画饼充饥
[词典] （比喻借空想安慰自己） draw cakes to allay hunger -- feed on illusions; a Barmecide feast; draw a cake and call it a dinner; draw [paint] a cake [pie] to satisfy (one's) hunger;
[例句]他禁不住想所有这些不过是“画饼充饥”的空话而已。
He can't help thinking it's all just 'pie in the sky' talk.