开发案例：Flutter开发天气预报小程序

import 'package:flutter/material.dart';
import 'package:http/http.dart' as http;
import 'dart:convert';
 
void main() => runApp(MyApp());
 
class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      home: WeatherForecast(),
    );
  }
}
 
class WeatherForecast extends StatefulWidget {
  @override
  _WeatherForecastState createState() => _WeatherForecastState();
}
 
class _WeatherForecastState extends State<WeatherForecast> {
  String apiKey = "您的API密钥";
  String city = "北京";
  var weatherData;
  var temp;
 
  @override
  void initState() {
    super.initState();
    getWeather();
  }
 
  getWeather() async {
    var url = 'http://api.openweathermap.org/data/2.5/weather?q=$city&appid=$apiKey';
    var response = await http.get(url);
    setState(() {
      weatherData = jsonDecode(response.body);
      temp = weatherData['main']['temp'];
    });
  }
 
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('天气预报'),
      ),
      body: Center(
        child: temp == null
            ? CircularProgressIndicator()
            : Text(
                '${(temp - 273.15).toStringAsFixed(1)}°C',
                style: Theme.of(context).textTheme.headline,
              ),
      ),
    );
  }
}

这段代码使用Flutter开发了一个简单的天气预报小程序。它从OpenWeatherMap的API获取天气数据，解析JSON响应，并在屏幕上显示当前城市的温度。代码简洁，注重教学，适合作为学习Flutter的入门案例。