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问题:

I'm trying to create an element with a image to a windows forms webbrowser control existing site. Then I want to move the created element to a certain position. I have this code, but it doesn't work.

 private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
    {
        webBrowser1.Document.GetElementById("gpu_notice").Style = "display:none"; 
        webBrowser1.Document.GetElementById("header").OuterHtml = "";
        webBrowser1.Document.GetElementById("ads").OuterHtml = "";
        webBrowser1.Document.GetElementById("the_game").Style += "position: absolute; top: 0px; right: 0px;";
        HtmlElement logo = webBrowser1.Document.CreateElement("logo");
        logo.SetAttribute("SRC", @"C:\Users\Susana\Documents\Projeto HaxballK\Design\Logo HK.png");
        webBrowser1.Document.Body.AppendChild(logo);
        logo.SetAttribute("float", "right");
    }

回答1:

Is the task inserting an element to an existing HTML document displayed with the WebBrowser class? If yes, then the steps could be (not tested, sorry)

download the document using WebClient as a HTML string
make <body> relative in the HTML string (insert style='position: relative' into the <body> element)
insert the element into the HTML string, just after <body>, make the element absolute (setting style='position: absolute; left=...; right=...'
set the modified HTML string into DocumentText property of the WebBrowser class

回答2:

You have to use "img" tag instead of "logo" and set the file path with using file protocol.

HtmlElement logo = webBrowser1.Document.CreateElement("img");
logo.SetAttribute("SRC", @"file:///C:/Users/Susana/Documents/Projeto HaxballK/Design/Logo HK.png");
webBrowser1.Document.Body.AppendChild(logo);
logo.SetAttribute("float", "right");

UPDATED

If you want to add the image after all the JavaScript initializations have run, simply use one off Timer.

System.Windows.Forms.Timer timer = new Timer();
void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
    // other processes

    timer.Interval = 1 * 1000 * 5; // 5 seconds
    timer.Tick += timer_Tick;
    timer.Start();
}

void timer_Tick(object sender, EventArgs e)
{
    timer.Tick -= timer_Tick;

    HtmlElement logo = webBrowser1.Document.CreateElement("img");
    logo.SetAttribute("SRC", @"file:///C:/Users/Susana/Documents/Projeto HaxballK/Design/Logo HK.png");
    webBrowser1.Document.Body.AppendChild(logo);
    logo.SetAttribute("float", "right");
}