 

ElseIf Cells(i, 4).Value < 2 Then 
    MsgBox "Invalid password", vbCritical 
    Cells(i, 4).Value = Cells(i, 4) + 1 
Exit Do 
Else 
    Cells(i, 4).Value = Cells(i, 4) + 1 
    Cells(i, 3).Value = "fail" 
    'Cells(i, 2).Value = "" 
    Cells(i, 2).Interior.ColorIndex = 3 
Exit Do 
End If 

ElseIf Username <> u And Password <> p Then 
    MsgBox "Username & Password not match", vbCritical + vbOKCancel 
Exit Do 

Else 
    i = i + 1 
End If 
Loop 
End If 
    Application.ScreenUpdating = True 
End Sub 

Answer 1

我認爲有以下可以更好地工作：

Private Sub LoginButton_Click() 
    Application.ScreenUpdating = False 
    Dim Username As String 
    Dim Password As String 
    'Use a variable to flag whether the userid is valid or not 
    Dim useridValid As Boolean 
    Dim i As Integer 
    'Dim j As Integer 
    Dim u As String 
    Dim p As String 
    If Trim(TextBox1.Text) = "" And Trim(TextBox2.Text) = "" Then 
     MsgBox "Enter username and password.", vbOKOnly 
    ElseIf Trim(TextBox1.Text) = "" Then 
     MsgBox "Enter the username ", vbOKOnly 
    ElseIf Trim(TextBox2.Text) = "" Then 
     MsgBox "Enter the Password ", vbOKOnly 
    Else 
     Username = Trim(TextBox1.Text) 
     Password = Trim(TextBox2.Text) 
     useridValid = False 
     i = 1 
     'Don't perform a loop which is dependent on a fixed cell that 
     'isn't updated within the loop 
     'Use a variable row counter instead 
     'Do While Cells(1, 1).Value <> "" 
     Do While Cells(i, 1).Value <> "" 
      'There is no point in having a variable simply to specify a 
      'column that doesn't change 
      'j = 1 
      u = Cells(i, "A").Value 
      'j = j + 1 
      p = Cells(i, "B").Value 
      'Only perform tests once a valid username has been found 
      If Username = u Then 
       'Flag that we have found the userid 
       useridValid = True 
       If Cells(i, "C").Value = "fail" Then 
        'Too many login attempts 
        MsgBox "Your Account temporarily locked", vbCritical 
       ElseIf Password = p Then 
        'Clear invalid attempts count 
        Cells(i, 4).Value = 0 
        Cells(i, 3).Value = "" 

        Call clr 
        Unload Me 
        MsgBox ("Welcome " + u + ", :)") 
       Else 
        'Invalid password 
        'Increment failed attempts counter 
        Cells(i, 4).Value = Cells(i, 4) + 1 
        'Lock account on 3rd failed password 
        If Cells(i, 4).Value > 2 Then 
         'lock the account 
         Cells(i, 3).Value = "fail" 
         'Cells(i, 2).Value = "" 
         Cells(i, 2).Interior.ColorIndex = 3 
         'Tell the user that password was invalid and now locked 
         MsgBox "Invalid password - account locked", vbCritical 
        Else 
         'Tell the user that password was invalid 
         MsgBox "Invalid password", vbCritical 
        End If 
       End If 
       'Don't check any further usernames 
       Exit Do 
      End If 
      i = i + 1 
     Loop 
     'If the flag saying that we found the userid isn't set, display 
     'a message 
     If Not useridValid Then 
      MsgBox "Username not matched", vbCritical + vbOKCancel 
     End If 
    End If 
    Application.ScreenUpdating = True 
End Sub 

注：這絕對是一個壞主意，一個工作表中持有明文密碼。人們很容易獲得整個列表。

Answer 2

因爲代碼沒有被照顧的情況下當兩個Username以及Password失敗，這是一個無限循環Do While Cells(1, 1).Value <> ""您收到此錯誤代碼。因此，數據類型設置爲Integer的計數器i的值不斷增加，一旦超過32,767的限制，它將生成Overflow錯誤。

在支持我的上述論斷，考慮在你的代碼中的這些參數：

條件1 - 登錄狀態爲 「失敗」：

If Username = u And Password = p And Cells(i, 3).Value = "fail" Then 

條件2 - 既Username和Password匹配：

ElseIf Username = u And Password = p Then 

條件3 - Username與之不匹配：

ElseIf Username <> u And Password = p Then 

條件4 - Password沒有匹配：

ElseIf Username = u And Password <> p Then 

解決方案：

我們需要將無限循環改爲有限，即一旦它到達的空白單元格，將停止 - 所以它會像Do While Cells(i, 1).Value <> ""。

此外，我們可以在上面添加Username和Password失敗的情況，您已經正確識別，但我懷疑，如果它仍然出現錯誤，它需要放在正確的位置，也就是循環後Do While。

另一個小的修正 - i應該從2開始，而不是1，因爲我們要從2 ^nd行查找。

因此，讓我們把它放在一起：

Private Sub LoginButton_Click() 
    Application.ScreenUpdating = False 
    Dim Username As String, Password As String, i As Integer, j As Integer, u As String, p As String 
    If Trim(TextBox1.Text) = "" And Trim(TextBox2.Text) = "" Then 
     MsgBox "Enter username and password.", vbOKOnly 
    ElseIf Trim(TextBox1.Text) = "" Then 
     MsgBox "Enter the username ", vbOKOnly 
    ElseIf Trim(TextBox2.Text) = "" Then 
     MsgBox "Enter the Password ", vbOKOnly 
    Else 
     Username = Trim(TextBox1.Text) 
     Password = Trim(TextBox2.Text) 
     i = 2 
     Do While Cells(i, 1).Value <> "" 
      j = 1 
      u = Cells(i, j).Value 
      j = j + 1 
      p = Cells(i, j).Value 
      If Username = u And Password = p And Cells(i, 3).Value = "fail" Then 
       MsgBox "Your Account temporarily locked", vbCritical 
      Exit Do 
      ElseIf Username = u And Password = p Then 
       Call clr 
       'LoginFlag = True 
       Unload Me 
       MsgBox ("Welcome " + u + ", :)") 
       Exit Do 
      ElseIf Username <> u And Password = p Then 
       MsgBox "Username not matched", vbCritical + vbOKCancel 
       Exit Do 
      ElseIf Username = u And Password <> p Then 
       If Cells(i, 3).Value = "fail" Then 
        MsgBox "Your account is blocked", vbCritical + vbOKCancel 
        Exit Do 
       ElseIf Cells(i, 4).Value < 2 Then 
        MsgBox "Invalid password", vbCritical 
        Cells(i, 4).Value = Cells(i, 4) + 1 
        Exit Do 
       Else 
        Cells(i, 4).Value = Cells(i, 4) + 1 
        Cells(i, 3).Value = "fail" 
        'Cells(i, 2).Value = "" 
        Cells(i, 2).Interior.ColorIndex = 3 
        Exit Do 
       End If 
      Else 
       i = i + 1 
      End If 
     Loop 
     If Username <> u And Password <> p Then MsgBox "Username & Password not match", vbCritical + vbOKCancel 
    End If 
    Application.ScreenUpdating = True 
End Sub 

但請記住，這僅僅是一個演示。實際上，消息警報不應該清楚地說明錯誤是在用戶標識，密碼還是兩者上。