BottomNavigationBar class

A material widget that's displayed at the bottom of an app for selecting among a small number of views, typically between three and five.

There is an updated version of this component, NavigationBar, that's preferred for new applications and applications that are configured for Material 3 (see ThemeData.useMaterial3).

The bottom navigation bar consists of multiple items in the form of text labels, icons, or both, laid out on top of a piece of material. It provides quick navigation between the top-level views of an app. For larger screens, side navigation may be a better fit.

A bottom navigation bar is usually used in conjunction with a Scaffold, where it is provided as the Scaffold.bottomNavigationBar argument.

The bottom navigation bar's type changes how its items are displayed. If not specified, then it's automatically set to BottomNavigationBarType.fixed when there are less than four items, and BottomNavigationBarType.shifting otherwise.

The length of items must be at least two and each item's icon and label must not be null.

BottomNavigationBarType.fixed, the default when there are less than four items. The selected item is rendered with the selectedItemColor if it's non-null, otherwise the theme's ColorScheme.primary color is used for Brightness.light themes and ColorScheme.secondary for Brightness.dark themes. If backgroundColor is null, The navigation bar's background color defaults to the Material background color, ThemeData.canvasColor (essentially opaque white).
BottomNavigationBarType.shifting, the default when there are four or more items. If selectedItemColor is null, all items are rendered in white. The navigation bar's background color is the same as the BottomNavigationBarItem.backgroundColor of the selected item. In this case it's assumed that each item will have a different background color and that background color will contrast well with white.

Updating to NavigationBar

The NavigationBar widget's visuals are a little bit different, see the Material 3 spec at m3.material-io.cn/components/navigation-bar/overview for more details.

The NavigationBar widget's API is also slightly different. To update from BottomNavigationBar to NavigationBar, you will need to make the following changes.

Instead of using BottomNavigationBar.items, which takes a list of BottomNavigationBarItems, use NavigationBar.destinations, which takes a list of widgets. Usually, you use a list of NavigationDestination widgets. Just like BottomNavigationBarItems, NavigationDestinations have a label and icon field.
Instead of using BottomNavigationBar.onTap, use NavigationBar.onDestinationSelected, which is also a callback that is called when the user taps on a navigation bar item.
Instead of using BottomNavigationBar.currentIndex, use NavigationBar.selectedIndex, which is also an integer that represents the index of the selected destination.
You may also need to make changes to the styling of the NavigationBar, see the properties in the NavigationBar constructor for more details.

Using BottomNavigationBar

This example shows a BottomNavigationBar as it is used within a Scaffold widget. The BottomNavigationBar has three BottomNavigationBarItem widgets, which means it defaults to BottomNavigationBarType.fixed, and the currentIndex is set to index 0. The selected item is amber. The _onItemTapped function changes the selected item's index and displays a corresponding message in the center of the Scaffold.

To create a local project with this code sample, run:
flutter create --sample=material.BottomNavigationBar.1 mysample

This example shows how you would migrate the above BottomNavigationBar to the new NavigationBar.

To create a local project with this code sample, run:
flutter create --sample=material.BottomNavigationBar.2 mysample

This example shows a BottomNavigationBar as it is used within a Scaffold widget. The BottomNavigationBar has four BottomNavigationBarItem widgets, which means it defaults to BottomNavigationBarType.shifting, and the currentIndex is set to index 0. The selected item is amber in color. With each BottomNavigationBarItem widget, backgroundColor property is also defined, which changes the background color of BottomNavigationBar, when that item is selected. The _onItemTapped function changes the selected item's index and displays a corresponding message in the center of the Scaffold.

To create a local project with this code sample, run:
flutter create --sample=material.BottomNavigationBar.3 mysample

This example shows BottomNavigationBar used in a Scaffold Widget with different interaction patterns. Tapping twice on the first BottomNavigationBarItem uses the ScrollController to animate the ListView to the top. The second BottomNavigationBarItem shows a Modal Dialog.

To create a local project with this code sample, run:
flutter create --sample=material.BottomNavigationBar.4 mysample

Constructors

BottomNavigationBar({Key? key, required List<BottomNavigationBarItem> items, ValueChanged<int>? 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, MouseCursor? mouseCursor, bool? enableFeedback, BottomNavigationBarLandscapeLayout? landscapeLayout, bool useLegacyColorScheme = true}): Creates a bottom navigation bar which is typically used as a Scaffold's Scaffold.bottomNavigationBar argument.

