Apple's and Android's refresh indicator to use with CupertinoSliverRefreshControl

sliver_refresh_indicator.dart

import 'dart:math';

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

Widget buildAppleRefreshIndicator(
  BuildContext context,
  RefreshIndicatorMode refreshState,
  double pulledExtent,
  double refreshTriggerPullDistance,
  double refreshIndicatorExtent,
) {
  const Curve opacityCurve = const Interval(0.4, 0.8, curve: Curves.easeInOut);
  return Align(
    alignment: Alignment.bottomCenter,
    child: Padding(
      padding: const EdgeInsets.only(bottom: 16.0),
      child: refreshState == RefreshIndicatorMode.drag
          ? Opacity(
              opacity: opacityCurve.transform(
                  min(pulledExtent / refreshTriggerPullDistance, 1.0)),
              child: const Icon(
                CupertinoIcons.down_arrow,
                color: CupertinoColors.inactiveGray,
                size: 36.0,
              ),
            )
          : Opacity(
              opacity: opacityCurve
                  .transform(min(pulledExtent / refreshIndicatorExtent, 1.0)),
              child: const CupertinoActivityIndicator(radius: 14.0),
            ),
    ),
  );
}

Widget buildAndroidRefreshIndicator(
  BuildContext context,
  RefreshIndicatorMode refreshState,
  double pulledExtent,
  double refreshTriggerPullDistance,
  double refreshIndicatorExtent,
) {
  const Curve opacityCurve = const Interval(0.4, 0.8, curve: Curves.easeInOut);
  return Align(
    alignment: Alignment.bottomCenter,
    child: Padding(
      padding: const EdgeInsets.only(bottom: 16.0),
      child: refreshState == RefreshIndicatorMode.drag
          ? Opacity(
              opacity: opacityCurve.transform(
                  min(pulledExtent / refreshTriggerPullDistance, 1.0)),
              child: const Icon(
                Icons.arrow_downward,
                color: CupertinoColors.inactiveGray,
                size: 24.0,
              ),
            )
          : Opacity(
              opacity: opacityCurve
                  .transform(min(pulledExtent / refreshIndicatorExtent, 1.0)),
              child: const CircularProgressIndicator(strokeWidth: 2.0),
            ),
    ),
  );
}

Refer to this issue on when and how to use this.