如何用android实现增删改查

在 Android 中实现增删改查，一般需要以下步骤：

1. 创建一个数据库表，定义表的字段和类型。

2. 创建一个 `SQLiteOpenHelper` 类，用于创建数据库和表，并提供对数据库的访问。

3. 在 `SQLiteOpenHelper` 类中实现增删改查的方法，例如 `insert()`、`delete()`、`update()` 和 `query()` 等。

4. 在需要使用数据库操作的地方，先获取 `SQLiteOpenHelper` 的实例，然后调用相应的方法进行操作。

具体实现步骤如下：

1. 定义数据库表

public class MyDatabaseHelper extends SQLiteOpenHelper {
    private static final String DB_NAME = "my_database.db";
    private static final int DB_VERSION = 1;

    private static final String TABLE_NAME = "my_table";
    private static final String COLUMN_ID = "_id";
    private static final String COLUMN_NAME = "name";
    private static final String COLUMN_AGE = "age";

    public MyDatabaseHelper(Context context) {
        super(context, DB_NAME, null, DB_VERSION);
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        String sql = "CREATE TABLE " + TABLE_NAME + " (" +
                COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                COLUMN_NAME + " TEXT, " +
                COLUMN_AGE + " INTEGER)";
        db.execSQL(sql);
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        String sql = "DROP TABLE IF EXISTS " + TABLE_NAME;
        db.execSQL(sql);
        onCreate(db);
    }

    public long insert(String name, int age) {
        SQLiteDatabase db = getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(COLUMN_NAME, name);
        values.put(COLUMN_AGE, age);
        long id = db.insert(TABLE_NAME, null, values);
        db.close();
        return id;
    }

    public int delete(long id) {
        SQLiteDatabase db = getWritableDatabase();
        String whereClause = COLUMN_ID + "=?";
        String[] whereArgs = {String.valueOf(id)};
        int rows = db.delete(TABLE_NAME, whereClause, whereArgs);
        db.close();
        return rows;
    }

    public int update(long id, String name, int age) {
        SQLiteDatabase db = getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(COLUMN_NAME, name);
        values.put(COLUMN_AGE, age);
        String whereClause = COLUMN_ID + "=?";
        String[] whereArgs = {String.valueOf(id)};
        int rows = db.update(TABLE_NAME, values, whereClause, whereArgs);
        db.close();
        return rows;
    }

    public Cursor query() {
        SQLiteDatabase db = getReadableDatabase();
        String[] columns = {COLUMN_ID, COLUMN_NAME, COLUMN_AGE};
        Cursor cursor = db.query(TABLE_NAME, columns, null, null, null, null, null);
        return cursor;
    }
}

2. 在需要使用数据库操作的地方，获取 `MyDatabaseHelper` 实例，并调用相应的方法进行操作。

MyDatabaseHelper dbHelper = new MyDatabaseHelper(this);

// 插入数据
long id = dbHelper.insert("张三", 20);

// 删除数据
int rows = dbHelper.delete(id);

// 更新数据
int rows = dbHelper.update(id, "李四", 25);

// 查询数据
Cursor cursor = dbHelper.query();
while (cursor.moveToNext()) {
    long id = cursor.getLong(cursor.getColumnIndexOrThrow(MyDatabaseHelper.COLUMN_ID));
    String name = cursor.getString(cursor.getColumnIndexOrThrow(MyDatabaseHelper.COLUMN_NAME));
    int age = cursor.getInt(cursor.getColumnIndexOrThrow(MyDatabaseHelper.COLUMN_AGE));
    Log.d(TAG, "id=" + id + ", name=" + name + ", age=" + age);
}
cursor.close();