Question

我的问题是我在我的程序中使用数据库中的数据时遇到了困难。我的意思是如何获取数据库中的用户名并将其用作VB中的变量？这是我的代码：

Imports System.Data.OleDb

Public Class LogIn
Dim provider As String
Dim dataFile As String
Dim connString As String
Dim myConnection As OleDbConnection = New OleDbConnection

'Default User Name and Password is set to "admin". 
Public userName As String = "admin"
Public userPassword As String = "admin"
Public btnClick As Integer = 0

Private Sub LogIn_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    txtPassword.PasswordChar = "*"
End Sub


Private Sub btnLogIn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLogIn.Click
    provider = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source ="

    'Change the following to your access database location

    dataFile = "C:\Users\Show Man\Desktop\LogIn1.accdb"

    connString = provider & dataFile

    myConnection.ConnectionString = connString



    'the query:

    Dim cmd As OleDbCommand = New OleDbCommand("SELECT * FROM [Users] WHERE [UserName] = '" & txtUserName.Text & "' AND [Password] = '" & txtPassword.Text & "'", myConnection)



    ' the following variable is hold true if user is found, and false if user is not found 

    Dim userFound As Boolean = False


    myConnection.Open()
    'if found:

    Dim dr As OleDbDataReader = cmd.ExecuteReader
    While dr.Read

        userFound = True 

    End While

    'Make Password not visible to the user. It only shows "*" and no text
    'If no User Name and Password entered, access is not granted
    txtPassword.PasswordChar = "*"
    If txtPassword.Text = "" Or txtUserName.Text = "" Then Exit Sub

    'If correct User Name and Password enterd, access is granted and opens the Student Form

    If txtUserName.Text = userName And txtPassword.Text = userPassword Then
        Me.Hide()
        btnClick = 0
        StudentDatabase.Show()

    Else
        'If wrong User Name or Password enterd a warning message box opens
        MsgBox("Invalid Username or Password", MsgBoxStyle.Exclamation, "Log In")
        txtPassword.Focus()
        btnClick += 1

    End If

    If btnClick = 3 Then
        MsgBox("3 Unsucessful attempts! Please Try Again Later!", vbCritical, "Locked Out")
        Me.Close()
    End If
End Sub

如何在数据库中使用UserName来测试密码是否正确，然后授予访问权限。

Answer 1

Imports System.Data.OleDb

Public Class LogIn
Dim connString As String
Dim myConnection As OleDbConnection = New OleDbConnection
Dim cmd As New OleDbCommand
Dim dr As OleDbDataReader

'Default User Name and Password is set to "admin". 
Public userName As String = "admin"
Public userPassword As String = "admin"
Public btnClick As Integer = 0

Private Sub LogIn_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    txtPassword.PasswordChar = "*"
End Sub


Private Sub btnLogIn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLogIn.Click
    'provider = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source ="
    'Change the following to your access database location
    'dataFile = "C:\Users\Show Man\Desktop\LogIn1.accdb"
    'Instead of doing that (above), you can copy and paste the database file in the folder the projects form are located.

    connString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source=" & IO.Path.Combine(My.Application.Info.DirectoryPath, "dbSample.accdb") & ";Persist Security Info=False;Jet OLEDB:Database Password=" & userPassword & ""
    'This password protects the database (the .accdb file is an MSAccess file, right? You can set a password to it so that not anyone can open it.)
    myConnection.ConnectionString = connString

    'the query:
 myConnection.Open()
 Dim cmd As OleDbCommand = New OleDbCommand("SELECT * FROM [Users] WHERE [UserName] = '" & txtUserName.Text & "' AND [Password] = '" & txtPassword.Text & "'", myConnection)

    dr = cmd.ExecuteReader
    If dr.Read Then
       'Login Success!
       btnCLick = 0
       Me.Hide()
       DirectForm.Show()
    Elseif Not dr.Read Then
       MsgBox("Invalid Username or Password", MsgBoxStyle.Exclamation, "Log In")
       txtPassword.Focus()
       btnClick += 1
       If btnClick = 3 Then
            MsgBox("3 Unsucessful attempts! Please Try Again Later!", vbCritical, "Locked Out")
            Me.Close()
           End If
        End If
myConnection.Close()
End Sub

在VB.Net中使用数据库中的数据

1 个答案: