在线程中执行Webbrowser控件的屏幕抓取

Question

在线程中执行Webbrowser控件的屏幕抓取

c#multithreadingwebbrowser-controlscreen-scrapingapartments

3

我正在使用以下技术：

在新线程中使用WebBrowser控件

尝试对网页进行屏幕截图。当WebBrowser控件放置在WinForm上时，我已经能够成功地运行下面的代码。但是，在线程内运行时，它会提供桌面的任意图像而失败。请注意不要删除任何HTML标签并准确保留格式。

Thread browserThread = new Thread(() =>
{
    WebBrowser br = new WebBrowser();
    br.DocumentCompleted += webBrowser1_DocumentCompleted;
    br.ProgressChanged += webBrowser1_ProgressChanged;
    br.ScriptErrorsSuppressed = true;
    br.Navigate(url);
    Application.Run();
});
browserThread.SetApartmentState(ApartmentState.STA);
browserThread.Start();

private Image TakeSnapShot(WebBrowser browser)
{
    int width;
    int height;

    width = browser.ClientRectangle.Width;
    height = browser.ClientRectangle.Height;

    Bitmap image = new Bitmap(width, height);

    using (Graphics graphics = Graphics.FromImage(image))
    {
        Point p = new Point(0, 0);
        Point upperLeftSource = browser.PointToScreen(p);
        Point upperLeftDestination = new Point(0, 0);

        Size blockRegionSize = browser.ClientRectangle.Size;
        blockRegionSize.Width = blockRegionSize.Width - 15;
        blockRegionSize.Height = blockRegionSize.Height - 15;
        graphics.CopyFromScreen(upperLeftSource, upperLeftDestination, blockRegionSize);
    }

    return image;
}

显然，这是由于方法Graphics.CopyFromScreen()引起的，但我不知道是否有其他方法来解决这个问题。任何人都能提出如何解决这个问题的建议吗？或者我的唯一选择是创建一个表单，添加控件，使其可见，然后进行屏幕截取？由于显而易见的原因，我希望避免这种方法。

- Maxim Gershkovich

2个回答

-1

using (Graphics graphics = Graphics.FromImage(image))
    {
        Point p = new Point(0, 0);
        Point upperLeftSource = browser.PointToScreen(p);
        Point upperLeftDestination = new Point(0, 0);

        Size blockRegionSize = browser.ClientRectangle.Size;
        blockRegionSize.Width = blockRegionSize.Width - 15;
        blockRegionSize.Height = blockRegionSize.Height - 15;
        graphics.CopyFromScreen(upperLeftSource, upperLeftDestination, blockRegionSize);
    }

你真的需要using语句吗？

你还使用了return image，但是复制的图像如何分配给它呢？

- Na Na

是的，你需要一个using，除非你有充分的理由不处理IDisposable对象。至于图像，它是通过以下代码行进行分配的：Graphics graphics = Graphics.FromImage(image)。 - Maxim Gershkovich

网页内容由stack overflow 提供, 点击上面的

可以查看英文原文，
原文链接

- I4V · Accepted Answer

您可以编写

private Image TakeSnapShot(WebBrowser browser)
{
     browser.Width = browser.Document.Body.ScrollRectangle.Width;
     browser.Height= browser.Document.Body.ScrollRectangle.Height;

     Bitmap bitmap = new Bitmap(browser.Width - System.Windows.Forms.SystemInformation.VerticalScrollBarWidth, browser.Height);

     browser.DrawToBitmap(bitmap, new Rectangle(0, 0, bitmap.Width, bitmap.Height));

     return bitmap;
}

一个完整的可用代码

var image = await WebUtils.GetPageAsImageAsync("http://www.stackoverflow.com");
image.Save(fname , System.Drawing.Imaging.ImageFormat.Bmp);

public class WebUtils
{
    public static Task<Image> GetPageAsImageAsync(string url)
    {
        var tcs = new TaskCompletionSource<Image>();

        var thread = new Thread(() =>
        {
            WebBrowser browser = new WebBrowser();
            browser.Size = new Size(1280, 768);

            WebBrowserDocumentCompletedEventHandler documentCompleted = null;
            documentCompleted = async (o, s) =>
            {
                browser.DocumentCompleted -= documentCompleted;
                await Task.Delay(2000); //Run JS a few seconds more

                Bitmap bitmap = TakeSnapshot(browser);

                tcs.TrySetResult(bitmap);
                browser.Dispose();
                Application.ExitThread();
            };

            browser.ScriptErrorsSuppressed = true;
            browser.DocumentCompleted += documentCompleted;
            browser.Navigate(url);
            Application.Run();
        });

        thread.SetApartmentState(ApartmentState.STA);
        thread.Start();

        return tcs.Task;
    }

    private static Bitmap TakeSnapshot(WebBrowser browser)
    {
         browser.Width = browser.Document.Body.ScrollRectangle.Width;
         browser.Height= browser.Document.Body.ScrollRectangle.Height;

         Bitmap bitmap = new Bitmap(browser.Width - System.Windows.Forms.SystemInformation.VerticalScrollBarWidth, browser.Height);

         browser.DrawToBitmap(bitmap, new Rectangle(0, 0, bitmap.Width, bitmap.Height));

         return bitmap;
    }
}