用Androidstudio做一个校园订餐系统

实现校园订餐系统需要以下几个步骤：

1. 设计数据库

首先需要设计数据库，至少需要包含以下几个表：用户表、商家表、菜品表、订单表。其中，用户表用于存储用户信息，商家表用于存储商家信息，菜品表用于存储菜品信息，订单表用于存储订单信息。

2. 实现用户登录和注册功能

在应用中创建登录和注册页面，用户输入账号和密码进行登录或注册。登录时需要验证用户输入的账号和密码是否正确，注册时需要将用户信息插入到用户表中。

3. 实现商家列表和菜品列表展示功能

在应用中创建商家列表和菜品列表页面，商家列表页面展示所有商家的信息，菜品列表页面展示某个商家的所有菜品信息。需要从数据库中查询商家和菜品信息，并将其展示在页面中。

4. 实现订单功能

在应用中创建订单页面，用户在该页面中可以选择商家和菜品，并下单购买。下单前需要验证用户是否已登录，如果未登录则需要先登录。下单后将订单信息插入到订单表中。

以下是一些示例代码，供参考：

1. 创建数据库：

CREATE TABLE IF NOT EXISTS users (
    user_id INTEGER PRIMARY KEY AUTOINCREMENT,
    username TEXT NOT NULL UNIQUE,
    password TEXT NOT NULL
);

CREATE TABLE IF NOT EXISTS shops (
    shop_id INTEGER PRIMARY KEY AUTOINCREMENT,
    shop_name TEXT NOT NULL,
    shop_address TEXT NOT NULL,
    shop_phone TEXT NOT NULL
);

CREATE TABLE IF NOT EXISTS dishes (
    dish_id INTEGER PRIMARY KEY AUTOINCREMENT,
    dish_name TEXT NOT NULL,
    dish_price REAL NOT NULL,
    shop_id INTEGER NOT NULL,
    FOREIGN KEY (shop_id) REFERENCES shops(shop_id)
);

CREATE TABLE IF NOT EXISTS orders (
    order_id INTEGER PRIMARY KEY AUTOINCREMENT,
    user_id INTEGER NOT NULL,
    shop_id INTEGER NOT NULL,
    dish_id INTEGER NOT NULL,
    order_time TIMESTAMP DEFAULT CURRENT_TIMESTAMP,
    FOREIGN KEY (user_id) REFERENCES users(user_id),
    FOREIGN KEY (shop_id) REFERENCES shops(shop_id),
    FOREIGN KEY (dish_id) REFERENCES dishes(dish_id)
);

2. 实现登录和注册功能：

public boolean login(String username, String password) {
    SQLiteDatabase db = getReadableDatabase();
    String[] columns = {"user_id"};
    String selection = "username = ? AND password = ?";
    String[] selectionArgs = {username, password};
    Cursor cursor = db.query("users", columns, selection, selectionArgs, null, null, null);
    boolean success = cursor.moveToFirst();
    cursor.close();
    db.close();
    return success;
}

public boolean register(String username, String password) {
    SQLiteDatabase db = getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put("username", username);
    values.put("password", password);
    long rowId = db.insert("users", null, values);
    db.close();
    return rowId != -1;
}

3. 实现商家和菜品列表展示功能：

public List<Shop> getShops() {
    SQLiteDatabase db = getReadableDatabase();
    Cursor cursor = db.query("shops", null, null, null, null, null, null);
    List<Shop> shops = new ArrayList<>();
    while (cursor.moveToNext()) {
        int shopId = cursor.getInt(cursor.getColumnIndex("shop_id"));
        String shopName = cursor.getString(cursor.getColumnIndex("shop_name"));
        String shopAddress = cursor.getString(cursor.getColumnIndex("shop_address"));
        String shopPhone = cursor.getString(cursor.getColumnIndex("shop_phone"));
        Shop shop = new Shop(shopId, shopName, shopAddress, shopPhone);
        shops.add(shop);
    }
    cursor.close();
    db.close();
    return shops;
}

public List<Dish> getDishes(int shopId) {
    SQLiteDatabase db = getReadableDatabase();
    String[] columns = {"dish_id", "dish_name", "dish_price"};
    String selection = "shop_id = ?";
    String[] selectionArgs = {String.valueOf(shopId)};
    Cursor cursor = db.query("dishes", columns, selection, selectionArgs, null, null, null);
    List<Dish> dishes = new ArrayList<>();
    while (cursor.moveToNext()) {
        int dishId = cursor.getInt(cursor.getColumnIndex("dish_id"));
        String dishName = cursor.getString(cursor.getColumnIndex("dish_name"));
        double dishPrice = cursor.getDouble(cursor.getColumnIndex("dish_price"));
        Dish dish = new Dish(dishId, dishName, dishPrice);
        dishes.add(dish);
    }
    cursor.close();
    db.close();
    return dishes;
}

4. 实现订单功能：

public boolean placeOrder(int userId, int shopId, int dishId) {
    SQLiteDatabase db = getWritableDatabase();
    ContentValues values = new ContentValues();
    values.put("user_id", userId);
    values.put("shop_id", shopId);
    values.put("dish_id", dishId);
    long rowId = db.insert("orders", null, values);
    db.close();
    return rowId != -1;
}

以上是一个简单的实现示例，具体实现方式可能因应用需求而有所不同。