Quiz App with SQLite Tutorial Part 12

activity_quiz.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorBackground"
    android:padding="16dp"
    tools:context="com.codinginflow.myawesomequiz.QuizActivity">

    <TextView
        android:id="@+id/text_view_score"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:freezesText="true"
        android:text="Score: 0"
        android:textColor="@android:color/black" />

    <TextView
        android:id="@+id/text_view_question_count"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/text_view_score"
        android:freezesText="true"
        android:text="Question: 1/x"
        android:textColor="@android:color/black" />

    <TextView
        android:id="@+id/text_view_difficulty"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@id/text_view_question_count"
        android:freezesText="true"
        android:text="Difficulty: "
        android:textColor="@android:color/black" />

    <TextView
        android:id="@+id/text_view_countdown"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentEnd="true"
        android:freezesText="true"
        android:text="00:30"
        android:textColor="@android:color/black"
        android:textSize="40sp" />

    <TextView
        android:id="@+id/text_view_question"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_above="@id/radio_group"
        android:layout_marginBottom="16dp"
        android:freezesText="true"
        android:text="Here will be the question text\nHere will be the question text\nHere will be the question text"
        android:textAlignment="center"
        android:textColor="@android:color/black"
        android:textSize="20sp" />

    <RadioGroup
        android:id="@+id/radio_group"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerVertical="true">

        <RadioButton
            android:id="@+id/radio_button1"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:freezesText="true"
            android:text="Option 1" />

        <RadioButton
            android:id="@+id/radio_button2"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:freezesText="true"
            android:text="Option 2" />

        <RadioButton
            android:id="@+id/radio_button3"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:freezesText="true"
            android:text="Option 3" />

    </RadioGroup>

    <Button
        android:id="@+id/button_confirm_next"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/radio_group"
        android:layout_marginTop="16dp"
        android:freezesText="true"
        android:text="Confirm" />

</RelativeLayout>

activity_starting_screen.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:background="@color/colorBackground"
    android:padding="16dp"
    tools:context="com.codinginflow.myawesomequiz.StartingScreenActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="30dp"
        android:text="My Awesome Quiz"
        android:textColor="@android:color/black"
        android:textSize="35sp" />

    <TextView
        android:id="@+id/text_view_highscore"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@id/button_start_quiz"
        android:layout_centerHorizontal="true"
        android:layout_marginBottom="32dp"
        android:text="Highscore: 0"
        android:textSize="20sp" />

    <Button
        android:id="@+id/button_start_quiz"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerInParent="true"
        android:text="Start Quiz" />

    <Spinner
        android:id="@+id/spinner_difficulty"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignStart="@+id/button_start_quiz"
        android:layout_below="@+id/button_start_quiz"
        android:layout_marginTop="16dp" />

</RelativeLayout>

Category.java

package com.codinginflow.myawesomequiz;

public class Category {
    public static final int PROGRAMMING = 1;
    public static final int GEOGRAPHY = 2;
    public static final int MATH = 3;

    private int id;
    private String name;

    public Category() {
    }

    public Category(String name) {
        this.name = name;
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

colors.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <color name="colorPrimary">#795548</color>
    <color name="colorPrimaryDark">#5D4037</color>
    <color name="colorAccent">#FFEB3B</color>

    <color name="colorBackground">#BCAAA4</color>
</resources>

Question.java

package com.codinginflow.myawesomequiz;

import android.os.Parcel;
import android.os.Parcelable;

public class Question implements Parcelable {
    public static final String DIFFICULTY_EASY = "Easy";
    public static final String DIFFICULTY_MEDIUM = "Medium";
    public static final String DIFFICULTY_HARD = "Hard";

    private int id;
    private String question;
    private String option1;
    private String option2;
    private String option3;
    private int answerNr;
    private String difficulty;
    private int categoryID;

    public Question() {
    }

    public Question(String question, String option1, String option2, String option3,
                    int answerNr, String difficulty, int categoryID) {
        this.question = question;
        this.option1 = option1;
        this.option2 = option2;
        this.option3 = option3;
        this.answerNr = answerNr;
        this.difficulty = difficulty;
        this.categoryID = categoryID;
    }

    protected Question(Parcel in) {
        id = in.readInt();
        question = in.readString();
        option1 = in.readString();
        option2 = in.readString();
        option3 = in.readString();
        answerNr = in.readInt();
        difficulty = in.readString();
        categoryID = in.readInt();
    }

