Opening keyboard causes stateful widgets to be re-initialized - flutter

Question

I am using Flutter 1.2.1 in the Stable branch. To illustrate my problem imagine I have pages A and B. A navigates to B using Navigator.push and B navigates back to A using Navigator.pop. Both are stateful widgets.
When I navigate from A to B and then pop back to A everything is fine and A keeps its state. However, if I navigate from A to B, tap a textfield in B opening the keyboard, then close the keyboard and pop back to A, A's entire state is refreshed and the initState() method for A is called again. I verified this by using print statements.
This only happens when I open the keyboard before popping back to A. If I navigate to B, then immediately navigate back to A without interacting with anything then A keeps its state and is not re-initialized.
From my understanding the build method is called all the time but initState() should not get called like this. Does anyone know what is going on?

Answer 1

After much trial and error I determined the problem. I forgot that I had setup a FutureBuilder for the / route in my MaterialApp widget. I was passing a function call that returns a future to the future parameter of the FutureBuilder constructor rather than a variable pointing to a future.
So every time the routes got updated a brand new future was being created. Doing the function call outside of the MaterialApp constructor and storing the resulting future in a variable, then passing that to the FutureBuilder did the trick.
It doesn't seem like this would be connected to the weird behavior I was getting when a keyboard opened, but it was definitely the cause. See below for what I mean.
Code with a bug:
return MaterialApp(
title: appTitle,
theme: ThemeData(
primarySwatch: Colors.teal,
accentColor: Colors.tealAccent,
buttonColor: Colors.lightBlue,
),
routes: {
'/': (context) => FutureBuilder<void>(
future: futureFun(), //Bug! I'm passing a function that returns a future when called. So a new future is returned each time
builder: (context, snapshot) {
...
}
...
}
...
}
Fixed Code:
final futureVar = futureFun(); //calling the function here instead and storing its future in a variable
return MaterialApp(
title: appTitle,
theme: ThemeData(
primarySwatch: Colors.teal,
accentColor: Colors.tealAccent,
buttonColor: Colors.lightBlue,
),
routes: {
'/': (context) => FutureBuilder<void>(
future: futureVar, //Fixed! Passing the reference to the future rather than the function call
builder: (context, snapshot) {
...
}
...
}
...
}

Answer 2

did you use AutomaticKeepAliveClientMixin in "A" widget ?
if you don't , see this https://stackoverflow.com/a/51738269/3542938
if you already use it , please give us a code that we can test it directly into "main.dart" to help you

Answer 3

Yup, happened to me, perhaps it's much better to wrap the FutureBuilder itu a PageWidget, and make it singleton
return MaterialApp(
title: appTitle,
theme: ThemeData(
primarySwatch: Colors.teal,
accentColor: Colors.tealAccent,
buttonColor: Colors.lightBlue,
),
routes: {
'/': (context) => PageWidget() // wrap it by PageWidget
...
}
...
}
class PageWidget extends StatelessWidget {
static final _instance = PageWidget._internal(); // hold instance
PageWidget._internal(); // internal consturctor
factory PageWidget() {
return _instance; // make it singleton
}
#override
Widget build(BuildContext context) {
return FutureBuilder<void>( ... );
}
}

Answer 4

I got a solution, I was initialising variables in the constructor of the superclass. I removed it and worked!

Answer 5

I just removed the FutureBuilder from the home of MaterialApp and changed the MyApp into a Stateful widget and fetched the requisite info in the initState and called setState in the .then(); of the future and instead of passing multiple conditions in the home of MaterialApp, I moved those conditions to a separate Stateful widget and the issue got resolved.
initState:
#override
void initState() {
// TODO: implement initState
// isSignedIn = SharedPrefHelper.getIsSignedIn();
getIsSignedInFromSharedPreference().then((value) {
setState(() {
isSignedInFromSharedPref = value ?? false;
if (isSignedInFromSharedPref) {
merchantKey = LocalDatabase.getMerchantKeyWithoutAsync();
}
isLoadingSharedPrefValue = false;
});
});
super.initState();
}
Future<bool?> getIsSignedInFromSharedPreference() async {
return SharedPrefHelper.getIsSignedIn();
}
MaterialApp (now):
MaterialApp(
title: 'Loveeatry POS',
debugShowCheckedModeBanner: false,
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: Home(
isLoadingSharedPrefValue: isLoadingSharedPrefValue,
isSignedInFromSharedPref: isSignedInFromSharedPref,
merchantKey: merchantKey,
),
),
Home:
class Home extends StatelessWidget {
final bool isLoadingSharedPrefValue;
final bool isSignedInFromSharedPref;
final String merchantKey;
const Home({
Key? key,
required this.isLoadingSharedPrefValue,
required this.isSignedInFromSharedPref,
required this.merchantKey,
}) : super(key: key);
#override
Widget build(BuildContext context) {
if (!isLoadingSharedPrefValue) {
if (isSignedInFromSharedPref) {
return const Homepage(
shouldLoadEverything: true,
);
} else if (merchantKey.isNotEmpty) {
return LoginPage(merchantKey: merchantKey);
} else {
return const AddMerchantKeyPage();
}
} else {
return loading(context);
}
}
}
P.S.: If you need any more info, please leave a comment.