lib/main.dart:1: Warning: Interpreting this as package URI, 'package:flutter_app/main.dart'.

import 'dart:ui' as ui show Paint, Path, Canvas;

解决：

Ref: https://*.com/questions/54072544/how-to-solved-dartui-error-when-going-to-run-flutter-app

Link: https://www.cnblogs.com/farwish/p/10428661.html