How do you set the FileTypeIndex in a DoExecute TFileSaveDialog Event if the extension is known?

Question

If a file extension is known how do you convert the extension to a FileTypeIndex in the TFileSaveDialog DoExecute event?

   function TIEWin7FileSaveDialog.DoExecute: Bool;
    begin
    ...
    {Set FileType (filter) index}
    iWideTextension := ExtractFileExt(FileName);
    FileTypeIndex := ???ExtensionToFileTypeIndex(iWideExtension);???
    FileDialog.SetFileTypeIndex(FileTypeIndex);
    ...
    end;

Answer 1

There's no explicit function that would do what you want at least since one file type may be contained in more file type masks, so you can only iterate the FileTypes and check if the file type is contained or equals to the FileMask like shown below:

function FindFirstFileType(FileDialog: TCustomFileDialog;
  const FileExt: string): UINT;
var
  TypeIndex: Integer;
  ExtIndex: Integer;
  ExtArray: TStringDynArray;
begin
  Result := 0;
  for TypeIndex := 0 to FileDialog.FileTypes.Count - 1 do
  begin
    ExtArray := SplitString(FileDialog.FileTypes[TypeIndex].FileMask, ';');
    for ExtIndex := 0 to High(ExtArray) do
      if ExtArray[ExtIndex] = FileExt then
        begin
          Result := TypeIndex;
          Break;
        end;
  end;
end;

And the usage (note that the input must match exactly to the filter mask):

procedure TForm1.Button1Click(Sender: TObject);
var
  I: UINT;
begin
  I := FindFirstFileType(FileOpenDialog1, '*.pas');
end;