请问如何获得打印机的HDC

// PrintDirect.cs
// Shows how to write data directly to the printer using Win32 API's
// Written 17th October 2002 By J O'Donnell - [email protected]
// Adapted from Microsoft Support article Q298141
// This code assumes you have a printer at share \\192.168.1.101\hpl
// This code sends Hewlett Packard PCL5 codes to the printer to print
// out a rectangle in the middle of the page.   using System;
using System.Text;
using System.Runtime.InteropServices;   [StructLayout( LayoutKind.Sequential)]
public struct DOCINFO 
{
            [MarshalAs(UnmanagedType.LPWStr)]public string pDocName;
            [MarshalAs(UnmanagedType.LPWStr)]public string pOutputFile; 
            [MarshalAs(UnmanagedType.LPWStr)]public string pDataType;
} public class PrintDirect
{
            [ DllImport( "winspool.drv",CharSet=CharSet.Unicode,ExactSpelling=false,
            CallingConvention=CallingConvention.StdCall )]
            public static extern long OpenPrinter(string pPrinterName,ref IntPtr phPrinter, int pDefault);
            [ DllImport( "winspool.drv",CharSet=CharSet.Unicode,ExactSpelling=false,
            CallingConvention=CallingConvention.StdCall )]
            public static extern long StartDocPrinter(IntPtr hPrinter, int Level, ref DOCINFO pDocInfo);
                        [ DllImport(
"winspool.drv",CharSet=CharSet.Unicode,ExactSpelling=true,
            CallingConvention=CallingConvention.StdCall)]
            public static extern long StartPagePrinter(IntPtr hPrinter);
            [ DllImport( "winspool.drv",CharSet=CharSet.Ansi,ExactSpelling=true,
            CallingConvention=CallingConvention.StdCall)]
            public static extern long WritePrinter(IntPtr hPrinter,string data, int buf,ref int pcWritten);                        [ DllImport( "winspool.drv" ,CharSet=CharSet.Unicode,ExactSpelling=true,
            CallingConvention=CallingConvention.StdCall)]
            public static extern long EndPagePrinter(IntPtr hPrinter);                          [ DllImport( "winspool.drv"
,CharSet=CharSet.Unicode,ExactSpelling=true,
            CallingConvention=CallingConvention.StdCall)]
            public static extern long EndDocPrinter(IntPtr hPrinter);                           [ DllImport(
"winspool.drv",CharSet=CharSet.Unicode,ExactSpelling=true,  
            CallingConvention=CallingConvention.StdCall )]
            public static extern long ClosePrinter(IntPtr hPrinter);
}   public class App
{
            public static void Main ()
            {                 
                        System.IntPtr lhPrinter=new System.IntPtr();
                        
                        DOCINFO di = new DOCINFO();
                        int pcWritten=0;
                        string st1;                                     // text to print with a form feed character     
                        st1="This is an example of printing directly to a printer\f";
                        di.pDocName="my test document";
                        di.pDataType="RAW";                                                // the \x1b means an ascii escape character
                        st1="\x1b*c600a6b0P\f";
                        //lhPrinter contains the handle for the printer opened
                        //If lhPrinter is 0 then an error has occured
                        PrintDirect.OpenPrinter("\\\\192.168.1.101\\hpl",ref lhPrinter,0);                      
                        PrintDirect.StartDocPrinter(lhPrinter,1,ref di);
                        PrintDirect.StartPagePrinter(lhPrinter);  
                        try
                        {
                                    // Moves the cursor 900 dots (3 inches at 300 dpi) in from the left margin, and
            // 600 dots (2 inches at 300 dpi) down from the top margin.
                                    st1="\x1b*p900x600Y";
                                   PrintDirect.WritePrinter(lhPrinter,st1,st1.Length,ref pcWritten);                                             // Using the print model commands for rectangle dimensions, "600a" specifies a rectangle
            // with a horizontal size or width of 600 dots, and "6b" specifies a vertical
            // size or height of 6 dots. The 0P selects the solid black rectangular area fill.
                                    st1="\x1b*c600a6b0P";
                                    PrintDirect.WritePrinter(lhPrinter,st1,st1.Length,ref pcWritten);                                             // Specifies a rectangle with width of 6 dots, height of 600 dots, and a
                                    // fill pattern of solid black.
                                    st1="\x1b*c6a600b0P";
 PrintDirect.WritePrinter(lhPrinter,st1,st1.Length,ref pcWritten);       
                                    // Moves the current cursor position to 900 dots, from the left margin and
            // 1200 dots down from the top margin.
                                    st1="\x1b*p900x1200Y";
 PrintDirect.WritePrinter(lhPrinter,st1,st1.Length,ref pcWritten);      
                                                      // Specifies a rectangle with a width of 606 dots, a height of 6 dots and a             // fill pattern of solid black.
                                    st1="\x1b*c606a6b0P";
                                    PrintDirect.WritePrinter(lhPrinter,st1,st1.Length,ref pcWritten);                                          // Moves the current cursor position to 1500 dots from the left margin and
            // 600 dots down from the top margin.
                                    st1="\x1b*p1500x600Y";
                                    PrintDirect.WritePrinter(lhPrinter,st1,st1.Length,ref pcWritten);                                            // Specifies a rectangle with a width of 6 dots, a height of 600 dots and a
            // fill pattern of solid black.
                                    st1="\x1b*c6a600b0P";
                                    PrintDirect.WritePrinter(lhPrinter,st1,st1.Length,ref pcWritten);                                          // Send a form feed character to the printer
                                    st1="\f";
                                    PrintDirect.WritePrinter(lhPrinter,st1,st1.Length,ref pcWritten);                   
                        }
                        catch (Exception e)
                        {
                                    Console.WriteLine(e.Message);
                        }                                                PrintDirect.EndPagePrinter(lhPrinter);
                        PrintDirect.EndDocPrinter(lhPrinter);
                        PrintDirect.ClosePrinter(lhPrinter);
            }
}