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeInt(id);
        dest.writeString(question);
        dest.writeString(option1);
        dest.writeString(option2);
        dest.writeString(option3);
        dest.writeInt(answerNr);
        dest.writeString(difficulty);
        dest.writeInt(categoryID);
    }

    @Override
    public int describeContents() {
        return 0;
    }

    public static final Creator<Question> CREATOR = new Creator<Question>() {
        @Override
        public Question createFromParcel(Parcel in) {
            return new Question(in);
        }

        @Override
        public Question[] newArray(int size) {
            return new Question[size];
        }
    };

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getQuestion() {
        return question;
    }

    public void setQuestion(String question) {
        this.question = question;
    }

    public String getOption1() {
        return option1;
    }

    public void setOption1(String option1) {
        this.option1 = option1;
    }

    public String getOption2() {
        return option2;
    }

    public void setOption2(String option2) {
        this.option2 = option2;
    }

    public String getOption3() {
        return option3;
    }

    public void setOption3(String option3) {
        this.option3 = option3;
    }

    public int getAnswerNr() {
        return answerNr;
    }

    public void setAnswerNr(int answerNr) {
        this.answerNr = answerNr;
    }

    public String getDifficulty() {
        return difficulty;
    }

    public void setDifficulty(String difficulty) {
        this.difficulty = difficulty;
    }

    public int getCategoryID() {
        return categoryID;
    }

    public void setCategoryID(int categoryID) {
        this.categoryID = categoryID;
    }

    public static String[] getAllDifficultyLevels() {
        return new String[]{
                DIFFICULTY_EASY,
                DIFFICULTY_MEDIUM,
                DIFFICULTY_HARD
        };
    }
}

QuizActivity.java

package com.codinginflow.myawesomequiz;

import android.content.Intent;
import android.content.res.ColorStateList;
import android.graphics.Color;
import android.os.CountDownTimer;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.TextView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Locale;

public class QuizActivity extends AppCompatActivity {
    public static final String EXTRA_SCORE = "extraScore";
    private static final long COUNTDOWN_IN_MILLIS = 30000;

    private static final String KEY_SCORE = "keyScore";
    private static final String KEY_QUESTION_COUNT = "keyQuestionCount";
    private static final String KEY_MILLIS_LEFT = "keyMillisLeft";
    private static final String KEY_ANSWERED = "keyAnswered";
    private static final String KEY_QUESTION_LIST = "keyQuestionList";

    private TextView textViewQuestion;
    private TextView textViewScore;
    private TextView textViewQuestionCount;
    private TextView textViewDifficulty;
    private TextView textViewCountDown;
    private RadioGroup rbGroup;
    private RadioButton rb1;
    private RadioButton rb2;
    private RadioButton rb3;
    private Button buttonConfirmNext;

    private ColorStateList textColorDefaultRb;
    private ColorStateList textColorDefaultCd;

    private CountDownTimer countDownTimer;
    private long timeLeftInMillis;

    private ArrayList<Question> questionList;
    private int questionCounter;
    private int questionCountTotal;
    private Question currentQuestion;

    private int score;
    private boolean answered;

    private long backPressedTime;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_quiz);

        textViewQuestion = findViewById(R.id.text_view_question);
        textViewScore = findViewById(R.id.text_view_score);
        textViewQuestionCount = findViewById(R.id.text_view_question_count);
        textViewDifficulty = findViewById(R.id.text_view_difficulty);
        textViewCountDown = findViewById(R.id.text_view_countdown);
        rbGroup = findViewById(R.id.radio_group);
        rb1 = findViewById(R.id.radio_button1);
        rb2 = findViewById(R.id.radio_button2);
        rb3 = findViewById(R.id.radio_button3);
        buttonConfirmNext = findViewById(R.id.button_confirm_next);

        textColorDefaultRb = rb1.getTextColors();
        textColorDefaultCd = textViewCountDown.getTextColors();

