[flutter] const_constructor

1)

빌드! 클릭

2) const 미사용

import 'package:flutter/material.dart';

class HomeScreen extends StatefulWidget {
  const HomeScreen({Key? key}) : super(key: key);

  @override
  State<HomeScreen> createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        width: MediaQuery.of(context).size.width,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            TestWidget(label: 'test1'),
            TestWidget(label: 'test2'),
            ElevatedButton(
              onPressed: () {
                setState(() {});
              },
              child: Text(
                '빌드!',
              ),
            ),
          ],
        ),
      ),
    );
  }
}

class TestWidget extends StatelessWidget {
  final String label;

  const TestWidget({
    Key? key,
    required this.label,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    print('$label 빌드 실행');

    return Container(
      child: Text(
        label,
      ),
    );
  }
}

3) const 사용

import 'package:flutter/material.dart';

class HomeScreen extends StatefulWidget {
  const HomeScreen({Key? key}) : super(key: key);

  @override
  State<HomeScreen> createState() => _HomeScreenState();
}

class _HomeScreenState extends State<HomeScreen> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        width: MediaQuery.of(context).size.width,
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,
          children: [
            TestWidget(label: 'test1'),
            const TestWidget(label: 'test2'),
            ElevatedButton(
              onPressed: () {
                setState(() {});
              },
              child: const Text(
                '빌드!',
              ),
            ),
          ],
        ),
      ),
    );
  }
}

class TestWidget extends StatelessWidget {
  final String label;

  const TestWidget({
    Key? key,
    required this.label,
  }) : super(key: key);

  @override
  Widget build(BuildContext context) {
    print('$label 빌드 실행');

    return Container(
      child: Text(
        label,
      ),
    );
  }
}

const를 사용하지 않은 빌드1만 실행된다!!!

- const를 사용하면 첫 빌드시 미리 저장해놓기 때문에 효율적이다!!