Question

如果输入的电子邮件/密码不正确，我希望显示一个消息框。我正在使用else语句，但如果登录不正确，则不显示该消息。

MyConn = New OleDbConnection 
        MyConn.ConnectionString = connString 
        MyConn.Open() 

        str1 = ("SELECT * FROM [UserData] WHERE [Username] = '" & TxtUserName.Text & "' AND [Password] = '" & TxtPassword.Text & "'") 
        Dim cmd1 As OleDbCommand = New OleDbCommand(str1, MyConn)
        dr = cmd1.ExecuteReader 
        While dr.Read() 
            userFound = True 
            TxtPassword.Text = dr("Username").ToString 
            TxtUserName.Text = dr("Password").ToString 
            FirstNameToPass = dr("First Name").ToString 
            LastNameToPass = dr("Last Name").ToString 
            AddressToPass = dr("Address").ToString 
            EmailToPass = dr("Email").ToString 
            If userFound = True Then
                UserAccountView.Show() 
                Me.Hide() 
                TxtPassword.Clear() 
                TxtUserName.Clear() 
            Else
                MsgBox("Login is incorrect")
            End If
        End While
        MyConn.Close() 
    End If

Answer 1

如果row存在，则

reader.Read()返回true;如果resultset为空，则返回false。在您的情况下，如果没有此类用户（使用提供的用户名和密码），程序将无法进入循环，并且无法访问If userFound = True阻止。

所以，跳过while循环并写下这样的东西：

If dr.HasRows
    dr.Read()
    TxtPassword.Text = dr("Username").ToString 
    TxtUserName.Text = dr("Password").ToString 
    FirstNameToPass = dr("First Name").ToString 
    LastNameToPass = dr("Last Name").ToString 
    AddressToPass = dr("Address").ToString 
    EmailToPass = dr("Email").ToString 

    UserAccountView.Show() 
    Me.Hide() 
    TxtPassword.Clear() 
    TxtUserName.Clear() 
Else
    MsgBox("Login is incorrect")
End If

修改

还有一件事：永远不要连接字符串来制作命令文本。相反，使用参数：

str1 = ("SELECT * FROM [UserData] WHERE [Username] = ? AND [Password] = ?") Dim cmd1 As OleDbCommand = New OleDbCommand(str1, MyConn) cmd1.Parameters.Add(New OleDbParameter("Username", CType(TxtUserName.Text, String))) cmd1.Parameters.Add(New OleDbParameter("Password", CType(TxtPassword.Text, String)))

如果错误地输入了电子邮件/密码，则无法显示错误消息

1 个答案: