Question

My problem is simple yet i cannot figure out why it’s not working inside of if/loop. Here are some examples:

Working one:

private void button1_Click(object sender, EventArgs e)
{
    webBrowser1.Document.GetElementById("login").SetAttribute("value", "something");
    webBrowser1.Document.GetElementById("password").SetAttribute("value", "something");
}

Non working one:

if (webBrowser1.IsBusy == false)
{
    webBrowser1.Document.GetElementById("login").SetAttribute("value", "something");
    webBrowser1.Document.GetElementById("password").SetAttribute("value", "something");
}

No matter what the “if” statement is, it’s not working. Also tried with “for”, also tried to get it out of the loop of “for”, i still get this error: “Object reference not set to an instance of an object.”

Answer 1

I’m taking a guess here because of the limited information.

I think you are trying to modify the page right after setting the Url property. The webpage will not yet be loaded then so the controls you are getting are not available yet.

Try adding the code to the DocumentCompleted event of the WebBrowser. This event will be triggered right after the document is fully loaded and the elements will be available then.

private void webBrowser1_DocumentCompleted(object sender, WebBrowserDocumentCompletedEventArgs e)
{
  var loginControl = webBrowser1.Document.GetElementById("login");
  var passwordControl = webBrowser1.Document.GetElementById("password");

  if (loginControl != null)
    loginControl.SetAttribute("value", "something");

  if (passwordControl != null)
    passwordControl.SetAttribute("value", "something");
}

more: http://msdn.microsoft.com/en-us/library/system.windows.forms.webbrowser.documentcompleted.aspx

Update

Your assumption about IsBusy is not completely correct. It starts out false when nothing is loaded. settings the Url property will not immediately set it to true.

For an alternative you requested you could use the ReadyState property that will have the value of WebBrowserReadyState.Complete when loading is done. you could use the following example. Although i personally don’t like it as there is the risk of endless loop when the page can’t load for some reason. I would advise to use the DocumentCompleted if possible and i modified that example to correctly handle non-login pages as well.

while (webBrowser1.ReadyState != WebBrowserReadyState.Complete)
{
  Thread.Sleep(0);
  Application.DoEvents();
}