Flutter中如何开启界面绘制边界线：debugPaintSizeEnabled = true

效果图在最下面

import 'package:flutter/material.dart';
import 'package:flutter/rendering.dart'; // 1.第一步
import 'login.dart';

void main() {
  debugPaintSizeEnabled = true; //2.第二步
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return
       MaterialApp(
          home: new LoginPage(),
        );
  }
}