webbrowser.drawtobitmap()或其他方法?

control.drawtobitmap并不总是起作用,因此我求助于以下提供更一致结果的本机API调用:

实用程序类。调用Utilities.CaptureWindow(control.handle)以捕获特定控件:

public static class Utilities
{
    public static Image CaptureScreen()
    {
        return CaptureWindow(User32.GetDesktopWindow());
    }

    public static Image CaptureWindow(IntPtr handle)
    {

        IntPtr hdcSrc = User32.GetWindowDC(handle);

        RECT windowRect = new RECT();
        User32.GetWindowRect(handle, ref windowRect);

        int width = windowRect.right - windowRect.left;
        int height = windowRect.bottom - windowRect.top;

        IntPtr hdcDest = Gdi32.CreateCompatibleDC(hdcSrc);
        IntPtr hBitmap = Gdi32.CreateCompatibleBitmap(hdcSrc, width, height);

        IntPtr hOld = Gdi32.SelectObject(hdcDest, hBitmap);
        Gdi32.BitBlt(hdcDest, 0, 0, width, height, hdcSrc, 0, 0, ApiConstants.SRCCOPY);
        Gdi32.SelectObject(hdcDest, hOld);
        Gdi32.DeleteDC(hdcDest);
        User32.ReleaseDC(handle, hdcSrc);

        Image image = Image.FromHbitmap(hBitmap);
        Gdi32.DeleteObject(hBitmap);

        return image;
    }
}

GDI32类:

public class Gdi32
{
    [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);
}

user32类:

public static class User32
{
    [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 GetWindowRect(IntPtr hWnd, ref RECT rect);
    [DllImport("user32.dll")]
    public static extern IntPtr ReleaseDC(IntPtr hWnd, IntPtr hDC);
}

使用的常数:

    public const int SRCCOPY = 13369376;

使用的结构:

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

友好的控制扩展方法:

public static class ControlExtensions
{
    public static Image DrawToImage(this Control control)
    {
        return Utilities.CaptureWindow(control.Handle);
    }
}

这是我的 CC.Utilities 我和project专门写它来从webbrowser控件中截图。

以下方法可以捕获整个窗口图像,即使窗口大于屏幕大小。如果窗口大小调整为 webBrowser.Document.OffsetRectangle.Size

class NativeMethods
{
    [ComImport]
    [Guid("0000010D-0000-0000-C000-000000000046")]
    [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    interface IViewObject
    {
        void Draw([MarshalAs(UnmanagedType.U4)] uint dwAspect, int lindex, IntPtr pvAspect, [In] IntPtr ptd, IntPtr hdcTargetDev, IntPtr hdcDraw, [MarshalAs(UnmanagedType.Struct)] ref RECT lprcBounds, [In] IntPtr lprcWBounds, IntPtr pfnContinue, [MarshalAs(UnmanagedType.U4)] uint dwContinue);
    }

    [StructLayout(LayoutKind.Sequential, Pack = 4)]
    struct RECT
    {
        public int Left;
        public int Top;
        public int Right;
        public int Bottom;
    }

    public static void GetImage(object obj, Image destination, Color backgroundColor)
    {
        using(Graphics graphics = Graphics.FromImage(destination))
        {
            IntPtr deviceContextHandle = IntPtr.Zero;
            RECT rectangle = new RECT();

            rectangle.Right = destination.Width;
            rectangle.Bottom = destination.Height;

            graphics.Clear(backgroundColor);

            try
            {
                deviceContextHandle = graphics.GetHdc();

                IViewObject viewObject = obj as IViewObject;
                viewObject.Draw(1, -1, IntPtr.Zero, IntPtr.Zero, IntPtr.Zero, deviceContextHandle, ref rectangle, IntPtr.Zero, IntPtr.Zero, 0);
            }
            finally
            {
                if(deviceContextHandle != IntPtr.Zero)
                {
                    graphics.ReleaseHdc(deviceContextHandle);
                }
            }
        }
    }
}

用途:

Bitmap screenshot = new Bitmap(1024, 768);
NativeMethods.GetImage(webBrowser.ActiveXInstance, screenshot, Color.White);

我使用drawtobitmap(visualstudio2008c)来捕获大图像(用户签名的发票,屏幕外的内容)。基本上它工作得很好,但我得到的是空白图像。大约100名员工正在使用这个软件,大约每两周我就可以看到一张空白图片。

我做了很多测试,我发现一件有趣的事是: 我创建了一个按钮来从webbrowser生成图像。通常是可以的,但是如果我先点击网页浏览器,然后点击创建按钮,空白图像就会出现。