Delphi - Hidden MDI child form creation

Question

Hi

My application has many many mdi forms and they are created after successfull user login. How can I best hide this creation process? It looks stupid and it takes longer time while mdi forms are painted after new form is created and so on.

So far I have used LockWindowUpdate, which doesn't hide everything, but I would like to use a splash screen showing the creation progress, but I can't with LockWindowUpdate.

Best Regards Janne

Answer 1

To create MDI child forms invisible you set their Visible property to False, and in addition you have to disable the VCL behaviour of force-showing them during creation. This happens by the FormStyle property setter of TCustomForm, which sets Visible to True for MDI child forms.

If you set the FormStyle in the object inspector, then the property setter will be called during form creation already, and the form will not be shown immediately, but only after the construction is complete. This allows you to reset the request to show the form, by overriding the AfterConstruction() method like so:

procedure TMDIChild.AfterConstruction;
begin
  Exclude(FFormState, fsVisible);
  inherited;
end;

This will create an invisible MDI child form.

To test this you can create a new MDI application in the IDE, override the method in the child form class like shown above, and simulate a long initialization:

procedure TMainForm.FileNew1Execute(Sender: TObject);
var
  i: integer;
begin
  for i := 1 to 10 do begin
    CreateMDIChild('NONAME' + IntToStr(MDIChildCount + 1));
    Update;
    Sleep(500);
  end;
  for i := 0 to MDIChildCount - 1 do
    MDIChildren[i].Visible := True;
end;

Without the overridden AfterConstruction() method it will create and show a MDI child every half second. With the overridden method it will show them all after a busy period of 5 seconds, which will give you the chance to show your splash screen instead.

Important:

Using LockWindowUpdate() to reduce flicker or suppress any screen output is wrong, wrong, wrong. Don't do it, read the series of Raymond Chen articles on the topic to understand why that is so.

Answer 2

I had a similar problem with flickering MDI childs. I used combination of overrinding AfterConstruction and WM_SETREDRAW message from this tip: http://stackoverflow.com/questions/3507144/controlling-the-placement-of-fsmdichild-windows-in-delphi

SendMessage(Application.MainForm.ClientHandle, WM_SETREDRAW, False, 0);
try
  Child := TChildForm.Create(Self);
  Child.Left := ...;
  Child.Top := ...;
  Child.Show;
finally
  SendMessage(Application.MainForm.ClientHandle, WM_SETREDRAW, True, 0);
  InvalidateRect(Application.MainForm.ClientHandle, nil, True);
end;

And everything works fine.