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

class CustomRefreshIndicator extends StatefulWidget {
  const CustomRefreshIndicator({
    Key key,
    this.child,
    this.displacement: 40.0,
    this.onRefresh,
    this.color,
    this.backgroundColor,
    this.notificationPredicate: defaultScrollNotificationPredicate,
    this.isFirstRefresh,
  })  : assert(child != null),
        assert(onRefresh != null),
        assert(notificationPredicate != null),
        super(key: key);

  final Widget child;
  final double displacement;
  final RefreshCallback onRefresh;
  final Color color;
  final Color backgroundColor;
  final ScrollNotificationPredicate notificationPredicate;
  final bool isFirstRefresh;

  @override
  CustomRefreshIndicatorState createState() =>
      new CustomRefreshIndicatorState();
}

class CustomRefreshIndicatorState extends State<CustomRefreshIndicator> {
  final GlobalKey<RefreshIndicatorState> _refreshKey =
      new GlobalKey<RefreshIndicatorState>();

  @override
  void initState() {
    super.initState();
    if (widget.isFirstRefresh) {
      _initRefreshAsync();
    }
  }

  void _initRefreshAsync() async {
    while (_refreshKey.currentState == null) {
      await Future.delayed(const Duration(
          milliseconds: 17)); //Wait about 1 frame, try every frame
    }
    _refreshKey.currentState.show();
  }

  @override
  Widget build(BuildContext context) {
    return new RefreshIndicator(
      key: _refreshKey,
      child: widget.child,
      displacement: widget.displacement,
      onRefresh: widget.onRefresh,
      color: widget.color,
      backgroundColor: widget.backgroundColor,
      notificationPredicate: widget.notificationPredicate,
    );
  }
}