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Calling ShowModal with PopupParent setting is a good idea and is it necessary in newer Delphi versions?

To prevent new modals from appearing under their modal parent window, I am used to always setting PopupParent

on call ShowModal

(as recommended here , here and here ):

function TMyForm.ShowModal(ParentForm: TCustomForm): Integer;
begin
    PopupParent := ParentForm;
    Result := inherited ShowModal;
end;

But on debugging (Lost Form placement issue set in FormCreate) I figured out that setting PopupParent

results in a call ReCreateWindow

, thereby destroying and recreating the underlying Windows display object.

My questions:

  • Is it always good to install PopupParent

    - what could be the problems that arise? Are there viable alternatives?
  • Is this still needed in newer versions of Delphi (I'm using D2006 at the moment, but plan to upgrade)?

EDIT:

I think all related questions are about the same problem, which is best described by the third link :

[Form opens] with ShowModal, this form opens another with ShowModal, so we have complex modal forms. Sometimes the problem arises when we call ShowModal on a new form, it hides behind the previous forms, instead of showing at the top. After pressing alt + tab, the form returns to the top [...]

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2 answers


This question is quite old, but still relevant. The best source of information on this is from Allen Bauer himself: http://blog.therealoracleatdelphi.com/2004/02/popupmode-and-popupparent_10.html

(Vaybak: https://web.archive.org/web/20160324062228/http://blogs.embarcadero.com/abauer/2004/02/10/295 )

And there you will find this: "If you explicitly set the PopupMode pmAuto property before ShowModal, for example at design time, then no re-creation is required."



Thus, your code should be:

function TMyForm.ShowModal(ParentForm: TCustomForm): Integer;
begin
    PopupMode := pmAuto;
    PopupParent := ParentForm;
    Result := inherited ShowModal;
end;
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After 2 hours of debugging and reading the VCL code, I'll add my findings to this thread. In Delphi 10 Seattle, the behavior looks like this:

  • window forms are processed when the form is created by its constructor, because the TCustomForm.ReadState(Reader: TReader)

    width of the form client is set, which leads to a callCreateWnd

  • so even if you put pmAuto

    up ShowModal

    , the window needs to be recreated

Finally, the documentation mentions:

The PopupMode property is automatically set to pmAuto

when the method is called ShowModal

.

So these lines in ShowModal

:



if (PopupMode = pmNone) and (Application.ModalPopupMode <> pmNone) then
begin
  RecreateWnd;
  //..

To make this work, you also need to modify Application.ModalPopupMode

, but this will recreate the window as well.

So my advice is:

  • set a value for PopupMode

    ( pmAuto

    ) directly in your form ( dfm

    file)

  • setting both PopupParent

    and PopupMode

    makes little sense because they are related PopupParent

    sets pmExplicit

    and pmAuto

    resets the pop-up parent tonil

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