How to get winform screenshot in C#?

Question

I'm trying to capture a form screen shot in C# and I'm using the following code. The code works properly but only if the form is in top every other application. If the form is below something else, it's not the form wich is captured.

Does anyone know any piece of code to perform that please ?

Thanks

    Public Function GetScreenShot(F As Form) As Bitmap
        Dim Bounds As Rectangle = F.Bounds

        Dim Bitmap As Bitmap = New Bitmap(Bounds.Width, Bounds.Height)
        Dim G As Graphics = Graphics.FromImage(Bitmap)
        G.CopyFromScreen(New Point(Bounds.Left, Bounds.Top), Point.Empty, Bounds.Size)

        Return Bitmap
    End Function

Answer 1

You can use the built-in way of drawing the whole form to a bitmap:

F.DrawToBitmap(Bitmap, F.ClientRectangle);

where F is an instance of a Form

Answer 2

This is a working copy, i created a windows form and took a screenshot from another application and saved it on disk.

using System;
using System.Diagnostics;
using System.Drawing;
using System.Drawing.Imaging;
using System.Runtime.InteropServices;
using System.Windows.Forms;

namespace ScreenshotApp
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        public void TakeScreenShot()
        {
            Process p = Process.GetProcessById(16416); //modify to use PID or use GetProcessByName
            IntPtr handle = p.MainWindowHandle;
            SomeImageThingy.CaptureWindow(handle);
        }

        private void button1_Click(object sender, System.EventArgs e)
        {
            TakeScreenShot();
        }
    }

    public class User32
    {
        [StructLayout(LayoutKind.Sequential)]
        public struct RECT
        {
            public int left;
            public int top;
            public int right;
            public int bottom;
        }

        [DllImport("user32.dll")]
        public static extern IntPtr GetDesktopWindow();
        [DllImport("user32.dll")]
        public static extern IntPtr GetWindowDC(IntPtr hWnd);
        [DllImport("user32.dll")]
        public static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDC);
        [DllImport("user32.dll")]
        public static extern IntPtr GetWindowRect(IntPtr hWnd, ref RECT rect);
    }

    public class GDI32
    {
        public const int SRCCOPY = 0x00CC0020; // BitBlt dwRop parameter

        [DllImport("gdi32.dll")]
        public static extern bool BitBlt(IntPtr hObject, int nXDest, int nYDest,
            int nWidth, int nHeight, IntPtr hObjectSource,
            int nXSrc, int nYSrc, int dwRop);
        [DllImport("gdi32.dll")]
        public static extern IntPtr CreateCompatibleBitmap(IntPtr hDC, int nWidth,
            int nHeight);
        [DllImport("gdi32.dll")]
        public static extern IntPtr CreateCompatibleDC(IntPtr hDC);
        [DllImport("gdi32.dll")]
        public static extern bool DeleteDC(IntPtr hDC);
        [DllImport("gdi32.dll")]
        public static extern bool DeleteObject(IntPtr hObject);
        [DllImport("gdi32.dll")]
        public static extern IntPtr SelectObject(IntPtr hDC, IntPtr hObject);
    }

    public static class SomeImageThingy
    {
        public static Image CaptureWindow(IntPtr handle)
        {
            // get te hDC of the target window
            IntPtr hdcSrc = User32.GetWindowDC(handle);
            // get the size
            User32.RECT windowRect = new User32.RECT();
            User32.GetWindowRect(handle, ref windowRect);
            int width = windowRect.right - windowRect.left;
            int height = windowRect.bottom - windowRect.top;
            // create a device context we can copy to
            IntPtr hdcDest = GDI32.CreateCompatibleDC(hdcSrc);
            // create a bitmap we can copy it to,
            // using GetDeviceCaps to get the width/height
            IntPtr hBitmap = GDI32.CreateCompatibleBitmap(hdcSrc, width, height);
            // select the bitmap object
            IntPtr hOld = GDI32.SelectObject(hdcDest, hBitmap);
            // bitblt over
            GDI32.BitBlt(hdcDest, 0, 0, width, height, hdcSrc, 0, 0, GDI32.SRCCOPY);
            // restore selection
            GDI32.SelectObject(hdcDest, hOld);
            // clean up 
            GDI32.DeleteDC(hdcDest);
            User32.ReleaseDC(handle, hdcSrc);

            // get a .NET image object for it
            Image img = Image.FromHbitmap(hBitmap);
            img.Save("capture.png", ImageFormat.Png);
            // free up the Bitmap object
            GDI32.DeleteObject(hBitmap);

            return img;
        }
    }
}

Answer 3

This is because your form is below the windows in z-order, which makes them cover the form area and hide it from being captured. What you could do is bring the form to front with Form.TopMost and then reset it for a quick and dirty fix to your problem:

Public Function GetScreenShot(F As Form) As Bitmap
    'Bring the form to top and reset afterwards        
    F.TopMost = True
    F.TopMost = False

    /.../
End Function