登录失败三次后网络摄像头自动捕获

Question

我正在为我的学校项目做一个应用程序，当用户插入USB驱动器时，登录将要求用户先登录，但如果用户登录失败三次，摄像头将自动捕获。这里的问题是，如何在登录失败三次后自动捕获网络摄像头？

登录代码

Imports System.Data.OleDb

Public Class Form4

Dim attempts As Integer = 0
Private Sub LoginButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles LoginButton.Click
    'Check if username or password is empty
    If PasswordTextBox.Text = "" Or UsernameTextBox.Text = "" Then
        MessageBox.Show("Please fill-up all fields!", "Authentication Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        'Clear all fields
        PasswordTextBox.Text = ""
        UsernameTextBox.Text = ""

        'Focus on Username field
        UsernameTextBox.Focus()
    Else
        ' Connect to DB
        Dim conn As New System.Data.OleDb.OleDbConnection()
        conn.ConnectionString = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=|DataDirectory|\\PutLock.mdb"

        Try
            'Open Database Connection
            conn.Open()

            Dim sql As String = "SELECT * FROM PutLockSignUp WHERE Username='" & UsernameTextBox.Text & "' AND Password = '" & PasswordTextBox.Text & "'"
            Dim cmd As OleDbCommand = New OleDbCommand(sql, conn)

            Dim sqlRead As OleDbDataReader = cmd.ExecuteReader()

            If sqlRead.Read() Then
                MessageBox.Show("Login success", "Database Connection Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
                Form2.Show()
                Me.Hide()

            ElseIf attempts = 3 Then
                ' If user enter wrong username or password
                MessageBox.Show("Maximum count of retries(3),And you'reach the maximum attempts!Try again", "Authentication Failure", MessageBoxButtons.OK, MessageBoxIcon.Error)
                Close()

            Else
                'If user attempts wrong login three times, it will exit automaticlly
                If MessageBox.Show("Username and Password is incorrect! re-enter again you currently have reached attempt " & attempts & " of 3.", "Database Connection Error", MessageBoxButtons.OK, MessageBoxIcon.Error) Then

                    'Clear all fields
                    PasswordTextBox.Text = ""
                    UsernameTextBox.Text = ""

                    'Focus on Username field
                    UsernameTextBox.Focus()
                End If
            End If

        Catch ex As Exception
            MessageBox.Show("Failed to connect to Database", "Database Connection Error", MessageBoxButtons.OK, MessageBoxIcon.Error)
        End Try

    End If
End Sub
Private Sub ExitButton_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ExitButton.Click
    End
End Sub

结束班

网络摄像头代码（我从谷歌发现这个，所以根据我的项目，我仍然没有修改此代码）

Imports System.Runtime.InteropServices

Public Class Form1     继承System.Windows.Forms.Form

地区＆＃34; Windows窗体设计器生成代码＆＃34;

Public Sub New()
    MyBase.New()

    'This call is required by the Windows Form Designer.
    InitializeComponent()

    'Add any initialization after the InitializeComponent() call

End Sub

'Form overrides dispose to clean up the component list.
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

'Required by the Windows Form Designer
Private components As System.ComponentModel.IContainer

