Apertura de un cajón conectado a una impresora desde VB.NET

Para abrir un cajón conectado a traves de una impresora con VB.NET sin necesidad de tocar en la configuración de la impresora ni imprimir nada, es necesario enviar un conjunto de caracteres propios de cada impresora sin formato a la misma para que proceda a abrir el cajon, en nuestro caso tenemos una Bixolon srp-350II plus, cuyo codigo es: 27,112,0,50,250, para consultar codigos de otras impresoras: http://keyhut.com/popopen.htm

En el caso de una impresora SEYPOS PRP-085 IIIV el código que debemos usar es 27,112,0,5,5

usaremos la siguiente clase (http://support.microsoft.com/kb/322090),

Imports System.IO
Imports System.Drawing.Printing
Imports System.Runtime.InteropServices

     Private Sub Button1_Click(ByVal sender As System.Object, ByVal e 

As System.EventArgs) Handles Button1.Click
        Dim s As String
        Dim pd As New PrintDialog()

        s = Chr(27) + Chr(112) + Chr(0) + Chr(50) + Chr(250)
        
        pd.PrinterSettings = New PrinterSettings()

        Dim impresora as String = "BIXOLON" 'nombre de la impresora 
        RawPrinterHelper.SendStringToPrinter(BIXOLON, s)
        
    End Sub 

Public Class RawPrinterHelper
    ' Structure and API declarions:
    <StructLayout(LayoutKind.Sequential, CharSet:=CharSet.Unicode)> _
    Structure DOCINFOW
        <MarshalAs(UnmanagedType.LPWStr)> Public pDocName As String
        <MarshalAs(UnmanagedType.LPWStr)> Public pOutputFile As String
        <MarshalAs(UnmanagedType.LPWStr)> Public pDataType As String
    End Structure

    <DllImport("winspool.Drv", EntryPoint:="OpenPrinterW", _
       SetLastError:=True, CharSet:=CharSet.Unicode, _
       ExactSpelling:=True, CallingConvention:=CallingConvention.StdCall)> _
    Public Shared Function OpenPrinter(ByVal src As String, ByRef hPrinter 

As IntPtr, ByVal pd As Long) As Boolean
    End Function
    <DllImport("winspool.Drv", EntryPoint:="ClosePrinter", _
       SetLastError:=True, CharSet:=CharSet.Unicode, _
       ExactSpelling:=True, CallingConvention:=CallingConvention.StdCall)> _
    Public Shared Function ClosePrinter(ByVal hPrinter As IntPtr) As Boolean
    End Function
    <DllImport("winspool.Drv", EntryPoint:="StartDocPrinterW", _
       SetLastError:=True, CharSet:=CharSet.Unicode, _
       ExactSpelling:=True, CallingConvention:=CallingConvention.StdCall)> _
    Public Shared Function StartDocPrinter(ByVal hPrinter As IntPtr, ByVal level 

As Int32, ByRef pDI As DOCINFOW) As Boolean
    End Function
    <DllImport("winspool.Drv", EntryPoint:="EndDocPrinter", _
       SetLastError:=True, CharSet:=CharSet.Unicode, _
       ExactSpelling:=True, CallingConvention:=CallingConvention.StdCall)> _
    Public Shared Function EndDocPrinter(ByVal hPrinter As IntPtr) As Boolean
    End Function
    <DllImport("winspool.Drv", EntryPoint:="StartPagePrinter", _
       SetLastError:=True, CharSet:=CharSet.Unicode, _
       ExactSpelling:=True, CallingConvention:=CallingConvention.StdCall)> _
    Public Shared Function StartPagePrinter(ByVal hPrinter As IntPtr) As Boolean
    End Function
    <DllImport("winspool.Drv", EntryPoint:="EndPagePrinter", _
       SetLastError:=True, CharSet:=CharSet.Unicode, _
       ExactSpelling:=True, CallingConvention:=CallingConvention.StdCall)> _
    Public Shared Function EndPagePrinter(ByVal hPrinter As IntPtr) As Boolean
    End Function
    <DllImport("winspool.Drv", EntryPoint:="WritePrinter", _
       SetLastError:=True, CharSet:=CharSet.Unicode, _
       ExactSpelling:=True, CallingConvention:=CallingConvention.StdCall)> _
    Public Shared Function WritePrinter(ByVal hPrinter As IntPtr, ByVal pBytes 

