由于“一个app”的复杂性和多变性，这里我不能直接提供一个完整的、适用于所有设备和平台的app代码。不过，我可以为你提供几种常见编程语言的简单“Hello, World!”程序示例，这些可以看作是创建-优快云博客

本文链接：https://blog.youkuaiyun.com/SigridFelix/article/details/139327878

在这里插入图片描述

Swift (用于iOS开发)dxwaiyan.cn
swift
import UIKit

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {

var window: UIWindow?  

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {  
    // Override point for customization after application launch.  
    window = UIWindow(frame: UIScreen.main.bounds)  
    window?.rootViewController = UINavigationController(rootViewController: ViewController())  
    window?.makeKeyAndVisible()  
    return true  
}

}

class ViewController: UIViewController {

override func viewDidLoad() {  
    super.viewDidLoad()  
    // Do any additional setup after loading the view.  
    let label = UILabel(frame: CGRect(x: 0, y: 0, width: 200, height: 21))  
    label.center = self.view.center  
    label.textAlignment = .center  
    label.text = "Hello, World!"  
    self.view.addSubview(label)  
}

}
Java (用于Android开发)
java
import android.os.Bundle;
import androidx.appcompat.app.AppCompatActivity;
import android.widget.TextView;

public class MainActivity extends AppCompatActivity {

@Override  
protected void onCreate(Bundle savedInstanceState) {  
    super.onCreate(savedInstanceState);  
    setContentView(R.layout.activity_main);  

    TextView textView = findViewById(R.id.textView);  
    textView.setText("Hello, World!");  
}

}
(注意：这里假设你有一个名为activity_main.xml的布局文件，其中包含一个ID为textView的TextView。)

Python (使用Kivy框架创建跨平台应用)
python
from kivy.app import App
from kivy.uix.label import Label

class TestApp(App):
def build(self):
return Label(text=‘Hello, World!’)

if name == ‘main’:
TestApp().run()
Flutter (用于跨平台应用开发)
dart
import ‘package:flutter/material.dart’;

void main() {
runApp(MyApp());
}

class MyApp extends StatelessWidget {
@override
Widget build(BuildContext context) {
return MaterialApp(
title: ‘Flutter Demo’,
theme: ThemeData(
primarySwatch: Colors.blue,
),
home: MyHomePage(title: ‘Flutter Demo Home Page’),
);
}
}

class MyHomePage extends StatefulWidget {
MyHomePage({Key? key, required this.title}) : super(key: key);

final String title;

@override
_MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State {
int _counter = 0;

void _incrementCounter() {
setState(() {
_counter++;
});
}

@override
Widget build(BuildContext context) {
return Scaffold(
appBar: AppBar(
title: Text(widget.title),
),
body: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text(
‘You have pushed the button this many times:’,
),
Text(
‘$_counter’,
style: Theme.of(context).textTheme.headline4,
),
],
),
),
floatingActionButton: FloatingActionButton(
onPressed: _incrementCounter,
tooltip: ‘Increment’,
child: Icon(Icons.add),
), // This trailing comma makes auto-formatting nicer for build methods.
);
}

// 这里只是为了演示Flutter的基本结构，你可以将body部分替换为显示"Hello, World!“的Text组件
}
(注意：Flutter示例中的body部分可以简化为只显示"Hello, World!”。)

这些示例只是起点，真正的app开发会涉及更多的功能和复杂性由于“一个app”的复杂性和多变性，这里我不能直接提供一个完整的、适用于所有设备和平台的app代码。不过，我可以为你提供几种常见编程语言的简单“Hello, World!”程序示例，这些可以看作是创建更复杂app的起点。

Swift (用于iOS开发)
swift
import UIKit