32.4 Flutter MaterialApp Scaffold AppBar

20210625

import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      home: Scaffold(
        appBar: AppBar(
          title: const Text('Home'),
        ),
      ),
      debugShowCheckedModeBanner: false,
    ),
  ), 
}

The Dart code for a Flutter app belongs in the file lib/main.dart. This will usually begin with import statements to load the required libraries. It then continues with a main() function which is invoked when the app starts up.

The main() function of a minimal Flutter app calls the runApp() function which takes as its argument a Widget which becomes the root of the widget tree. Any app will generally construct a tree of widgets, starting with the root.

The root widget for the minimal app here is an instance of the MaterialApp() class which provides a widget which brings together a number of standard widgets that make up a typical app. Instances of the class have a home: slot which takes a widget to be the default route (so called) of the app (also referred to as /). This is displayed when the application is started.

In the example here a Scaffold() widget provides the common AppBar() with a Text() widget to specify the title. Other common functionalities provided by the Scaffold() include the BottomNavigatorBar(), Drawer(), and FloatingActionButton().

The example here targets an Android smart phone.



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