'NOTE: The following procedure is required by the Windows Form Designer
'It can be modified using the Windows Form Designer.  
'Do not modify it using the code editor.
Friend WithEvents picCapture As System.Windows.Forms.PictureBox
Friend WithEvents lstDevices As System.Windows.Forms.ListBox
Friend WithEvents lblDevice As System.Windows.Forms.Label
Friend WithEvents btnStart As System.Windows.Forms.Button
Friend WithEvents btnSave As System.Windows.Forms.Button
Friend WithEvents btnStop As System.Windows.Forms.Button
Friend WithEvents sfdImage As System.Windows.Forms.SaveFileDialog
<System.Diagnostics.DebuggerStepThrough()> Private Sub InitializeComponent()
    Me.picCapture = New System.Windows.Forms.PictureBox()
    Me.lstDevices = New System.Windows.Forms.ListBox()
    Me.lblDevice = New System.Windows.Forms.Label()
    Me.btnStart = New System.Windows.Forms.Button()
    Me.btnSave = New System.Windows.Forms.Button()
    Me.btnStop = New System.Windows.Forms.Button()
    Me.sfdImage = New System.Windows.Forms.SaveFileDialog()
    Me.SuspendLayout()
    '
    'picCapture
    '
    Me.picCapture.BorderStyle = System.Windows.Forms.BorderStyle.Fixed3D
    Me.picCapture.Location = New System.Drawing.Point(208, 24)
    Me.picCapture.Name = "picCapture"
    Me.picCapture.Size = New System.Drawing.Size(256, 272)
    Me.picCapture.TabIndex = 0
    Me.picCapture.TabStop = False
    '
    'lstDevices
    '
    Me.lstDevices.Location = New System.Drawing.Point(8, 55)
    Me.lstDevices.Name = "lstDevices"
    Me.lstDevices.Size = New System.Drawing.Size(184, 238)
    Me.lstDevices.TabIndex = 1
    '
    'lblDevice
    '
    Me.lblDevice.Location = New System.Drawing.Point(8, 32)
    Me.lblDevice.Name = "lblDevice"
    Me.lblDevice.Size = New System.Drawing.Size(184, 16)
    Me.lblDevice.TabIndex = 2
    Me.lblDevice.Text = "Available Devices"
    Me.lblDevice.TextAlign = System.Drawing.ContentAlignment.TopCenter
    '
    'btnStart
    '
    Me.btnStart.Location = New System.Drawing.Point(20, 320)
    Me.btnStart.Name = "btnStart"
    Me.btnStart.Size = New System.Drawing.Size(112, 32)
    Me.btnStart.TabIndex = 3
    Me.btnStart.Text = "Start Preview"
    '
    'btnSave
    '
    Me.btnSave.Anchor = (System.Windows.Forms.AnchorStyles.Bottom Or System.Windows.Forms.AnchorStyles.Right)
    Me.btnSave.Location = New System.Drawing.Point(348, 320)
    Me.btnSave.Name = "btnSave"
    Me.btnSave.Size = New System.Drawing.Size(112, 32)
    Me.btnSave.TabIndex = 4
    Me.btnSave.Text = "Save Image"
    '
    'btnStop
    '
    Me.btnStop.Location = New System.Drawing.Point(184, 320)
    Me.btnStop.Name = "btnStop"
    Me.btnStop.Size = New System.Drawing.Size(112, 32)
    Me.btnStop.TabIndex = 5
    Me.btnStop.Text = "Stop Preview"
    '
    'sfdImage
    '
    Me.sfdImage.FileName = "Webcam1"
    Me.sfdImage.Filter = "Bitmap|*.bmp"
    '
    'Form1
    '
    Me.AutoScaleBaseSize = New System.Drawing.Size(5, 13)
    Me.ClientSize = New System.Drawing.Size(480, 382)
    Me.Controls.AddRange(New System.Windows.Forms.Control() {Me.btnStop, Me.btnSave, Me.btnStart, Me.lblDevice, Me.lstDevices, Me.picCapture})
    Me.Name = "Form1"
    Me.StartPosition = System.Windows.Forms.FormStartPosition.CenterScreen
    Me.Text = "Video Capture"
    Me.ResumeLayout(False)

End Sub

结束地区

Const WM_CAP As Short = &H400S

Const WM_CAP_DRIVER_CONNECT As Integer = WM_CAP + 10
Const WM_CAP_DRIVER_DISCONNECT As Integer = WM_CAP + 11
Const WM_CAP_EDIT_COPY As Integer = WM_CAP + 30

Const WM_CAP_SET_PREVIEW As Integer = WM_CAP + 50
Const WM_CAP_SET_PREVIEWRATE As Integer = WM_CAP + 52
Const WM_CAP_SET_SCALE As Integer = WM_CAP + 53
Const WS_CHILD As Integer = &H40000000
Const WS_VISIBLE As Integer = &H10000000
Const SWP_NOMOVE As Short = &H2S
Const SWP_NOSIZE As Short = 1
Const SWP_NOZORDER As Short = &H4S
Const HWND_BOTTOM As Short = 1

Dim iDevice As Integer = 0 ' Current device ID
Dim hHwnd As Integer ' Handle to preview window

Declare Function SendMessage Lib "user32" Alias "SendMessageA" _
    (ByVal hwnd As Integer, ByVal wMsg As Integer, ByVal wParam As Integer, _
    <MarshalAs(UnmanagedType.AsAny)> ByVal lParam As Object) As Integer

Declare Function SetWindowPos Lib "user32" Alias "SetWindowPos" (ByVal hwnd As Integer, _
    ByVal hWndInsertAfter As Integer, ByVal x As Integer, ByVal y As Integer, _
    ByVal cx As Integer, ByVal cy As Integer, ByVal wFlags As Integer) As Integer

Declare Function DestroyWindow Lib "user32" (ByVal hndw As Integer) As Boolean

Declare Function capCreateCaptureWindowA Lib "avicap32.dll" _
    (ByVal lpszWindowName As String, ByVal dwStyle As Integer, _
    ByVal x As Integer, ByVal y As Integer, ByVal nWidth As Integer, _
    ByVal nHeight As Short, ByVal hWndParent As Integer, _
    ByVal nID As Integer) As Integer

