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Not able to solve "Null check operator used on a null value"

I am trying to create a to-do list app in flutter. I am facing an issue with a widget that helps me to edit an already created to-do widget with respect to the title or description.

This is the pic of my todo list HomePage

enter image description here

This pic of my edit button

enter image description here

I am facing an issue after I press the save button in this widget

enter image description here

This is the error that I am getting

════════ Exception caught by gesture ═══════════════════════════════════════════
The following _CastError was thrown while handling a gesture:
Null check operator used on a null value
When the exception was thrown, this was the stack
#0      _EditTodoPageState.saveTodo
package:todolist/Edit_Todo_Page.dart:47
#1      _InkResponseState._handleTap
package:flutter/…/material/ink_well.dart:989
#2      GestureRecognizer.invokeCallback
package:flutter/…/gestures/recognizer.dart:198
#3      TapGestureRecognizer.handleTapUp
package:flutter/…/gestures/tap.dart:608
#4      BaseTapGestureRecognizer._checkUp
package:flutter/…/gestures/tap.dart:296
#5      BaseTapGestureRecognizer.handlePrimaryPointer
package:flutter/…/gestures/tap.dart:230
#6      PrimaryPointerGestureRecognizer.handleEvent
package:flutter/…/gestures/recognizer.dart:563
#7      PointerRouter._dispatch
package:flutter/…/gestures/pointer_router.dart:94
#8      PointerRouter._dispatchEventToRoutes.<anonymous closure>
package:flutter/…/gestures/pointer_router.dart:139
    (elided 3 frames from dart:async)
Handler: "onTap"
Recognizer: TapGestureRecognizer#25bd2
    debugOwner: GestureDetector
    state: possible
    won arena
    finalPosition: Offset(189.1, 309.1)
    finalLocalPosition: Offset(67.7, 11.1)
    button: 1
    sent tap down
════════════════════════════════════════════════════════════════════════════════

This is my edit todo widget

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:todolist/todo.dart';
import './todos.dart';
import './todo_form_widget.dart';

class EditTodoPage extends StatefulWidget {
  final Todo todo;
  const EditTodoPage({Key? key, required this.todo}) : super(key: key);

  @override
  State<EditTodoPage> createState() => _EditTodoPageState();
}

class _EditTodoPageState extends State<EditTodoPage> {
  final _formKey = GlobalKey<FormState>();
  late String title;
  late String description;
  @override
  void initState() {
    super.initState();
    title = widget.todo.title;
    description = widget.todo.description;
  }

  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("Edit Todo"),
        ),
        body: Padding(
          padding: EdgeInsets.all(16),
          child: Form(
            child: TodoFormWidget(
              title: title,
              description: description,
              onChangedTitle: (title) => setState(() => this.title = title),
              onChangedDescription: (description) =>
                  setState(() => this.description = description),
              onSavedTodo: saveTodo,
            ),
          ),
        ));
  }

  saveTodo() {
    final isValid = _formKey.currentState!.validate();
    if (!isValid) {
      return;
    } else {
      final provider = Provider.of<TodosProvider>(context, listen: false);
      provider.updateTodo(widget.todo, title, description);
      Navigator.of(context).pop();
    }
  }
}

I am getting an error in the "saveTodo()" method. I am not able to solve this error.

This is my Provider widget

import 'package:flutter/cupertino.dart';
import 'package:todolist/todo.dart';
import 'package:provider/provider.dart';

class TodosProvider extends ChangeNotifier {
  List<Todo> _todos = [
    Todo(
      createdTime: DateTime.now(),
      title: "Wake up at 6:00 AM in the morning😀!!!",
    ),
    Todo(
      createdTime: DateTime.now(),
      title: "Wake up at 6:00 AM in the morning😀!!!",
    ),
    Todo(
      createdTime: DateTime.now(),
      title: "Wake up at 6:00 AM in the morning😀!!!",
    ),
    Todo(
      createdTime: DateTime.now(),
      title: "Wake up at 6:00 AM in the morning😀!!!",
    ),
    Todo(
      createdTime: DateTime.now(),
      title: "Wake up at 6:00 AM in the morning😀!!!",
    ),
    Todo(
      createdTime: DateTime.now(),
      title: "Wake up at 6:00 AM in the morning😀!!!",
    ),
    Todo(
      createdTime: DateTime.now(),
      title: "Wake up at 6:00 AM in the morning😀!!!",
    ),
    Todo(
      createdTime: DateTime.now(),
      title: "Wake up at 6:00 AM in the morning😀!!!",
    ),
  ];
  List<Todo> get todos => _todos.where((todo) => todo.isDone == false).toList();
  List<Todo> get todosCompleted =>
      _todos.where((todo) => todo.isDone == true).toList();

  void addTodo([Todo? todo]) {
    _todos.add(todo!);
    notifyListeners();
  }

  void removeTodo(Todo todo) {
    _todos.remove(todo);
    notifyListeners();
  }

  bool toggleTodoStatus(Todo todo) {
    todo.isDone = !todo.isDone;
    notifyListeners();
    return todo.isDone;
  }

  void updateTodo(Todo todo, String title, String description) {
    todo.title = title;
    todo.description = description;
    notifyListeners();
  }
}

Please help me solve this error.

Solution

  • I think, you haven't used _formKey in Form widget thats why _formKey currentState is getting null. Try to use _formKey in the Form widget and check it is not equal to null.

    import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:todolist/todo.dart';
import './todos.dart';
import './todo_form_widget.dart';

class EditTodoPage extends StatefulWidget {
  final Todo todo;
  const EditTodoPage({Key? key, required this.todo}) : super(key: key);

  @override
  State<EditTodoPage> createState() => _EditTodoPageState();
}

class _EditTodoPageState extends State<EditTodoPage> {
  final _formKey = GlobalKey<FormState>();
  late String title;
  late String description;

  @override
  void initState() {
    super.initState();
    title = widget.todo.title;
    description = widget.todo.description;
  }

  Widget build(BuildContext context) {
    return Scaffold(
        appBar: AppBar(
          title: Text("Edit Todo"),
        ),
        body: Padding(
          padding: EdgeInsets.all(16),
          child: Form(
            key: _formKey,
            child: TodoFormWidget(
              title: title,
              description: description,
              onChangedTitle: (title) => setState(() => this.title = title),
              onChangedDescription: (description) =>
                  setState(() => this.description = description),
              onSavedTodo: saveTodo,
            ),
          ),
        ),
     );
  }

  saveTodo() {
    final isValid = _formKey.currentState != null && _formKey.currentState!.validate();
    if (!isValid) {
      return;
    } else {
      final provider = Provider.of<TodosProvider>(context, listen: false);
      provider.updateTodo(widget.todo, title, description);
      Navigator.of(context).pop();
    }
  }
}