I want to know how to control the flow of code when using webbrowser?

Question

I have a loop and with in the loop i call

   webbrowser.navigate("www.example.com");

After this you know the documentcompleted function is called and i do some work int that function ,but after all the work is done ,Nothing happens the code does not come back to the loop and flow as it does in loops.Am i doing something wrong.

Thank you

Answer 1

This problem is caused by having a loop. The web browser's navigation can only complete and the DocumentCompleted event can only fire when your UI thread goes idle again. This is core to the way multi-threaded components work, they can only fire their 'the job is done' event on the UI thread when the UI thread is idle and pumps the message loop. The BackgroundWorker class for example has the exact same requirement.

The proper way to solve it is to create a state machine. You kick it off by telling the browser to navigate to the first url. You let your DocumentCompleted event handler process the response and then tell the browser navigate to the next url. Or stop when there are no more urls to process.

The improper way is to call Application.DoEvents() in the loop. That pumps the message loop and allows the events to fire. But is a very dangerous thing to do, DoEvents() is not selective about exactly what events are processed. Be sure to read this answer if you contemplate using it anyway.

The next way is the upcoming support for the async and await keywords in the next version of C#. Currently available in CTP.

Answer 2

When you leave the webpage your javascript is on by navigating away, it's analogous to closing your application and starting some other application.

If you had a desktop application in which you wrote:

Application.ExitAndStartOtherApplication("SomeOtherApplication.exe");

You wouldn't expect whatever code came after that line to run.

It's the same thing.