diameter/lib/components/progress_indicator.dart

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

class ViewWithProgressIndicator extends StatefulWidget {
  final AsyncSnapshot snapshot;
  final Widget child;
  final double progressIndicatorSize;
  final EdgeInsets padding;

  const ViewWithProgressIndicator(
      {Key? key,
      required this.snapshot,
      required this.child,
      this.progressIndicatorSize = 100,
      this.padding = const EdgeInsets.all(0)})
      : super(key: key);

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

class _ViewWithProgressIndicatorState extends State<ViewWithProgressIndicator> {
  @override
  Widget build(BuildContext context) {
    switch (widget.snapshot.connectionState) {
      case ConnectionState.none:
      case ConnectionState.waiting:
        return Container(
          alignment: Alignment.center,
          padding: widget.padding,
          child: Center(
            child: SizedBox(
              width: widget.progressIndicatorSize,
              height: widget.progressIndicatorSize,
              // TODO: only show if loading takes longer than 30ms
              child: const CircularProgressIndicator(),
            ),
          ),
        );
      default:
        if (widget.snapshot.hasError) {
          return Center(
            child: Text(widget.snapshot.error.toString()),
          );
        }
        if (!widget.snapshot.hasData) {
          return const Center(
            child: Text("No data"),
          );
        } else {
          return widget.child;
        }
    }
  }
}