Todo App Step 4 (User Interaction)

main.dart

// Instead of autogenerating a todo item, _addTodoItem now accepts a string
void _addTodoItem(String task) {
  // Only add the task if the user actually entered something
  if(task.length > 0) {
    setState(() => _todoItems.add(task));
  }
}

Widget build(BuildContext context) {
  return new Scaffold(
    appBar: new AppBar(
      title: new Text('Todo List')
    ),
    body: _buildTodoList(),
    floatingActionButton: new FloatingActionButton(
      onPressed: _pushAddTodoScreen, // pressing this button now opens the new screen
      tooltip: 'Add task',
      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(
            title: new Text('Add a new task')
          ),
          body: new 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(16.0)
            ),
          )
        );
      }
    )
  );
}