C# Signature:

   [DllImport("user32.dll", SetLastError = true)]
   [return: MarshalAs(UnmanagedType.Bool)]
   static extern bool PrintWindow(IntPtr hwnd, IntPtr hDC, uint nFlags);

VB Signature:

<DllImport("user32.dll", SetLastError:=True)> _
Private Shared Function PrintWindow(ByVal hwnd As IntPtr, ByVal hDC As IntPtr, ByVal nFlags As UInteger) As Boolean
End Function

User-Defined Types:

None.

Notes:

This function is only available on Windows XP or higher. Windows 2000/9x/ME do not support it.

Tips & Tricks:

To capture only the client area of window, use PW_CLIENTONLY = 0x1 as nFlags

Sample Code:

Screenshotting a form to a Bitmap in C#:

Graphics g = form.CreateGraphics();
Bitmap bmp = new Bitmap(form.Size.Width, form.Size.Height, g);
Graphics memoryGraphics = Graphics.FromImage(bmp);
IntPtr dc = memoryGraphics.GetHdc();
bool success = PrintWindow(form.Handle, dc, 0);
memoryGraphics.ReleaseHdc(dc);
// bmp now contains the screenshot

Me.AutoRedraw = True
PrintWindow Me.hWnd, Me.hDC, 0

Alternative Managed API:

Control.DrawToBitmap()

Or call Control.InvokePaintBackground() followed by Control.InvokePaint().

The ManagedWindowsApi project (http://mwinapi.sourceforge.net) provides a

class ManagedWinapi.SystemWindow that has a Image property

What if it doesn't work:

This function might not work on some windows, like chrome browser as an example, in such scenarios another flag has to be used:

#define PW_RENDERFULLCONTENT 0x00000002

https://stackoverflow.com/questions/30965343/printwindow-could-not-print-google-chrome-window-chrome-widgetwin-1

Quote from https://stackoverflow.com/users/7019029/geoff:
I was stuck for ages on this, then found that I can pass a parameter of PW_RENDERFULLCONTENT as the last parameter to PrintWindow.  Googling that shows it's new in Windows 8.1 so presumably doesn't work on 7. It may be worth trying it though, Winuser.h defines it  as
#if(_WIN32_WINNT >= 0x0603)
#define PW_RENDERFULLCONTENT    0x00000002
#endif /* _WIN32_WINNT >= 0x0603 */  

Quote from https://stackoverflow.com/users/7019029/geoff:

I was stuck for ages on this, then found that I can pass a parameter of PW_RENDERFULLCONTENT as the last parameter to PrintWindow. Googling that shows it's new in Windows 8.1 so presumably doesn't work on 7. It may be worth trying it though, Winuser.h defines it as

#if(WIN32WINNT >= 0x0603)

#define PW_RENDERFULLCONTENT 0x00000002

#endif /* WIN32WINNT >= 0x0603 */

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