我想创建一个使用在Android手机上的本地数据库源码。

我有一个辅助类，如下图所示，用于创建数据库并提供帮助。

我想在我的code的主要部分创建这个类的一个对象，它创建的数据库和表有作为。

的问题：

每当我创建一个类的对象时，它似乎并没有被要求在助手的的onCreate 方法。我认为这是应该发生。我认为，的onCreate 基本上是一个类构造函数。 （我相信我错了）

那么，为什么不调用的onCreate 的方法？ 或者我如何得到它来创建数据库和表在那里我创建的类的对象呢？ 在什么将是一个更好的方式来做到这一点，这是不是一个好方法？

 公共类SmartDBHelper扩展SQLiteOpenHelper {

    私有静态最后弦乐DATABASE_NAME =smart_lite_db.db;
    私有静态最终诠释DATABASE_VERSION = 2;
    私有静态最后弦乐NOTIFY_TABLE_NAME =user_notify_data;
    私有静态最后弦乐HR_TABLE_NAME =user_hr_data;
    私有静态最后弦乐NOTIFY_TABLE_CREATE =
        CREATE TABLE+ NOTIFY_TABLE_NAME +
        （计数器INTEGER PRIMARY KEY，+
        userresponse INTEGER，+
        notifytime整数）;
    私有静态最后弦乐DATA_TABLE_CREATE =
        CREATE TABLE+ HR_TABLE_NAME +
        （计数器INTEGER PRIMARY KEY，+
        HR INTEGER，+
        行动INTEGER，+
        时间戳整数）;

    公共SmartDBHelper（上下文的背景下）{
        超（背景下，DATABASE_NAME，空，DATABASE_VERSION）;
        // TODO自动生成构造函数存根
    }


    @覆盖
    公共无效的onCreate（SQLiteDatabase DB）{
        // TODO自动生成方法存根
        Log.v（smartdbhelper，创世以前）;
        db.execSQL（NOTIFY_TABLE_CREATE）;
        Log.v（smartdbhelper，中创建）;
        db.execSQL（DATA_TABLE_CREATE）;
        Log.v（smartdbhelper，创建后）;
    }


    @覆盖
    公共无效onUpgrade（SQLiteDatabase分贝，INT oldVersion，诠释静态网页）{
        // TODO自动生成方法存根

    }

}
 

 公共类SmartApp扩展活动实现OnShared preferenceChangeListener {
   私人SmartDBHelper dBHelper;
   公共无效的onCreate（包savedInstanceState）{
      //我在哪里想创建数据库和表
      dBHelper =新SmartDBHelper（的getContext（））;
   }
}
 

解决方案

在的onCreate 不是构造数据库类。如果你试图打开一个不存在的数据库它只调用。 要打开/创建数据库，你需要添加一个调用这些方法之一：

 公共类SmartApp扩展活动实现OnShared preferenceChangeListener {
   私人SmartDBHelper dBHelper;
   公共无效的onCreate（包savedInstanceState）{
      //我在哪里想创建数据库和表
      dBHelper =新SmartDBHelper（的getContext（））;
      //打开读写
      dBHelper.getWritableDatabase（）;
      //或者只读
      // dBHelper.getReadableDatabase（）;
   }
}
 

这是一个有点大，但这里是我的DatabaseAdapter你可以看看：http://saintfeintcity.org/projects/sfc/repository/entry/trunk/src/org/saintfeintcity/database/GameDbAdapter.java

I am trying to create a local database on an android phone using sqlite.

I have a helper class, shown below, that is used to create the database and provide the "help".

I am wanting to create an object of this class in the main part of my code and it create the database and tables there as well.

The problem:

Whenever i create an object of the class, it does not seem to be calling the onCreate method in the helper. I thought this is supposed to happen. I thought that onCreate was basically a constructor for the class. (I believe i am wrong)

So, why is it not calling the onCreate method? Or how do i get it to create the database and tables where i am creating the object of the class? What would be a better way to do this, if this is not a good approach?

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());
   }
}

解决方案

The onCreate is not a constructor for the database class. It is only called if you try to open a database that does not exist. To open/create the database you need to add a call to one of these methods:

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();
   }
}

It is a bit big but here is my DatabaseAdapter you can take a look at: http://saintfeintcity.org/projects/sfc/repository/entry/trunk/src/org/saintfeintcity/database/GameDbAdapter.java