problem in vb to C# converter

elnaz z

hi all
i hava a piece vb code
i convert it to c# but when it convert to C# i have error in my program
can anybody help me?

vb code(this code is true)
Do Until vreadyState = 4
                  Application.DoEvents()
                  vreadyState = Me.WebBrowser1.ReadyState
            Loop
            Dim eleminput As HtmlElementCollection
            Dim DocCol As HtmlDocument
            DocCol = WebBrowser1.Document
            eleminput = DocCol.GetElementsByTagName("input")

c# code
for (; (vreadystate == 4); )
                  {
                        Application.DoEvents();
                        vreadystate = Convert.ToInt32(this.webBrowser1.ReadyState);

                  }
                  HtmlElementCollection eleminput = default(HtmlElementCollection);
                  HtmlDocument DocCol = default(HtmlDocument);
                  DocCol = webBrowser1.Document;
                  eleminput =DocCol.GetElementsByTagName("input");

run this code
but my program has error in last line
"Object reference not set to an instance of an object."

how to change this code that solve this error?

6 Replies

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Purushottam Rathore15y ago
Accepted answer
Hello friend...

Please try to convert your code by using this converter

http://www.tangiblesoftwaresolutions.com/Product_Details/CSharp_to_VB_NET_Converter.html?gclid=CKyJ0rf2pagCFYZ66wodNzReHQ
Sam Hobbs15y ago
You simply need to wait until the document exists. See my Introduction to Web Site Scraping for an example of doing that. You need to wait for the DocumentComplete event.

I am suspicious of any C# code that uses DoEvents. DoEvents is something that VB programmers used when VB was unable to receive messages directly. DoEvents can be a convenient solution but usually there is a better solution that does not use it. In this case, the solution is probably as easy as double-clicking on the WebBrowser control at design time to create a DocumentComplete event handler instead of looping for a ReadyState of 4.
Suthish Nair15y ago
ya oops.. my mistake
Vulpes15y ago
That's what these lines do as the default value for all reference types is null:

HtmlElementCollection eleminput = default(HtmlElementCollection);
HtmlDocument DocCol = default(HtmlDocument);

VB.Net differs from C# in that local variables are always given a default value if you don't assign them one. In contrast, the C# compiler won't let you use a local variable until it's been assigned a value and it's considered 'unassigned' in the meantime.

VB to C# translators have a problem with this and may come up with weird stuff like the above, though the better ones would substitute null instead.

So I don't think the explanation for the error is anything to do with the translation but, of course, DocCol will be null if there's currently no page loaded in the web-browser control.
Suthish Nair15y ago
try..

HtmlElementCollection eleminput = null;
HtmlDocument DocCol = null;
Vulpes15y ago
The code (whilst a little strange) looks OK to me

It looks like DocCol is null. Are you sure that there is a page loaded in the webbrowser control at that point in the code?