************************************************************************
strings.xml
************************************************************************
<resources>
    <string name="app_name">Flag Quiz</string>
    <string name="action_settings">Settings</string>
    <string name="number_of_choices">Number of Choices</string>
    <string name="number_of_choices_description">Display 2, 4, 6 or 8 guess buttons</string>
    <string name="world_regions">Regions</string>
    <string name="world_regions_description">Regions to include in the quiz</string>
    <string name="guess_country">Guess the country</string>
    <string name="results">%1$d guesses, %2$.02f%% correct</string>
    <string name="incorrect_answer">Incorrect!</string>
    <string name="default_region_message">One region must be selected. Setting North America as the default region.</string>
    <string name="restarting_quiz">Quiz will restart with your new settings</string>
    <string name="question">Question %1$d of %2$d</string>
    <string name="reset_quiz">Reset Quiz</string>
    <string name="image_description">Image of the current flag in the quiz</string>
    <string name="default_region">North_America</string>
</resources>


************************************************************************
arrays.xml
************************************************************************
<?xml version="1.0" encoding="utf-8"?>
<resources>
    <string-array name="regions_list">
        <item>Africa</item>
        <item>Asia</item>
        <item>Europe</item>
        <item>North_America</item>
        <item>Oceania</item>
        <item>South_America</item>
    </string-array>

    <string-array name="regions_list_for_settings">
        <item>Africa</item>
        <item>Asia</item>
        <item>Europe</item>
        <item>North America</item>
        <item>Oceania</item>
        <item>South America</item>
    </string-array>

    <string-array name="guesses_list">
        <item>2</item>
        <item>4</item>
        <item>6</item>
        <item>8</item>
    </string-array>
</resources>

************************************************************************
colors.xml
************************************************************************
<?xml version="1.0" encoding="utf-8"?>
<resources>
    <color name="colorPrimary">#3F51B5</color>
    <color name="colorPrimaryDark">#303F9F</color>
    <color name="colorAccent">#448AFF</color>
    <color name="correct_answer">#00CC00</color>
    <color name="incorrect_answer">#FF0000</color>
</resources>


************************************************************************
button_text_color.xml
************************************************************************
<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:color="@android:color/primary_text_dark"
        android:state_enabled="true" />

    <item
        android:color="@android:color/darker_gray"
        android:state_enabled="false" />
</selector>

************************************************************************
incorrect_shake.xml
************************************************************************
<?xml version="1.0" encoding="utf-8"?>
<set xmlns:android="http://schemas.android.com/apk/res/android"
    android:interpolator="@android:anim/decelerate_interpolator">

    <translate android:duration="100" android:fromXDelta="0"
        android:toXDelta="-5%p" />

    <translate android:duration="100" android:fromXDelta="-5%p"
        android:toXDelta="5%p" android:startOffset="100"/>

    <translate android:duration="100" android:fromXDelta="5%p"
        android:toXDelta="-5%p" android:startOffset="200"/>

</set>


************************************************************************
preferences.xml
************************************************************************
<?xml version="1.0" encoding="utf-8"?>
<PreferenceScreen xmlns:android="http://schemas.android.com/apk/res/android">

    <ListPreference
        android:entries="@array/guesses_list"
        android:entryValues="@array/guesses_list"
        android:key="pref_numberOfChoices"
        android:title="@string/number_of_choices"
        android:summary="@string/number_of_choices_description"
        android:persistent="true"
        android:defaultValue="4" />

    <MultiSelectListPreference
        android:entries="@array/regions_list_for_settings"
        android:entryValues="@array/regions_list"
        android:key="pref_regionsToInclude"
        android:title="@string/world_regions"
        android:summary="@string/world_regions_description"
        android:persistent="true"
        android:defaultValue="@array/regions_list" />

</PreferenceScreen>



************************************************************************
MainActivity.java - onCreate()
************************************************************************
    // keys for reading data from SharedPreferences
    public static final String CHOICES = "pref_numberOfChoices";
    public static final String REGIONS = "pref_regionsToInclude";

    private boolean phoneDevice = true; // used to force portrait mode
    private boolean preferencesChanged = true;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        // set default values in the app's SharedPreferences
        PreferenceManager.setDefaultValues(this, R.xml.preferences, false);

