Question

请原谅我，自从我使用VB.Net以来已经有一段时间了，所以这可能很容易。

我有一个简单的登录表单，带有文本框，组合框和按钮。组合框绑定到SQL数据库，并显示Users表中的用户名。这个想法是你选择一个名字，输入一个密码，然后你登录到一个新的表格（这部分很棒！）。如果您输入了错误的密码，表单会弹出一条“无效”的消息。由于某些原因，在这个阶段，组合框变得空白。下拉列表现在有空格，名称曾经是空格。在此处键入带有密码的名称会导致对象引用错误。我已经尝试了一切，让组合框重置并搜索网络，但没有任何作用！

（我知道这不是安全登录，这只是将数据绑定到组合框并根据SQL表进行检查的简单示例）。谢谢你的帮助！

enter code here


    Private Sub Button1_Click(sender As Object, e As EventArgs) Handles BTN_Logon.Click  

    Try  
    Dim STR_User As String = Users_nameComboBox.SelectedValue  
    Dim STR_Pwd As String = TB_Pwd.Text  
    STR_User = STR_User.Trim  

    'MessageBox.Show(STR_User & "|" & STR_Pwd)'Used to verify this stage works  
    Dim numRecords As Int16 = UsersTableAdapter.FillByLogin(Me.Login_testDataSet.users, STR_User, STR_Pwd)  
    'MessageBox.Show(numRecords) 'Used to verify this stage works  

     If (numRecords > 0) Then
     Dim DB_User As String = Me.Login_testDataSet.users(0).users_name.Trim
     Dim DB_Pwd As String = Me.Login_testDataSet.users(0).users_pwd.Trim
     'MessageBox.Show(DB_User & "|" & DB_Pwd)'Used to verify this stage works

     If DB_User.Equals(STR_User) And DB_Pwd.Equals(STR_Pwd) Then
     'User is authenticated for application
     'This section works (removed to cleanup code)

     Else
     MessageBox.Show("ERROR" & STR_User & "|" & STR_Pwd) 'Shows that this stage works
     'Need to figure out why combobox doesn't refill, using restart for now
     'Application.Restart()

     End If
     End If

     MessageBox.Show("ERROR" & STR_User & "|" & STR_Pwd) 'Shows that this stage works
     'Need to figure out why combobox doesn't refill, using restart for now
     'Application.Restart()


     Catch ex As Exception
     MessageBox.Show(ex.Message)
     'Need to figure out why combobox doesn't refill, using restart for now
     'Application.Restart()

     End Try

     End Sub









     InitializeComponent

     'Users_nameComboBox

     Me.Users_nameComboBox.DataBindings.Add(New System.Windows.Forms.Binding("Text", 
     Me.UsersBindingSource, "users_name", True))
     Me.Users_nameComboBox.DataBindings.Add(New System.Windows.Forms.Binding("SelectedValue", Me.UsersBindingSource, "users_name", True))
     Me.Users_nameComboBox.DataSource = Me.UsersBindingSource
     Me.Users_nameComboBox.DisplayMember = "users_name"
     Me.Users_nameComboBox.Name = "Users_nameComboBox"
     Me.Users_nameComboBox.ValueMember = "users_name"

VB.NET - 单击按钮时，Combobox变为空白，数据绑定不会更新

0 个答案: