01課 〜とき 教科書 p.16
When〜
接続：V辞書形・Vている・Vない／いA／なAな／Nの + うちに
during / before the state changes. Used when taking advantage of the length of time a state continues, or when a natural change occurs during that time.
注意 / Note：Do not use it directly after the past form to say something has been completed. When you want to emphasize an objective period of time, consider 間に.
比較 / Compare：うちに emphasizes ‘before the opportunity/state changes’; 間に only determines that B occurs in interval A. Same 課: 〜間／〜間に／〜てからでないと／〜てからでなければ／〜ところだ(+助詞) — these samples are often mistakenly chosen for each other, read line 接続 carefully and then decide.
熱いうちに、スープを飲んでください。
Drink the soup while it's still hot.
日本にいるうちに、京都へ行きたいです。
While I was in Japan, I wanted to go to Kyoto.
バッテリーが残っているうちに、写真をクラウドへ保存しておこう。
While the battery lasts, save your photos to the cloud.