android studio加上SQLite数据库实现点餐系统

要在Android Studio中使用SQLite来实现点餐系统，需要遵循以下步骤：

1. 创建一个新的Android Studio项目
2. 在app模块下的build.gradle文件中添加以下依赖项：

dependencies {
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation 'com.android.support:design:28.0.0'
    implementation 'com.android.support:support-v4:28.0.0'
    implementation 'android.arch.persistence.room:runtime:1.1.1'
    annotationProcessor 'android.arch.persistence.room:compiler:1.1.1'
}

3. 创建一个SQLiteOpenHelper类，以帮助创建和管理数据库。在该类中，您需要定义表格和列，并实现onCreate（）和onUpgrade（）方法。

public class DBHelper extends SQLiteOpenHelper {

    public static final int DATABASE_VERSION = 1;
    public static final String DATABASE_NAME = "Order.db";

    private static final String SQL_CREATE_ENTRIES =
            "CREATE TABLE " + OrderContract.OrderEntry.TABLE_NAME + " (" +
                    OrderContract.OrderEntry._ID + " INTEGER PRIMARY KEY," +
                    OrderContract.OrderEntry.COLUMN_NAME_ITEM + " TEXT," +
                    OrderContract.OrderEntry.COLUMN_NAME_PRICE + " TEXT)";

    private static final String SQL_DELETE_ENTRIES =
            "DROP TABLE IF EXISTS " + OrderContract.OrderEntry.TABLE_NAME;

    public DBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }
    public void onCreate(SQLiteDatabase db) {
        db.execSQL(SQL_CREATE_ENTRIES);
    }
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL(SQL_DELETE_ENTRIES);
        onCreate(db);
    }
}

4. 在MainActivity中使用DBHelper类来创建和操作数据库。您可以使用以下代码插入数据：

DBHelper dbHelper = new DBHelper(this);
SQLiteDatabase db = dbHelper.getWritableDatabase();

ContentValues values = new ContentValues();
values.put(OrderContract.OrderEntry.COLUMN_NAME_ITEM, "Pizza");
values.put(OrderContract.OrderEntry.COLUMN_NAME_PRICE, "10");
db.insert(OrderContract.OrderEntry.TABLE_NAME, null, values);

5. 使用Cursor和Adapter来显示数据。您可以使用以下代码从数据库中检索数据：

DBHelper dbHelper = new DBHelper(this);
SQLiteDatabase db = dbHelper.getReadableDatabase();

String[] projection = {
        OrderContract.OrderEntry._ID,
        OrderContract.OrderEntry.COLUMN_NAME_ITEM,
        OrderContract.OrderEntry.COLUMN_NAME_PRICE
};

Cursor cursor = db.query(
        OrderContract.OrderEntry.TABLE_NAME,   
        projection,                               
        null,                                    
        null,                                    
        null,                                    
        null,                                    
        null                                     
);

int[] views = {R.id.item_name, R.id.item_price};
SimpleCursorAdapter adapter = new SimpleCursorAdapter(this,
        R.layout.item_layout, cursor, projection, views, 0);

ListView listView = (ListView) findViewById(R.id.listview);
listView.setAdapter(adapter);

以上是使用SQLite实现点餐系统的基本步骤。您可以根据自己的需求进行修改和扩展。