Idea for aIdea for a Non-blocking dialoguing mechanism (https://plus.google.com/u/0/115543678481226143222/posts/46dTfcuVVLP?cfem=1)

NonBlockingDlgHelperU.pas

unit NonBlockingDlgHelperU;

interface

uses
  Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
  Vcl.Controls, Vcl.Forms, Vcl.Dialogs;

const
  WM_ShowDlgA = WM_APP + 1;
  WM_ShowDlgB = WM_APP + 2;

type
  (*
    Idea for a Non-blocking dialoguing mechanism.

    In other parts of your software you cal it like this:
      PostMessage(NonBlockingDlgHelper.Handle, WM_ShowDlgA, PChar(aString), CastAnnoMethodToLParam(SomeFunc));
  *)
  TNonBlockingDlgHelper = class(TForm)
  private
  public
    procedure WMShowDlgA(var Message: TMessage); message WM_SHOWDLGA;
    procedure WMShowDlgB(var Message: TMessage); message WM_SHOWDLGB;
  end;

var
  NonBlockingDlgHelper: TNonBlockingDlgHelper;

implementation

{$R *.dfm}

procedure TNonBlockingDlgHelper.WMShowDlgA(var Message: TMessage);
begin
  inherited;
  if Application.MessageBox(PChar(Message.WParam), '', MB_OKCANCEL) = IDCANCEL then
    PostMessage(Self.Handle, WM_ShowDlgB, 0, 0);

   // note: Also consider to use TMessage.LParam to pass in a 'OnClose' Anno. method object.
end;

procedure TNonBlockingDlgHelper.WMShowDlgB(var Message: TMessage);
begin
  inherited;
  Application.MessageBox('So you have cancelled', '', MB_OKCANCEL);
end;

end.