Use get_version package . It's the easiest way
Installing :
 dependencies:
   get_version: any
Usage:
String projectAppID;
// Platform messages may fail, so we use a try/catch PlatformException.
try {
  projectAppID = await GetVersion.appID;
} on PlatformException {
  projectAppID = 'Failed to get app ID.';
}
You can use it as String inside anything you want like Text widget etc ...
Another extract of get_version in a small application :
import 'package:get_version/get_version.dart';    
  class _MyAppState extends State<MyApp> {
  String _projectAppID = '';
  @override
  initState() {
    super.initState();
    initPlatformState();
  }    
  // Platform messages are asynchronous, so we initialize in an async method.
  initPlatformState() async {
    String projectAppID;
    try {
      projectAppID = await GetVersion.appID;
    } catch (e) {
      projectAppID = 'Failed to get app ID.';
    }
    setState(() {
      _projectAppID = projectAppID;
    });
  }
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: Scaffold(
        body: ListTile(
          leading: new Icon(Icons.info),
          title: const Text('App ID'),
          subtitle: new Text(_projectAppID),
        ),
      ),
    );
  }
}
Output :