As IntPtr, ByVal dwCount As Int32, ByRef dwWritten As Int32) As Boolean
    End Function

    ' SendBytesToPrinter()
    ' When the function is given a printer name and an unmanaged array of  
    ' bytes, the function sends those bytes to the print queue.
    ' Returns True on success or False on failure.
    Public Shared Function SendBytesToPrinter(ByVal szPrinterName As String, 

ByVal pBytes As IntPtr, ByVal dwCount As Int32) As Boolean
        Dim hPrinter As IntPtr   ' The printer handle.
        Dim dwError As Int32     ' Last error - in case there was trouble.
        Dim di As DOCINFOW       ' Describes your document (name, port,data type).
        Dim dwWritten As Int32   ' The number of bytes written by WritePrinter().
        Dim bSuccess As Boolean  ' Your success code.

        ' Set up the DOCINFO structure.
        With di
            .pDocName = "My Visual Basic .NET RAW Document"
            .pDataType = "RAW"
        End With
        ' Assume failure unless you specifically succeed.
        bSuccess = False
        If OpenPrinter(szPrinterName, hPrinter, 0) Then
            If StartDocPrinter(hPrinter, 1, di) Then
                If StartPagePrinter(hPrinter) Then
                    ' Write your printer-specific bytes to the printer.
                    bSuccess = WritePrinter(hPrinter, pBytes, dwCount, dwWritten)
                    EndPagePrinter(hPrinter)
                End If
                EndDocPrinter(hPrinter)
            End If
            ClosePrinter(hPrinter)
        End If
        ' If you did not succeed, GetLastError may give more information
        ' about why not.
        If bSuccess = False Then
            dwError = Marshal.GetLastWin32Error()
        End If
        Return bSuccess
    End Function ' SendBytesToPrinter()

    ' SendFileToPrinter()
    ' When the function is given a file name and a printer name, 
    ' the function reads the contents of the file and sends the
    ' contents to the printer.
    ' Presumes that the file contains printer-ready data.
    ' Shows how to use the SendBytesToPrinter function.
    ' Returns True on success or False on failure.
    Public Shared Function SendFileToPrinter(ByVal szPrinterName As String, 

ByVal szFileName As String) As Boolean
        ' Open the file.
        Dim fs As New FileStream(szFileName, FileMode.Open)
        ' Create a BinaryReader on the file.
        Dim br As New BinaryReader(fs)
        ' Dim an array of bytes large enough to hold the file's contents.
        Dim bytes(fs.Length) As Byte
        Dim bSuccess As Boolean
        ' Your unmanaged pointer.
        Dim pUnmanagedBytes As IntPtr

        ' Read the contents of the file into the array.
        bytes = br.ReadBytes(fs.Length)
        ' Allocate some unmanaged memory for those bytes.
        pUnmanagedBytes = Marshal.AllocCoTaskMem(fs.Length)
        ' Copy the managed byte array into the unmanaged array.
        Marshal.Copy(bytes, 0, pUnmanagedBytes, fs.Length)
        ' Send the unmanaged bytes to the printer.
        bSuccess = SendBytesToPrinter(szPrinterName, pUnmanagedBytes, fs.Length)
        ' Free the unmanaged memory that you allocated earlier.
        Marshal.FreeCoTaskMem(pUnmanagedBytes)
        Return bSuccess
    End Function ' SendFileToPrinter()

    ' When the function is given a string and a printer name,
    ' the function sends the string to the printer as raw bytes.
    Public Shared Function SendStringToPrinter(ByVal szPrinterName As String, 

ByVal szString As String)
        Dim pBytes As IntPtr
        Dim dwCount As Int32
        ' How many characters are in the string?
        dwCount = szString.Length()
        ' Assume that the printer is expecting ANSI text, and then convert
        ' the string to ANSI text.
        pBytes = Marshal.StringToCoTaskMemAnsi(szString)
        ' Send the converted ANSI string to the printer.
        SendBytesToPrinter(szPrinterName, pBytes, dwCount)
        Marshal.FreeCoTaskMem(pBytes)
    End Function
End Class