        Intent intent = getIntent();
        String difficulty = intent.getStringExtra(StartingScreenActivity.EXTRA_DIFFICULTY);

        textViewDifficulty.setText("Difficulty: " + difficulty);

        if (savedInstanceState == null) {
            QuizDbHelper dbHelper = new QuizDbHelper(this);
            questionList = dbHelper.getQuestions(difficulty);
            questionCountTotal = questionList.size();
            Collections.shuffle(questionList);

            showNextQuestion();
        } else {
            questionList = savedInstanceState.getParcelableArrayList(KEY_QUESTION_LIST);
            questionCountTotal = questionList.size();
            questionCounter = savedInstanceState.getInt(KEY_QUESTION_COUNT);
            currentQuestion = questionList.get(questionCounter - 1);
            score = savedInstanceState.getInt(KEY_SCORE);
            timeLeftInMillis = savedInstanceState.getLong(KEY_MILLIS_LEFT);
            answered = savedInstanceState.getBoolean(KEY_ANSWERED);

            if (!answered) {
                startCountDown();
            } else {
                updateCountDownText();
                showSolution();
            }
        }

        buttonConfirmNext.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (!answered) {
                    if (rb1.isChecked() || rb2.isChecked() || rb3.isChecked()) {
                        checkAnswer();
                    } else {
                        Toast.makeText(QuizActivity.this, "Please select an answer", Toast.LENGTH_SHORT).show();
                    }
                } else {
                    showNextQuestion();
                }
            }
        });
    }

    private void showNextQuestion() {
        rb1.setTextColor(textColorDefaultRb);
        rb2.setTextColor(textColorDefaultRb);
        rb3.setTextColor(textColorDefaultRb);
        rbGroup.clearCheck();

        if (questionCounter < questionCountTotal) {
            currentQuestion = questionList.get(questionCounter);

            textViewQuestion.setText(currentQuestion.getQuestion());
            rb1.setText(currentQuestion.getOption1());
            rb2.setText(currentQuestion.getOption2());
            rb3.setText(currentQuestion.getOption3());

            questionCounter++;
            textViewQuestionCount.setText("Question: " + questionCounter + "/" + questionCountTotal);
            answered = false;
            buttonConfirmNext.setText("Confirm");

            timeLeftInMillis = COUNTDOWN_IN_MILLIS;
            startCountDown();
        } else {
            finishQuiz();
        }
    }

    private void startCountDown() {
        countDownTimer = new CountDownTimer(timeLeftInMillis, 1000) {
            @Override
            public void onTick(long millisUntilFinished) {
                timeLeftInMillis = millisUntilFinished;
                updateCountDownText();
            }

            @Override
            public void onFinish() {
                timeLeftInMillis = 0;
                updateCountDownText();
                checkAnswer();
            }
        }.start();
    }

    private void updateCountDownText() {
        int minutes = (int) (timeLeftInMillis / 1000) / 60;
        int seconds = (int) (timeLeftInMillis / 1000) % 60;

        String timeFormatted = String.format(Locale.getDefault(), "%02d:%02d", minutes, seconds);

        textViewCountDown.setText(timeFormatted);

        if (timeLeftInMillis < 10000) {
            textViewCountDown.setTextColor(Color.RED);
        } else {
            textViewCountDown.setTextColor(textColorDefaultCd);
        }
    }

    private void checkAnswer() {
        answered = true;

        countDownTimer.cancel();

        RadioButton rbSelected = findViewById(rbGroup.getCheckedRadioButtonId());
        int answerNr = rbGroup.indexOfChild(rbSelected) + 1;

        if (answerNr == currentQuestion.getAnswerNr()) {
            score++;
            textViewScore.setText("Score: " + score);
        }

        showSolution();
    }

    private void showSolution() {
        rb1.setTextColor(Color.RED);
        rb2.setTextColor(Color.RED);
        rb3.setTextColor(Color.RED);

        switch (currentQuestion.getAnswerNr()) {
            case 1:
                rb1.setTextColor(Color.GREEN);
                textViewQuestion.setText("Answer 1 is correct");
                break;
            case 2:
                rb2.setTextColor(Color.GREEN);
                textViewQuestion.setText("Answer 2 is correct");
                break;
            case 3:
                rb3.setTextColor(Color.GREEN);
                textViewQuestion.setText("Answer 3 is correct");
                break;
        }

        if (questionCounter < questionCountTotal) {
            buttonConfirmNext.setText("Next");
        } else {
            buttonConfirmNext.setText("Finish");
        }
    }

    private void finishQuiz() {
        Intent resultIntent = new Intent();
        resultIntent.putExtra(EXTRA_SCORE, score);
        setResult(RESULT_OK, resultIntent);
        finish();
    }

