Flutter: currentState is null while using AnimatedList

Question

I'm new to Flutter and I'm experimenting AnimatedList in my todolist app. I have ensured that:

• globalkey is initialised
• Uniquekey is used

But, whenever I tried to execute my app, it says that currentState is null.

//TaskList.dart, where it shows all the TaskTile
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import '../models/TaskData.dart';
import 'task_tile.dart';
import 'package:todoey/models/Task.dart';

class TasksList extends StatelessWidget {
  final GlobalKey<AnimatedListState> _key = GlobalKey();

  //the acccess the state of Animated list
  void removeTask(int index, TaskData taskData) {
    final task = taskData.tasks[index];
    Future.delayed(Duration(milliseconds: 700), () {
      if (_key.currentState == null) {
        print('currentState is null');
      } else {
        _key.currentState!.removeItem(index, (context, animation) {
          return SizeTransition(
            sizeFactor: animation,
            child: TaskTile(
              text: task.name,
              isChecked: task.isDone,
              checkBoxCallBack: (checkboxState) {},
              onLongPressCallback: () {},
            ),
          );
        }, duration: Duration(milliseconds: 700));
        taskData.deleteTask(task);
      }
    });
  }

  @override
  Widget build(BuildContext context) {
    //ListView
    //which builds the children on demand
    //This constructor is appropriate for list views with a large (or infinite) number of children
    // the builder is called only for those children that are actually visible.

    //Consumer widget simplifies the 'Provider.of<TaskData>(context)' into just 'taskData'
    //when taskData is updated it gonna rebuild
    return Consumer<TaskData>(
      builder: (context, taskData, child) {
        return AnimatedList(
          itemBuilder: (context, index, animation) {
            final task = taskData.tasks[index];
            return SizeTransition(
              key: UniqueKey(),
              sizeFactor: animation,
              child: TaskTile(
                text: task.name,
                isChecked: task.isDone,
                checkBoxCallBack: (checkboxState) {
                  taskData.doneToggle(task);
                },
                onLongPressCallback: () {
                  removeTask(index, taskData);
                },
              ),
            );
          },
          initialItemCount: taskData.taskCount,
        );
      },
    );
  }
}

\\TaskTile
import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:todoey/models/TaskData.dart';

import '../models/Task.dart';

class TaskTile extends StatefulWidget {
  final String text;
  final bool isChecked;
  final Function(bool?) checkBoxCallBack;
  final Function() onLongPressCallback;

  TaskTile({
    required this.text,
    required this.isChecked,
    required this.checkBoxCallBack,
    required this.onLongPressCallback,
  });

  @override
  State<TaskTile> createState() => _TaskTileState();
}

class _TaskTileState extends State<TaskTile> {
  // void checkBoxCallBack(bool? checkBoxState) {
  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onLongPress: widget.onLongPressCallback,
      child: CheckboxListTile(
          title: Text(
            widget.text,
            style: TextStyle(
                color: Colors.black,
                decoration:
                    widget.isChecked ? TextDecoration.lineThrough : null),
          ),
          value: widget.isChecked,
          onChanged: widget.checkBoxCallBack),
    );
  }
}

\\TaskData
import 'package:flutter/foundation.dart';
import 'Task.dart';
import 'dart:collection';

class TaskData extends ChangeNotifier {
  List<Task> _tasks = [
    Task('Buy milk'),
    Task('watch hentai'),
    Task('watch hentai'),
  ];

  //The tasks return is not modifiable
  //unmodifiable view of a list (not listview)
  //the prevent we modify the task through the getter
  UnmodifiableListView<Task> get tasks {
    return UnmodifiableListView(_tasks);
  }

  void addTask(String text) {
    final task = Task(text);
    _tasks.add(task);
    notifyListeners();
  }

  int get taskCount {
    return _tasks.length;
  }

  void doneToggle(Task task) {
    task.doneToggle();
    notifyListeners();
  }

  void deleteTask(Task task) {
    _tasks.remove(task);
    notifyListeners();
  }
}

1. I tried to change TaskList to stateful widget
2. I tried to Future.delay to see if there's any positive effect

None of my approaches worked. I need some help on this, any advice will be highly appreciated as I'm still a uni student and my universtiy haven't taught anything about mobile dev, thanks in advance!!!