Does flutter have a method like Activity.resume() which can tell developer the user has gone back to the activity.
When I pick the data from internet in Page-B and go back to Page-A, how can I let Page-A know that the data is prepared.
Life cycle in flutter
174.3k Views Asked by zhang qinglian At
10
There are 10 best solutions below
0
On
There's an example here: https://github.com/flutter/flutter/blob/master/examples/layers/services/lifecycle.dart
You need to use WidgetsBindingObserver
0
On
Since everyone here is talking about app life cycle and not addressing the question which OP is asking. here is the answer to the question.
The requirement is he want to open page B from page A, let say to choose file from page B, and once file selected he want to go back to page A and need to process that selected file in page A. Like in android we can do it in onActivityResult() method. Below is the way we can achieve in flutter.
You can open the page B from page A as below
Map results = await Navigator.of(context).push(MaterialPageRoute(
builder: (BuildContext context) {
return new PageB(title: "Choose File");
},
));
if (results != null && results.containsKey('selection')) {
setState(() {
_selection = results['selection'];
});
**//here you can do whatever you want to do with selection variable.**
}
In Page B you can select the file or what ever things you need to return to page A as below (return file or any other variable after selection.
Navigator.of(context).pop({'selection':file});
0
On
I know I might be a little bit late but will answer this question in case someone else needs an answer,
please refer to this solution https://stackoverflow.com/a/58504433/3037840
but I want to clarify something, in your stateful widget after implementing the RouteAware mixin, please note that:
@override
void didPushNext() { //similar to onPause
// will be called when a new route has been pushed, and the current route is no longer visible. acts similar to onPause
}
@override
void didPopNext() { //similar to onResume
// will be called when the top route has been popped off, and the current route shows up. acts similar to onResume when you are navigated back to your activity/fragment
}
0
On
You can simulate onResume and onPause states in your Flutter extending LifecycleState class. Make sure to push new routes using push() or pushNamed() method.
/// Inherit this State to be notified of lifecycle events, including popping and pushing routes.
///
/// Use `pushNamed()` or `push()` method to track lifecycle events when navigating to another route.
abstract class LifecycleState <T extends StatefulWidget> extends State<T>
with WidgetsBindingObserver {
ResumeResult resumeResult = new ResumeResult();
bool _isPaused = false;
AppLifecycleState lastAppState = AppLifecycleState.resumed;
void onResume() {}
void onPause() {}
/// Use instead of Navigator.push(), it fires onResume() after route popped
Future<T> push<T extends Object>(BuildContext context, Route<T> route, [String source]) {
_isPaused = true;
onPause();
return Navigator.of(context).push(route).then((value) {
_isPaused = false;
resumeResult.data = value;
resumeResult.source = source;
onResume();
return value;
});
}
/// Use instead of Navigator.pushNamed(), it fires onResume() after route popped
Future<T> pushNamed<T extends Object>(BuildContext context, String routeName, {Object arguments}) {
_isPaused = true;
onPause();
return Navigator.of(context).pushNamed<T>(routeName, arguments: arguments).then((value) {
_isPaused = false;
resumeResult.data = value;
resumeResult.source = routeName;
onResume();
return value;
});
}
@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.paused) {
if (!_isPaused) {
onPause();
}
} else if (state == AppLifecycleState.resumed &&
lastAppState == AppLifecycleState.paused) {
if (!_isPaused) {
onResume();
}
}
lastAppState = state;
}
}
class ResumeResult {
dynamic data;
String source;
}
5
On
Only StatefulWidget hold state . Lifecyle of it is as follow
- createState () : When we build a new StatefulWidget, this one calls createState() right away and this override method must exist
- initState() :it is the first method called after the Widget is created.This is our equivalent to onCreate() and viewDidLoad()
- didChangeDependencies() : This method is called immediately after initState() on the first time the widget is built
- build() : called right after didChangeDependencies(). All the GUI is render here and will be called every single time the UI needs to be render
- didUpdateWidget() : it’ll be called once the parent Widget did a change and needs to redraw the UI
- deactivate() : framework calls this method whenever it removes this State object from the tree
- dispose() :is called when this object and its State is removed from the tree permanently and will never build again.
AppLifecycleState are as follows
inactive - The application is in an inactive state and is not receiving user input. iOS only
paused - The application is not currently visible to the user, not responding to user input, and running in the background.
resumed - The application is visible and responding to user input.
suspending - The application will be suspended momentarily. Android only
1
On
Constructor
This function is not part of the life cycle, because this time the State of the widget property is empty, if you want to access the widget properties in the constructor will not work. But the constructor must be to the first call.
createState
When Flutter is instructed to build a StatefulWidget, it immediately calls createState()
Init State
Called when this object is inserted into the tree.
When inserting the render tree when invoked, this function is called only once in the life cycle. Here you can do some initialization, such as initialization State variables.
setState
The setState() method is called often from the Flutter framework itself and from the developer.
didChangeDependencies
Called when a dependency of this [State] object changes.
didUpdateWidget
Called whenever the widget configuration changes.
deactivate
Called when this object is removed from the tree. Before dispose, we will call this function.
dispose
Called when this object is removed from the tree permanently.
didChangeAppLifecycleState
Called when the system puts the app in the background or returns the app to the foreground.
Here is a good detail document: https://www.bookstack.cn/read/flutterbyexample/aebe8dda4df3319f.md
import 'package:flutter/material.dart';
class ScreenLifecyle extends StatefulWidget {
ScreenLifecyleState state;
//createState(): When the Framework is instructed to build a StatefulWidget, it immediately calls createState()
@override
State<StatefulWidget> createState() {
// TODO: implement createState
return ScreenLifecyleState();
}
}
class ScreenLifecyleState extends State<ScreenLifecyle> {
/*
mounted is true: When createState creates your state class, a buildContext is assigned to that state.
