In Flutter docs about AppLifecycle Event, it's have 4 Event .
inactive
paused
resumed
suspending
In 4 event above, i can print AppLifecycle event inactive, paused, resumed, but i can't handle suspending event.
Because i want check if the user kill/destroy the App from task manager. if the user kill/destroy the app , i want show Security Code (like PinCode etc).
How can i handle suspending event ?
class _HomePageState extends State<HomePage> with WidgetsBindingObserver {
AppLifecycleState _appLifecycleState;
FunctionHelper functionHelper = FunctionHelper();
PageController _pageController;
#override
void initState() {
WidgetsBinding.instance.addObserver(this);
_pageController = PageController(initialPage: 0);
super.initState();
}
#override
void didChangeAppLifecycleState(AppLifecycleState appLifecycleState) {
setState(() {
_appLifecycleState = appLifecycleState;
});
print(appLifecycleState);
}
#override
void dispose() {
WidgetsBinding.instance.removeObserver(this);
super.dispose();
}
#override
Widget build(BuildContext context) {
if (_appLifecycleState == null) {
return Center(
child: Text('This widget has not observed any lifecycle changes.'),
);
} else {
return Center(
child: Text(
'The most recent lifecycle state this widget observed was: $_appLifecycleState'),
);
}
}
Flutter does not have any API to use onDestroy method of Activity flutter/flutter#21982. During the suspending event the application is suspended momentarily which is equivalent to onStop in Android. When user kills or destroys the App, the onDestroy is triggered in Android therefore it cannot be handled using suspending event.
Related
I am building a QR code scanner app with a couple of tabs wrapped up within CupertinoTabBar in a CupertinoTabScaffold. I have a CupertinoTabController to take care of the switching between the tabs. One of this tabs has a CameraPreview widget from the Camera plugin of Flutter along with a proper dispose mechanism. However, whenever the tab are switched, the Camera stream still persists, causing the phone to heat up and also causes janky UX. Now I read that the BottomNavigationBar from Material widgets does not persist in this way. Any idea on how to achieve the same behaviour with CupertinoTabBar?
You can use the StatefulWidget for each a page of the tabs and then try to listening AppLifecycleState. Disponse controller if state inactive/paused.
In my case it's working fine.
class Example extends StatefulWidget {
#override
ExampleState createState() => ExampleState();
}
//Implement WidgetsBindingObserver to listen Lifecycle State
class ExampleState extends State<Example> with WidgetsBindingObserver {
late CameraController _controller;
...
...
#override
void initState() {
super.initState();
// Add Listener (Lifecycle State)
WidgetsBinding.instance!.addObserver(this);
}
Future<void> _setupController() async {
//todo setup/init controller
}
//Implements this method to listen Lifecycle State
#override
void didChangeAppLifecycleState(AppLifecycleState state) {
if (state == AppLifecycleState.resumed) {
_controller.dispose();
_setupCameraAndControllerFuture = _setupController();
}
if (state == AppLifecycleState.inactive) {
_controller.dispose();
} else if (state == AppLifecycleState.paused) {
_controller.dispose();
}
}
#override
void dispose() {
// Remove Listener (Lifecycle State)
WidgetsBinding.instance!.removeObserver(this);
// dispose controller
_controller.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
return Scaffold(
...
...
);
}
}
In my app, I am playing music (local) in a loop, which plays continuously unless the user stops it. I am using audioplayers package.
Future playLoop(String filePath) async {
player.stop();
player = await cache.loop(filePath);
}
Currently, when app is minimised, the music is not getting stoped. The feature I want to implement is that when the app is minimised, it should stop playing music in the background.
Thanks in advance.
Solutions :
#override
void didChangeAppLifecycleState(AppLifecycleState state) {
if (state == AppLifecycleState.paused) {
//stop your audio player
}else{
print(state.toString());
}
}
#override
void initState() {
super.initState();
WidgetsBinding.instance.addObserver(this);
}
There are mainly 4 states for it:
resumed: The application is visible and responding to user input.
inactive: The application is in an inactive state and is not receiving
user input.
paused: The application is not currently visible to the user, not
responding user input, and running in the background.
detached: The application is still hosted on a flutter engine but is
detached from any host views.
The solution above is correct, but some steps are needed before to get it
1 add WidgetsBindingObserver to your class
class AnyClass extends StatefulWidgets {
_AnyClassState createState() => _AnyClassState();
}
class _AnyClassState extends State<AnyClass> with
WidgetsBindingObserver {
Widget build(BuildContext context) {
return ...
