Unhandled Exception: NoSuchMethodError: The method 'next' was called on null - flutter

Question

I have 4 classes SignUp , Auth, PageOne and InWidget (inherited widget). In the classe signUpState i have a swiper that i can control using a controller.
SignUp
class SignUp extends StatefulWidget {
static const String id = 'history_page';
#override
SignUpState createState() => SignUpState();
goto(bool x) => createState().goto(x);
}
SignUpState
class SignUpState extends State<SignUp> {
SwiperController _swOneCtrl;
#override
void initState() {
_swOneCtrl = new SwiperController();
super.initState();
}
goto(bool anim){
_swOneCtrl.next(animation: anim);
print("goto fired");
}
}
Auth
class Auth extends StatelessWidget {
SignUp s = SignUp();
verifyPhoneNumber() {
s.goto(true);
}
}
PageOne
class PageOneState extends State<PageOne> {
#override
Widget build(BuildContext context) {
final MyInheritedWidgetState state = MyInheritedWidget.of(context);
return RaisedButton(
color: Colors.blueGrey,
disabledColor: Colors.grey[100],
textColor: Colors.white,
elevation: 0,
onPressed: !phonebtn
? null
: () {
final MyInheritedWidgetState state =
MyInheritedWidget.of(context);
state.verifyPhoneNumber();
},
child: Text("CONTINUER"),
),
);
}
}
The thing is i want to call verifyPhoneNumber() from auth that will call the goto() method from pageone using inwidget as intermediary but i'm getting this error :
Unhandled Exception: NoSuchMethodError: The method 'next' was called on null.
do you know why ?

Answer 1

Try to initialize at the time of declaration.
class SignUpState extends State<SignUp> {
SwiperController _swOneCtrl = new SwiperController();
#override
void initState() {
super.initState();
}
goto(bool anim){
_swOneCtrl.next(animation: anim);
print("goto fired");
}
}
Respond me if it works.

Answer 2

initState() is a method that is called once when the stateful widget is inserted in the widget tree.
We generally override this method if we need to do some sort of initialization work like registering a listener because unlike build() this method is called once.
As I think you are declaring Swipe controller in your SignUPState class.
class SignUpState extends State<SignUp> {
SwiperController _swOneCtrl;
#override
void initState() {
_swOneCtrl = new SwiperController();
super.initState();
}
goto(bool anim){
_swOneCtrl.next(animation: anim);
print("goto fired");
}
}
But you have initialized it in initState(). the problem is because you are not inserting your SignUp widget in widget tree so your swipe controller is not initializing and become null. So when you are calling the next method to null it is showing error.
As Solution first insert your Sign up widget in your Widget tree.
if my solution helped you. Please rate me.