[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]

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[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

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 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