Determine which form in activepage, delphi

Question

I have a mainform (frmMain) with a pagecontrol. The pagecontrol is populated at startup by several forms, let us say Form1, Form2, and Form3

procedure TForm1.FormCreate(Sender: TObject);
begin
   ManualDock(frmMain.PageControl1);
   show;
end;
procedure TForm2.FormCreate(Sender: TObject);
begin
   ManualDock(frmMain.PageControl1);
   show;
end;
procedure TForm3.FormCreate(Sender: TObject);
begin
   ManualDock(frmMain.PageControl1);
   show;
end;

That works great. When I then change activepage, I want the OnActivate method called on the form corresponding to the activepage, so I tried this;

procedure TfrmMain.PageControl1Change(Sender: TObject);
begin
  with pagecontrol1 do
  begin
     lbHeading.Caption := activepage.Caption;
     with tform(activepage) do        // <= This does 
     if assigned(onactivate) then     // <= not
     onactivate(self);                // <= work
  end;
end;

Activepage is of type TTabsheet

Answer 1

I found a solution:

with pagecontrol1 do
begin
  with tform(activepage.controls[0]) do
  if assigned(onactivate) then
  onactivate(self);
end;