Displaying splash screen in Delphi when main thread is busy

Question

I'd like to display splash screen while the application is loading. However some 3rd party components block main thread during initilization for several seconds, which causes all forms not to update. Is it possible to have splash screen with own thread so it would update also when main thread is busy?

The application is win32 and Delphi version 2007.

Edit: I'm trying to avoid "undrawn splash screen" effect, which happens if some other windows (from other applications) are on the top of splash screen, eg alt-tabbing to another application and back.

Answer 1

You can run the splash screen in another thread, but then you will need to use raw Windows API calls or a third-party library (like Key Objects Library) that implements VCL-like classes. Do however not access VCL stuff from splash thread.

If you go that route (which I don't think you should, as it is a lot of work for little gain), be sure to observe the rules about Windows API access from multiple threads. Google for example for "user interface threads" for more information.

Edit:

I wasn't aware of it before, but there is actually a component implementing a Threaded Splashscreen for Delphi on CodeCentral. Using this component it may (haven't tried it) actually be easy to have the splash screen in a different thread, but the warning against VCL access from secondary threads remains.

Answer 2

Actually WinApi way is quite simple as long as you use dialog resources. Check this (working even on D7 and XP):

type
  TDlgThread = class(TThread)
  private
    FDlgWnd: HWND;
    FCaption: string;
  protected
    procedure Execute; override;
    procedure ShowSplash;
  public
    constructor Create(const Caption: string);
  end;

{ TDlgThread }

// Create thread for splash dialog with custom Caption and show the dialog
constructor TDlgThread.Create(const Caption: string);
begin
  FCaption := Caption;
  inherited Create(False);
  FreeOnTerminate := True;
end;

procedure TDlgThread.Execute;
var Msg: TMsg;
begin
  ShowSplash;
  // Process window messages until the thread is finished
  while not Terminated and GetMessage(Msg, 0, 0, 0) do
  begin
    TranslateMessage(Msg);
    DispatchMessage(Msg);
  end;
  EndDialog(FDlgWnd, 0);
end;

procedure TDlgThread.ShowSplash;
const
  PBM_SETMARQUEE = WM_USER + 10;
  {$I 'Dlg.inc'}
begin
  FDlgWnd := CreateDialogParam(HInstance, MakeIntResource(IDD_WAITDLG), 0, nil, 0);
  if FDlgWnd = 0 then Exit;
  SetDlgItemText(FDlgWnd, IDC_LABEL, PChar(FCaption));           // set caption
  SendDlgItemMessage(FDlgWnd, IDC_PGB, PBM_SETMARQUEE, 1, 100);  // start marquee
end;

procedure TForm1.Button3Click(Sender: TObject);
var th: TDlgThread;
begin
  th := TDlgThread.Create('Connecting to DB...');
  Sleep(3000); // blocking wait
  th.Terminate;
end;

Of course you must prepare dialog resource (Dlg.rc) and add it to your project:

#define IDD_WAITDLG 1000
#define IDC_PGB 1002
#define IDC_LABEL 1003

#define PBS_SMOOTH  0x00000001
#define PBS_MARQUEE 0x00000008

IDD_WAITDLG DIALOGEX 10,10,162,33
STYLE WS_POPUP|WS_VISIBLE|WS_DLGFRAME|DS_CENTER
EXSTYLE WS_EX_TOPMOST
BEGIN
  CONTROL "",IDC_PGB,"msctls_progress32",WS_CHILDWINDOW|WS_VISIBLE|PBS_SMOOTH|PBS_MARQUEE,9,15,144,15
  CONTROL "",IDC_LABEL,"Static",WS_CHILDWINDOW|WS_VISIBLE,9,3,144,9
END

Note these PBS_* defines. I had to add them because Delphi 7 knows nothing of these constants. And definition of constants (Dlg.inc)

const IDD_WAITDLG = 1000;
const IDC_PGB = 1002;
const IDC_LABEL = 1003;

(I use RadAsm resource editor which generates include file automatically).

What we get under XP

What is better in this way comparing to VCL tricks (ordering of forms creation and so n) is that you can use it multiple times when your app needs some time to think.