Flutter: Multiple Instances of Shared Preferences? - flutter

Question

I am having a problem with SharedPreferences and multiple Modules I am generating on a Form using ListView.builder
The form is basically asking for some parents details and their childs details - by default the form assumes the parent has one child, but more can be added by clicking a button. The ChildModule has the ability to "close" but when "re-opened" the data doesn't persist, hence using SharedPreferences, it works fine with one Child, but once a second child is added it seems to be creating multiple Instances of SharedPreferences.
I have cut out everything to show what I am trying to achieve. NOTE this is being used as a Web App if it matters.
Oh and ChildModule needs to have its own state because it has a widget which requires it (not shown)
ENQUIRY FORM
final GlobalKey<FormBuilderState> _enquiryFormKey = GlobalKey<FormBuilderState>();
class EnquiryForm extends StatefulWidget {
static List<int> numberOfChildren = [1];
#override
_EnquiryFormState createState() => _EnquiryFormState();
}
class _EnquiryFormState extends State<EnquiryForm> {
int defaultNumberOfChildren = 1;
removeModule(){
setState(() {});
}
#override
Widget build(BuildContext context) {
return FormBuilder(
key: _enquiryFormKey,
child: Column(
children: <Widget>[
Row(
children: <Widget>[
Expanded(
child: CustomTextField(
label: 'Parent First Name',
isRequired: true,
),
),
),
//ChildModuleList
ListView.builder(
shrinkWrap: true,
itemCount: EnquiryForm.numberOfChildren.length,
itemBuilder: (context,int index){
return ChildModule(EnquiryForm.numberOfChildren[index], removeModule);
}
),
SizedBox(height: 20,),
Row(
mainAxisAlignment: MainAxisAlignment.end,
children: <Widget>[
ThemedButton(
onPressed: (){
setState(() {
defaultNumberOfChildren++;
EnquiryForm.numberOfChildren.add(defaultNumberOfChildren);
});
},
child: Text(
'Add Additional Child',
style: TextStyle(color: Colors.white),)
),
SizedBox(width: 10,),
ThemedButton(
onPressed: (){},
child: Text('Enquire Now', style: TextStyle(color: Colors.white),))
],
)
],
));
}
}
CHILD MODULE
class ChildModule extends StatefulWidget {
final int number;
final Function() callback;
ChildModule(this.number,this.callback);
#override
_ChildModule createState() => _ChildModule();
}
class _ChildModule extends State<ChildModule> {
SharedPreferences childModuleData;
String firstName;
bool loading = true;
bool isOpen;
#override
void initState() {
print('this module number is ${widget.number}');
_spInstance();
isOpen = true;
super.initState();
}
Future<void> _spInstance() async {
if(childModuleData == null && widget.number == 1) {
childModuleData = await SharedPreferences.getInstance();
print('got instance');
} else {
print('broken');
print(childModuleData);
};
String _testValue = childModuleData.getString('Child First Name');
if(_testValue == null){
childModuleData.setString('Child First Name', '');
loading = false;
} else {
childModuleData.clear();
_spInstance();
}
}
#override
Widget build(BuildContext context) {
return loading ? Loading() : Column(
children: <Widget>[
GestureDetector(
onTap: () {
setState(() {
if (isOpen == false) {
isOpen = true;
} else {
isOpen = false;
}
});
},
child: Container(
height: 40,
padding: EdgeInsets.only(left: 10, right: 10),
decoration: BoxDecoration(
borderRadius: BorderRadius.all(Radius.circular(4.0)),
color: Colors.blue[50],
),
child: Row(
mainAxisAlignment: MainAxisAlignment.spaceBetween,
children: <Widget>[
Text(
'Child Details',
style: TextStyle(color: Colors.blue[300], fontSize: 16),
),
Row(
children: <Widget>[
isOpen
? Icon(
Icons.arrow_drop_down,
size: 30,
)
: Transform.rotate(
angle: math.pi / 2,
child: Icon(
Icons.arrow_drop_down,
size: 30,
),
),
widget.number > 1
? IconButton(icon: Icon(Icons.clear), onPressed: () async {
await FormFunctions().removeModule(widget.number, EnquiryForm.numberOfChildren);
widget.callback();
})
: Container(),
],
),
],
),
),
),
AnimatedContainer(
duration: Duration(seconds: 2),
curve: Curves.fastOutSlowIn,
padding: EdgeInsets.fromLTRB(10, 5, 10, 5),
height: isOpen ? null : 0,
decoration: BoxDecoration(
border: Border.all(color: Colors.grey[300]),
borderRadius: BorderRadius.all(Radius.circular(4.0)),
),
child: Column(
children: <Widget>[
Row(
children: <Widget>[
CustomTextField(
label: fieldFirstName,
isRequired: true,
initalValue: childModuleData.getString(fieldFirstName) ?? '',
onChanged: (value){
childModuleData.setString(fieldFirstName, value);
},
),
],
),
],
),
),
],
);
}
}
CONSOLE ERROR AFTER SECOND MODULE IS CREATED
Launching lib/main.dart on Chrome in debug mode...
Syncing files to device Chrome...
Debug service listening on ws://127.0.0.1:58490/EkMAy9CGY74=
Debug service listening on ws://127.0.0.1:58490/EkMAy9CGY74=
this module number is 1
got instance
Instance of 'SharedPreferences'
null
this module number is 2 //Number 2 Module is created
broken
null
null
TypeError: Cannot read property 'getString' of null
at child_module._ChildModule.new._spInstance$ (http://localhost:58433/packages/webenrol/shared/widgets/day_button.dart.lib.js:3704:47)
at _spInstance$.next (<anonymous>)
at runBody (http://localhost:58433/dart_sdk.js:43121:34)
at Object._async [as async] (http://localhost:58433/dart_sdk.js:43149:7)
at child_module._ChildModule.new.[_spInstance] (http://localhost:58433/packages/webenrol/shared/widgets/day_button.dart.lib.js:3694:20)
at child_module._ChildModule.new.initState (http://localhost:58433/packages/webenrol/shared/widgets/day_button.dart.lib.js:3689:24)
at framework.StatefulElement.new.[_firstBuild] (http://localhost:58433/packages/flutter/src/widgets/widget_span.dart.lib.js:41219:58)
at framework.StatefulElement.new.mount (http://localhost:58433/packages/flutter/src/widgets/widget_span.dart.lib.js:12605:24)
at framework.SingleChildRenderObjectElement.new.inflateWidget (http://localhost:58433/packages/flutter/src/widgets/widget_span.dart.lib.js:11420:16)

Answer 1

in your case the concern is at the level of recording data in shared preferences. one solution would be to add the widget number in the key to save like this (await SharedPreferences.getInstance()).setString("Your Key${widgetNumber}");
and edit your function _spInstance
class ChildModule extends StatefulWidget {
final int number;
final Function() callback;
ChildModule(this.number,this.callback);
#override
_ChildModule createState() => _ChildModule();
}
class _ChildModule extends State<ChildModule> {
SharedPreferences childModuleData;
...
Future<void> _spInstance() async {
if(childModuleData == null) {
childModuleData = await SharedPreferences.getInstance();
print('got instance');
}
String _testValue = childModuleData.getString('Child First Name${widget.number}');
//NB: do not clear data on chlidModuleData any more.
...
}
...
}