BuildContext is, overly simplified, the place in the widget tree in which this widget is placed.
Here's a longer explanation. All widgets have a bool this.mounted property.
It is turned true when the buildContext is assigned. It is an error to call setState when a widget is unmounted.
mounted is false: The state object can never remount, and an error is thrown is setState is called.
*/
/*
This is the first method called when the widget is created (after the class constructor, of course.)
initState is called once and only once. It must called super.initState().
*/
@override
void initState() {
// TODO: implement initState
super.initState();
print("initState");
}
/*
This method is called immediately after initState on the first time the widget is built.
*/
@override
void didChangeDependencies() {
// TODO: implement didChangeDependencies
super.didChangeDependencies();
print("didChangeDependencies");
}
/*
build(): This method is called often. It is required, and it must return a Widget.
*/
@override
Widget build(BuildContext context) {
print("build");
// TODO: implement build
return Container();
}
/*
If the parent widget changes and has to rebuild this widget (because it needs to give it different data),
but it's being rebuilt with the same runtimeType, then this method is called.
This is because Flutter is re-using the state, which is long lived.
In this case, you may want to initialize some data again, as you would in initState.
*/
@override
void didUpdateWidget(ScreenLifecyle oldWidget) {
print("didUpdateWidget");
// TODO: implement didUpdateWidget
super.didUpdateWidget(oldWidget);
}
@override
void setState(fn) {
print("setState");
// TODO: implement setState
super.setState(fn);
}
/*
Deactivate is called when State is removed from the tree,
but it might be reinserted before the current frame change is finished.
This method exists basically because State objects can be moved from one point in a tree to another.
*/
@override
void deactivate() {
// TODO: implement deactivate
print("deactivate");
super.deactivate();
}
/*
Dispose is called when the State object is removed, which is permanent.
This method is where you should unsubscribe and cancel all animations, streams, etc.
*/
@override
void dispose() {
// TODO: implement dispose
super.dispose();
}
@override
void didChangeAppLifecycleState(AppLifecycleState state) {
super.didChangeAppLifecycleState(state);
switch (state) {
case AppLifecycleState.inactive:
print('appLifeCycleState inactive');
break;
case AppLifecycleState.resumed:
print('appLifeCycleState resumed');
break;
case AppLifecycleState.paused:
print('appLifeCycleState paused');
break;
case AppLifecycleState.suspending:
print('appLifeCycleState suspending');
break;
}
}
}
0
On
App Lifecycle
For LifeCycle, you need to use WidgetsBindingObserver it works when the app goes on foreground and background.
import 'package:flutter/widgets.dart';
class YourWidgetState extends State<YourWidget> 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) {
//do your stuff
}
}
}
But in my case, i was unable to catch the situation of OnResume when I move from one screen to another. so below code working similarly as startActivityForResult.
use this code when your reaching to another activity
Navigator.push(context,
MaterialPageRoute(builder: (context) => ProductDetails(pid: productList[index]["pid"],),
settings: RouteSettings(name: '/productdetail')),).then((value){
setState(() {
length=value;
});
debugPrint('CHECK BACK FROM DETAIL $length');
});
when you press back
onPressed: (){Navigator.pop(context,length);}
2
On
I don't think flutter app lifecycle callbacks are going to help you here. You can try this logic.
In 1st page (when navigating to 2nd page)
Navigator.push(context, MaterialPageRoute(builder: (context) => Page2())).then((value) {
print("Value returned form Page 2 = $value");
};
In 2nd page (when navigating back to 1st page)
Navigator.pop(context, returnedValue);
Lifecycle callback
void main() => runApp(HomePage());
class HomePage extends StatefulWidget {
@override
_HomePageState createState() => _HomePageState();
}
class _HomePageState extends State<HomePage> with WidgetsBindingObserver {
@override
void initState() {
super.initState();
WidgetsBinding.instance.addObserver(this);
}
@override
void didChangeAppLifecycleState(AppLifecycleState state) {
super.didChangeAppLifecycleState(state);
print("Current state = $state");
}
@override
Widget build(BuildContext context) {
return MaterialApp(
home: Scaffold(
appBar: AppBar(title: Text("Lifecycle")),
body: Center(child: Text("Center"),),
),
);
}
@override
void dispose() {
WidgetsBinding.instance.removeObserver(this);
super.dispose();
}
}
0
On
You can use focus_detector package:
import 'package:focus_detector/focus_detector.dart';
...
class ScreenState extends State<Screen> {
void onResume() {
print("onResume");
}
void onPause() {
print("onPause");
}
@override
Widget build(BuildContext context) {
return FocusDetector(
onFocusGained: onResume,
onFocusLost: onPause,
child: Text('example'),
);
}
}
createState()createState()mountedis truecreateStatecreates your state class, abuildContextis assigned to that state.buildContextis the place in the widget tree in which this widget is placed. All widgets have abool this.mountedproperty. It is turned true when thebuildContextis assigned. It is an error to callsetStatewhen a widget is unmounted.initState()initStateis called once and only once. It must callsuper.initState().didChangeDependencies()initStateon the first time the widget is built.build()didUpdateWidget(Widget oldWidget)runtimeType, then this method is called. This is because Flutter is re-using the state, which is long-lived. In this case, you may want to initialize some data again, as you would ininitState.setState()deactivate()deactivate()is called when the State object is removed from the tree, but it might be reinserted before the current frame change is finished. This method exists because State objects can be moved from one point in a tree to another.dispose()dispose()is called when the State object is removed, which is permanent. This method is where you should unsubscribe and cancel all animations, streams, etc.mountedis falsesetStateis called.