Question

I create my forms at runtime something like this:

AboutForm := TAboutForm.Create(AboutForm);
try
  AboutForm.ShowModal;
finally
  AboutForm.Free;
end;

But what is the difference though in using any of these:

AboutForm := TAboutForm.Create(Self);
AboutForm := TAboutForm.Create(nil);
AboutForm := TAboutForm.Create(Application);

They all seem to work the same from what I can see but which is correct, or are they all correct, which is generally the best one to use?

Appreciate your comments thanks 🙂

Answer 1

The TForm.Create takes an Owner as parameter.

In your first example, AboutForm is the owner. Which obviously is a bad idea, since it’s not created yet.

When Self is the parameter, the instance that makes the call is the owner.
When Application is the parameter, the Application is the owner.
When nil is the parameter, the AboutForm doen not have a owner. That is all fine, but in those cases you must remember to free the form yourself.

When you do pass in a owner, you actually don’t need to free i explicitly. The owner will free it when the owner is freed.

This is how your code should look like:

AboutForm := TAboutForm.Create(nil);
try
  AboutForm.ShowModal;
finally
  AboutForm.Free;
end;