无法创建数据库对象并在广播接收器中访问它

Question

我正在编写一个可以发送和接收消息并显示对话的demo sms应用程序。为此，我编写了一个处理完整数据库部分的类。但问题是我无法在广播接收器类中创建数据库对象用于接收短信.package com.example.demosmsapp;

import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;

public class DBAdapter {
    static final String KEY_ID="_id";
    static final String KEY_NUM="number";
        static final String KEY_TEXT="contents";
        static final String KEY_FLAG="flag";

        static final String DATABASE_NAME="smsapp";
        static final String DATABASE_TABLE="sms";
        static final int DATABASE_VERSION=1;

    static final String DATABASE_CREATE="create table sms(_id integer primary key auto increment, number text not null,contents text not null,flag text not null );";
    final Context context;

    DatabaseHelper DBHelper;
    SQLiteDatabase db;
    public DBAdapter(Context ctx)
    {
        this.context=ctx;
        DBHelper=new DatabaseHelper(context);

    }

    private static class DatabaseHelper extends SQLiteOpenHelper
    {
        DatabaseHelper(Context context)
        {
            super(context,DATABASE_NAME,null,DATABASE_VERSION);
        }

        public void onCreate(SQLiteDatabase db)
        {
            try{
                db.execSQL(DATABASE_CREATE);
            }catch (SQLException e){
                e.printStackTrace();
            }
        }
        public void onUpgrade(SQLiteDatabase db,int oldVersion,int newVersion)
        {
            //Log.w(TAG,"upgrading from version:"+oldVersion+"to"+newVersion);
            db.execSQL("DROP TABLE IF EXISTS sms");
        }
    }
    public DBAdapter open() throws SQLException
    {
        db=DBHelper.getWritableDatabase();
        return this;
    }
    public void close()
    {
        DBHelper.close();
    }
    public long insertSms(String number,String contents,String flag)
    {
        ContentValues initialValues=new ContentValues();
        initialValues.put(KEY_NUM,number);
        initialValues.put(KEY_TEXT,contents);
        initialValues.put(KEY_FLAG,flag);
        return db.insert(DATABASE_TABLE,null,initialValues);

    }
    public Cursor getAllSms()
    {
        return db.query(true,DATABASE_TABLE,new String[]{KEY_NUM},null,null,KEY_NUM,null,null,null);
    }
    public Cursor getConv(String num)
    { 

        Cursor mCursor= db.query(true,DATABASE_TABLE,new String[]{KEY_TEXT,KEY_FLAG,KEY_NUM},KEY_NUM + "=" +num ,null,null,null,null,null);
        if(mCursor !=null){
            mCursor.moveToFirst();
        }
        return mCursor;
    }
    public boolean deleteConv(String del)
    {
        return db.delete(DATABASE_TABLE, "number="+del, null)>0;
    }

}

` 以上是我的数据库实现，下面是我的短信接收器实现

public class SMSBroadcastReceiver extends BroadcastReceiver

{

@Override
public void onReceive(Context context, Intent intent) {
    //DBAdapter db = new DBAdapter(this);
            //db.open();
              .....
              .....
           } 

}

当我试图在第二个代码中编写commentet out部分时，它显示错误“构造函数DBAdapter（SMSBroadcastReceiver）未定义”。但是使用相同的statemnt我能够在我的主要活动中执行所有操作。 它为什么以及如何解决它