I have created in my seperate index.dart file my Navigation Bar Widget. I want to implement it on my homescreen in the main.dart File.

My approach to add it as children in a Column Widet only showed me a black screen and at the place of the navigation bar an Error Message: "Bottom overflowed by infinity pixel".

Main File:

import 'package:flutter/material.dart';
import 'navigationbar/index.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: 'Flutter Demo',
      theme: ThemeData(
        // This is the theme of your application.
        //
        // Try running your application with "flutter run". You'll see the
        // application has a blue toolbar. Then, without quitting the app, try
        // changing the primarySwatch below to Colors.green and then invoke
        // "hot reload" (press "r" in the console where you ran "flutter run",
        // or simply save your changes to "hot reload" in a Flutter IDE).
        // Notice that the counter didn't reset back to zero; the application
        // is not restarted.
        primarySwatch: Colors.amber,
      ),
      home: new Column(
        mainAxisSize: MainAxisSize.min,
        children: <Widget>[
          MyHomePage(title: 'Flutter Demo Home Page'),
          NavigationbarXXX(),
        ],
      )

    );
  }

}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key, this.title}) : super(key: key);

  // This widget is the home page of your application. It is stateful, meaning
  // that it has a State object (defined below) that contains fields that affect
  // how it looks.

  // This class is the configuration for the state. It holds the values (in this
  // case the title) provided by the parent (in this case the App widget) and
  // used by the build method of the State. Fields in a Widget subclass are
  // always marked "final".

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      // This call to setState tells the Flutter framework that something has
      // changed in this State, which causes it to rerun the build method below
      // so that the display can reflect the updated values. If we changed
      // _counter without calling setState(), then the build method would not be
      // called again, and so nothing would appear to happen.
      _counter = _counter +2 ;
    });
  }

  @override
  Widget build(BuildContext context) {
    // This method is rerun every time setState is called, for instance as done
    // by the _incrementCounter method above.
    //
    // The Flutter framework has been optimized to make rerunning build methods
    // fast, so that you can just rebuild anything that needs updating rather
    // than having to individually change instances of widgets.
    return Scaffold(
      appBar: AppBar(
        // Here we take the value from the MyHomePage object that was created by
        // the App.build method, and use it to set our appbar title.
        title: Text(widget.title),
      ),
      body: Center(
        // Center is a layout widget. It takes a single child and positions it
        // in the middle of the parent.
        child: Column(
          // Column is also a layout widget. It takes a list of children and
          // arranges them vertically. By default, it sizes itself to fit its
          // children horizontally, and tries to be as tall as its parent.
          //
          // Invoke "debug painting" (press "p" in the console, choose the
          // "Toggle Debug Paint" action from the Flutter Inspector in Android
          // Studio, or the "Toggle Debug Paint" command in Visual Studio Code)
          // to see the wireframe for each widget.
          //
          // Column has various properties to control how it sizes itself and
          // how it positions its children. Here we use mainAxisAlignment to
          // center the children vertically; the main axis here is the vertical
          // axis because Columns are vertical (the cross axis would be
          // horizontal).
          mainAxisAlignment: MainAxisAlignment.center,
          children: <Widget>[
            Text(
              'You have pushed the button this many times:',
            ),
            Text(
              '$_counter',
              style: Theme.of(context).textTheme.display1,
            ),
          ],
        ),
      ),
      floatingActionButton: IconButton(
        onPressed: _incrementCounter,
        //tooltip: 'Increment',
        icon: Icon(Icons.add),
      ), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}

And my extra file:

import 'package:flutter/material.dart';

class NavigationbarXXX extends  StatelessWidget{
 @override
 Widget build(BuildContext context) {
   // TODO: implement build
   return Scaffold(
       bottomNavigationBar : BottomNavigationBar(
         items: const <BottomNavigationBarItem>[
           BottomNavigationBarItem(
             icon: Icon(Icons.ac_unit),
             title: Text("AC"),
           ),
           BottomNavigationBarItem(
             icon: Icon(Icons.access_alarm),
             title: Text("Alarm"),
           ),
           BottomNavigationBarItem(
             icon: Icon(Icons.add_call),
             title: Text("Call"),
           ),
         ],
       )

   );
 }

}


Solution 1: Akio Alex

You can try this.

home: Container(
       child: new Column(
       mainAxisSize: MainAxisSize.min,
       children: <Widget>[
        MyHomePage(title: 'Flutter Demo Home Page'),
        NavigationbarXXX(),
      ],
  ),
)

Or still have issue. Use Stack Widget with positioned widget or or SingleChildScrollView .


Solution 2: hb22

In your NavigationBarXXX class, try returning the BottomNavigationBarItem list directly instead of wrapping it in a scaffold. Then, in your main file pass NavigationBarXXX as the bottomNavigationBar property of the Scaffold, instead of as a child.

navigationbar/index.dart

  @override
  Widget build(BuildContext context) {
    return BottomNavigationBar(
        backgroundColor: Colors.blue,
        items: const <BottomNavigationBarItem>[
          BottomNavigationBarItem(
            icon: Icon(Icons.x),
            title: Text('x'),
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.y),
            title: Text('y'),
          ),
          BottomNavigationBarItem(
            icon: Icon(Icons.z),
            title: Text('z'),
          ),
        ],
      );
  }
}

main.dart

... 

floatingActionButton: IconButton(
  onPressed: _incrementCounter,
  //tooltip: 'Increment',
  icon: Icon(Icons.add),
),
bottomNavigationBar: NavigationBarXXX(),

...