flutterで画面遷移とパラメータの受け渡しをする

はじめに

• 久しぶりにflutterの勉強を再開してみる。

flutter doctorでエラーの解消

• 久しぶりに動かそうとしたら、flutter doctorでエラーになった

C:\Users\user>flutter doctor
Doctor summary (to see all details, run flutter doctor -v):
[√] Flutter (Channel stable, 2.5.3, on Microsoft Windows [Version 10.0.19043.1415], locale ja-JP)
[!] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    X cmdline-tools component is missing
      Run `path/to/sdkmanager --install "cmdline-tools;latest"`
      See https://developer.android.com/studio/command-line for more details.
    X Android license status unknown.
      Run `flutter doctor --android-licenses` to accept the SDK licenses.
      See https://flutter.dev/docs/get-started/install/windows#android-setup for more details.
[√] Chrome - develop for the web
[√] Android Studio (version 2020.3)
[√] VS Code (version 1.62.3)
[√] Connected device (2 available)

! Doctor found issues in 1 category.

cmdline-tools component is missingエラー

• 下記の赤枠の箇所にチェックを入れて Applyボタンをクリックすることで解消できました。

Android license status unknown.エラー

• 下記のコマンドを実行するとことでエラーを解消することが出来ました。

 flutter doctor --android-licenses

画面遷移するサンプル

• トップ画面

import 'dart:ui';

import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:winlogic/next_page.dart';

// よいサンプル
// https://github.com/kenta-wakasa/riverpod_sample

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: const MyHomePage(title: 'トップページ'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({Key? key, required this.title}) : super(key: key);
  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;
  String _text ="";

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  void _changeText(input) {
    print(input);
    setState(() {
      _text = input;
    });
  }

  final ButtonStyle style =
  ElevatedButton.styleFrom(textStyle: const TextStyle(fontSize: 20));

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),
        actions: <Widget>[Icon(Icons.add), Icon(Icons.share)],
      ),
      body: Container(
          width: double.infinity,
          child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            crossAxisAlignment: CrossAxisAlignment.center,
            children: [
              //Image.network('https://flutter.github.io/assets-for-api-docs/assets/widgets/owl.jpg'),
              Image.asset('images/sample.jpg', height: 200),
              Icon(Icons.holiday_village,size:30),
              Text(_text),
              Text("テストテスト",
                style: TextStyle(
                  fontSize: 40,
                  color: Colors.green,
                  fontWeight: FontWeight.w900,
                  fontStyle: FontStyle.italic,
                )
              ),
              Text("サンプルテキスト"),
              ElevatedButton(
                  child: Text("次へ"),
                  onPressed: () async {
                    final result = await Navigator.push(
                        context,
                        MaterialPageRoute(builder: (context) => NextPage('１ページ目から渡すパラメータ'))
                    );
                    _text = result;
                    _changeText(result);
                    print(_text);
                  }
              )
            ],
          )
      ),
      floatingActionButton: FloatingActionButton(
      onPressed: _incrementCounter,
      tooltip: 'Increment',
      child: const Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
  );
  }
}

• 2画面目

import 'package:flutter/material.dart';

class NextPage extends StatelessWidget {
  NextPage(this.name);
  final String name;
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('２ページ目'),
        actions: <Widget>[Icon(Icons.add), Icon(Icons.share)],
      ),
      body: Container(
        height: double.infinity,
        color: Colors.greenAccent,
        child: Column(
            mainAxisAlignment: MainAxisAlignment.center,
            children: <Widget>[
            Text(name),
            Center(
              child: ElevatedButton(
                  child: Text('戻る'),
                  onPressed: () {
                    Navigator.pop(context, "２ページ目から渡すパラメータ");
                  }
              )
            ),
          ]
        )
      )
    );
  }
}

• pubspec.yamlに下記の記述をしないとassetで画像を表示することが出来ない

flutter:
  assets:
    - images/sample.jpg