幫Login加上驗證碼

驗證碼一直是避免網頁機器人透過程式的方式自動登入、輸入的一種常見方式


Private Function GenerateCheckCode() As String
    Dim number As Integer
    Dim code As Char
    Dim checkCode As String = String.Empty
    Dim random As System.Random = New Random()
    '要製造出幾個驗證碼
    For i As Integer = 0 To 3
        'number = random.[Next]()
        number = random.Next
        '亂數決定哪一個是數字或字母
        If number Mod 2 = 0 Then
            code = CChar(ChrW(Asc("0") + (number Mod 10)))
        Else
            code = CChar(ChrW(Asc("A") + (number Mod 26)))
        End If
        checkCode += code.ToString()
    Next
    '寫入Cook
    Response.Cookies.Add(New HttpCookie("CheckCode", checkCode))
    Return checkCode
End Function




Private Sub CreateCheckCodeImage(ByVal checkCode As String)
    If checkCode Is Nothing OrElse checkCode.Trim() = [String].Empty Then
        Return
    End If

    'System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 12.5)), 22);
    'System.Drawing.Bitmap image = new System.Drawing.Bitmap((int)Math.Ceiling((checkCode.Length * 20)), 40);
    Dim image As New System.Drawing.Bitmap(100, 30)

    Dim g As Graphics = Graphics.FromImage(image)

    Try
        '生成隨機生成器
        Dim random As New Random()

        '清空圖片背景色
        g.Clear(Color.White)

        '畫圖片的背景噪音線
        For i As Integer = 0 To 24
            Dim x1 As Integer = random.[Next](image.Width)
            Dim x2 As Integer = random.[Next](image.Width)
            Dim y1 As Integer = random.[Next](image.Height)
            Dim y2 As Integer = random.[Next](image.Height)

            g.DrawLine(New Pen(Color.Silver), x1, y1, x2, y2)
        Next

        Dim font As Font = New System.Drawing.Font("Arial", 22, (System.Drawing.FontStyle.Bold Or System.Drawing.FontStyle.Italic))
        Dim brush As New System.Drawing.Drawing2D.LinearGradientBrush(New Rectangle(0, 0, image.Width, image.Height), Color.Blue, Color.DarkRed, 1.2F, True)
        'g.DrawString(checkCode, font, brush, 2, 2);
        g.DrawString(checkCode, font, brush, 2, 2)

        '畫圖片的前景噪音點
        For i As Integer = 0 To 499
            Dim x As Integer = random.[Next](image.Width)
            Dim y As Integer = random.[Next](image.Height)

            image.SetPixel(x, y, Color.FromArgb(random.Next))
        Next

        '畫圖片的邊框線
        g.DrawRectangle(New Pen(Color.Silver), 0, 0, image.Width - 1, image.Height - 1)

        Dim ms As New System.IO.MemoryStream()
        image.Save(ms, System.Drawing.Imaging.ImageFormat.Gif)
        Response.ClearContent()
        Response.ContentType = "image/Gif"
        Response.BinaryWrite(ms.ToArray())
    Finally
        g.Dispose()
        image.Dispose()
    End Try
End Sub



Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    CreateCheckCodeImage(GenerateCheckCode())
End Sub




其他更進一步的資訊請看這