Руководство Flutter BottomAppBar

BottomAppBar
child
shape
color
clipBehavior

1. BottomAppBar

Нижнее меню - это традиционный стиль iOS-приложений. В Flutter вы можете сделать это с помощью BottomAppBar. Кроме того, BottomAppBar также имеет удобную функцию, которая позволяет прикрепить к ней FloatingActionButton.

BottomAppBar Constructor:

BottomAppBar constructor

const BottomAppBar(
    {Key key,
    Color color,
    double elevation,
    NotchedShape shape,
    Clip clipBehavior: Clip.none,
    double notchMargin: 4.0,
    Widget child}
)

BottomAppBar обычно помещается в Scaffold через свойство AppBar.bottomNavigationBar, и она появится в нижней части Scaffold.

Руководство Flutter BottomNavigationBar

2. child

child - это самое важное свойство BottomAppBar. В большинстве случаев это будет Row, и этот объект Row содержит один или несколько Widget, таких как IconButton, PopupMenuButton и т. д.

Widget child

Пример панели BottomAppBar, action(s) которой являются IconButton, PopupMenuButton.

main.dart (child - ex1)

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Title of Application',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("BottomAppBar Example"),
        ),
        body: Center(
            child:  Text(
              'Flutter BottomAppBar Example',
            )
        ),
        bottomNavigationBar: BottomAppBar(
          child: new Row(
            mainAxisSize: MainAxisSize.max,
            mainAxisAlignment: MainAxisAlignment.start,
            children: <Widget>[
              IconButton(icon: Icon(Icons.home), onPressed: () {},),
              PopupMenuButton(
                icon: Icon(Icons.share),
                itemBuilder: (context) => [
                  PopupMenuItem(
                    value: 1,
                    child: Text("Facebook"),
                  ),
                  PopupMenuItem(
                    value: 2,
                    child: Text("Instagram"),
                  ),
                ],
              ),
              IconButton(icon: Icon(Icons.email), onPressed: () {},),
            ],
          ),
        )
    );
  }
}

Чтобы расширить приведенный выше пример, мы прикрепляем FloatingActionButton к правой стороне BottomAppBar.

main.dart (child ex2)

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Title of Application',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("BottomAppBar Example"),
        ),
        body: Center(
            child:  Text(
              'Flutter BottomAppBar Example',
            )
        ),
        floatingActionButton: FloatingActionButton.extended (
          elevation: 4.0,
          icon: const Icon(Icons.add),
          label: const Text('Add a task'),
          onPressed: () {},
        ),
        floatingActionButtonLocation: FloatingActionButtonLocation.endDocked,
        bottomNavigationBar: BottomAppBar(
          child: new Row(
            mainAxisSize: MainAxisSize.max,
            mainAxisAlignment: MainAxisAlignment.start,
            children: <Widget>[
              IconButton(icon: Icon(Icons.home), onPressed: () {},),
              PopupMenuButton(
                icon: Icon(Icons.share),
                itemBuilder: (context) => [
                  PopupMenuItem(
                    value: 1,
                    child: Text("Facebook"),
                  ),
                  PopupMenuItem(
                    value: 2,
                    child: Text("Instagram"),
                  ),
                ],
              ),
              IconButton(icon: Icon(Icons.email), onPressed: () {},),
            ],
          ),
        )
    );
  }
}

Например: BottomAppBar вместе с FloatingActionButton закреплена посередине.

main.dart (child ex3)

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Title of Application',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("BottomAppBar Example"),
        ),
        body: Center(
            child:  Text(
              'Flutter BottomAppBar Example',
            )
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: () { },
          tooltip: 'Increment',
          child: Icon(Icons.add),
          elevation: 2.0,
        ),
        floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
        bottomNavigationBar: BottomAppBar(
          child: new Row(
            mainAxisSize: MainAxisSize.max,
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: <Widget>[
              IconButton(icon: Icon(Icons.menu), onPressed: () {},),
              IconButton(icon: Icon(Icons.search), onPressed: () {},),
            ],
          ),
        )
    );
  }
}

Например: настройка высоты BottomAppBar:

main.dart (child ex4)

