Flutter setState() function being called but not doing anything - ios

Question

Managed to create a simple reproduction of an error I've come across in my real program, and I'm not sure why this kind of a thing happens. I think if I can understand this, it might help me.
The key here is that I HAVE to have the two pieces of the program separated in this manner, and they need to communicate, but that communication isn't happening the way I would expect. (So please don't suggest I put the timer function inside the rest of the program).
import 'package:flutter/material.dart';
import 'dart:async';
void main() => runApp(MyApp());
class MyApp extends StatelessWidget {
// This widget is the root of your application.
#override
Widget build(BuildContext context) {
return MaterialApp(
title: 'Flutter Demo',
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: 'Flutter Demo Home Page'),
);
}
}
class MyHomePage extends StatefulWidget {
MyHomePage({Key key, this.title}) : super(key: key);
final String title;
#override
_MyHomePageState createState() => _MyHomePageState();
}
class _MyHomePageState extends State<MyHomePage> {
bool textBool = false;
void textChanger() {
if (textBool) {
setState(() {
textBool = false;
});
} else {
setState(() {
textBool = true;
});
}
}
Text myText() {
if (textBool) {
Text newText = new Text('Original Text');
return newText;
} else {
Text newText = new Text('New Text');
return newText;
}
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: myText(),
),
floatingActionButton: FloatingActionButton(
onPressed: stateModify,
tooltip: 'Change Text',
),
);
}
}
Future<void> stateModify() {
Duration waitTimer = new Duration(seconds: 5);
new Timer.periodic(waitTimer, (timer) {
_MyHomePageState().textChanger();
timer.cancel();
});
}
Expected functionality: Click the button and 5 seconds later it should change to the second set of text. Then I should be able to click the button again and switch it back.
Instead in this example I receive the following error:
[VERBOSE-2:ui_dart_state.cc(157)] Unhandled Exception: setState() called in constructor: _MyHomePageState#a5177(lifecycle state: created, no widget, not mounted)
And google doesn't seem to be super helpful on this particular issue.
Any suggestions?

Answer 1

Your stateModify function is not a method of _MyHomePageState. Also when you are accessing the _MyHomePageState().textChanger() in stateModify you are eventually creating a new object of _MyHomePageState() but not inserting in render tree.
You should use Timer instead of Timer.periodic. The Timer.periodic will repeat the task until the Timer.cancel is called. Timer will do a callback after the given time period which you require.
Pass the function textChanger when you are calling stateModify that way you will be able to call the function of _MyHomePageState without creating a new object.
Do the following changes.
floatingActionButton: FloatingActionButton(
onPressed: ()=> stateModify(textChanger),
tooltip: 'Change Text',
),
stateModify(dynamic function) {
Timer(Duration(seconds: 5), function);
}