    @Override
    public void onBackPressed() {
        if (backPressedTime + 2000 > System.currentTimeMillis()) {
            finishQuiz();
        } else {
            Toast.makeText(this, "Press back again to finish", Toast.LENGTH_SHORT).show();
        }

        backPressedTime = System.currentTimeMillis();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
        if (countDownTimer != null) {
            countDownTimer.cancel();
        }
    }

    @Override
    protected void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);
        outState.putInt(KEY_SCORE, score);
        outState.putInt(KEY_QUESTION_COUNT, questionCounter);
        outState.putLong(KEY_MILLIS_LEFT, timeLeftInMillis);
        outState.putBoolean(KEY_ANSWERED, answered);
        outState.putParcelableArrayList(KEY_QUESTION_LIST, questionList);
    }
}

QuizContract.java

package com.codinginflow.myawesomequiz;

import android.provider.BaseColumns;

public final class QuizContract {

    private QuizContract() {
    }

    public static class CategoriesTable implements BaseColumns {
        public static final String TABLE_NAME = "quiz_categories";
        public static final String COLUMN_NAME = "name";
    }

    public static class QuestionsTable implements BaseColumns {
        public static final String TABLE_NAME = "quiz_questions";
        public static final String COLUMN_QUESTION = "question";
        public static final String COLUMN_OPTION1 = "option1";
        public static final String COLUMN_OPTION2 = "option2";
        public static final String COLUMN_OPTION3 = "option3";
        public static final String COLUMN_ANSWER_NR = "answer_nr";
        public static final String COLUMN_DIFFICULTY = "difficulty";
        public static final String COLUMN_CATEGORY_ID = "category_id";
    }
}

QuizDbHelper.java

package com.codinginflow.myawesomequiz;

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

import com.codinginflow.myawesomequiz.QuizContract.*;

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


public class QuizDbHelper extends SQLiteOpenHelper {
    private static final String DATABASE_NAME = "MyAwesomeQuiz.db";
    private static final int DATABASE_VERSION = 1;

    private static QuizDbHelper instance;

    private SQLiteDatabase db;

    private QuizDbHelper(Context context) {
        super(context, DATABASE_NAME, null, DATABASE_VERSION);
    }

    public static synchronized QuizDbHelper getInstance(Context context) {
        if (instance == null) {
            instance = new QuizDbHelper(context.getApplicationContext());
        }
        return instance;
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        this.db = db;

        final String SQL_CREATE_CATEGORIES_TABLE = "CREATE TABLE " +
                CategoriesTable.TABLE_NAME + "( " +
                CategoriesTable._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                CategoriesTable.COLUMN_NAME + " TEXT " +
                ")";

        final String SQL_CREATE_QUESTIONS_TABLE = "CREATE TABLE " +
                QuestionsTable.TABLE_NAME + " ( " +
                QuestionsTable._ID + " INTEGER PRIMARY KEY AUTOINCREMENT, " +
                QuestionsTable.COLUMN_QUESTION + " TEXT, " +
                QuestionsTable.COLUMN_OPTION1 + " TEXT, " +
                QuestionsTable.COLUMN_OPTION2 + " TEXT, " +
                QuestionsTable.COLUMN_OPTION3 + " TEXT, " +
                QuestionsTable.COLUMN_ANSWER_NR + " INTEGER, " +
                QuestionsTable.COLUMN_DIFFICULTY + " TEXT, " +
                QuestionsTable.COLUMN_CATEGORY_ID + " INTEGER, " +
                "FOREIGN KEY(" + QuestionsTable.COLUMN_CATEGORY_ID + ") REFERENCES " +
                CategoriesTable.TABLE_NAME + "(" + CategoriesTable._ID + ")" + "ON DELETE CASCADE" +
                ")";

        db.execSQL(SQL_CREATE_CATEGORIES_TABLE);
        db.execSQL(SQL_CREATE_QUESTIONS_TABLE);
        fillCategoriesTable();
        fillQuestionsTable();
    }

