Delphi Change main form while application is running

Question

I have this problem. When I hide my main form, then the taskbar icon of my application is also hidden. I saw a new question about this problem as well and the answers didn\'

Answer 1

I've had an additional issue working with Delphi XE2 MDI apps that are also COM servers. My main form Main calls a secondary form MenuForm which contains shared icons and popup menus for the whole app.

In my example, the app works perfectly when run standalone.

Main gets created, and then creates a MenuForm at the end of FormCreate. All good.

But when called from a COM server, Main.FormCreate is called first, but somehow MenuForm gets assigned to Application.MainForm. There is a race condition in the underlying RTL. This causes havoc when trying to create the first SDI child, as Application.MainForm is not MDI.

I tried working around this by Main.FormCreate posting a message back to itself, to delay creation of MenuForm until after Main.FormCreate has returned.

But there is still a race condition here - MenuForm was still assigned to Application.MainForm.

I was eventually able to work around this using code to poll Application.MainForm every 10ms, with a maximum of 10 seconds. I also had to remove any reference in Main to MenuForm's icon list (in the .dfm) until after MenuForm was created explicitly - otherwise MenuForm would get created implicitly at the end of MainForm.create.

Hope this helps someone!

const
  CM_INITIAL_EVENT = WM_APP + 400;


TmainForm = class(TForm)
  ...
  procedure afterCreate(var Message: TMessage); message CM_INITIAL_EVENT;
  ...
end;


procedure TmainForm.FormCreate(Sender : TObject);
begin
  ...
  ...standard init code
  ...

  postmessage( handle, CM_INITIAL_EVENT, 0, 0 );
End;


procedure TmainForm.AfterCreate(var Message: TMessage);
var
  i: Integer;
begin

  //must assign these AFTER menuform has been created
  if menuForm = nil then
  begin
    //wait for mainform to get assigned
    //wait up to 10*1000ms = 10 seconds
    for i := 0 to 1000 do
    begin
      if Application.Mainform = self then break;
      sleep(10);
    end;

    Application.CreateForm(TmenuForm, menuForm);
    menuForm.parent := self;
  end;

  //NOW we can assign the icons
  Linktothisfilterfile1.SubMenuImages := menuForm.treeIconList;
  ActionManager.Images := menuForm.treeIconList;
  allFilters.Images := menuForm.treeIconList;
  MainMenu.Images := menuForm.treeIconList;
  ...
end;