Nello sviluppo di applicazioni si può avere la necessità di dover inviare dei dati direttamente alla stampante.
Un caso di esempio può essere rappresentato dalla stampa di un file di testo attraverso una stampante che utilizza il driver Geneirc/text di Windows; in questo caso può capitare di ottenere una stampa con l'aggiunta di caratteri imprevisti nell'intestazione o in fondo al documento. Mentre in alcuni casi questo problema è irrilevante, in altri può compromettere il funzionamento di applicazioni.
Il seguente codice ci aiuterà a risolvere il porblema.
Innanzitutto dovremo aggiungere questi riferimenti:
Imports System.io
Imports System.Drawing.Printing
Imports System.Runtime.InteropServices
poi, dopo aver creato un pulsante sulla Form, assiociamo all'evento Click del pulsante il codice
Dim tipo As String
Dim stampante As String = "generica"
Dim printFont As System.Drawing.Font
tipo = Stampante.Chars(0)
If tipo = ">" Then
Dim st As String = Stampante.Substring(1, Stampante.Length - 1)
FileCopy("c:\prova.txt", st)
Else
printFont = New System.Drawing.Font("Arial", 10)
Dim pd As New System.Drawing.Printing.PrintDocument
pd.PrinterSettings.PrinterName = stampante
If pd.PrinterSettings.IsValid Then
RawPrinterHelper.SendFileToPrinter(stampante, "c:\prova.txt")
Else
MessageBox.Show("Stampante non trovata.")
End If
End If
dove Generica è il nome della stampante, mentre prova.txt è il nome del file che invieremo alla stampante.
Ora non rimarra che aggiungere la classe RawPrinterHelper al nostro progetto scrivendo il seguente codice:
Public Class RawPrinterHelper
< 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)> _
Private Shared Function OpenPrinter(ByVal pPrinterName As String, _
ByRef hPrinter As IntPtr, ByVal pd As Integer) As Boolean
End Function
' Nel caso si utilizzi Visual Basic 2003 la funzione OpenPrinter corretta sarà la seguente:
' < 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
' Nel caso si utilizzi Visual Basic 2005 la funzione OpenPrinter corretta sarà la seguente:
< 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
' Invio i dati alla stampante
Public Shared Function SendBytesToPrinter(ByVal szPrinterName As String, ByVal pBytes As IntPtr, ByVal dwCount As Int32) As Boolean
Dim hPrinter As IntPtr
Dim dwError As Int32
Dim di As DOCINFOW
Dim dwWritten As Int32
Dim bSuccess As Boolean
With di
.pDocName = "My Visual Basic .NET RAW Document"
.pDataType = "RAW"
End With
bSuccess = False
If OpenPrinter(szPrinterName, hPrinter, 0) Then
If StartDocPrinter(hPrinter, 1, di) Then
If StartPagePrinter(hPrinter) Then
bSuccess = WritePrinter(hPrinter, pBytes, dwCount, dwWritten)
EndPagePrinter(hPrinter)
End If
EndDocPrinter(hPrinter)
End If
ClosePrinter(hPrinter)
End If
If bSuccess = False Then
dwError = Marshal.GetLastWin32Error()
End If
Return bSuccess
End Function
Public Shared Function SendFileToPrinter(ByVal szPrinterName As String, ByVal szFileName As String) As Boolean
Dim fs As New FileStream(szFileName, FileMode.Open)
Dim br As New BinaryReader(fs)
Dim bytes(fs.Length) As Byte
Dim bSuccess As Boolean
Dim pUnmanagedBytes As IntPtr
bytes = br.ReadBytes(fs.Length)
pUnmanagedBytes = Marshal.AllocCoTaskMem(fs.Length)
Marshal.Copy(bytes, 0, pUnmanagedBytes, fs.Length)
bSuccess = SendBytesToPrinter(szPrinterName, pUnmanagedBytes, fs.Length)
Marshal.FreeCoTaskMem(pUnmanagedBytes)
Return bSuccess
End Function
Public Shared Function SendStringToPrinter(ByVal szPrinterName As String, ByVal szString As String)
Dim pBytes As IntPtr
Dim dwCount As Int32
dwCount = szString.Length()
pBytes = Marshal.StringToCoTaskMemAnsi(szString)
SendBytesToPrinter(szPrinterName, pBytes, dwCount)
Marshal.FreeCoTaskMem(pBytes)
End Function
End Class
Ora, dopo aver avviato il porgramma, basterà premere sul pulsante e il contenuto del file verrà inviato direttamente alla stampante.