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Title of Application',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("BottomAppBar Example"),
        ),
        body: Center(
            child:  Text(
              'Flutter BottomAppBar Example',
            )
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: () { },
          tooltip: 'Increment',
          child: Icon(Icons.add),
          elevation: 2.0,
        ),
        floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
        bottomNavigationBar: BottomAppBar(
          child: Container(
            height: 90.0,
            child: new Row(
              mainAxisSize: MainAxisSize.max,
              mainAxisAlignment: MainAxisAlignment.spaceBetween,
              children: <Widget>[
                IconButton(icon: Icon(Icons.menu), onPressed: () {},),
                IconButton(icon: Icon(Icons.settings), onPressed: () {},),
                IconButton(icon: Icon(Icons.search), onPressed: () {},),
              ],
            ),
          )
        )
    );
  }
}

3. shape

Свойство shape используется для определения формы notch при размещении FloatingActionButton на BottomAppBar.

NotchedShape shape

NotchedShape - это абстрактный класс, который имеет два подкласса CircularNotchedRectangle и AutomaticNotchedShape.

Класс CircularNotchedRectangle помогает создать круговую notch, соответствующую круговым FloatingActionButton.
Класс AutomaticNotchedShape помогает создавать настраиваемые notches, соответствующие различным формам FloatingActionButton.

CircularNotchedRectangle
AutomaticNotchedShape

Теперь взгляните на пример использования CircularNotchedRectangle для создания круговой notch:

main.dart (shape ex1)

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Title of Application',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("BottomAppBar Example"),
        ),
        body: Center(
            child:  Text(
              'Flutter BottomAppBar Example',
            )
        ),
        floatingActionButton: FloatingActionButton(
          onPressed: () { },
          tooltip: 'Increment',
          child: Icon(Icons.add),
          elevation: 2.0,
        ),
        floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
        bottomNavigationBar: BottomAppBar(
          child: Row(
            mainAxisSize: MainAxisSize.max,
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: <Widget>[
              IconButton(icon: Icon(Icons.menu), onPressed: () {},),
              IconButton(icon: Icon(Icons.search), onPressed: () {},),
            ],
          ),
          shape: CircularNotchedRectangle(),
        )
    );
  }
}

Примечание: нельзя использовать CircularNotchedRectangle с FloatingActionButton, которая не является кругом. В противном случае вы получите неудовлетворительный результат:

Например, использование AutomaticNotchedShape с прямоугольной FloatingActionButton:

main.dart (shape ex3)

import 'package:flutter/material.dart';

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

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Title of Application',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        visualDensity: VisualDensity.adaptivePlatformDensity,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatelessWidget {
  MyHomePage({Key key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("BottomAppBar Example"),
        ),
        body: Center(
            child:  Text(
              'Flutter BottomAppBar Example',
            )
        ),
        floatingActionButton: FloatingActionButton.extended (
          elevation: 4.0,
          icon: const Icon(Icons.add),
          label: const Text('Add a task'),
          onPressed: () {},
        ),
        floatingActionButtonLocation: FloatingActionButtonLocation.centerDocked,
        bottomNavigationBar: BottomAppBar(
          child: Row(
            mainAxisSize: MainAxisSize.max,
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: <Widget>[
              IconButton(icon: Icon(Icons.menu), onPressed: () {},),
              IconButton(icon: Icon(Icons.search), onPressed: () {},),
            ],
          ),
          shape: AutomaticNotchedShape(
              RoundedRectangleBorder(),
              StadiumBorder(side: BorderSide())
          ),
        )
    );
  }
}

4. color

Свойство color используется для задания цвета BottomAppBar.

Color color

color (ex1)

BottomAppBar(
  child: Row(
    mainAxisSize: MainAxisSize.max,
    mainAxisAlignment: MainAxisAlignment.spaceBetween,
    children: <Widget>[
      IconButton(icon: Icon(Icons.menu), onPressed: () {},),
      IconButton(icon: Icon(Icons.search), onPressed: () {},),
    ],
  ),
  shape: CircularNotchedRectangle(),
  color: Colors.greenAccent
)

5. clipBehavior

Clip clipBehavior: Clip.none

Руководство Flutter Clipping