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Flutter TabBar Tutorial

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1- Flutter Tab

TAB is an interface layout that is widely used in different application frameworks, and Flutter is no exception. Flutter offers an easy way for you to create a TAB layout with the Material library.
Basically, in order to create a TAB layout in Flutter, you need to implement the following steps:
  1. Create a TabController.
  2. Create a TabBar.
  3. Create a​​​​​​​ TabBarView.

TabController

To make the TAB layout work, you need to synchronize the selected Tab with its contents, which is the job of the TabController.
You can create a TabController manually, or use an available Widget, known as DefaultTabController, which supports some common features.
TabController
DefaultTabController(
  // The number of tabs / content sections to display.
  length: 3,
  child: // Complete this code in the next step.
);

TabBar

TabBar helps you to create Tab(s), as in the example below, a TabBar contains three subTab(s).
TabBar
DefaultTabController(
  length: 3,
  child: Scaffold(
    appBar: AppBar(
      bottom: TabBar(
        tabs: [
          Tab(icon: Icon(Icons.directions_car)),
          Tab(icon: Icon(Icons.directions_transit)),
          Tab(icon: Icon(Icons.directions_bike)),
        ],
      ),
    ),
  ),
);
Note: You can put many TabBar(s) into a DefaultTabController, but the DefaultTabController will only work with the nearest TabBar (Searching by the tree structure). In this case, you need to consider creating your own TabController manually.

TabBarView

You can use TabBarView to contain the content corresponding to every Tab on the TabBar.
TabBarView
TabBarView (
  children: [
    Icon(Icons.directions_car),
    Icon(Icons.directions_transit),
    Icon(Icons.directions_bike),
  ],
);

2- TabBar example

main.dart (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 DefaultTabController(
        length: 3,
        child: Scaffold(
          appBar: AppBar(
            bottom: TabBar(
              tabs: [
                Tab(icon: Icon(Icons.directions_car)),
                Tab(icon: Icon(Icons.directions_transit)),
                Tab(icon: Icon(Icons.directions_bike)),
              ],
            ),
            title: Text('Flutter Tabs Example'),
          ),
          body: TabBarView(
            children: [
              Center(child: Text("Car")),
              Center(child: Text("Transit")),
              Center(child: Text("Bike"))
            ],
          ),
        )
    );
  }
}

3- TabController, TabBar ... Constructor

TabController Constructor
TabController Constructor
TabController(
    {int initialIndex: 0,
    @required int length,
    @required TickerProvider vsync}
)
DefaultTabController Constructor:
DefaultTabController Constructor
const DefaultTabController(
    {Key key,
    @required int length,
    int initialIndex: 0,
    @required Widget child}
)
TabBar Constructor:
TabBar Constructor
const TabBar(
    {Key key,
    @required List<Widget> tabs,
    TabController controller,
    bool isScrollable: false,
    Color indicatorColor,
    double indicatorWeight: 2.0,
    EdgeInsetsGeometry indicatorPadding: EdgeInsets.zero,
    Decoration indicator,
    TabBarIndicatorSize indicatorSize,
    Color labelColor,
    TextStyle labelStyle,
    EdgeInsetsGeometry labelPadding,
    Color unselectedLabelColor,
    TextStyle unselectedLabelStyle,
    DragStartBehavior dragStartBehavior: DragStartBehavior.start,
    MouseCursor mouseCursor,
    ValueChanged<int> onTap,
    ScrollPhysics physics}
)
TabBarView Constructor:
TabBarView Constructor
const TabBarView(
    {Key key,
    @required List<Widget> children,
    TabController controller,
    ScrollPhysics physics,
    DragStartBehavior dragStartBehavior: DragStartBehavior.start}
)

4- isScrollable

If the isScrollable is true, each Tab will fit its content in width, and the TabBar will have a horizontal scrollbar.
main.dart (isScrollable 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) {
    EdgeInsets a2; EdgeInsetsDirectional a;
    return DefaultTabController(
        length: 6,
        child: Scaffold(
          appBar: AppBar(
            bottom: createTabBar(),
            title: Text('Flutter TabBar Example'),
          ),
          body: TabBarView(
            children: [
              Center(child: Text("Car")),
              Center(child: Text("Transit")),
              Center(child: Text("Bike")),
              Center(child: Text("Boat")),
              Center(child: Text("Railway")),
              Center(child: Text("Bus"))
            ],
          ),
        )
    );
  }

