[sms] 02_群组-（数据库创建，内容提供者，异步数据查询，ListView-CursorAdapter数据填充，内容观察者）

package cn.zengfansheng.sms.db;
 
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteDatabase.CursorFactory;
import android.database.sqlite.SQLiteOpenHelper;
 
/**
* 群组SQLiteOpenHelper实现
*
* @author hacket
*
*/
public class GroupSQLiteOpenHelper extends SQLiteOpenHelper {
 
    private static final String DB_NAME = "mysms.db";
    private static final int DB_VERSION = 1;
    // 单例
 
    private static GroupSQLiteOpenHelper helper;
    private GroupSQLiteOpenHelper(Context context, String name,
            CursorFactory factory, int version) {
        super(context, name, factory, version);
    }
 
    // 懒汉式
    public static GroupSQLiteOpenHelper getInstance(Context context) {
 
        if (helper == null) {// 2、效率问题，防止多次判断锁
 
            synchronized (GroupSQLiteOpenHelper.class) {// 1、多线程安全问题1
 
                if (helper == null) {// 3、多线程安全问题2
                    helper = new GroupSQLiteOpenHelper(context, DB_NAME, null,DB_VERSION);
                }
            }
        }
        return helper;
    }
 
    @Override
    public void onCreate(SQLiteDatabase db) {
        String sql = "CREATE TABLE groups(_id INTEGER PRIMARY KEY AUTOINCREMENT,name VARCHAR(20));";
        db.execSQL(sql);
        sql = "CREATE TABLE thread_group(_id INTEGER PRIMARY KEY AUTOINCREMENT,group_id INTEGER,thread_id INTEGER);";
        db.execSQL(sql);
    }
 
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
 
    }
 
}