安卓基础库数据库封装 案例

以下是一个基于Android SQLite数据库的封装示例：

1. 创建DatabaseHelper类

public class DatabaseHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "mydatabase.db";
    private static final int DATABASE_VERSION = 1;

    public DatabaseHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        // 创建表格
        String createTable = "CREATE TABLE IF NOT EXISTS mytable" +
                " (id INTEGER PRIMARY KEY AUTOINCREMENT, name TEXT, age INTEGER)";
        db.execSQL(createTable);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // 升级数据库
        db.execSQL("DROP TABLE IF EXISTS mytable");
        onCreate(db);
    }
}

2. 创建DatabaseManager类

public class DatabaseManager {

    private static DatabaseManager instance;
    private SQLiteDatabase database;
    private DatabaseHelper dbHelper;

    public static synchronized void initialize(Context context) {
        if (instance == null) {
            instance = new DatabaseManager();
            instance.dbHelper = new DatabaseHelper(context);
        }
    }

    public static synchronized DatabaseManager getInstance() {
        if (instance == null) {
            throw new IllegalStateException(DatabaseManager.class.getSimpleName() +
                    " is not initialized, call initialize(..) method first.");
        }
        return instance;
    }

    public synchronized SQLiteDatabase openDatabase() {
        if (database == null) {
            database = dbHelper.getWritableDatabase();
        }
        return database;
    }

    public synchronized void closeDatabase() {
        if (database != null) {
            database.close();
            database = null;
        }
    }
}

3. 创建实体类

public class MyEntity {
    private int id;
    private String name;
    private int age;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }
}

4. 创建DAO类

public class MyEntityDao {

    private SQLiteDatabase database;

    public void open() {
        database = DatabaseManager.getInstance().openDatabase();
    }

    public void close() {
        DatabaseManager.getInstance().closeDatabase();
    }

    public void insert(MyEntity entity) {
        ContentValues values = new ContentValues();
        values.put("name", entity.getName());
        values.put("age", entity.getAge());
        database.insert("mytable", null, values);
    }

    public void update(MyEntity entity) {
        ContentValues values = new ContentValues();
        values.put("name", entity.getName());
        values.put("age", entity.getAge());
        database.update("mytable", values, "id=?", new String[]{String.valueOf(entity.getId())});
    }

    public void delete(int id) {
        database.delete("mytable", "id=?", new String[]{String.valueOf(id)});
    }

    public MyEntity findById(int id) {
        Cursor cursor = database.query("mytable", null, "id=?", new String[]{String.valueOf(id)}, null, null, null);
        if (cursor != null && cursor.moveToFirst()) {
            MyEntity entity = new MyEntity();
            entity.setId(cursor.getInt(cursor.getColumnIndex("id")));
            entity.setName(cursor.getString(cursor.getColumnIndex("name")));
            entity.setAge(cursor.getInt(cursor.getColumnIndex("age")));
            cursor.close();
            return entity;
        }
        return null;
    }

    public List<MyEntity> findAll() {
        List<MyEntity> entities = new ArrayList<>();
        Cursor cursor = database.query("mytable", null, null, null, null, null, null);
        if (cursor != null && cursor.moveToFirst()) {
            do {
                MyEntity entity = new MyEntity();
                entity.setId(cursor.getInt(cursor.getColumnIndex("id")));
                entity.setName(cursor.getString(cursor.getColumnIndex("name")));
                entity.setAge(cursor.getInt(cursor.getColumnIndex("age")));
                entities.add(entity);
            } while (cursor.moveToNext());
            cursor.close();
        }
        return entities;
    }
}

5. 在Activity中使用

public class MainActivity extends AppCompatActivity {

    private MyEntityDao dao;

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

        DatabaseManager.initialize(getApplicationContext());
        dao = new MyEntityDao();
        dao.open();

        // 插入数据
        MyEntity entity = new MyEntity();
        entity.setName("Tom");
        entity.setAge(20);
        dao.insert(entity);

        // 更新数据
        entity.setName("Jerry");
        dao.update(entity);

        // 删除数据
        dao.delete(entity.getId());

        // 查询数据
        MyEntity e = dao.findById(1);
        List<MyEntity> entities = dao.findAll();

        dao.close();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        DatabaseManager.getInstance().closeDatabase();
    }
}

这样就完成了基于Android SQLite数据库的封装，使得操作更加简单方便，同时也提高了代码的可维护性。