Flutter ScrollController not working under StreamBuilder with ConnectionState condition - dart

Question

I'm new with flutter & just learned how to retrieve data from firestore & did some UI. Right now I have 2 problems;
1- This is a Setting Page which has CustomScrollView contains ScrollController for the controller.
SettingsPage
The controller working fine with this code
class _SettingsPageState extends State<SettingsPage> {
ScrollController _scrollController;
#override
void initState() {
super.initState();
_scrollController = new ScrollController();
_scrollController.addListener(() => setState(() {}));
}
#override
void dispose() {
_scrollController.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
return StreamBuilder(
stream: Shared.firestore.collection('client').document(Shared.firebaseUser.uid).snapshots(),
builder: (BuildContext context, AsyncSnapshot snapshot) {
return Scaffold(
backgroundColor: Colors.grey[50],
body: Stack(
children: <Widget>[
CustomScrollView(
controller: _scrollController,
slivers: <Widget>[
SliverAppBar(
expandedHeight: 140.0,
pinned: true,
),
SliverFillRemaining(
child: Row(
crossAxisAlignment: CrossAxisAlignment.start,
children: <Widget>[
Expanded(
flex: 8,
child: Column(
children: <Widget>[
Container(
decoration: BoxDecoration(
color: Colors.white,
),
child: Padding(
padding: EdgeInsets.only(
left: 18.0,
top: 18.0,
),
child: Row(
children: <Widget>[
Text(
"Account",
style: TextStyle(
color: Colors.blue[700],
fontSize: 15,
fontWeight: FontWeight.w500,
),
),
],
),
),
),
Container(
decoration: BoxDecoration(
color: Colors.white,
),
child: ListTile(
onTap: () {},
contentPadding: EdgeInsets.only(left: 18.0),
title: Text(
"+${snapshot.data['countryCode']} ${snapshot.data['phoneNumber']}",
style: TextStyle(fontSize: 16),
),
subtitle: Row(
children: <Widget>[
Text(
"Phone Number",
style: TextStyle(
fontSize: 12,
),
),
],
),
),
),
],
),
),
],
),
),
],
),
],
),
);
},
);
}
}
but this error happened
I/flutter ( 8691): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════
I/flutter ( 8691): The following NoSuchMethodError was thrown building StreamBuilder<DocumentSnapshot>(dirty, state:
I/flutter ( 8691): _StreamBuilderBaseState<DocumentSnapshot, AsyncSnapshot<DocumentSnapshot>>#7db43):
I/flutter ( 8691): The method '[]' was called on null.
I/flutter ( 8691): Receiver: null
I/flutter ( 8691): Tried calling: []("countryCode")
I/flutter ( 8691):
I/flutter ( 8691): When the exception was thrown, this was the stack:
I/flutter ( 8691): #0 Object.noSuchMethod (dart:core/runtime/libobject_patch.dart:50:5)
I/flutter ( 8691): #1 _SettingsPageState.build.<anonymous closure> (package:silkwallet/page/settings.dart:81:54)
I/flutter ( 8691): #2 StreamBuilder.build (package:flutter/src/widgets/async.dart:423:74)
I/flutter ( 8691): #3 _StreamBuilderBaseState.build (package:flutter/src/widgets/async.dart:125:48)
I/flutter ( 8691): #4 StatefulElement.build (package:flutter/src/widgets/framework.dart:3809:27)
I/flutter ( 8691): #5 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3721:15)
I/flutter ( 8691): #6 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter ( 8691): #7 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter ( 8691): #8 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11)
I/flutter ( 8691): #9 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter ( 8691): #10 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter ( 8691): #11 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter ( 8691): #12 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter ( 8691): #13 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter ( 8691): #14 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter ( 8691): #15 StatefulElement._firstBuild (package:flutter/src/widgets/framework.dart:3848:11)
I/flutter ( 8691): #16 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter ( 8691): #17 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter ( 8691): #18 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter ( 8691): #19 SingleChildRenderObjectElement.mount (package:flutter/src/widgets/framework.dart:4860:14)
I/flutter ( 8691): #20 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter ( 8691): #21 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
I/flutter ( 8691): #22 ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:3732:16)
I/flutter ( 8691): #23 Element.rebuild (package:flutter/src/widgets/framework.dart:3547:5)
I/flutter ( 8691): #24 ComponentElement._firstBuild (package:flutter/src/widgets/framework.dart:3701:5)
I/flutter ( 8691): #25 ComponentElement.mount (package:flutter/src/widgets/framework.dart:3696:5)
I/flutter ( 8691): #26 Element.inflateWidget (package:flutter/src/widgets/framework.dart:2950:14)
I/flutter ( 8691): #27 Element.updateChild (package:flutter/src/widgets/framework.dart:2753:12)
.
.
.
I/flutter ( 8691): #135 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding&PaintingBinding&SemanticsBinding&RendererBinding._handlePersistentFrameCallback (package:flutter/src/rendering/binding.dart:219:5)
I/flutter ( 8691): #136 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:990:15)
I/flutter ( 8691): #137 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:930:9)
I/flutter ( 8691): #138 _WidgetsFlutterBinding&BindingBase&GestureBinding&ServicesBinding&SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:842:5)
I/flutter ( 8691): #139 _invoke (dart:ui/hooks.dart:154:13)
I/flutter ( 8691): #140 _drawFrame (dart:ui/hooks.dart:143:3)
2- After some research for this error, I add connectionState condition inside StreamBuilder which solved above problem
this is the new code, i put the Scaffold inside active connectionState
class _SettingsPageState extends State<SettingsPage> {
ScrollController _scrollController;
#override
void initState() {
super.initState();
_scrollController = new ScrollController();
_scrollController.addListener(() => setState(() {}));
}
#override
void dispose() {
_scrollController.dispose();
super.dispose();
}
#override
Widget build(BuildContext context) {
return StreamBuilder(
stream: Shared.firestore.collection('client').document(Shared.firebaseUser.uid).snapshots(),
builder: (BuildContext context, AsyncSnapshot snapshot) {
if (snapshot.connectionState == ConnectionState.active) {
return Scaffold(
backgroundColor: Colors.grey[50],
body: Stack(
.
.
.
),
);
} else if (snapshot.connectionState == ConnectionState.waiting) {
return Container(child: Center(child: CircularProgressIndicator()));
} else {
return Container(
child: Column(
children: <Widget>[
Padding(
padding: const EdgeInsets.all(8.0),
child: Icon(Icons.warning),
),
Text('Error in loadind data')
],
),
);
}
},
);
}
}
and I realized that when I scrolled the connectionState will change to waiting and the ScrollController not working under this state as shown in the image below
ScrollController: page keep flashing when try to scroll
The reason I want to use the ScrollController because I want to add FloatingActionButton inside Positioned which will scroll along & disappear when reach certain position, here's the image with FloatingActionButton

Answer 1

NoSuchMethodError the method was called on null errors are usually thrown when the method that you're trying to call from the object is yet to be initialized. The error seems to be coming from snapshot.data['countryCode']. What you can do here is add a null-check on snapshot before displaying the data.
if (snapshot != null && snapshot.hasData) {
// Display data
} else {
// Display circular progress...
}