c# - Using XPath and WebBrowser Control to select multiple nodes

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c# - Using XPath and WebBrowser Control to select multiple nodes

posted Oct 24, 2021 in Technique[技术] by 深蓝 (71.8m points)

c# - Using XPath and WebBrowser Control to select multiple nodes

In C# WinForms sample application I have used WebBrowser control and JavaScript-XPath to select single node and change that node .innerHtml by the following code:

    private void MainForm_Load(object sender, EventArgs e)
    {
        webBrowser1.DocumentText = @"
            <html>
            <head>
                <script src=""http://svn.coderepos.org/share/lang/javascript/javascript-xpath/trunk/release/javascript-xpath-latest-cmp.js""></script>
            </head>
            <body>
            <img alt=""0764547763 Product Details"" 
                src=""http://ecx.images-amazon.com/images/I/51AK1MRIi7L._AA160_.jpg"">
            <hr/>
            <h2>Product Details</h2>
            <ul>
            <li><b>Paperback:</b> 648 pages</li>
            <li><b>Publisher:</b> Wiley; Unlimited Edition edition (October 15, 2001)</li>
            <li><b>Language:</b> English</li>
            <li><b>ISBN-10:</b> 0764547763</li>
            </ul>
            </body>
            </html>
        ";
    }

    private void cmdTest_Click(object sender, EventArgs e)
    {
        string xPath = "//li";
        string code = string.Format("document.evaluate('{0}', document, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null).singleNodeValue;", xPath);
        var li = webBrowser1.Document.InvokeScript("eval", new object[] { code }) as mshtml.IHTMLElement;

        li.innerHTML = string.Format("<span style='text-transform: uppercase;font-family:verdana;color:green;'>{0}</span>", li.innerText);

    }

The result of running this code is as the following:

Sample code execution result

Now I'd like to use the same technique to select multiple <li>nodes under <ul> node and I'm writing:

        xPath = "//ul//*";
        code = string.Format("document.evaluate('{0}', document, null, XPathResult.ORDERED_NODE_ITERATOR_TYPE, null);", xPath);
        var allLI = webBrowser1.Document.InvokeScript("eval", new object[] { code }) as mshtml.IHTMLElementCollection;

but the returned value of allLI variable is NULL .

If I'll write

        xPath = "//ul//*";
        code = string.Format("document.evaluate('{0}', document, null, XPathResult.ORDERED_NODE_ITERATOR_TYPE, null);", xPath);
        var allLI = webBrowser1.Document.InvokeScript("eval", new object[] { code });

then the returned allLI variable isn't null and its value type is COM Object but what more specific type this COM Object can be cast to is unclear for me.

Is there a way to select multiple nodes by used here technique?

[EDITED]

xPath = "ul//*";

to

xPath = "//ul//*";

[Addition]

I have added two javaScript functions to my sample HTML:

<script type=""text/javascript"">
    function GetElementsText (XPath) {
            var xPathRes = document.evaluate ( XPath, document, null, XPathResult.ORDERED_NODE_ITERATOR_TYPE, null);              
            var nextElement = xPathRes.iterateNext ();
            var text = """";
            while (nextElement) {
               text += nextElement.innerText;
               nextElement = xPathRes.iterateNext ();
            }
        return text;
        };

    function GetElements (XPath) {
            var xPathRes = document.evaluate ( XPath, document, null, XPathResult.ORDERED_NODE_ITERATOR_TYPE, null);              
            var nextElement = xPathRes.iterateNext ();
            var elements = new Object();
            var elementIndex = 1;
            while (nextElement) {
               elements[elementIndex++] = nextElement;
               nextElement = xPathRes.iterateNext ();
            }
        return elements;
        };
</script>

Now when I'm runnung the following C# code line within my cmd_TestClick method:

var text = webBrowser1.Document.InvokeScript("eval", new object[] { "GetElementsText('//ul')" });

I'm getting text of all li elements:

"Paperback: 648 pages 
Publisher: Wiley; Unlimited Edition edition (October 15, 2001) 
Language: English 
ISBN-10: 0764547763 "

And when I'm running the following C# code line within my cmd_TestClick method:

var elements = webBrowser1.Document.InvokeScript("eval", new object[] { "GetElements('//ul')" });

I'm getting COM Object, which I cannot cast to IEnumerable<mshtml.IHtmlElement> .

Is there any way to process within C# code a javaScript collection of HTML nodes returned by

var elements = webBrowser1.Document.InvokeScript("eval", new object[] { "GetElements('//ul')" });

?

