【走り書き】StatelessWidgetとStatefulwidget【Flutter】 https://shuhey-hashimoto.com/flutter/%e3%80%90%e8%b5%b0%e3%82%8a%e6%9b%b8%e3%81%8d%e3%80%91statelesswidget%e3%81%a8statefulwidget%e3%80%90flutter%e3%80%91/