Testing, if form exists

Sometimes a form may be launched from several places in a program. If it already exists, it only needs to be brought to the front. If not, it needs to be created.

This method is only needed if the form is not auto created (ie not listed under Project|Project Options|Forms|Available forms).

The easiest way is:

if (MyForm = nil) then Application.CreateForm(TMyForm, MyForm);
    MyForm.Show;

Use CloseAction := caFree in the form's OnClose event, like so:

procedure TMyForm.FormClose(Sender: Tobject; var Closeaction: Tcloseaction);
    begin
      CloseAction := caFree;
      MyForm := nil;
    End;

This method is taken from forum discussions.

Warning: This method has some limitations:

• Not more than one instance of that form class should exist at any time.
• Reference to any created form of that class should be stored in a single global variable.

From the Free Pascal wiki, page "Testing, if form exists", as the Internet Archive kept it on 2024-12-06, last changed on 2020-02-29. Copyright stays with the author who wrote it, according to the old wiki's Licensing page. If you have concerns about this material, message the admin.