Reference Form Control within Class

If both classes are defined within the same application, then they should be able to access each other whether they're declared public or internal (the default). You don't need any additional 'using' directives as the Application class is in the System.Windows.Forms namespace.

Also, Form1 (the startup form) must be in the OpenForms collection (at index zero) because, if it had somehow been closed, then the whole application would have terminated.

So, it's very puzzling that you can't access it. What error message are you getting?

There are, of course, other ways of getting a reference to Form1 such as passing it as a constructor argument when you instantiate your other class or exposing it as a public static property which is set in Form1's constructor.

That is what I thought but it wont let me referance Form1 as a class. I am not sure what the issue is. At first I thought that it is a private class or something like that but it doesnt seem to be. So there is something strange about this. Do I need to make any using referances in the code to use that class?

Thanks for the quick reply.

If you're using .NET 2.0 or later, then you can reference it like this:

Form1 form1  = (Form1)Application.OpenForms["Form1"];

form1.TextBox1.Text = "Some error message";

Your TextBox needs to be public for this to work.