How to show CircularProgressIndicator before Flutter App Start?

Question

In my demo app I need to load a 2 JSON file from server. Both JSON has large data in it. I my Flutter app I call the json using Future + async + await than I call to create a widget with runApp. In the body I try to activate a CircularProgressIndicator. It shows appBar and its content as well as empty white page body and 4 or 5 seconds later loads the data in actual body.

My question is I need to show the CircularProgressIndicator first and once the data load I will call runApp(). How do I do that?

// MAIN
void main() async {
    _isLoading = true;

  // Get Currency Json
  currencyData = await getCurrencyData();

  // Get Weather Json
  weatherData = await getWeatherData();

   runApp(new MyApp());
}



// Body
body: _isLoading ? 
new Center(child: 
    new CircularProgressIndicator(
        backgroundColor: Colors.greenAccent.shade700,
    )
) :
new Container(
    //… actual UI
)

Answer 1

You need to put the data/or loading indicator inside a scaffold, show the scaffold everytime whether you have data or not, the content inside you can then do what you want to do.`

import 'dart:async';
import 'package:flutter/material.dart';

void main() {
  runApp(
    MaterialApp(
      debugShowCheckedModeBanner: false,
      title: 'Hello Rectangle',
      home: Scaffold(
        appBar: AppBar(
          title: Text('Hello Rectangle'),
        ),
        body: HelloRectangle(),
      ),
    ),
  );
}

class HelloRectangle extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Center(
      child: Container(
        color: Colors.greenAccent,
        height: 400.0,
        width: 300.0,
        child: Center(
          child: FutureBuilder(
            future: buildText(),
            builder: (BuildContext context, AsyncSnapshot snapshot) {
              if (snapshot.connectionState != ConnectionState.done) {
               return CircularProgressIndicator(backgroundColor: Colors.blue);
              } else {
               return Text(
                  'Hello!',
                  style: TextStyle(fontSize: 40.0),
                  textAlign: TextAlign.center,
                );
              }
            },
          ),
        ),
      ),
    );
  }

  Future buildText() {
    return new Future.delayed(
        const Duration(seconds: 5), () => print('waiting'));
  }
}

`