SQLiteOpenHelper无法调用onCreate？

Question

我正在尝试使用Android手机创建本地数据库sqlite.

我有一个帮助类,如下所示,用于创建数据库并提供"帮助".

我想在我的代码的主要部分创建这个类的对象,它也在那里创建数据库和表.

问题:

每当我创建类的对象时,它似乎都没有调用onCreate帮助器中的方法.我以为这应该发生.我认为这onCreate基本上是班级的构造函数.(我相信我错了)

• 那么,为什么不调用这个onCreate方法呢？
• 或者我如何创建数据库和表格来创建类的对象？
• 如果这不是一个好方法,那么更好的方法是什么？

---

public class SmartDBHelper extends SQLiteOpenHelper {

    private static final String DATABASE_NAME = "smart_lite_db.db";
    private static final int DATABASE_VERSION = 2;
    private static final String NOTIFY_TABLE_NAME = "user_notify_data";
    private static final String HR_TABLE_NAME = "user_hr_data";
    private static final String NOTIFY_TABLE_CREATE = 
        "CREATE TABLE " + NOTIFY_TABLE_NAME + 
        " (counter INTEGER PRIMARY KEY, " + 
        "userresponse INTEGER, " + 
        "notifytime INTEGER);";
    private static final String DATA_TABLE_CREATE = 
        "CREATE TABLE " + HR_TABLE_NAME +
        " (counter INTEGER PRIMARY KEY, " +
        "hr INTEGER, " +
        "act INTEGER, " +
        "timestamp INTEGER);";      

    public SmartDBHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
        // TODO Auto-generated constructor stub
    }


    @Override
    public void onCreate(SQLiteDatabase db) {
        // TODO Auto-generated method stub
        Log.v("smartdbhelper", "before creation");
        db.execSQL(NOTIFY_TABLE_CREATE);
        Log.v("smartdbhelper", "middle creation");
        db.execSQL(DATA_TABLE_CREATE);
        Log.v("smartdbhelper", "after creation");
    }


    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        // TODO Auto-generated method stub

    }

}

---

public class SmartApp extends Activity implements OnSharedPreferenceChangeListener {
   private SmartDBHelper dBHelper;
   public void onCreate(Bundle savedInstanceState) {
      //where i am wanting to create the database and tables
      dBHelper = new SmartDBHelper(getContext());
   }
}

Answer 1

该onCreate不是数据库类的构造函数.只有在尝试打开不存在的数据库时才会调用它.要打开/创建数据库,您需要添加对这些方法之一的调用:

public class SmartApp extends Activity implements OnSharedPreferenceChangeListener {
   private SmartDBHelper dBHelper;
   public void onCreate(Bundle savedInstanceState) {
      //where i am wanting to create the database and tables
      dBHelper = new SmartDBHelper(getContext());
      // open to read and write
      dBHelper.getWritableDatabase();
      // or to read only
      // dBHelper.getReadableDatabase();
   }
}

它有点大,但是我的DatabaseAdapter你可以查看:http://saintfeintcity.org/projects/sfc/repository/entry/trunk/src/org/saintfeintcity/database/GameDbAdapter.java

Answer 2

你必须打电话getWritableDatabase()或getReadableDatabase().