// The contents of views

// Only the content associated with the selected tab is displayed on the screen

final List _mainContents = [

// Content for Home tab

Container(

color: Colors.yellow.shade100,

alignment: Alignment.center,

child: const Text(

‘Home’,

style: TextStyle(fontSize: 40),

),

),

// Content for Feed tab

Container(

color: Colors.purple.shade100,

alignment: Alignment.center,

child: const Text(

‘Feed’,

style: TextStyle(fontSize: 40),

),

),

// Content for Favorites tab

Container(

color: Colors.red.shade100,

alignment: Alignment.center,

child: const Text(

‘Favorites’,

style: TextStyle(fontSize: 40),

),

),

// Content for Settings tab

Container(

color: Colors.pink.shade300,

alignment: Alignment.center,

child: const Text(

‘Settings’,

style: TextStyle(fontSize: 40),

),

)

];

// The index of the selected tab

// In the beginning, the Home tab is selected

int _selectedIndex = 0;

@override

Widget build(BuildContext context) {

return Scaffold(

appBar: AppBar(

title: const Text(‘大前端之旅’),

),

// Show the bottom tab bar if screen width < 640

bottomNavigationBar: MediaQuery.of(context).size.width < 640

? BottomNavigationBar(

currentIndex: _selectedIndex,

unselectedItemColor: Colors.grey,

selectedItemColor: Colors.indigoAccent,

// called when one tab is selected

onTap: (int index) {

setState(() {

_selectedIndex = index;

});

},

// bottom tab items

items: const [

BottomNavigationBarItem(

icon: Icon(Icons.home), label: ‘Home’),

BottomNavigationBarItem(

icon: Icon(Icons.feed), label: ‘Feed’),

BottomNavigationBarItem(

icon: Icon(Icons.favorite), label: ‘Favorites’),

BottomNavigationBarItem(

icon: Icon(Icons.settings), label: ‘Settings’)

])

null,

body: Row(

mainAxisSize: MainAxisSize.max,

children: [

// Show the navigaiton rail if screen width >= 640

if (MediaQuery.of(context).size.width >= 640)

NavigationRail(

minWidth: 55.0,

selectedIndex: _selectedIndex,

// Called when one tab is selected

onDestinationSelected: (int index) {

setState(() {

_selectedIndex = index;

});

},

labelType: NavigationRailLabelType.all,

selectedLabelTextStyle: const TextStyle(

color: Colors.amber,

),

leading: Column(

children: const [

SizedBox(

height: 8,

),

CircleAvatar(

radius: 20,

child: Icon(Icons.person),

),

],

),

unselectedLabelTextStyle: const TextStyle(),

// navigation rail items

destinations: const [

NavigationRailDestination(

icon: Icon(Icons.home), label: Text(‘Home’)),

NavigationRailDestination(

icon: Icon(Icons.feed), label: Text(‘Feed’)),

NavigationRailDestination(

icon: Icon(Icons.favorite), label: Text(‘Favorites’)),

NavigationRailDestination(

icon: Icon(Icons.settings), label: Text(‘Settings’)),

],

),

// Main content

// This part is always shown

// You will see it on both small and wide screen

Expanded(child: _mainContents[_selectedIndex]),

],

),

);

}

}

构造函数和引用

---

NavigationRail 构造函数：

NavigationRail({

Key? key,

Color? backgroundColor,

bool extended = false,

Widget? leading,

Widget? trailing,

required List destinations,

required int selectedIndex,

ValueChanged? onDestinationSelected,

double? elevation,

double? groupAlignment,

NavigationRailLabelType? labelType,

TextStyle? unselectedLabelTextStyle,

TextStyle? selectedLabelTextStyle,

IconThemeData? unselectedIconTheme,

IconThemeData? selectedIconTheme,

double? minWidth,

double? minExtendedWidth,

bool? useIndicator,

Color? indicatorColor

})

BottomNavigationBar 构造函数：

BottomNavigationBar({

Key? key,

required List items,

ValueChanged? onTap,

int currentIndex = 0,

double? elevation,

BottomNavigationBarType? type,

Color? fixedColor,

Color? backgroundColor,

double iconSize = 24.0,

Color? selectedItemColor,

Color? unselectedItemColor,

IconThemeData? selectedIconTheme,

IconThemeData? unselectedIconTheme,

double selectedFontSize = 14.0,

double unselectedFontSize = 12.0,

TextStyle? selectedLabelStyle,

TextStyle? unselectedLabelStyle,

bool? showSelectedLabels,

bool? showUnselectedLabels,

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