}
}
2 Now it will work, we can added the methods inside class
class _AnyClassState extends State<AnyClass> with
WidgetsBindingObserver {
// ADD THIS AppLifecycleState VARIABLE
late AppLifecycleState appLifecycle;
// ADD THIS FUNCTION WITH A AppLifecycleState PARAMETER
didChangeAppLifecycleState(AppLifecycleState state) {
appLifecycle = state;
setStae(() {});
if(state == AppLifecycle.paused) {
// IF YOUT APP IS IN BACKGROUND...
// YOU CAN ADDED THE ACTION HERE
print('My app is in background');
}
}
// CREATE INITSTATE AND DISPOSE METHODS
initState() {
super.initState();
WidgetsBinding.instance.addObserver(this);
}
dispose() {
WidgetsBinding.instance.removeObserver(this);
super.dispose();
}
Widget build(BuildContext context) {
return ...
}
}
NOW IT WILL WORK FINE!
I hope I understand how didChangeAppLifecycleState worked correctly.
I have page A and page B . When I click the back device button from page B ( Navigator.of(context).pop(); ), I expect didChangeAppLifecycleState in pageA will get called, but it doesn't.
PageA
class _ABCState extends State<ABCrList> with WidgetsBindingObserver {
#override
void initState() {
super.initState();
WidgetsBinding.instance.addObserver(this);
....
}
#override
void dispose() {
WidgetsBinding.instance.removeObserver(this);
super.dispose();
}
#override
void didChangeAppLifecycleState(AppLifecycleState state) {
if (state == AppLifecycleState.resumed) {
setState(() {
print(...);
});
}else{
print(state.toString());
}
}
....
This is the initState in pageA. The function used to call backend service.
#override
void initState() {
super.initState();
_bloc.getList(context); // return list and populate to ListView
});
}
The way you're thinking it is Android's way where onResume works, but in Flutter, things don't happen this way.
Generally, this gets called when the system puts the app in the background or returns the app to the foreground.
There are mainly 4 states for it:
resumed: The application is visible and responding to user input.
inactive: The application is in an inactive state and is not receiving user input.
paused: The application is not currently visible to the user, not responding user input, and running in the background.
detached: The application is still hosted on a flutter engine but is detached from any host views.
Edit:
When you're navigating to PageB from PageA, use something like:
Navigator.pushNamed(context, "/pageB").then((flag) {
if (flag) {
// you're back from PageB, perform your function here
setState(() {}); // you may need to call this if you want to update UI
}
});
And from PageB, you'll can use
Navigator.pop(context, true);
I am working on a Flutter app and need to pop the screen. I tried initState() method but no luck. initState() gets called when I open a class for the first time.
Do we have an equivalent of Android onResume() method in Flutter?
Any ideas?
You can use the WidgetsBindingObserver and check the AppLifeCycleState like this example:
class YourWidgetState extends State<YourWidget> with WidgetsBindingObserver {
#override
void initState() {
WidgetsBinding.instance?.addObserver(this);
super.initState();
}
#override
void dispose() {
WidgetsBinding.instance?.removeObserver(this);
super.dispose();
}
#override
void didChangeAppLifecycleState(AppLifecycleState state) {
if (state == AppLifecycleState.resumed) {
//do your stuff
}
}
}
Take in mind that It will called every time you open the app or go the background and return to the app. (if your widget is active)
If you just want a listener when your Widget is loaded for first time, you can listen using addPostFrameCallback, like this example:
class YourWidgetState extends State<YourWidget> {
_onLayoutDone(_) {
//do your stuff
}
#override
void initState() {
WidgetsBinding.instance?.addPostFrameCallback(_onLayoutDone);
super.initState();
}
}
Info : https://docs.flutter.io/flutter/widgets/WidgetsBindingObserver-class.html
Update: Null safety compliance
If you go to another page, then is called when you comeback
Navigator.push(
context,
MaterialPageRoute(
builder: (context) => SecondPage(),
),
).then((value) {
_refreshFirstPage();
});
You can accomplish this by registering a didChangeAppLifecycleState observer:
class _MyAppState extends State<MyApp> with WidgetsBindingObserver {
#override
void initState() {
super.initState();
WidgetsBinding.instance.addObserver(this);
}
#override
void dispose() {
WidgetsBinding.instance.removeObserver(this);
super.dispose();
}
#override
void didChangeAppLifecycleState(final AppLifecycleState state) {
if (state == AppLifecycleState.resumed) {
setState(() {
// ...your code goes here...
});
}
}
#override
Widget build(final BuildContext context) {
// ...your code goes here...
}
}
See WidgetsBindingObserver for more information.
Use focus_detector more information can see visibility_detector
Get notified every time your widget appears or disappears from the screen.