Declare Function capGetDriverDescriptionA Lib "avicap32.dll" (ByVal wDriver As Short, _
    ByVal lpszName As String, ByVal cbName As Integer, ByVal lpszVer As String, _
    ByVal cbVer As Integer) As Boolean

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
    LoadDeviceList()
    If lstDevices.Items.Count > 0 Then
        btnStart.Enabled = True
        lstDevices.SelectedIndex = 0
        btnStart.Enabled = True
    Else
        lstDevices.Items.Add("No Capture Device")
        btnStart.Enabled = False
    End If

    btnStop.Enabled = False
    btnSave.Enabled = False
    picCapture.SizeMode = PictureBoxSizeMode.StretchImage
End Sub

Private Sub LoadDeviceList()
    Dim strName As String = Space(100)
    Dim strVer As String = Space(100)
    Dim bReturn As Boolean
    Dim x As Integer = 0

    ' 
    ' Load name of all avialable devices into the lstDevices
    '

    Do
        '
        '   Get Driver name and version
        '
        bReturn = capGetDriverDescriptionA(x, strName, 100, strVer, 100)

        '
        ' If there was a device add device name to the list
        '
        If bReturn Then lstDevices.Items.Add(strName.Trim)
        x += 1
    Loop Until bReturn = False
End Sub

Private Sub OpenPreviewWindow()
    Dim iHeight As Integer = picCapture.Height
    Dim iWidth As Integer = picCapture.Width

    '
    ' Open Preview window in picturebox
    '
    hHwnd = capCreateCaptureWindowA(iDevice, WS_VISIBLE Or WS_CHILD, 0, 0, 640, _
        480, picCapture.Handle.ToInt32, 0)

    '
    ' Connect to device
    '
    If SendMessage(hHwnd, WM_CAP_DRIVER_CONNECT, iDevice, 0) Then
        '
        'Set the preview scale
        '
        SendMessage(hHwnd, WM_CAP_SET_SCALE, True, 0)

        '
        'Set the preview rate in milliseconds
        '
        SendMessage(hHwnd, WM_CAP_SET_PREVIEWRATE, 66, 0)

        '
        'Start previewing the image from the camera
        '
        SendMessage(hHwnd, WM_CAP_SET_PREVIEW, True, 0)

        '
        ' Resize window to fit in picturebox
        '
        SetWindowPos(hHwnd, HWND_BOTTOM, 0, 0, picCapture.Width, picCapture.Height, _
                SWP_NOMOVE Or SWP_NOZORDER)

        btnSave.Enabled = True
        btnStop.Enabled = True
        btnStart.Enabled = False
    Else
        '
        ' Error connecting to device close window
        ' 
        DestroyWindow(hHwnd)

        btnSave.Enabled = False
    End If
End Sub

Private Sub btnStart_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStart.Click
    iDevice = lstDevices.SelectedIndex
    OpenPreviewWindow()
End Sub

Private Sub ClosePreviewWindow()
    '
    ' Disconnect from device
    '
    SendMessage(hHwnd, WM_CAP_DRIVER_DISCONNECT, iDevice, 0)

    '
    ' close window
    '

    DestroyWindow(hHwnd)
End Sub

Private Sub btnStop_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnStop.Click
    ClosePreviewWindow()
    btnSave.Enabled = False
    btnStart.Enabled = True
    btnStop.Enabled = False
End Sub

Private Sub btnSave_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSave.Click
    Dim data As IDataObject
    Dim bmap As Image

    '
    ' Copy image to clipboard
    '
    SendMessage(hHwnd, WM_CAP_EDIT_COPY, 0, 0)

    '
    ' Get image from clipboard and convert it to a bitmap
    '
    data = Clipboard.GetDataObject()
    If data.GetDataPresent(GetType(System.Drawing.Bitmap)) Then
        bmap = CType(data.GetData(GetType(System.Drawing.Bitmap)), Image)
        picCapture.Image = bmap
        ClosePreviewWindow()
        btnSave.Enabled = False
        btnStop.Enabled = False
        btnStart.Enabled = True

        If sfdImage.ShowDialog = DialogResult.OK Then
            bmap.Save(sfdImage.FileName, Imaging.ImageFormat.Bmp)
        End If

    End If
End Sub

Private Sub Form1_Closing(ByVal sender As Object, ByVal e As System.ComponentModel.CancelEventArgs) Handles MyBase.Closing
    If btnStop.Enabled Then
        ClosePreviewWindow()
    End If
End Sub

结束班