Question

I am trying to create a reusable function that can open a single instance of form. Means if a form is not already open it should create and show the new form and if already open it should bring the existing form to front.

I was using the following function,

if (Application.OpenForms["FPSStorageDemo"] == null)
            {
                FPSStorageDemo fp = new FPSStorageDemo();
                fp.Name = "FPSStorageDemo";
                fp.Show();
            }
            else
            {
                ((FPSStorageDemo)Application.OpenForms["FPSStorageDemo"]).BringToFront();
            }

But I have to write this code again and again whereever I have to open a form. But I need a single reusable function that can do this job.

I wrote a function like,

void OpenSingleInstanceForm(Type TypeOfControlToOpen)
        {
            bool IsFormOpen = false;
            foreach (Form fm in Application.OpenForms)
            {
                if (fm.GetType() == TypeOfControlToOpen)
                {
                    IsFormOpen = true;
                    fm.BringToFront();
                    break;
                }
            }

            if (!IsFormOpen)
            {
                Object obj = Activator.CreateInstance(TypeOfControlToOpen);
                //obj.Show(); //Here is the problem
            }
        }

But at the end I don’t know how to show the new form instance. Can anybody suggest how to do it? Is this wrong or there is another way to do this?

Thanks in advance.

Answer 1

public static class FormUtility
{
public static FormType GetInstance<FormType>() where FormType : Form, new()
{
  FormType output = Application.OpenForms.OfType<FormType>().FirstOrDefault();
  if(output == null)
  {
    output = new FormType();
  }
  //you could add the show/bring to front here if you wanted to, or have the more general method
  //that just gives a form that you can do whatever you want with (or have one of each).
  return output;
}
}

//elsewhere
FormUtility.GetInstance<Form1>.BringToFront();

I’d also like to take the time to mention that while having methods like this are quick and easy to use, in most cases they are not good design. It leads you to the practice of just accessing forms globally rather than ensuring that when forms need to communicate with each other they do so by exposing the appropriate information through the appropriate scope. It makes programs easier to maintain, understand, extend, increases reusability, etc. If you have trouble determining how best for two or more forms to communicate without resorting to public static references to your forms (which is exactly what Application.OpenForms is) then you should feel free to post that question here for us to help you solve.