    @Override
    public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
        db.execSQL("DROP TABLE IF EXISTS " + CategoriesTable.TABLE_NAME);
        db.execSQL("DROP TABLE IF EXISTS " + QuestionsTable.TABLE_NAME);
        onCreate(db);
    }

    @Override
    public void onConfigure(SQLiteDatabase db) {
        super.onConfigure(db);
        db.setForeignKeyConstraintsEnabled(true);
    }

    private void fillCategoriesTable() {
        Category c1 = new Category("Programming");
        addCategory(c1);
        Category c2 = new Category("Geography");
        addCategory(c2);
        Category c3 = new Category("Math");
        addCategory(c3);
    }

    private void addCategory(Category category) {
        ContentValues cv = new ContentValues();
        cv.put(CategoriesTable.COLUMN_NAME, category.getName());
        db.insert(CategoriesTable.TABLE_NAME, null, cv);
    }

    private void fillQuestionsTable() {
        Question q1 = new Question("Programming, Easy: A is correct",
                "A", "B", "C", 1,
                Question.DIFFICULTY_EASY, Category.PROGRAMMING);
        addQuestion(q1);
        Question q2 = new Question("Geography, Medium: B is correct",
                "A", "B", "C", 2,
                Question.DIFFICULTY_MEDIUM, Category.GEOGRAPHY);
        addQuestion(q2);
        Question q3 = new Question("Math, Hard: C is correct",
                "A", "B", "C", 3,
                Question.DIFFICULTY_HARD, Category.MATH);
        addQuestion(q3);
        Question q4 = new Question("Math, Easy: A is correct",
                "A", "B", "C", 1,
                Question.DIFFICULTY_EASY, Category.MATH);
        addQuestion(q4);
        Question q5 = new Question("Non existing, Easy: A is correct",
                "A", "B", "C", 1,
                Question.DIFFICULTY_EASY, 4);
        addQuestion(q5);
        Question q6 = new Question("Non existing, Medium: B is correct",
                "A", "B", "C", 2,
                Question.DIFFICULTY_MEDIUM, 5);
        addQuestion(q6);
    }

    private void addQuestion(Question question) {
        ContentValues cv = new ContentValues();
        cv.put(QuestionsTable.COLUMN_QUESTION, question.getQuestion());
        cv.put(QuestionsTable.COLUMN_OPTION1, question.getOption1());
        cv.put(QuestionsTable.COLUMN_OPTION2, question.getOption2());
        cv.put(QuestionsTable.COLUMN_OPTION3, question.getOption3());
        cv.put(QuestionsTable.COLUMN_ANSWER_NR, question.getAnswerNr());
        cv.put(QuestionsTable.COLUMN_DIFFICULTY, question.getDifficulty());
        cv.put(QuestionsTable.COLUMN_CATEGORY_ID, question.getCategoryID());
        db.insert(QuestionsTable.TABLE_NAME, null, cv);
    }

    public List<Category> getAllCategories() {
        List<Category> categoryList = new ArrayList<>();
        db = getReadableDatabase();
        Cursor c = db.rawQuery("SELECT * FROM " + CategoriesTable.TABLE_NAME, null);

        if (c.moveToFirst()) {
            do {
                Category category = new Category();
                category.setId(c.getInt(c.getColumnIndex(CategoriesTable._ID)));
                category.setName(c.getString(c.getColumnIndex(CategoriesTable.COLUMN_NAME)));
                categoryList.add(category);
            } while (c.moveToNext());
        }

        c.close();
        return categoryList;
    }

    public ArrayList<Question> getAllQuestions() {
        ArrayList<Question> questionList = new ArrayList<>();
        db = getReadableDatabase();
        Cursor c = db.rawQuery("SELECT * FROM " + QuestionsTable.TABLE_NAME, null);

        if (c.moveToFirst()) {
            do {
                Question question = new Question();
                question.setId(c.getInt(c.getColumnIndex(QuestionsTable._ID)));
                question.setQuestion(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_QUESTION)));
                question.setOption1(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_OPTION1)));
                question.setOption2(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_OPTION2)));
                question.setOption3(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_OPTION3)));
                question.setAnswerNr(c.getInt(c.getColumnIndex(QuestionsTable.COLUMN_ANSWER_NR)));
                question.setDifficulty(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_DIFFICULTY)));
                question.setCategoryID(c.getInt(c.getColumnIndex(QuestionsTable.COLUMN_CATEGORY_ID)));
                questionList.add(question);
            } while (c.moveToNext());
        }

        c.close();
        return questionList;
    }

    public ArrayList<Question> getQuestions(int categoryID, String difficulty) {
        ArrayList<Question> questionList = new ArrayList<>();
        db = getReadableDatabase();

