Question

我目前正在开发一个简单的Android测验应用程序。

代码如下：

package com.example.darel.geogame;

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

import java.util.ArrayList;
import java.util.List;


public class QuizHelper extends SQLiteOpenHelper {
    private static final int DATABASE_VERSION = 1;
    // Database Name
    private static final String DATABASE_NAME = "mathsone";
    // tasks table name
    private static final String TABLE_QUEST = "quest";
    // tasks Table Columns names
    private static final String KEY_ID = "qid";
    private static final String KEY_QUES = "question";
    private static final String KEY_ANSWER = "answer"; // correct option
    private static final String KEY_OPTA = "opta"; // option a
    private static final String KEY_OPTB = "optb"; // option b
    private static final String KEY_OPTC = "optc"; // option c
    private SQLiteDatabase dbase;
    public QuizHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }
    @Override
    public void onCreate(SQLiteDatabase db) {
        dbase = db;
        String sql = "CREATE TABLE IF NOT EXISTS " + TABLE_QUEST + " ( "
                + KEY_ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " + KEY_QUES
                + " TEXT, " + KEY_ANSWER + " TEXT, " + KEY_OPTA + " TEXT, "
                + KEY_OPTB + " TEXT, " + KEY_OPTC + " TEXT)";
        db.execSQL(sql);
        addQuestion();
// db.close();
    }
    private void addQuestion() {
        Question q1 = new Question("5+2 = ?", "7", "8", "6", "7");
        this.addQuestion(q1);
        Question q2 = new Question("2+18 = ?", "18", "19", "20", "20");
        this.addQuestion(q2);
        Question q3 = new Question("10-3 = ?", "6", "7", "8", "7");
        this.addQuestion(q3);
        Question q4 = new Question("5+7 = ?", "12", "13", "14", "12");
        this.addQuestion(q4);
        Question q5 = new Question("3-1 = ?", "1", "3", "2", "2");
        this.addQuestion(q5);
        Question q6 = new Question("0+1 = ?", "1", "0", "10", "1");
        this.addQuestion(q6);
        Question q7 = new Question("9-9 = ?", "0", "9", "1", "0");
        this.addQuestion(q7);
        Question q8 = new Question("3+6 = ?", "8", "7", "9", "9");
        this.addQuestion(q8);
        Question q9 = new Question("1+5 = ?", "6", "7", "5", "6");
        this.addQuestion(q9);
        Question q10 = new Question("7-5 = ?", "3", "2", "6", "2");
        this.addQuestion(q10);
        Question q11 = new Question("7-2 = ?", "7", "6", "5", "5");
        this.addQuestion(q11);
        Question q12 = new Question("3+5 = ?", "8", "7", "5", "8");
        this.addQuestion(q12);
        Question q13 = new Question("0+6 = ?", "7", "6", "5", "6");
        this.addQuestion(q13);
        Question q14 = new Question("12-10 = ?", "1", "2", "3", "2");
        this.addQuestion(q14);
        Question q15 = new Question("12+2 = ?", "14", "15", "16", "14");
        this.addQuestion(q15);
        Question q16 = new Question("2-1 = ?", "2", "1", "0", "1");
        this.addQuestion(q16);
        Question q17 = new Question("6-6 = ?", "6", "12", "0", "0");
        this.addQuestion(q17);
        Question q18 = new Question("5-1 = ?", "4", "3", "2", "4");
        this.addQuestion(q18);
        Question q19 = new Question("4+2 = ?", "6", "7", "5", "6");
        this.addQuestion(q19);
        Question q20 = new Question("5+1 = ?", "6", "7", "5", "6");
        this.addQuestion(q20);
        Question q21 = new Question("5-4 = ?", "5", "4", "1", "1");
        this.addQuestion(q21);
// END
    }
    @Override
    public void onUpgrade(SQLiteDatabase db, int oldV, int newV) {
// Drop older table if existed
        db.execSQL("DROP TABLE IF EXISTS " + TABLE_QUEST);
// Create tables again
        onCreate(db);
    }
    // Adding new question
    public void addQuestion(Question quest) {
// SQLiteDatabase db = this.getWritableDatabase();
        ContentValues values = new ContentValues();
        values.put(KEY_QUES, quest.getQUESTION());
        values.put(KEY_ANSWER, quest.getANSWER());
        values.put(KEY_OPTA, quest.getOPTA());
        values.put(KEY_OPTB, quest.getOPTB());
        values.put(KEY_OPTC, quest.getOPTC());
// Inserting Row
        dbase.insert(TABLE_QUEST, null, values);
    }
    public List<Question> getAllQuestions() {
        List<Question> quesList = new ArrayList<Question>();
// Select All Query
        String selectQuery = "SELECT * FROM " + TABLE_QUEST;
        dbase = this.getReadableDatabase();
        Cursor cursor = dbase.rawQuery(selectQuery, null);
// looping through all rows and adding to list
        if (cursor.moveToFirst()) {
            do {
                Question quest = new Question();
                quest.setID(cursor.getInt(0));
                quest.setQUESTION(cursor.getString(1));
                quest.setANSWER(cursor.getString(2));
                quest.setOPTA(cursor.getString(3));
                quest.setOPTB(cursor.getString(4));
                quest.setOPTC(cursor.getString(5));
                quesList.add(quest);
            } while (cursor.moveToNext());
        }
// return quest list
        return quesList;
    }
}

根据上面的代码，应用程序按编写的代码顺序列出问题我希望应用程序随机选择一个问题而不是按顺序而不重复。

有人可以帮助我吗？

Answer 1

According to the above code, the app is listing the questions in order of the code written. 错误。

您永远不会被授予从表中获取行的顺序这就是ORDER BY子句存在的原因。

除了各种修饰符（ASC，DESC）之外，您还可以使用RANDOM()来对行集进行随机播放。

因此，而不是

String selectQuery = "SELECT * FROM " + TABLE_QUEST;

使用

String selectQuery = "SELECT * FROM " + TABLE_QUEST + " ORDER BY RANDOM()";

如果您需要单问题，可以使用

String selectQuery = "SELECT * FROM " + TABLE_QUEST + " ORDER BY RANDOM() LIMIT 1";

但是，这不会授予下次执行查询时您再也看不到相同的行。

因此，我一次获取所有行并一次消耗一行光标。

如何在Android Studio中从数据库中随机选择一行？

1 个答案: