function GetDirectoryCount(const DirName: string): Integer;
begin
  Result := Length(TDirectory.GetDirectories(DirName));
end;

TDirectory.GetDirectories实际上返回一个包含目录名称的动态数组,所以这有点低效.如果你想要最有效的解决方案,那么你应该使用FindFirst枚举.

function GetDirectoryCount(const DirName: string): Integer;
var
  res: Integer;
  SearchRec: TSearchRec;
  Name: string;
begin
  Result := 0;
  res := FindFirst(TPath.Combine(DirName,'*'),faAnyFile,SearchRec);
  if res=0 then begin
    try
      while res=0 do begin
        if SearchRec.FindData.dwFileAttributes and faDirectory<>0 then begin
          Name := SearchRec.FindData.cFileName;
          if (Name<>'.') and (Name<>'..') then begin
            inc(Result);
          end;
        end;
        res := FindNext(SearchRec);
      end;
    finally
      FindClose(SearchRec);
    end;
  end;
end;