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1 Reply

深蓝 · Answer 1 · 2021-10-23T19:36:25+0000

I have found solution, here is the code:

using System;
using System.Collections.Generic;
using System.Reflection;
using System.Windows.Forms;

namespace myTest.WinFormsApp
{
public partial class MainForm : Form
{
    public MainForm()
    {
        InitializeComponent();
    }

    private void MainForm_Load(object sender, EventArgs e)
    {
        webBrowser1.DocumentText = @"
            <html>
            <body>
            <img alt=""0764547763 Product Details"" 
                src=""http://ecx.images-amazon.com/images/I/51AK1MRIi7L._AA160_.jpg"">
            <hr/>
            <h2>Product Details</h2>
            <ul>
            <li><b>Paperback:</b> 648 pages</li>
            <li><b>Publisher:</b> Wiley; Unlimited Edition edition (October 15, 2001)</li>
            <li><b>Language:</b> English</li>
            <li><b>ISBN-10:</b> 0764547763</li>
            </html>
        ";
    }

    private void cmdTest_Click(object sender, EventArgs e)
    {
        var processor = new WebBrowserControlXPathQueriesProcessor(webBrowser1);

        // change attributes of the first element of the list
        {
            var li = processor.GetHtmlElement("//li");
            li.innerHTML = string.Format("<span style='text-transform: uppercase;font-family:verdana;color:green;'>{0}</span>", li.innerText);
        }

        // change attributes of the second and subsequent elements of the list
        var list = processor.GetHtmlElements("//ul//li");
        int index = 1;
        foreach (var li in list)
        {
            if (index++ == 1) continue;
            li.innerHTML = string.Format("<span style='text-transform: uppercase;font-family:verdana;color:blue;'>{0}</span>", li.innerText);
        }

    }

    /// <summary>
    /// Enables IE WebBrowser control to evaluate XPath queries 
    /// by injecting http://svn.coderepos.org/share/lang/javascript/javascript-xpath/trunk/release/javascript-xpath-latest-cmp.js
    /// and to return XPath queries results to the calling C# code as strongly typed
    /// mshtml.IHTMLElement and IEnumerable<mshtml.IHTMLElement>
    /// </summary>
    public class WebBrowserControlXPathQueriesProcessor
    {
        private System.Windows.Forms.WebBrowser _webBrowser;
        public WebBrowserControlXPathQueriesProcessor(System.Windows.Forms.WebBrowser webBrowser)
        {
            _webBrowser = webBrowser;
            injectScripts();
        }

        private void injectScripts()
        {
            // Thanks to: http://stackoverflow.com/questions/7998996/how-to-inject-javascript-in-webbrowser-control

            HtmlElement head = _webBrowser.Document.GetElementsByTagName("head")[0];
            HtmlElement scriptEl = _webBrowser.Document.CreateElement("script");
            mshtml.IHTMLScriptElement element = (mshtml.IHTMLScriptElement)scriptEl.DomElement;
            element.src = "http://svn.coderepos.org/share/lang/javascript/javascript-xpath/trunk/release/javascript-xpath-latest-cmp.js";
            head.AppendChild(scriptEl);

            string javaScriptText = @"
                    function GetElements (XPath) {
                            var xPathRes = document.evaluate ( XPath, document, null, XPathResult.ORDERED_NODE_ITERATOR_TYPE, null);              
                            var nextElement = xPathRes.iterateNext ();
                            var elements = new Object();
                            var elementIndex = 1;
                            while (nextElement) {
                            elements[elementIndex++] = nextElement;
                            nextElement = xPathRes.iterateNext ();
                            }
                        elements.length = elementIndex -1;
                        return elements;
                        };
                   ";
            scriptEl = _webBrowser.Document.CreateElement("script");
            element = (mshtml.IHTMLScriptElement)scriptEl.DomElement;
            element.text = javaScriptText;
            head.AppendChild(scriptEl);
        }

        /// <summary>
        /// Gets Html element's mshtml.IHTMLElement object instance using XPath query
        /// </summary>
        public mshtml.IHTMLElement GetHtmlElement(string xPathQuery)
        {
            string code = string.Format("document.evaluate('{0}', document, null, XPathResult.FIRST_ORDERED_NODE_TYPE, null).singleNodeValue;", xPathQuery);
            return _webBrowser.Document.InvokeScript("eval", new object[] { code }) as mshtml.IHTMLElement;
        }

        /// <summary>
        /// Gets Html elements' IEnumerable<mshtml.IHTMLElement> object instance using XPath query
        /// </summary>
        public IEnumerable<mshtml.IHTMLElement> GetHtmlElements(string xPathQuery)
        {
            // Thanks to: http://stackoverflow.com/questions/5278275/accessing-properties-of-javascript-objects-using-type-dynamic-in-c-sharp-4
            var comObject = _webBrowser.Document.InvokeScript("eval", new object[] { string.Format("GetElements('{0}')", xPathQuery) });
            Type type = comObject.GetType();
            int length = (int)type.InvokeMember("length", BindingFlags.GetProperty, null, comObject, null);

            for (int i = 1; i <= length; i++)
            {
                yield return type.InvokeMember(i.ToString(), BindingFlags.GetProperty, null, comObject, null) as mshtml.IHTMLElement;
            }
        }
    }

}
}

And here are the code running results:

Code running results

I have put credits' references to my code inline. If you'll find I have missed some please point me in your comments and I will add them.

If you know better solution - shorter code, more effective code - please comment and/or post your answer.

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c# - Using XPath and WebBrowser Control to select multiple nodes

c# - Using XPath and WebBrowser Control to select multiple nodes

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