Question

我想扩展SQLiteDataBase类，以便能够覆盖一些方法（比如rawQuery，execSQL，...），并且可以查看有关查询执行时间的一些统计信息。

我称这些功能有数百个地方。因此，从基类SQLiteDatabase创建派生类将对我有所帮助！

问题是：在扩展SQLiteDataBase时，它无法从超类中找到任何构造函数。

import android.database.sqlite.SQLiteDatabase;

public class MySQLiteDatabase extends SQLiteDatabase
{

    MySQLiteDatabase()
    {
        super(); // <<<--- can't find any visible constructor
    }

}

Answer 1

我称之为功能的地方有数百个。所以，从基类SQLiteDatabase创建派生类将有所帮助我很多！。

您无法扩展SQLiteDatabase，因为它已声明为final，您无法在java中扩展final类。

另一种方法是创建一个“包装器”SQLiteDatabase，它将使用其方法复制SQLiteDatabase类，并在包装器方法中插入测量逻辑：

public class SQLiteDatabaseWrapper {

    private SQLiteDatabase mDatabase;

    public void initDatabase() {
      //obtain the database here and assign it to mDatabase 
    }

    // replicate the SQLiteDatabase methods 
    public void execSQL(String sql) {
       //insert whatever logic you have for measurement
       // do the measurement
       mDatabase.execSQL(sql); 
    }
    // other methods from SQLiteDatabase 
}

Answer 2

您实际上不需要扩展它已经可用的扩展，因为您导入了sqliteDatabase类简单定义：

Sqlitedatabase dbname;
dbname.execSQL(Query);

或者：

public class MySQLiteHelper extends SQLiteOpenHelper {

  public static final String TABLE_COMMENTS = "comments";
  public static final String COLUMN_ID = "_id";
  public static final String COLUMN_COMMENT = "comment";

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

  // Database creation sql statement
  private static final String DATABASE_CREATE = "create table "
      + TABLE_COMMENTS + "(" + COLUMN_ID
      + " integer primary key autoincrement, " + COLUMN_COMMENT
      + " text not null);";

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

  @Override
  public void onCreate(SQLiteDatabase database) {
    database.execSQL(DATABASE_CREATE);
  }

  @Override
  public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    Log.w(MySQLiteHelper.class.getName(),
        "Upgrading database from version " + oldVersion + " to "
            + newVersion + ", which will destroy all old data");
    db.execSQL("DROP TABLE IF EXISTS " + TABLE_COMMENTS);
    onCreate(db);
  }
}

如何扩展SQLiteDatabase类？

2 个答案: