How To Add Todo List Mark In Flutter Android App

Scaffold(
  appBar: new AppBar(
    centerTitle: true,
      title: new Text('Todo List'),
    backgroundColor: Colors.lightGreen,
  ),
  body: _buildTodoList(),
  floatingActionButton: new FloatingActionButton(
      onPressed: _pushAddTodoScreen, // pressing this button now opens the new screen
      tooltip: 'Add task',
      backgroundColor: Colors.lightGreen,
      child: new Icon(Icons.add)
  ),
);

  void _pushAddTodoScreen() {
    // Push this page onto the stack
    Navigator.of(context).push(
      // MaterialPageRoute will automatically animate the screen entry, as well
      // as adding a back button to close it
        new MaterialPageRoute(
            builder: (context) {
              return new Scaffold(
                  appBar: new AppBar(
                    centerTitle: true,
                      backgroundColor: Colors.lightGreen,
                      title: new Text('Add a new task')
                  ),
                  body: Center(
                    child: TextField(
                      autofocus: true,
                      onSubmitted: (val) {
                        _addTodoItem(val);
                        Navigator.pop(context); // Close the add todo screen
                      },
                      decoration: new InputDecoration(
                          hintText: 'Enter something to do...',
                          contentPadding: const EdgeInsets.all(14.0)
                      ),
                    ),
                  ),
              );
            }
        )
    );
  }

  void _removeTodoItem(int index) {
    setState(() => _todoItems.removeAt(index));
  }

// Show an alert dialog asking the user to confirm that the task is done
  void _promptRemoveTodoItem(int index) {
    showDialog(
        context: context,
        builder: (BuildContext context) {
          return new AlertDialog(
              title: new Text('Mark "${_todoItems[index]}" as done?'),
              actions: <Widget>[
                new FlatButton(
                    child: new Text('CANCEL'),
                    onPressed: () => Navigator.of(context).pop()
                ),
                new FlatButton(
                    child: new Text('MARK AS DONE'),
                    onPressed: () {
                      _removeTodoItem(index);
                      Navigator.of(context).pop();
                    }
                )
              ]
          );
        }
    );
  }

import 'package:flutter/material.dart';

void main() => runApp(new TodoApp());

class TodoApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return new MaterialApp(
      debugShowCheckedModeBanner: false,
        title: 'Todo List',
        home: new TodoList()
    );
  }
}

class TodoList extends StatefulWidget {
  @override
  createState() => new TodoListState();
}

class TodoListState extends State<TodoList> {
  List<String> _todoItems = [];

  // This will be called each time the + button is pressed
  void _addTodoItem(String task) {
    // Only add the task if the user actually entered something
    if(task.length > 0) {
      setState(() => _todoItems.add(task));
    }
  }


  // Build the whole list of todo items
  Widget _buildTodoList() {
    return new ListView.builder(
      itemBuilder: (context, index) {
        if(index < _todoItems.length) {
          return _buildTodoItem(_todoItems[index], index);
        }
      },
    );
  }

  // Build a single todo item
  Widget _buildTodoItem(String todoText, int index) {
    return new ListTile(
        title: new Text(todoText),
        onTap: () => _promptRemoveTodoItem(index)
    );
  }


  @override
  Widget build(BuildContext context) {
    return new Scaffold(
      appBar: new AppBar(
        centerTitle: true,
          title: new Text('Todo List'),
        backgroundColor: Colors.lightGreen,
      ),
      body: _buildTodoList(),
      floatingActionButton: new FloatingActionButton(
          onPressed: _pushAddTodoScreen, // pressing this button now opens the new screen
          tooltip: 'Add task',
          backgroundColor: Colors.lightGreen,
          child: new Icon(Icons.add)
      ),
    );
  }


  void _pushAddTodoScreen() {
    // Push this page onto the stack
    Navigator.of(context).push(
      // MaterialPageRoute will automatically animate the screen entry, as well
      // as adding a back button to close it
        new MaterialPageRoute(
            builder: (context) {
              return new Scaffold(
                  appBar: new AppBar(
                    centerTitle: true,
                      backgroundColor: Colors.lightGreen,
                      title: new Text('Add a new task')
                  ),
                  body: Center(
                    child: TextField(
                      autofocus: true,
                      onSubmitted: (val) {
                        _addTodoItem(val);
                        Navigator.pop(context); // Close the add todo screen
                      },
                      decoration: new InputDecoration(
                          hintText: 'Enter something to do...',
                          contentPadding: const EdgeInsets.all(14.0)
                      ),
                    ),
                  ),
              );
            }
        )
    );
  }

  void _removeTodoItem(int index) {
    setState(() => _todoItems.removeAt(index));
  }

// Show an alert dialog asking the user to confirm that the task is done
  void _promptRemoveTodoItem(int index) {
    showDialog(
        context: context,
        builder: (BuildContext context) {
          return new AlertDialog(
              title: new Text('Mark "${_todoItems[index]}" as done?'),
              actions: <Widget>[
                new FlatButton(
                    child: new Text('CANCEL'),
                    onPressed: () => Navigator.of(context).pop()
                ),
                new FlatButton(
                    child: new Text('MARK AS DONE'),
                    onPressed: () {
                      _removeTodoItem(index);
                      Navigator.of(context).pop();
                    }
                )
              ]
          );
        }
    );
  }
}