        String selection = QuestionsTable.COLUMN_CATEGORY_ID + " = ? " +
                " AND " + QuestionsTable.COLUMN_DIFFICULTY + " = ? ";
        String[] selectionArgs = new String[]{String.valueOf(categoryID), difficulty};

        Cursor c = db.query(
                QuestionsTable.TABLE_NAME,
                null,
                selection,
                selectionArgs,
                null,
                null,
                null
        );

        if (c.moveToFirst()) {
            do {
                Question question = new Question();
                question.setId(c.getInt(c.getColumnIndex(QuestionsTable._ID)));
                question.setQuestion(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_QUESTION)));
                question.setOption1(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_OPTION1)));
                question.setOption2(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_OPTION2)));
                question.setOption3(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_OPTION3)));
                question.setAnswerNr(c.getInt(c.getColumnIndex(QuestionsTable.COLUMN_ANSWER_NR)));
                question.setDifficulty(c.getString(c.getColumnIndex(QuestionsTable.COLUMN_DIFFICULTY)));
                question.setCategoryID(c.getInt(c.getColumnIndex(QuestionsTable.COLUMN_CATEGORY_ID)));
                questionList.add(question);
            } while (c.moveToNext());
        }

        c.close();
        return questionList;
    }
}

StartingScreenActivity.java

package com.codinginflow.myawesomequiz;

import android.content.Intent;
import android.content.SharedPreferences;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.Spinner;
import android.widget.TextView;

public class StartingScreenActivity extends AppCompatActivity {
    private static final int REQUEST_CODE_QUIZ = 1;
    public static final String EXTRA_DIFFICULTY = "extraDifficulty";

    public static final String SHARED_PREFS = "sharedPrefs";
    public static final String KEY_HIGHSCORE = "keyHighscore";

    private TextView textViewHighscore;
    private Spinner spinnerDifficulty;

    private int highscore;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_starting_screen);

        textViewHighscore = findViewById(R.id.text_view_highscore);
        spinnerDifficulty = findViewById(R.id.spinner_difficulty);

        String[] difficultyLevels = Question.getAllDifficultyLevels();

        ArrayAdapter<String> adapterDifficulty = new ArrayAdapter<String>(this,
                android.R.layout.simple_spinner_item, difficultyLevels);
        adapterDifficulty.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
        spinnerDifficulty.setAdapter(adapterDifficulty);

        loadHighscore();

        Button buttonStartQuiz = findViewById(R.id.button_start_quiz);
        buttonStartQuiz.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startQuiz();
            }
        });
    }

    private void startQuiz() {
        String difficulty = spinnerDifficulty.getSelectedItem().toString();

        Intent intent = new Intent(StartingScreenActivity.this, QuizActivity.class);
        intent.putExtra(EXTRA_DIFFICULTY, difficulty);
        startActivityForResult(intent, REQUEST_CODE_QUIZ);
    }

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
        super.onActivityResult(requestCode, resultCode, data);

        if (requestCode == REQUEST_CODE_QUIZ) {
            if (resultCode == RESULT_OK) {
                int score = data.getIntExtra(QuizActivity.EXTRA_SCORE, 0);
                if (score > highscore) {
                    updateHighscore(score);
                }
            }
        }
    }

    private void loadHighscore() {
        SharedPreferences prefs = getSharedPreferences(SHARED_PREFS, MODE_PRIVATE);
        highscore = prefs.getInt(KEY_HIGHSCORE, 0);
        textViewHighscore.setText("Highscore: " + highscore);
    }

    private void updateHighscore(int highscoreNew) {
        highscore = highscoreNew;
        textViewHighscore.setText("Highscore: " + highscore);

        SharedPreferences prefs = getSharedPreferences(SHARED_PREFS, MODE_PRIVATE);
        SharedPreferences.Editor editor = prefs.edit();
        editor.putInt(KEY_HIGHSCORE, highscore);
        editor.apply();
    }
}