  TabBar createTabBar()  {
    return TabBar(
      tabs: [
        Row (children: [Icon(Icons.directions_car), SizedBox(width:5), Text("Car")]),
        Row (children: [Icon(Icons.directions_transit), SizedBox(width:5), Text("Transit")]),
        Row (children: [Icon(Icons.directions_bike), SizedBox(width:5), Text("Bike")]),
        Row (children: [Icon(Icons.directions_boat), SizedBox(width:5), Text("Boat")]),
        Row (children: [Icon(Icons.directions_railway), SizedBox(width:5), Text("Railway")]),
        Row (children: [Icon(Icons.directions_bus), SizedBox(width:5), Text("Bus")]),
      ],
      isScrollable: true,
    );
  }
}
For example, align Tab(s) left in case of TabBar.isScrollable = true.
main.dart (isScrollable 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) {
    EdgeInsets a2; EdgeInsetsDirectional a;
    return DefaultTabController(
        length: 3,
        child: Scaffold(
          appBar: AppBar(
            bottom: PreferredSize(
              preferredSize: Size.fromHeight(40),
              child: Align(
                alignment: Alignment.centerLeft,
                child: TabBar(
                  isScrollable: true,
                  tabs: [ Row (children: [Icon(Icons.directions_car), SizedBox(width:5), Text("Car")]),
                    Row (children: [Icon(Icons.directions_transit), SizedBox(width:5), Text("Transit")]),
                    Row (children: [Icon(Icons.directions_bike), SizedBox(width:5), Text("Bike")])],
                ),
              ),
            ),
            title: Text('Flutter TabBar Example'),
          ),
          body: TabBarView(
            children: [
              Center(child: Text("Car")),
              Center(child: Text("Transit")),
              Center(child: Text("Bike"))
            ],
          ),
        )
    );
  }

}

5- indicatorColor

indicatorColor property allows you to specify the color of the line under the currently selected Tab. This property will be ignored if the indicator property is specified.
Color indicatorColor
For example: Set the color red for the line under the currently selected Tab:
indicatorColor (ex1)
TabBar (
  tabs: [
    Row (children: [Icon(Icons.directions_car), SizedBox(width:5), Text("Car")]),
    Row (children: [Icon(Icons.directions_transit), SizedBox(width:5), Text("Transit")]),
    Row (children: [Icon(Icons.directions_bike), SizedBox(width:5), Text("Bike")]),
  ],
  indicatorColor: Color(0xffE74C3C),
);
  • TODO Link?

6- indicatorWeight

indicatorWeight property is used to set the thickness of the line under the currently selected Tab. Its value is greater than 0, and the default value is 2. This property will be ignored if the indicator property is specified.
double indicatorWeight;
For example, set the thickness of the line under the currently selected Tab.
indicatorWeight (ex1)
TabBar(
  tabs: [
    Row (children: [Icon(Icons.directions_car), SizedBox(width:5), Text("Car")]),
    Row (children: [Icon(Icons.directions_transit), SizedBox(width:5), Text("Transit")]),
    Row (children: [Icon(Icons.directions_bike), SizedBox(width:5), Text("Bike")]),
  ],
  indicatorColor: Color(0xffE74C3C),
  indicatorWeight: 10
);

7- indicatorPadding

indicatorPadding property specifies the padding horizontally for the line under the currently selected Tab.
EdgeInsetsGeometry indicatorPadding
 
For example:
indicatorPadding (ex1)
TabBar(
  tabs: [
    Row (children: [Icon(Icons.directions_car), SizedBox(width:5), Text("Car")]),
    Row (children: [Icon(Icons.directions_transit), SizedBox(width:5), Text("Transit")]),
    Row (children: [Icon(Icons.directions_bike), SizedBox(width:5), Text("Bike")]),
  ],
  indicatorColor: Color(0xffE74C3C),
  indicatorWeight: 10,
  indicatorPadding: EdgeInsets.only(right: 20),
);

8- indicator

indicator property allows you to define the appearance of the currently selected Tab. If this property is used, other properties such as indicatorColor, indicatorWeight and indicatorPadding will be ignored.
Decoration indicator;
 
For example:
indicator (ex1)
TabBar(
  tabs: [
    Row (children: [Icon(Icons.directions_car), SizedBox(width:5), Text("Car")]),
    Row (children: [Icon(Icons.directions_transit), SizedBox(width:5), Text("Transit")]),
    Row (children: [Icon(Icons.directions_bike), SizedBox(width:5), Text("Bike")]),
  ],
  indicator: ShapeDecoration (
      shape: UnderlineInputBorder (
          borderSide: BorderSide(
              color: Colors.transparent,
              width: 0,
              style: BorderStyle.solid
          )
      ),
      gradient: LinearGradient(colors: [Color(0xff0081ff), Color(0xff01ff80)])
  )
);
  • TODO Link?

