C＃非托管代码不起作用

Question

This is supposed to be very simple. I basically copied the code from MSDN for printing a form in my C# winforms application. All I get when i click on "Print" is a blank sheet of paper but no error messages.

This is the link. https://msdn.microsoft.com/en-us/library/aa287529%28v=vs.71%29.aspx

The code is:

    [System.Runtime.InteropServices.DllImport("gdi32.dll")]
    public static extern long BitBlt (IntPtr hdcDest, int nXDest, int   nYDest, int nWidth, int nHeight, IntPtr hdcSrc, int nXSrc, int nYSrc, int dwRop);
    private Bitmap memoryImage;

private void CaptureScreen()
{
   Graphics mygraphics = this.CreateGraphics();
   Size s = this.Size;
   memoryImage = new Bitmap(s.Width, s.Height, mygraphics);
   Graphics memoryGraphics = Graphics.FromImage(memoryImage);
   IntPtr dc1 = mygraphics.GetHdc();
   IntPtr dc2 = memoryGraphics.GetHdc();
   BitBlt(dc2, 0, 0, this.ClientRectangle.Width, this.ClientRectangle.Height, dc1, 0, 0, 13369376);
   mygraphics.ReleaseHdc(dc1);
   memoryGraphics.ReleaseHdc(dc2);
}

private void printDocument1_PrintPage(System.Object sender, System.Drawing.Printing.PrintPageEventArgs e)
{
   e.Graphics.DrawImage(memoryImage, 0, 0);
}

private void printButton_Click(System.Object sender, System.EventArgs e)
{
   CaptureScreen();
   printDocument1.Print();
}

All I need to do is print the current form. I just get a blank sheet of paper. I think its because of the unmanaged code(calling the dll). How do I fix this?

Answer 1

I tested the sample in .NET 4.5.2 and it works great.

I just get a blank sheet of paper. I think its because of the unmanaged code(calling the dll). How do I fix this?

You will get a blank sheet of paper if you don't hook up the subscriber for PrintDocument.PrintPage event.

private void printDocument1_PrintPage(Object sender, PrintPageEventArgs e)
{
    e.Graphics.DrawImage(memoryImage, 0, 0);
}

Answer 2

The page you linked to is from 2003, likely not going to work anymore.

Here is a more recent MSDN page: How to: Print a Windows Form

You only require permissions to access the printer.

And the full code:

using System;
using System.Windows.Forms;
using System.Drawing;
using System.Drawing.Printing;

public class Form1 :
    Form
{
    private Button printButton = new Button();
    private PrintDocument printDocument1 = new PrintDocument();

    public Form1()
    {
        printButton.Text = "Print Form";
        printButton.Click += new EventHandler(printButton_Click);
        printDocument1.PrintPage += new PrintPageEventHandler(printDocument1_PrintPage);
        this.Controls.Add(printButton);
    }

    void printButton_Click(object sender, EventArgs e)
    {
        CaptureScreen();
        printDocument1.Print();
    }


    Bitmap memoryImage;

    private void CaptureScreen()
    {
        Graphics myGraphics = this.CreateGraphics();
        Size s = this.Size;
        memoryImage = new Bitmap(s.Width, s.Height, myGraphics);
        Graphics memoryGraphics = Graphics.FromImage(memoryImage);
        memoryGraphics.CopyFromScreen(this.Location.X, this.Location.Y, 0, 0, s);
    }

    private void printDocument1_PrintPage(System.Object sender,  
           System.Drawing.Printing.PrintPageEventArgs e)
    {
        e.Graphics.DrawImage(memoryImage, 0, 0);
    }



    public static void Main()
    {
        Application.Run(new Form1());
    }
}