How to get all Class names from CefSharp Browser URL

Question

How to get all Class names from CefSharp Browser URL

Andreas ss 721

Hello,

I am using the CefSharp Chromium browser control.

I now enter the url: "https://www.test.com/". Now I try to get all class names which exist on this URL using the code below but I get the error for this line like this:

MessageBox.Show($"{((dynamic)result.Result).Count}"); //**Cannot perform runtime binding on a null reference**

I wonder how I can get all class names which exist on this URL, - in a List correctly with the below code?

This code installs the cefsharp browser from Nuget:
Install-Package CefSharp.WinForms -Version 91.1.211

Thank you!

using CefSharp;  
using CefSharp.WinForms;  
  
        public ChromiumWebBrowser browser;  
        public void InitBrowser()  
        {  
            Cef.Initialize(new CefSettings());  
            browser = new ChromiumWebBrowser("https://uniswapv3.flipsidecrypto.com");  
            this.Controls.Add(browser);  
            browser.Dock = DockStyle.Fill;  
        }  
        public Form1()  
        {  
            InitializeComponent();  
            InitBrowser();      
        }  
  
        async void getAllClasses()  
        {  
            var script = @"(function() { return document.querySelectorAll('[class]'); })();";  
            var result = await browser.EvaluateScriptAsync(script);  
  
            //How to get all classes in a List?  
            List<String> allClassLIST = new List<String>();  
            MessageBox.Show($"{((dynamic)result.Result).Count}"); //Cannot perform runtime binding on a null reference  
        }

Answer 1

Timon Yang-MSFT 9,511

Please note that the await browser.EvaluateScriptAsync method does not get any substantive content, result.Result is null.

We cannot cast null to dynamic.

If the response is helpful, please click "Accept Answer" and upvote it.
Note: Please follow the steps in our documentation to enable e-mail notifications if you want to receive the related email notification for this thread.

Andreas ss 721

I removed await/async this was good to know.

However I am still not sure how to iterate all found classes. The below code that I have cant cast the "obj" as a List and gives this error message below. I am not sure this is the correct way to do it overall?
Cannot implicitly convert type 'CefSharp.JavascriptResponse' to 'System.Collections.IEnumerable'. An explicit conversion exists (are you missing a cast?

                    var script = @"(function() { return document.querySelectorAll('[class]'); })();";
                    var result = browser.EvaluateScriptAsync(script);

                    //How to iterate all found classes?
                    dynamic obj = result.Result;
                    foreach (var n in obj) //'Cannot implicitly convert type 'CefSharp.JavascriptResponse' to 'System.Collections.IEnumerable'. An explicit conversion exists (are you missing a cast?)'
                    {
                        MessageBox.Show(n.ToString());
                    }

Timon Yang-MSFT 9,511 Reputation points

2021-07-12T02:56:38.637+00:00

@Andreas ss
Did you get Result after removing await? When I tested it, it was still null.
This is still the cause of the problem. When I changed the class in js to div, the problem no longer appeared.

Timon Yang-MSFT 9,511

You can also add a if statement, if it is empty, these statements are not executed:

          if (obj == null)
            {
                ...
            }
            else
            {
                foreach (var n in obj) //'Cannot implicitly convert type 'CefSharp.JavascriptResponse' to 'System.Collections.IEnumerable'. An explicit conversion exists (are you missing a cast?)'
                {
                    MessageBox.Show(n.ToString());
                }
            }

Andreas ss 721 Reputation points

2021-07-12T11:31:09.25+00:00
Thank you, yes, it seems to have dissapeared when changing to div. I added the if statement there also. It was a good idéa!

However, it seems that I still get this error below. I am not sure exactly how to iterate all DIV as this example is. I thought the obj would hold a list of all DIV somehow but something might be missing?

The variable obj gets the below error:

Cannot implicitly convert type 'CefSharp.JavascriptResponse' to 'System.Collections.IEnumerable'. An explicit conversion exists (are you missing a cast?

foreach (var n in obj) { MessageBox.Show(n.ToString()); }
Timon Yang-MSFT 9,511 Reputation points

2021-07-13T08:00:42.633+00:00
@Andreas ss
When we use await, the result of this code is the object of JavascriptResponse.

JavascriptResponse result = await browser.EvaluateScriptAsync(script);

At this point, we use dynamic obj = result.Result; to get JavascriptResponse.Result.
When we do not use await, it is TaskJavascriptResponse.

Task<JavascriptResponse> result = browser.EvaluateScriptAsync(script);

What result.Result gets is Task.Result, the JavascriptResponse object, so we need to call its Result, like this:

dynamic obj = result.Result.Result;

Andreas ss 721

Thank you TimonYang, now I understand. There was a difference there. This was good to understand.
I got a bit confused there but this makes sense now. I managed it to work like this:

                            String html = "";
                            JavascriptResponse result = await browser.EvaluateScriptAsync(@"document.getElementById('" + "someelement" + "').innerHTML;");
                            if (result != null)
                            {
                                dynamic obj = result.Result;
                                if (obj != null) { html = obj.ToString(); }
                            }

Thank you for your help!

How to get all Class names from CefSharp Browser URL

0 additional answers

Activity