Continuous Requests Mixin

continuous_mixin.dart

import 'dart:async';

import 'package:flutter/material.dart';

import 'package:mobile/utils/lifecycle_event_handler.dart';

/// Attaches to a [Widget] and calls [fetchData] every [interval] seconds
/// or upon app reactivation.
mixin ContinuousRequest<T extends StatefulWidget> on State<T> {
  /// A subscription that calls [fetch] data every [interval] seconds
  StreamSubscription _streamSubscription;

  /// A handler to the app lifecycle
  LifecycleEventHandler _handler;

  /// The interval in `seconds` between calls to [fetchData]
  int interval = 30;

  /// Only true on initial load
  bool isLoading = true;

  @override
  void initState() {
    // Wrapped in future to avoid any issues with calling setState inside fetchData
    Future(() async {
      await fetchData();
      setState(() => isLoading = false);
    });

    _streamSubscription = Stream.periodic(
      Duration(seconds: interval),
    ).listen((_) => fetchData());

    _handler = LifecycleEventHandler(resumeCallBack: fetchData);
    WidgetsBinding.instance.addObserver(_handler);

    super.initState();
  }

  @override
  void dispose() {
    _streamSubscription?.cancel();

    WidgetsBinding.instance.removeObserver(_handler);

    super.dispose();
  }

  Future<void> fetchData() async {}
}