flutter.devでブラウザ上で簡易的なソースを動かしてみる

はじめにflutterを初めて知った状態でいろいろと触っていたときのメモのです。暖かい目でみてください。flutter.devというのが初めての人にはお試しとして使うには便利なツールであることだけ共有できれば幸いです。

初心者向け

flutter.devというサイトにアクセスすると、ブラウザ上で簡単なflutterを実行することができる。 まず試しにhello,world!をflutterで表示するには下記のコードだけで実装できる

import 'package:flutter/material.dart';

void main() {
  runApp(
    Center(
      child: Text(
        'Hello, world!',
        textDirection: TextDirection.ltr,
      ),
    ),
  );
}

実装するときにイメージは下記のようになります。

サンプルソース①

import 'package:flutter/material.dart';

class MyAppBar extends StatelessWidget {
  MyAppBar({this.title});

  // Fields in a Widget subclass are always marked "final".

  final Widget title;

  @override
  Widget build(BuildContext context) {
    return Container(
      height: 56.0, // in logical pixels
      padding: const EdgeInsets.symmetric(horizontal: 8.0),
      decoration: BoxDecoration(color: Colors.blue[500]),
      // Row is a horizontal, linear layout.
      child: Row(
        // <Widget> is the type of items in the list.
        children: <Widget>[
          IconButton(
            icon: Icon(Icons.menu),
            tooltip: 'Navigation menu',
            onPressed: null, // null disables the button
          ),
          // Expanded expands its child to fill the available space.
          Expanded(
            child: title,
          ),
          IconButton(
            icon: Icon(Icons.search),
            tooltip: 'Search',
            onPressed: null,
          ),
        ],
      ),
    );
  }
}

class MyScaffold extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // Material is a conceptual piece of paper on which the UI appears.
    return Material(
      // Column is a vertical, linear layout.
      child: Column(
        children: <Widget>[
          MyAppBar(
            title: Text(
              'Example title',
              style: Theme.of(context).primaryTextTheme.headline6,
            ),
          ),
          Expanded(
            child: Center(
              child: Text('Hello, world!'),
            ),
          ),
          Expanded(
            child: Container(
              margin: const EdgeInsets.fromLTRB(25.0, 25.0, 25.0, 25.0),
              child: Text('''hogehogehehogehogehogeogehogehog
             ehogehogehogehogehogehogehogehogehogehogehogeehogehogehoge
              '''),
      ),
    ),
          
        ],
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    title: 'My app', // used by the OS task switcher
    home: MyScaffold(),
  ));
}

実行例①

サンプルソース②

import 'package:flutter/material.dart';

class Product {
  const Product({this.name});
  final String name;
}

typedef void CartChangedCallback(Product product, bool inCart);

class ShoppingListItem extends StatelessWidget {
  ShoppingListItem({this.product, this.inCart, this.onCartChanged})
      : super(key: ObjectKey(product));

  final Product product;
  final bool inCart;
  final CartChangedCallback onCartChanged;

  Color _getColor(BuildContext context) {
    // The theme depends on the BuildContext because different parts
    // of the tree can have different themes.
    // The BuildContext indicates where the build is
    // taking place and therefore which theme to use.

    return inCart ? Colors.black54 : Theme.of(context).primaryColor;
  }

  TextStyle _getTextStyle(BuildContext context) {
    if (!inCart) return null;

    return TextStyle(
      color: Colors.black54,
      decoration: TextDecoration.lineThrough,
    );
  }

  @override
  Widget build(BuildContext context) {
    return ListTile(
      onTap: () {
        onCartChanged(product, inCart);
      },
      leading: CircleAvatar(
        backgroundColor: _getColor(context),
        child: Text(product.name[0]),
      ),
      title: Text(product.name, style: _getTextStyle(context)),
    );
  }
}


class ShoppingList extends StatefulWidget {
  ShoppingList({Key key, this.products}) : super(key: key);

  final List<Product> products;

  // The framework calls createState the first time a widget
  // appears at a given location in the tree.
  // If the parent rebuilds and uses the same type of
  // widget (with the same key), the framework re-uses the State object
  // instead of creating a new State object.

  @override
  _ShoppingListState createState() => _ShoppingListState();
}

class _ShoppingListState extends State<ShoppingList> {
  Set<Product> _shoppingCart = Set<Product>();

  void _handleCartChanged(Product product, bool inCart) {
    setState(() {
      // When a user changes what's in the cart, you need to change
      // _shoppingCart inside a setState call to trigger a rebuild.
      // The framework then calls build, below,
      // which updates the visual appearance of the app.

      if (!inCart)
        _shoppingCart.add(product);
      else
        _shoppingCart.remove(product);
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('Shopping List'),
      ),
      body: ListView(
        padding: EdgeInsets.symmetric(vertical: 8.0),
        children: widget.products.map((Product product) {
          return ShoppingListItem(
            product: product,
            inCart: _shoppingCart.contains(product),
            onCartChanged: _handleCartChanged,
          );
        }).toList(),
      ),
    );
  }
}

void main() {
  runApp(MaterialApp(
    title: 'Shopping App',
    home: ShoppingList(
      products: <Product>[
        Product(name: 'Eggs'),
        Product(name: 'Flour'),
        Product(name: 'Chocolate chips'),
      ],
    ),
  ));
}

実装イメージ②