(Save Dialog) How to change file extension automatically on file filter change in Vista/Win7?

Question

While showing a save dialog, I want to hook user's filter type change and change file extension automatically. (e.g. like MSPaint's "Save As" operation.)

With TSaveDialog and setting UseLatestCommonDialogs := False, I can handle this by the following code. (without latest common dialog support, of cource.)

procedure TForm1.SaveDialog1TypeChange(Sender: TObject);
var
  FName, Ext: string;
begin
  with TSaveDialog(Sender) do
  begin
    if DirectoryExists(FileName) then // FileName is Empty
      exit;
    case FilterIndex of
    1: Ext := '.png';
    2: Ext := '.bmp';
    3: Ext := '.jpg';
    end;
    FName := ChangeFileExt(ExtractFileName(FileName), Ext);
    SendMessage(Windows.GetParent(Handle), CDM_SETCONTROLTEXT, 1152, LongInt(PChar(FName)));
  end;
end;

I want to support both XP, and vista/7 with Delphi 2007.

Should I use TFileSaveDialog instead of TSaveDialog with internal wrapper ? (And I have to struggle with COM programming using IFileDialogControlEvents ?)

Or can I achieve this with TFileSaveDialog and it's standard properties only ? (My development environment is still on XP machine, so I've never tried. sorry.)

I think it's very common task, but I couldn't find any sample code supporting Vista/7...

Answer 1

As far as I know, TFileSaveDialog will raise an exception on XP. It needs Vista or up.

Update: some D2010 code for TFileSaveDialog adapted from your event handler....
(I don't have D2007 on Vista; use PWideChar instead of PChar)

procedure TForm1.FileSaveDialog1TypeChange(Sender: TObject);
var
  FName, Ext: string;
  pName: PChar;
begin
  with TFileSaveDialog(Sender) do
  begin
    if DirectoryExists(FileName) then // FileName is Empty
      exit;
    case FileTypeIndex of
    1: Ext := '.png';
    2: Ext := '.bmp';
    3: Ext := '.jpg';
    end;
    Dialog.GetFileName(pName);
    FName := ChangeFileExt(ExtractFileName(pName), Ext);
    Dialog.SetFileName(PChar(FName));
  end;
end;

Where the FileSaveDialog is:

object FileSaveDialog1: TFileSaveDialog
  FavoriteLinks = <>
  FileTypes = <
    item
      DisplayName = 'png files'
      FileMask = '*.png'
    end
    item
      DisplayName = 'bmp files'
      FileMask = '*.bmp'
    end
    item
      DisplayName = 'jpg files'
      FileMask = '*.jpg'
    end>
  Options = []
  OnTypeChange = FileSaveDialog1TypeChange
end