怎么实现SQLiteOpenHelper？

补充一下，export class XyDBHelper extends SQLiteOpenHelper

export class ProductDBHelper extends SQLiteOpenHelper {  
    private static readonly DATABASE_NAME : string = "goods_product.db"  
    private static readonly DATABASE_VERSION : Int = 4  
    private static readonly TABLE_NAME : string = "products"  
    private static readonly COLUMN_ID : string = "_id"  
    private static readonly COLUMN_NAME : string = "name"  
    private static readonly COLUMN_PRICE : string = "price"  
    private static readonly CREATE_TABLE : string = "CREATE TABLE " + this.TABLE_NAME + " (" +  
        this.COLUMN_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +  
        this.COLUMN_NAME + " TEXT NOT NULL, " +  
        this.COLUMN_PRICE + " REAL NOT NULL, " +  
        ");"  

    constructor(p0 : Context | null) {  
        super(p0, ProductDBHelper.DATABASE_NAME, null, ProductDBHelper.DATABASE_VERSION);  
    }  
    override onCreate(db : SQLiteDatabase) {  
        db.execSQL(ProductDBHelper.CREATE_TABLE);  
    }  
    override onUpgrade(db : SQLiteDatabase, oldVersion : Int, newVersion : Int) {  
        db.execSQL("DROP TABLE IF EXISTS " + ProductDBHelper.TABLE_NAME);  
        onCreate(db);  
    }  

    // 获取字段  
    getColumnNames() : string {  

        let db = this.writableDatabase  
        let cursor = db.query("products", null, null, null, null, null, null)  

        // 获取所有列名  
        let columnNames = cursor.getColumnNames();  

        console.log(columnNames)  

        // 关闭 cursor  
        cursor.close();  
        return ""  
    }  
}

使用
let pp = new ProductDBHelper(UTSAndroid?.getAppContext())
pp.getColumnNames()