Question

我正在尝试捕获WebBrowser控件的内容。 DrawToBitmap()可以完美地工作，但WebBrowser控件的文档中不支持它。我一直试图找到另一种方法来捕获WebBrowser控件的内容并将它们保存到本地图像文件。

是否有人有任何变通办法或其他方法将WebBrowser控件的内容保存到本地图像文件？

Answer 1

Control.DrawToBitmap并不总是有效，所以我采用了以下本机API调用来提供更一致的结果：

Utilities类。调用Utilities.CaptureWindow（Control.Handle）来捕获特定控件：

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课程：

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CC.Utilities项目的代码片段，我专门编写它来从WebBrowser控件中截取屏幕截图。

Answer 2

即使窗口大于屏幕大小，以下方法也可以捕获整个窗口图像。然后，如果将窗口调整为webBrowser.Document.OffsetRectangle.Size

，则可以捕获页面内容的图像

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);
                }
            }
        }
    }
}

用法：

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

Answer 3

我正在使用DrawToBitmap（Visual Studio 2008 C＃）来捕获大图像（用户签名的发票，屏幕外的内容）。基本上它运作良好，但我得到空白的图像。大约有100名员工正在使用该软件，大约每两周我就会看到一张空白图像。

我做了很多测试，发现一件有趣的事情是：我创建了一个按钮来从webbrowser生成图像。通常没问题，但如果我先点击网页浏览器，然后点击创建按钮，就会出现空白图片。

Answer 4

我在SO上的this topic中使用了OleDraw方法，但是将其集成在从WebBrowser派生的类中。这样，不仅可以对WebBrowser进行正常的Control.DrawToBitmap映射，还可以对其中包含WebBrowser的表单进行正常的Control.DrawToBitmap映射。如果该表单是隐藏的（也被其他表单（包括MDI父表单）覆盖），它也可以使用，并且在用户锁定与Win + L的会话（我尚未对其进行测试）时也可以使用。

public class WebBrowserEx : WebBrowser
{
    private const uint DVASPECT_CONTENT = 1;

    [DllImport("ole32.dll", PreserveSig = false)]
    private static extern void OleDraw([MarshalAs(UnmanagedType.IUnknown)] object pUnk,
        uint dwAspect,
        IntPtr hdcDraw,
        [In] ref System.Drawing.Rectangle lprcBounds
    );

    protected override void WndProc(ref Message m)
    {
        const int WM_PRINT = 0x0317;

        switch (m.Msg)
        {
            case WM_PRINT:
                Rectangle browserRect = new Rectangle(0, 0, this.Width, this.Height);

                // Don't know why, but drawing with OleDraw directly on HDC from m.WParam.
                // results in badly scaled (stretched) image of the browser.
                // So, drawing to an intermediate bitmap first.
                using (Bitmap browserBitmap = new Bitmap(browserRect.Width, browserRect.Height))
                {
                    using (var graphics = Graphics.FromImage(browserBitmap))
                    {
                        var hdc = graphics.GetHdc();
                        OleDraw(this.ActiveXInstance, DVASPECT_CONTENT, hdc, ref browserRect);
                        graphics.ReleaseHdc(hdc);
                    }

                    using (var graphics = Graphics.FromHdc(m.WParam))
                    {
                        graphics.DrawImage(browserBitmap, Point.Empty);
                    }
                }
                // ignore default WndProc
                return;

        }

        base.WndProc(ref m);
    }
}

WebBrowser.DrawToBitmap（）还是其他方法？

4 个答案: