Android 构造函数DataBaseHelper未定义

我的应用程序中有一个DataBaseHelper类

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.sql.SQLException;
import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;
public class DataBaseHelper extends SQLiteOpenHelper{

    //The Android's default system path of your application database.
    private static String DB_PATH = "/data/data/YOUR_PACKAGE/databases/";

    private static String DB_NAME = "myDBName";

    private SQLiteDatabase myDataBase; 

    private final Context myContext;

    /**
     * Constructor
     * Takes and keeps a reference of the passed context in order to access to the application assets and resources.
     * @param context
     */
    public DataBaseHelper(Context context) {

        super(context, DB_NAME, null, 1);
        this.myContext = context;
    }   



/**
     * Creates a empty database on the system and rewrites it with your own database.
     * */
    public void createDataBase() throws IOException{

        boolean dbExist = checkDataBase();

        if(dbExist){
            //do nothing - database already exist
        }else{

            //By calling this method and empty database will be created into the default system path
               //of your application so we are gonna be able to overwrite that database with our database.
            this.getReadableDatabase();

            try {

                copyDataBase();

            } catch (IOException e) {

                throw new Error("Error copying database");

            }
        }

    }

    /**
     * Check if the database already exist to avoid re-copying the file each time you open the application.
     * @return true if it exists, false if it doesn't
     */
    private boolean checkDataBase(){

        SQLiteDatabase checkDB = null;

        try{
            String myPath = DB_PATH + DB_NAME;
            checkDB = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

        }catch(SQLiteException e){

            //database does't exist yet.

        }

        if(checkDB != null){

            checkDB.close();

        }

        return checkDB != null ? true : false;
    }

    /**
     * Copies your database from your local assets-folder to the just created empty database in the
     * system folder, from where it can be accessed and handled.
     * This is done by transfering bytestream.
     * */
    private void copyDataBase() throws IOException{

        //Open your local db as the input stream
        InputStream myInput = myContext.getAssets().open(DB_NAME);

        // Path to the just created empty db
        String outFileName = DB_PATH + DB_NAME;

        //Open the empty db as the output stream
        OutputStream myOutput = new FileOutputStream(outFileName);

        //transfer bytes from the inputfile to the outputfile
        byte[] buffer = new byte[1024];
        int length;
        while ((length = myInput.read(buffer))>0){
            myOutput.write(buffer, 0, length);
        }

        //Close the streams
        myOutput.flush();
        myOutput.close();
        myInput.close();

    }

    public void openDataBase() throws SQLException{

        //Open the database
        String myPath = DB_PATH + DB_NAME;
        myDataBase = SQLiteDatabase.openDatabase(myPath, null, SQLiteDatabase.OPEN_READONLY);

    }

    @Override
    public synchronized void close() {

            if(myDataBase != null)
                myDataBase.close();

            super.close();

    }

    @Override
    public void onCreate(SQLiteDatabase db) {

    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

    }



}

但是，当我在主要活动中创建这个类的实例只是为了检索数据时，我得到了以下错误。 （主要活动内）

帮帮我

 [ ... represents lines of code I dint include. ]

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必须在构造函数中传递上下文对象

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您只需使用：

DataBaseHelper myDbHelper=newdatabasehelper（this）如果它是在活动类中发出的，则构造函数将上下文实例作为参数：

public DataBaseHelper(Context context) {

当你打电话的时候

DataBaseHelper myDbHelper = new DataBaseHelper();

它正在寻找一个无参数构造函数。
您还没有提供参数
上下文
在提供之后，我得到一个错误：如果我使用这个：DataBaseHelper myDbHelper=newdatabasehelper（this）；我得到一个新的错误，它是：令牌上的语法错误“{应在该令牌之后。令牌上的语法错误”；“{应在该令牌之后。如果我使用这个：DataBaseHelper myDbHelper=new DataBaseHelper（this）；我得到一个新的错误，它是：令牌上的语法错误”；“{应在该令牌之后。您缺少一些{可能是。或者有语法错误。请粘贴新代码好吗？只需在新的DataBaseHelper（）中添加“this”或“getApplicationContext（）”）方括号是否将此代码放入onCreate方法中？如果是，则正确。如果它说这是语法错误，我认为您是在方法之外编写代码。请检查DatabaseHelper创建之前是否没有右括号。是否存在语法错误。如何在主活动中读取数据库内容？
DataBaseHelper myDbHelper = new DataBaseHelper();