Multiple widgets used the same GlobalKey

Question

I'm using Flutter. I have a simple app with 3 tabs. There is a RefreshIndicator in each tab with a ListView. The rows are built in another method. This is the code:

 @override  Widget build(BuildContext context) {     final GlobalKey<RefreshIndicatorState> _RIKey1 = new GlobalKey<RefreshIndicatorState>();     final GlobalKey<RefreshIndicatorState> _RIKey2 = new GlobalKey<RefreshIndicatorState>();     final GlobalKey<RefreshIndicatorState> _RIKey3 = new GlobalKey<RefreshIndicatorState>();      debugPrint(_RIKey1.toString());     debugPrint(_RIKey2.toString());     debugPrint(_RIKey3.toString());     return new Scaffold(       body: new DefaultTabController(         length: 3,         child: new Scaffold(           appBar: new AppBar(             bottom: new TabBar(               tabs: [                 new Tab(icon: new Icon(Icons.view_list)),                 new Tab(icon: new Icon(Icons.hotel)),                 new Tab(icon: new Icon(Icons.assessment)),               ],             ),             title: new Text('Data'),           ),           body: new TabBarView(             children: [               new RefreshIndicator(                 key: _RIKey1,                 onRefresh: _actualizoData,                 child: new ListView.builder(                     padding: new EdgeInsets.only(top: 5.0),                     itemCount: linea_reservas.length * 2,                     itemBuilder: (BuildContext context, int position) {                       if (position.isOdd) return new Divider();                       final index = position ~/ 2;                       return _buildRow(index);                     }),               ),               new RefreshIndicator(                 key: _RIKey2,                 onRefresh: _actualizoData,                 child: new ListView.builder(                     padding: new EdgeInsets.only(top: 8.0),                     itemCount: linea_inouthouse.length * 2,                     itemBuilder: (BuildContext context, int position) {                       if (position.isOdd) return new Divider();                       final index = position ~/ 2;                       return _buildRowInOutHouse(index);                     }),               ),               new RefreshIndicator(                 key: _RIKey3,                 onRefresh: _actualizoData,                 child: new ListView.builder(                     padding: new EdgeInsets.only(top: 5.0),                     itemCount: linea_ocupacion.length * 2,                     itemBuilder: (BuildContext context, int position) {                       if (position.isOdd) return new Divider();                       final index = position ~/ 2;                       return _buildRowOcupacion(index);                     }),               ),             ],           ),         ),       ),     );   } 

I'd added the debugPrints and the output are 6 lines, instead of 3.

I/flutter ( 5252): [LabeledGlobalKey<RefreshIndicatorState>#4d76c] I/flutter ( 5252): [LabeledGlobalKey<RefreshIndicatorState>#59b9e] I/flutter ( 5252): [LabeledGlobalKey<RefreshIndicatorState>#2c88b] I/flutter ( 5252): [LabeledGlobalKey<RefreshIndicatorState>#7bd42] I/flutter ( 5252): [LabeledGlobalKey<RefreshIndicatorState>#1c984] I/flutter ( 5252): [LabeledGlobalKey<RefreshIndicatorState>#dbe20] 

the app works, but after changing tabs a few times, it crashes with this error:

    I/flutter ( 5252): ══╡ EXCEPTION CAUGHT BY WIDGETS LIBRARY ╞═══════════════════════════════════════════════════════════ I/flutter ( 5252): The following assertion was thrown building NotificationListener<KeepAliveNotification>: I/flutter ( 5252): Multiple widgets used the same GlobalKey. I/flutter ( 5252): The key [LabeledGlobalKey<RefreshIndicatorState>#7bd42] was used by multiple widgets. The parents of I/flutter ( 5252): those widgets were: I/flutter ( 5252): - RepaintBoundary-[<[LabeledGlobalKey<RefreshIndicatorState>#7bd42]>](renderObject: I/flutter ( 5252):   RenderRepaintBoundary#60a4a DETACHED) I/flutter ( 5252): - RepaintBoundary-[<[LabeledGlobalKey<RefreshIndicatorState>#7bd42]>](renderObject: I/flutter ( 5252):   RenderRepaintBoundary#c8cdb NEEDS-LAYOUT NEEDS-PAINT) I/flutter ( 5252): A GlobalKey can only be specified on one widget at a time in the widget tree. 

The keys are generated in the Build method, so, I don't understand why the Multiple widgets used the same GlobalKey error

Why the key is generated again, and why it's not unique? I'm not talking of a thousand intents, the error appears after changing between tabs 4 or 5 times. Thank you for any help.

Answer 1

Could you create your keys "by hand" and use static/constant values? e.g. ...

import 'package:flutter/widgets.dart';  class RIKeys {   static final riKey1 = const Key('__RIKEY1__');   static final riKey2 = const Key('__RIKEY2__');   static final riKey3 = const Key('__RIKEY3__'); } 

then in ...

    body: new TabBarView(             children: [               new RefreshIndicator(new RefreshIndicator( // Use the Manual Static Value instead ...                 key: RIKeys.riKey1,                 onRefresh: _actualizoData,                 child: new ListView.builder(                     padding: new EdgeInsets.only(top: 5.0),                     itemCount: linea_reservas.length * 2,                     itemBuilder: (BuildContext context, int position) {                       if (position.isOdd) return new Divider();                       final index = position ~/ 2;                       return _buildRow(index);                     }),               ), 

I have done this in a similar situation with some success ... especially with redux or other similar patterns ...

Answer 2

this code worked for me ... I want to create a List of Form Key ...

just Changing GlobalKey with GlobalObjectKey

like below.

final List<GlobalObjectKey<FormState>> formKeyList = List.generate(10, (index) => GlobalObjectKey<FormState>(index));