9- labelColor

labelColor property is used to specify the font color for the label of the currently selected Tab.
Color labelColor;
For example:
TabBar(
    tabs: [
      Row (children: [Icon(Icons.directions_car), SizedBox(width:5), Text("Car")]),
      Row (children: [Icon(Icons.directions_transit), SizedBox(width:5), Text("Transit")]),
      Row (children: [Icon(Icons.directions_bike), SizedBox(width:5), Text("Bike")]),
    ],
    labelColor: Colors.red,
    unselectedLabelColor: Colors.black,
);

10- unselectedLabelColor

unselectedLabelColor property is used to specify the font color for the label of the unselected Tab(s).
Color unselectedLabelColor;
For example:
unselectedLabelColor (ex1)
TabBar(
  tabs: [
    Row (children: [Icon(Icons.directions_car), SizedBox(width:5), Text("Car")]),
    Row (children: [Icon(Icons.directions_transit), SizedBox(width:5), Text("Transit")]),
    Row (children: [Icon(Icons.directions_bike), SizedBox(width:5), Text("Bike")]),
  ],
  labelColor: Colors.white,
  unselectedLabelColor: Colors.cyanAccent,
);

11- labelPadding

labelPadding property is used to add padding to each label of the Tab(s).
EdgeInsetsGeometry labelPadding;
 
For example:
labelPadding (ex1)
TabBar(
  tabs: [
    Row (children: [Icon(Icons.directions_car), SizedBox(width:5), Text("Car")]),
    Row (children: [Icon(Icons.directions_transit), SizedBox(width:5), Text("Transit")]),
    Row (children: [Icon(Icons.directions_bike), SizedBox(width:5), Text("Bike")]),
  ],
  labelPadding: EdgeInsets.all( 20),
);

12- labelStyle

labelStyle property is used to specify the text style on the label of the currently selected Tab(s).
TextStyle labelStyle;
labelStyle (ex1)
TabBar(
  tabs: [
    Row (children: [Icon(Icons.directions_car), SizedBox(width:5), Text("Car")]),
    Row (children: [Icon(Icons.directions_transit), SizedBox(width:5), Text("Transit")]),
    Row (children: [Icon(Icons.directions_bike), SizedBox(width:5), Text("Bike")]),
  ],
  labelStyle: TextStyle(fontWeight: FontWeight.bold, fontSize: 22),
  unselectedLabelStyle: TextStyle(fontStyle: FontStyle.normal, fontSize: 18),
);
  • TODO Link?

13- unselectedLabelStyle

unselectedLabelStyle property is used to specify the text style on the label of the unselected Tab(s).
TextStyle unselectedLabelStyle;
unselectedLabelStyle (ex1)
TabBar(
  tabs: [
    Row (children: [Icon(Icons.directions_car), SizedBox(width:5), Text("Car")]),
    Row (children: [Icon(Icons.directions_transit), SizedBox(width:5), Text("Transit")]),
    Row (children: [Icon(Icons.directions_bike), SizedBox(width:5), Text("Bike")]),
  ],
  labelStyle: TextStyle(fontWeight: FontWeight.bold, fontSize: 22),
  unselectedLabelStyle: TextStyle(fontStyle: FontStyle.italic),
);
  • TODO Link?

14- onTap

onTap is a callback function called when the user taps one Tab on the TabBar.
ValueChanged<int> onTap;
main.dart (onTap 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 StatefulWidget {
  MyHomePage({Key key}) : super(key: key);

  @override
  State<StatefulWidget> createState() {
    return MyHomePageState();
  }
}

class MyHomePageState extends State<MyHomePage> {
  int carClick = 0;
  int transitClick = 0;
  int bikeClick = 0;

  @override
  Widget build(BuildContext context) {
    return DefaultTabController(
        length: 3,
        child: Scaffold(
          appBar: AppBar(
            bottom: createTabBar(),
            title: Text('Flutter TabBar Example'),
          ),
          body: TabBarView(
            children: [
              Center(child: Text("Car")),
              Center(child: Text("Transit")),
              Center(child: Text("Bike"))
            ],
          ),
        )
    );
  }

  TabBar createTabBar()  {
    return TabBar(
        isScrollable: true,
        labelStyle: TextStyle(fontSize: 20),
        tabs: [
          Text("Car " + this.carClick.toString()),
          Text("Transit " + this.transitClick.toString()),
          Text("Bike " + this.bikeClick.toString())
        ],
        onTap: (index) {
          this.onTapHandler(index);
        }
    );
  }

  void onTapHandler(int index)  {
    setState(()  {
      switch(index){
        case 0:
          carClick++;
          break;
        case 1:
          transitClick++;
          break;
        case 2:
          bikeClick++;
          break;
      }
    });
  }

}

15- dragStartBehavior

DragStartBehavior dragStartBehavior: DragStartBehavior.start
  • TODO Link?

16- mouseCursor

MouseCursor mouseCursor
  • TODO Link?

17- physics

ScrollPhysics physics
  • TODO Link?

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