Similar to onResume()/onPause() on Android and viewDidAppear()/viewDidDisappear() on iOS.
Focus Detector fires callbacks for you whenever something happens to take or give your widget focus. Such an event might be, for instance, the user:
Navigating to/from another screen;
Turning the device’s screen on/off while your widget is visible;
Switching to/from another app while your widget is visible;
Scrolling your widget in/out the screen;
#override
Widget build(BuildContext context) =>
FocusDetector(
onFocusLost: () {
logger.i(
'Focus Lost.'
'\nTriggered when either [onVisibilityLost] or [onForegroundLost] '
'is called.'
'\nEquivalent to onPause() on Android or viewDidDisappear() on iOS.',
);
},
onFocusGained: () {
logger.i(
'Focus Gained.'
'\nTriggered when either [onVisibilityGained] or [onForegroundGained] '
'is called.'
'\nEquivalent to onResume() on Android or viewDidAppear() on iOS.',
);
},
onVisibilityLost: () {
logger.i(
'Visibility Lost.'
'\nIt means the widget is no longer visible within your app.',
);
},
onVisibilityGained: () {
logger.i(
'Visibility Gained.'
'\nIt means the widget is now visible within your app.',
);
},
onForegroundLost: () {
logger.i(
'Foreground Lost.'
'\nIt means, for example, that the user sent your app to the background by opening '
'another app or turned off the device\'s screen while your '
'widget was visible.',
);
},
onForegroundGained: () {
logger.i(
'Foreground Gained.'
'\nIt means, for example, that the user switched back to your app or turned the '
'device\'s screen back on while your widget was visible.',
);
},
child: Container(),
);
Android's LiveData allows to update the UI when the activity is in an active state. So if a background operation has finished while the activity is paused, the activity won't be notified and thus the app won't crush. Can Flutter perform the same behavior?
For people interested in an equivalent of LiveData for other scenarios, I present you StreamController:
class ExampleViewModel {
StreamController<bool> loggedInStream = StreamController<bool>();
logIn() { loggedInStream.add(true); }
}
class ExampleScreen extends StatefulWidget {
#override
State<StatefulWidget> createState() => ExampleScreenState();
}
class ExampleScreenState extends State<ExampleScreen> {
ExampleViewModel _viewModel;
BuildContext _ctx;
#override
void initState() {
super.initState();
_viewModel = ExampleViewModel()
_viewModel.loggedInStream.stream.listen( (loggedIn) {
if ( loggedIn != null && loggedIn ) {
Navigator.of(_ctx).pushReplacementNamed("/home");
}
});
}
#override
Widget build(BuildContext context) {
_ctx = context;
var loginBtn =
RaisedButton(
onPressed: _viewModel.logIn(true),
child: Text(
"LOGIN",
style: new TextStyle(
fontSize: 24.0,
)
),
color: Colors.green,
textColor: Colors.white,
);
return loginBtn;
}
#override
void dispose() {
super.dispose();
_viewModel.loggedInStream.close();
}
}
You can subscribe to it just like a LiveData, using:
loggedInStream.stream.listen( (data) { code } )
And you should clear the listeners in dispose to avoid memory leaks:
loggedInStream.close()
This code basically do the following things:
Creates a screen with a button.
Listen to a Stream (observe a LiveData).
When you click the button, it changes the value.
The listener (observer) is triggered.
Launches new screen.
You can use WidgetsBindingObserver to listen to the application state.
class AppLifecycleReactor extends StatefulWidget {
const AppLifecycleReactor({ Key key }) : super(key: key);
#override
_AppLifecycleReactorState createState() => new _AppLifecycleReactorState();
}
class _AppLifecycleReactorState extends State<AppLifecycleReactor> with WidgetsBindingObserver {
#override
void initState() {
super.initState();
WidgetsBinding.instance.addObserver(this);
}
#override
void dispose() {
WidgetsBinding.instance.removeObserver(this);
super.dispose();
}
AppLifecycleState _notification;
#override
void didChangeAppLifecycleState(AppLifecycleState state) {
setState(() { _notification = state; });
}
#override
Widget build(BuildContext context) {
return new Text('Last notification: $_notification');
}
}
Easy: Flutterx Live Data
There is no need to observe App lifecycle: widget are built only when the app is resumend
This library integrates perfectly LiveData concepts, also is well documented.
Is developed on Flutter 1.14.x-dev you need master flutter channel at the moment
Sorry to be late for the party,
My colleague and I have developed a library that mimics the live data of android, on flutter.
Check it out:
https://pub.dev/packages/stream_live_data