Solved: Flutter: Update Widgets On Resume?

Question

Asked by Josh on April 17, 2018 (source).

In Flutter, is there a way to update widgets when the user leaves the app and come right back to it? My app is time based, and it would be helpful to update the time as soon as it can.

Answer

Question answered by Günter Z (source).

You can listen to lifecycle events by doing this for example :

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

class LifecycleEventHandler extends WidgetsBindingObserver {
  final AsyncCallback resumeCallBack;
  final AsyncCallback suspendingCallBack;

  LifecycleEventHandler({
    this.resumeCallBack,
    this.suspendingCallBack,
  });

  @override
  Future<void> didChangeAppLifecycleState(AppLifecycleState state) async {
    switch (state) {
      case AppLifecycleState.resumed:
        if (resumeCallBack != null) {
          await resumeCallBack();
        }
        break;
      case AppLifecycleState.inactive:
      case AppLifecycleState.paused:
      case AppLifecycleState.detached:
        if (suspendingCallBack != null) {
          await suspendingCallBack();
        }
        break;
    }
  }
}



class AppWidgetState extends State<AppWidget> {
  void initState() {
    super.initState();

    WidgetsBinding.instance.addObserver(
      LifecycleEventHandler(resumeCallBack: () async => setState(() {
        // do something
      }))
    );
  }
  ...
}
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