How to fix "Failed assertion: 'create != null': is not true" error with Provider package in Flutter?

Question

Here is the error message from Android Studio:

════════ Exception caught by widgets library ═══════════════════════════════════════════════════════
The following assertion was thrown building MyZippyApp(dirty):
'package:provider/src/provider.dart': Failed assertion: line 181 pos 16: 'create != null': is not true.

The relevant error-causing widget was: 
  MyZippyApp file:///Users/mgav/AndroidStudioProjects/streakers_journal_beta/lib/main.dart:5:23
When the exception was thrown, this was the stack: 
#2      new Provider (package:provider/src/provider.dart:181:16)
#3      MyZippyApp.build (package:streakers_journal_beta/main.dart:10:12)
#4      StatelessElement.build (package:flutter/src/widgets/framework.dart:4701:28)
#5      ComponentElement.performRebuild (package:flutter/src/widgets/framework.dart:4627:15)
#6      Element.rebuild (package:flutter/src/widgets/framework.dart:4343:5)

It appears as soon as I wrap 'MaterialApp' in a 'Provider' widget (using package version provider: ^4.3.2 in pubspec.yaml > ran 'Pub get'), then try to run the app.

Here is the main.dart code before wrapping with the 'Provider' widget (works perfectly well):

import 'package:flutter/material.dart';
import 'package:streakers_journal_beta/screens/tasks_screen.dart';
import 'package:provider/provider.dart';

void main() => runApp(MyZippyApp());

class MyZippyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home:
          TasksScreen(), // matches "TasksScreen" class created on tasks_screen.dart
    );
  }
}

Here is the main.dart code after wrapping with the provider widget:

import 'package:flutter/material.dart';
import 'package:streakers_journal_beta/screens/tasks_screen.dart';
import 'package:provider/provider.dart';

void main() => runApp(MyZippyApp());

class MyZippyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Provider(
      child: MaterialApp(
        home:
            TasksScreen(), // matches "TasksScreen" class created on tasks_screen.dart
      ),
    );
  }
}

And per Farhan Syah's answer below, here is the revised code that reflects his answer (and fixes the problem):

import 'package:flutter/material.dart';
import 'package:streakers_journal_beta/screens/tasks_screen.dart';
import 'package:provider/provider.dart';

void main() => runApp(MyZippyApp());

class MyZippyApp extends StatelessWidget {
  final String testingText = 'Thank you Farhan Syah';

  @override
  Widget build(BuildContext context) {
    return Provider(
      create: (context) => testingText,
      child: MaterialApp(
        home:
            TasksScreen(), // matches "TasksScreen" class created on tasks_screen.dart
      ),
    );
  }
}

Screenshot of error in Android emulator is at i.sstatic.net/Uuj6k.png — Mark Gavagan
– Mark Gavagan, Commented Nov 13, 2020 at 17:40

Farhan Syah · Accepted Answer · 2020-11-13 17:40:11Z

2

Provider widget has a required create properties.

you should use 'create' to create an object which you want to provide.

return Provider(
      create: (context)=> ObjectToBeProvidedHere(),
      child: MaterialApp(
        home:
            TasksScreen(), // matches "TasksScreen" class created on tasks_screen.dart
      ),
    );

answered Nov 13, 2020 at 17:40

Farhan Syah

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