VB.Net中使用Access数据库的登录表单不起作用

Question

我很确定这段代码过去允许我使用下面的SQL语句登录，但现在它不允许了，只是清除了文本框。当用户名和密码与数据库中的不匹配时，我希望显示一条错误消息。与另一个标签一样，这是一个可见性需要更改的标签。我有这个代码：

Try
UserType = GetUserType(txtUsername.Text.Trim, txtPass.Text.Trim)
Catch ex As Exception
lblErrorMatch.Visible = True
End Try

但是，这只是在细节不匹配时清除文本框。

Imports System.Data.OleDb
Public Class frmLogin
Private DBCmd As New OleDbCommand
Private ConStr As String = "Provider=Microsoft.ACE.OLEDB.12.0;" &
"Data Source=|DataDirectory|NewHotel.mdb;"
Private Sub btnLogIn_Click(sender As Object, e As EventArgs) Handles btnLogIn.Click
Dim UserType As Object
'Distinguishing beetween different users
If UserType Is Nothing Then
lblErrorEmpty.Visible = True
ElseIf UserType.ToString = "MANAGER" Then
frmHomeManager.Show()
ElseIf UserType.ToString = "RECEPTIONIST" Then
frmHomeReceptionist.Show()
End If
'Username and password not matching error message

'Empty textboxes error message
If txtUsername.Text = "" OrElse txtPass.Text = "" Then lblErrorEmpty.Visible = True : Exit Sub
txtUsername.Clear()
txtPass.Clear()
chkShowPass.Checked = False
End Sub
Private Function GetUserType(Username As String, Pass As String) As Object
Dim UserType As Object
'Pull username and password from the database to check against the entered login details
Using DBCon As New OleDb.OleDbConnection(ConStr),
DBCmd As New OleDbCommand("SELECT UserType FROM tblEmployeeLogin WHERE [Username] = @Username AND [Pass] = @Pass", DBCon)
DBCmd.Parameters.Add("@Username", OleDbType.VarChar).Value = Username
DBCmd.Parameters.Add("@Pass", OleDbType.VarChar).Value = Pass
DBCon.Open()
UserType = DBCmd.ExecuteScalar.ToString
End Using
Return UserType
End Function
Private Sub chkShowPass_CheckedChanged(sender As Object, e As EventArgs) Handles chkShowPass.CheckedChanged
'Show password when checkbox is checked
If chkShowPass.Checked = True Then
txtPass.PasswordChar = Nothing
ElseIf chkShowPass.Checked = False Then
txtPass.PasswordChar = "*"
End If
End Sub
Private Sub txtUsername_TextChanged(sender As Object, e As EventArgs) Handles txtUsername.TextChanged, txtPass.TextChanged
'Make error message disappear after text is enetered into either of the text boxes
lblErrorEmpty.Visible = False
lblErrorMatch.Visible = False
End Sub
Private Sub lnkClear_LinkClicked(sender As Object, e As LinkLabelLinkClickedEventArgs) Handles lnkClear.LinkClicked
txtUsername.Clear()
txtPass.Clear()
chkShowPass.Checked = False
End Sub
Private Sub btnClose_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnClose.Click
'Close the form down which stops the application
Me.Close()
End Sub
End Class

感谢您抽出时间：(

Answer 1

我最近进行了一次登录，就像你试图做的那样。希望你能理解这段代码，它会有所帮助：

Dim CMD As OleDbCommand = New OleDbCommand("SELECT * FROM Staff WHERE Login = '" & ID & "'", Con)
Dim user As String
Try
Con.Open()
Dim sdr As OleDbDataReader = CMD.ExecuteReader()
If (sdr.Read() = True) Then
user = sdr("Login")
MessageBox.Show("Login Successful!")
ActiveUser.IsLoggedIn = True
Else
MessageBox.Show("Invalid username or password!")
End If
Catch ex As Exception
MsgBox(ex.Message)
Finally
Con.Close()
End Try