setState() or markNeedsBuild() called when widget tree was locked - flutter

Question

Flutter
i am trying to display a widget into Stack IF an condition (true or false ) , and it work with no problems
but when i need to change the condition bool into SetState to hide the Widget again , it is also work but with annoying error messages whish is setState() or markNeedsBuild() called when widget tree was locked.
my code is so complicated but i am gonna show a simple similar example
bool displayWidget = false;
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(),
body: Stack(
children: [
Container(
child: TextButton(
onPressed: () {
final result = await FilePicker.platform.pickFiles(allowMultiple: false );
if (result == null) return;
final path = result.files.single.path;
setState(() => displayWidget = true);
},
child: Text ("studio")
),
),
displayWidget?
GestureDetector(
onTap: ()=> setState(() => displayWidget = false), // the error happen when i click here
child: Container(
child: Image.asset("here is the picture in full secreen"),
),
):Container()
],
),
);
}
}
i know there is a photo viewer better than this way :D but i only give a simple example for other real case

Answer 1

First of all I would like to ask you where is #override? Did you forget to add that in your question? If yes then that error might have something to do with that. If no then try declaring the bool value above #override.

Answer 2

please see if this example can be helpful to you (I simplified yours just a little bit more so it can be easily run in dartpad).
in your case onPressed function should contain your file picking logic and have a return type as you expect it to be (probably, String?) and check if returned value isn't null, then show your image
class MyWidget extends StatefulWidget {
#override
State<MyWidget> createState() => MyWidgetState();
}
class MyWidgetState extends State<MyWidget> {
bool displayWidget = false;
bool onPressed(bool isShown) {
//instead of this mocked function pickFile here
return !isShown;
}
#override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(),
body: Row(
children: [
Container(
child: TextButton(
onPressed: () {
displayWidget = onPressed(displayWidget);
setState(() => displayWidget);
},
child: Text ("Show or hide text"),
),
),
if(displayWidget)
GestureDetector(
onTap: ()=> setState(() => displayWidget = !displayWidget),
child: Container(
child: Text('This text is to be shown'),
),
),
],
),
);
}
}

Answer 3

I found the solution from the official website of flutter
simply wrap set state into
in this solution would be for most cases
if(!mounted) {
setState
}
or
if(mounted) { // depends on your widget case
setState
}
source https://www.kindacode.com/article/flutter-error-setstate-called-after-dispose/
if not , try this
WidgetsBinding.instance
.addPostFrameCallback((_) => setState(() {}));
source https://www.thetopsites.net/article/50288698.shtml
and i find same error with many answers in stackoverflow
press below
Flutter setState() or markNeedsBuild() called when widget tree was locked