Properties

backgroundColor → Color?: The color of the BottomNavigationBar itself.
final
currentIndex → int: The index into items for the current active BottomNavigationBarItem.
final
elevation → double?: The z-coordinate of this BottomNavigationBar.
final
enableFeedback → bool?: Whether detected gestures should provide acoustic and/or haptic feedback.
final
fixedColor → Color?: The value of selectedItemColor.
no setter
hashCode → int: The hash code for this object.
no setterinherited
iconSize → double: The size of all of the BottomNavigationBarItem icons.
final
items → List<BottomNavigationBarItem>: Defines the appearance of the button items that are arrayed within the bottom navigation bar.
final
key → Key?: Controls how one widget replaces another widget in the tree.
finalinherited
landscapeLayout → BottomNavigationBarLandscapeLayout?: The arrangement of the bar's items when the enclosing MediaQueryData.orientation is Orientation.landscape.
final
mouseCursor → MouseCursor?: The cursor for a mouse pointer when it enters or is hovering over the items.
final
onTap → ValueChanged<int>?: Called when one of the items is tapped.
final
runtimeType → Type: A representation of the runtime type of the object.
no setterinherited
selectedFontSize → double: The font size of the BottomNavigationBarItem labels when they are selected.
final
selectedIconTheme → IconThemeData?: The size, opacity, and color of the icon in the currently selected BottomNavigationBarItem.icon.
final
selectedItemColor → Color?: The color of the selected BottomNavigationBarItem.icon and BottomNavigationBarItem.label.
final
selectedLabelStyle → TextStyle?: The TextStyle of the BottomNavigationBarItem labels when they are selected.
final
showSelectedLabels → bool?: Whether the labels are shown for the selected BottomNavigationBarItem.
final
showUnselectedLabels → bool?: Whether the labels are shown for the unselected BottomNavigationBarItems.
final
type → BottomNavigationBarType?: Defines the layout and behavior of a BottomNavigationBar.
final
unselectedFontSize → double: The font size of the BottomNavigationBarItem labels when they are not selected.
final
unselectedIconTheme → IconThemeData?: The size, opacity, and color of the icon in the currently unselected BottomNavigationBarItem.icons.
final
unselectedItemColor → Color?: The color of the unselected BottomNavigationBarItem.icon and BottomNavigationBarItem.labels.
final
unselectedLabelStyle → TextStyle?: The TextStyle of the BottomNavigationBarItem labels when they are not selected.
final
useLegacyColorScheme → bool: This flag is controlling how BottomNavigationBar is going to use the colors provided by the selectedIconTheme, unselectedIconTheme, selectedItemColor, unselectedItemColor. The default value is true as the new theming logic is a breaking change. To opt-in the new theming logic set the flag to false
final

Methods

createElement() → StatefulElement: Creates a StatefulElement to manage this widget's location in the tree.
inherited
createState() → State<BottomNavigationBar>: Creates the mutable state for this widget at a given location in the tree.
override
debugDescribeChildren() → List<DiagnosticsNode>: Returns a list of DiagnosticsNode objects describing this node's children.
inherited
debugFillProperties(DiagnosticPropertiesBuilder properties) → void: Add additional properties associated with the node.
inherited
noSuchMethod(Invocation invocation) → dynamic: Invoked when a nonexistent method or property is accessed.
inherited
toDiagnosticsNode({String? name, DiagnosticsTreeStyle? style}) → DiagnosticsNode: Returns a debug representation of the object that is used by debugging tools and by DiagnosticsNode.toStringDeep.
inherited
toString({DiagnosticLevel minLevel = DiagnosticLevel.info}) → String: A string representation of this object.
inherited
toStringDeep({String prefixLineOne = '', String? prefixOtherLines, DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String: Returns a string representation of this node and its descendants.
inherited
toStringShallow({String joiner = ', ', DiagnosticLevel minLevel = DiagnosticLevel.debug}) → String: Returns a one-line detailed description of the object.
inherited
toStringShort() → String: A short, textual description of this widget.
inherited

Operators

operator ==(Object other) → bool: The equality operator.
inherited