[一个登录窗体的完整范例，包括登录，密码更改，输入错误三次退出] 2004-12-31
运行效果如下：（请参考设置窗体布局）
（登录主窗体效果） （修改密码窗体效果）
控件名称说明：‘cboUser就是图中的combobox控件
Public Class frmLogin
Inherits System.Windows.Forms.Form
Public Sub New()
MyBase.New()
'该调用是 Windows 窗体设计器所必需的。
InitializeComponent()
'在 InitializeComponent() 调用之后添加任何初始化
' 填充数据，并定义datatable的主键
‘ 请根据情况选择连接方式和数据库类型
Dim constr As String = "server=localhost;uid=sa;pwd=;database=sheeronerp"
Dim str As String = "SELECT id,name,password,power FROM Login ORDER BY name"
Dim sqlcon As New SqlClient.SqlConnection()
Dim sqldpr As New SqlClient.SqlDataAdapter(str, sqlcon)
Try
sqlcon.ConnectionString = constr
sqlcon.Open() ‘其实没有sqlcon.open()和sqlcon.close()语句也没关系，适配器会自动进行
sqldpr.Fill(table)
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
sqlcon.Close()
End Try
‘设置主键，目的是使用find()方法
table.PrimaryKey = New DataColumn() {table.Columns("id")}
Me.cboUser.DataSource = table
Me.cboUser.DisplayMember = "name"
Me.cboUser.ValueMember = "id"
'初始时不选中任何项
Me.cboUser.SelectedIndex = -1
Me.cboUser.Focus()
End Sub
'窗体重写处置以清理组件列表。
Protected Overloads Overrides Sub Dispose(ByVal disposing As Boolean)
If disposing Then
If Not (components Is Nothing) Then
components.Dispose()
End If
End If
MyBase.Dispose(disposing)
End Sub
Dim count As Integer = 0 '登录出错记数器,登录时输入3次均错误则自动退出
Dim table As New DataTable()
‘确定按钮代码
Private Sub btnok_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnok.Click
If Me.cboUser.Text = "" Then
MessageBox.Show("请选择用户名称！")
cboUser.Focus()
Return
End If
If Me.txtPwd.Text = "" Then
MessageBox.Show("请输入用户密码！")
txtPwd.Focus()
Exit Sub
End If
'获取combobox 中选择的用户id,检索这条记录
Dim getrows As DataRow = table.Rows.Find(cboUser.SelectedValue)
If Not (getrows Is Nothing) Then
Dim password As String = Trim(getrows("password"))
If password.Trim(" ") = txtPwd.Text.Trim(" ") Then
UserId = cboUser.SelectedIndex
UserName = cboUser.Text
UserPower = getrows.Item("power")
Me.Dispose()
'???????????????????????
'显示主窗体
Dim newform1 As New frmorder()
newform1.ShowDialog()
Else
'输入不正确的话，则判断输入次数，3次错误则退出
If count = 2 Then
MessageBox.Show("密码错误输入3次，即将退出系统！")
End
Else
MessageBox.Show("密码有误，请重新输入！")
count = count + 1
Me.txtPwd.Focus()
Me.txtPwd.SelectAll()
Return
End If
End If
End If
End Sub
‘取消按钮代码
Private Sub btncancle_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btncancle.Click
End
End Sub
‘更改密码按钮代码
Private Sub btnupdate_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnupdate.Click
If Me.cboUser.Text = "" Then
MessageBox.Show("请输入或选择登录帐户！")
cboUser.Focus()
Return
End If
Dim findrows As DataRow
findrows = table.Rows.Find(cboUser.SelectedValue)
'获取所选id对应的密码
Dim strpassword As String = Trim(findrows("password"))
'定义窗体实例，并传递参数过去
Dim formnew As New frmUpdatePWD(cboUser.SelectedValue, strpassword)
formnew.ShowDialog()
End Sub
Private Sub cboUser_KeyPress(ByVal sender As Object, ByVal e As System.Windows.Forms.KeyPressEventArgs) Handles cboUser.KeyPress
‘按下回车键响应TAB键操作
If e.KeyChar = Chr(13) Then
e.Handled = True
SendKeys.Send("{TAB}")
End If
End Sub
End Class
‘----------------------------------------------------------------------------
Public Class frmUpdatePWD
Inherits System.Windows.Forms.Form
' 重载构造函数 主要是为了传递过来用户ID和密码两个属性
Public Sub New(ByVal userid As Integer, ByVal password As String)
MyBase.New()
'该调用是 Windows 窗体设计器所必需的。
InitializeComponent()
'在 InitializeComponent() 调用之后添加任何初始化
Me.m_id = userid
Me.m_password = password
txtNew.Enabled = False
txtNew2.Enabled = False
btnOk.Enabled = False
End Sub
Private m_id As Integer '记录用户ID
Private m_password As String '记录用户密码(正确的原密码)
Public Property getid() As Integer
Get
Return m_id
End Get
Set(ByVal Value As Integer)
m_id = Value
End Set
End Property
Public Property getpassword() As String
Get
Return m_password
End Get
Set(ByVal Value As String)
m_password = Value
End Set
End Property
Private Sub btnok_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnOk.Click
Dim constr As String = "server=localhost;uid=sa;pwd=;database=sheeronerp"
Dim sqlcon As New SqlClient.SqlConnection()
Try
sqlcon.ConnectionString = constr
Catch ex As Exception
MessageBox.Show(ex.Message)
End Try
'定义sql语句，直接进行修改
Dim str As String = "UPDATE Login SET password='" + txtNew.Text + "'" + " where id=" + CStr(Me.getid)
Dim cmd As New SqlClient.SqlCommand(str, sqlcon)
Dim rowcount As Integer
Try
sqlcon.Open()
rowcount = cmd.ExecuteNonQuery
If rowcount <> 1 Then
MessageBox.Show("密码更新失败！")
Exit Sub
Else
MessageBox.Show("密码更新成功，请记住您的新密码！")
End If
Catch ex As Exception
MessageBox.Show(ex.Message)
Finally
sqlcon.Close()
End Try
End Sub
Private Sub txtold_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtOld.TextChanged
If txtOld.Text = Me.getpassword Then
txtNew.Enabled = True
txtNew2.Enabled = True
Else
txtNew.Enabled = False
txtNew2.Enabled = False
End If
End Sub
Private Sub txtnew2_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles txtNew2.TextChanged
If txtNew2.Text = txtNew.Text Then
btnOk.Enabled = True
Else
btnOk.Enabled = False
End If
End Sub
End Class
‘-----------------------------------------------------------------------------------------------
写在结束的话：
[呵呵，我也是一个VB.NET的新手，在学习和使用它的时候遇到了很多困难，在网上找了很多文章来看，得到了不少帮助，现在也来写些文章，希望可以给那些和我一样的初学者以些许帮助。更希望，“高手们”不吝赐教，多多帮忙。如有转载，请注明作者和联系信息。谢谢！
--作者：长春（何秋蔑）
--email:heqiumie@163.net
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--向那些热心帮助过我的相识和不相识的朋友们致敬！
--2004/12/31