Question

我已经阅读了很多类似问题的答案，但似乎这些答案都没有解决我的问题。

我将一个SQLite数据库复制到＆＃34;资产＆＃34;我的应用程序的文件夹，我使用在网站上找到的代码导入它（我没有理解这段代码中的所有内容）：

package com.example.quizone_2;

import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import android.content.Context;
import android.database.SQLException;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteException;
import android.database.sqlite.SQLiteOpenHelper;

public class DataBase extends SQLiteOpenHelper{

    //The Android's default system path of your application database.
    private static String DB_PATH = "/data/data/com.example.quizone_2/databases/";

    private static String DB_NAME = "QuizOne_DB";

    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 DataBase(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) {

}

    // Add your public helper methods to access and get content from the database.
   // You could return cursors by doing "return myDataBase.query(....)" so it'd be easy
   // to you to create adapters for your views.

}

我的数据库包含一个包含问题和答案的表。

现在，我想要的是搜索要在活动中显示的随机问题，然后将答案（真或假）与数据库中的答案进行比较。

问题是我在网上找不到类似的东西，首先是因为我的数据库是导入的而不是在应用程序中创建的，其次是因为我还没有真正理解如何从我的数据库中读取数据。更不用说我甚至不知道如何随机搜索。

如果你完整地阅读了这个问题，谢谢你，我希望有人可以帮助我，因为我不知道从哪里开始。

非常感谢

Answer 1

一种选择： 1）为表中的每个问题分配一个数字id。（从1到n，其中n是问题数） 2）在您的活动中生成1到n之间的随机数。您可以使用Math.round（（Math.random（）* n）+1）来执行此操作。 3）然后查询您的表，其中数字id（点1）等于随机数。

Android - 如何从导入的数据库中读取随机数据

1 个答案: