这是不可能的。
TimeOfDay 仅保留小时和分钟。尽管 DateTime 还具有日/月/年

This is not possible. TimeOfDay holds only the hour and minute. While a DateTime also has day/month/year

如果要进行转换，则需要更多信息。如当前的DateTime。然后将两者合并为一个最终日期时间。

If you want to convert it, you will need more informations. Such as the current DateTime. And then merge the two into one final datetime.

TimeOfDay t;
final now = new DateTime.now();
return new DateTime(now.year, now.month, now.day, t.hour, t.minute);