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Report From: Delphi-BCB/VCL/MDI Support [ Add a report in this area ]

Report #: 66204

Status: Reported

Closing mainform, the childs OnClose isn't called

Project: Delphi

Build #: 11.0.2902.1047

Version: 11.2

Submitted By: Henrik R. Carlsen

Report Type: Minor failure / Design problem

Date Reported: 8/29/2008 12:43:32 AM

Severity: Commonly encountered problem

Last Updated: 8/29/2008 12:46:53 AM

Platform: All platforms

Internal Tracking #:

Resolution: None

Resolved in Build: : None

Duplicate of: None

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Description

The attached example is an MDI-application with one child. The child has two events, OnClose and OnDestroy. The OnClose sets Action = caFree.

Opening the child and closing it again, calls the OnClose, then the OnDestroy event.

Same scenario, one child-form open. If I try to close the MDIForm hoping it'll rid the child properly, only the OnDestroy is called. There's no telling that the child form is to free itself.

If I debug it seems that the Application.MainForm is nil before the child is gone. It therefore raises this exception.

procedure TCustomForm.CreateWindowHandle(const Params: TCreateParams);
var
  CreateStruct: TMDICreateStruct;
  NewParams: TCreateParams;
begin
  if (FormStyle = fsMDIChild) and not (csDesigning in ComponentState) then
  begin
    if (Application.MainForm = nil) or
      (Application.MainForm.ClientHandle = 0) then
      raise EInvalidOperation.Create(SNoMDIForm); // 'ere!

Steps to Reproduce:

See attachment

Workarounds

Main form OnClose event:

procedure TfrmMain.FormClose(Sender: TObject; var Action: TCloseAction);
var
  i: integer;
begin
  for i := MDIChildCount - 1 downto 0 do
    MDIChildren[i].Close;
end;

Attachment

66204.zip

Comments

Lucian Radulescu at 9/4/2008 12:58:14 PM -

It works like this since day Delphi 1 - so, I don't think a bit it is going to change.

I too had this issues in MDI apps and what I learned is that you should not rely at all on what VCL does. What I do is override CloseQuery in my mainforms with code like this:

function TWILLMainForm.CloseQuery: Boolean;
var
  I: Integer;
begin
  if MDIChildCount <> 0 then
  repeat
    I := MDIChildCount;
    SendMessage(ActiveMdiChild.Handle, WM_CLOSE, 0, 0);
    Application.ProcessMessages;
  until (MDIChildCount = 0) or (I = MDIChildCount);
  Result := (MDIChildCount = 0) and inherited CloseQuery;
end;

I don't like it that I have to call Application.ProcessMessages in that loop, but .... that's the best I could do :-)

BTW, your FormClose does not guarantee all the children are closed. (Overriding) Mainform CloseQuery execution is guaranteed. So your app is still safe up and running if one child does not want to close.

hth

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