procedure TForm1.Button1Click(Sender: TObject);
var
  r:HINST;
begin
  OpenDialog1.Execute;//选择文件
  r:=ShellExecute(Handle,'open',PChar(OpenDialog1.FileName),nil,PChar(ExtractFileDir(OpenDialog1.FileName)),SW_SHOW);//打开文件
  if r =SE_ERR_NOASSOC then//如果没有关联的打开方式
    ShellExecute(Handle, 'open', 'Rundll32.exe', PChar('shell32.dll,OpenAs_RunDLL ' + OpenDialog1.Filename), nil, SW_SHOWNORMAL);//调用打开方式对话框
end;