在Flutter中的TimePicker上点击“完成”后，如何更新文本字段的文本？

import 'package:flutter/material.dart';

class MyTimePicker extends StatefulWidget {
  @override
  _MyTimePickerState createState() => _MyTimePickerState();
}

class _MyTimePickerState extends State<MyTimePicker> {
  DateTime selectedTime;

  Future<void> _showTimePickerDialog() async {
    final TimeOfDay pickedTime = await showTimePicker(
      context: context,
      initialTime: TimeOfDay.now(),
    );

    if (pickedTime != null) {
      setState(() {
        selectedTime = DateTime(
          DateTime.now().year,
          DateTime.now().month,
          DateTime.now().day,
          pickedTime.hour,
          pickedTime.minute,
        );
      });
    }
  }

  @override
  Widget build(BuildContext context) {
    return Column(
      children: [
        RaisedButton(
          onPressed: _showTimePickerDialog,
          child: Text('选择时间'),
        ),
        SizedBox(height: 10),
        Text(
          selectedTime != null
              ? '选定的时间：${selectedTime.toString()}'
              : '未选择时间',
        ),
      ],
    );
  }
}