        // register listener for SharedPreferences changes
        PreferenceManager.getDefaultSharedPreferences(this)
                .registerOnSharedPreferenceChangeListener(preferencesChangeListener);

        // determine screen size
        int screenSize = getResources().getConfiguration().screenLayout
                & Configuration.SCREENLAYOUT_SIZE_MASK;

        // if device is a tablet, set phoneDevice to false
        if (screenSize == Configuration.SCREENLAYOUT_SIZE_LARGE
                || screenSize == Configuration.SCREENLAYOUT_SIZE_XLARGE) {
            phoneDevice = false;
        }

        // if running on phone-sized device, allow only portrait orientation
        if (phoneDevice) {
            setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
        }
    }


************************************************************************
MainActivity.java - onStart()
************************************************************************
    @Override
    protected void onStart() {
        super.onStart();

        if (preferencesChanged) {
            // now that the default preferences have been set
            // initialize MainActivityFragment and start the quiz
            MainActivityFragment quizFragment = (MainActivityFragment)
                    getSupportFragmentManager().findFragmentById(R.id.quizFragment);
            quizFragment.updateGuessRows(PreferenceManager.getDefaultSharedPreferences(this));
            quizFragment.updateRegions(PreferenceManager.getDefaultSharedPreferences(this));
            quizFragment.resetQuiz();
            preferencesChanged = false;
        }
    }


************************************************************************
MainActivity.java - onCreateOptionsMenu()
************************************************************************
    // show menu if app is running on a phone or a portrait-oriented tablet
    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // get the device's current orientation
        int orientation = getResources().getConfiguration().orientation;

        // display the app's menu only in portrait orientation
        if (orientation == Configuration.ORIENTATION_PORTRAIT) {
            // inflate the menu
            getMenuInflater().inflate(R.menu.menu_main, menu);
            return true;
        } else {
            return false;
        }
    }


************************************************************************
MainActivity.java - onOptionsItemSelected()
************************************************************************
    // displays the SettingsActivity when running a phone
    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
        Intent preferencesIntent = new Intent(this, SettingsActivity.class);
        startActivity(preferencesIntent);
        return super.onOptionsItemSelected(item);
    }


************************************************************************
MainActivity.java - OnSharedPreferenceChangeListener
************************************************************************
    // listener for changes on the app's SharedPreferences
    private OnSharedPreferenceChangeListener preferencesChangeListener =
            new OnSharedPreferenceChangeListener() {
                // called when the user changes the map's preferences
                @Override
                public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
                    preferencesChanged = true; // user changes app settings

                    MainActivityFragment quizFragment = (MainActivityFragment)
                            getSupportFragmentManager().findFragmentById(R.id.quizFragment);

                    if (key.equals(CHOICES)) { // # of choices to display changed
                        quizFragment.updateGuessRows(sharedPreferences);
                        quizFragment.resetQuiz();
                    } else if (key.equals(REGIONS)) {  // regions to include changed
                        Set<String> regions = sharedPreferences.getStringSet(REGIONS, null);

                        if (regions != null && regions.size() > 0) {
                            quizFragment.updateRegions(sharedPreferences);
                            quizFragment.resetQuiz();
                        } else {
                            // must select one region
                            SharedPreferences.Editor editor = sharedPreferences.edit();
                            regions.add(getString(R.string.default_region));
                            editor.putStringSet(REGIONS, regions);
                            editor.apply();

                            Toast.makeText(MainActivity.this,
                                    R.string.default_region_message,
                                    Toast.LENGTH_SHORT).show();
                        }
                    }
                    Toast.makeText(MainActivity.this,
                            R.string.restarting_quiz,
                            Toast.LENGTH_SHORT).show();
                }
            };


************************************************************************
MainActivityFragment.java - fields (w/o private)
************************************************************************
    // String used when logging error messages
    private static final String LOG_TAG = MainActivityFragment.class.getSimpleName();

    private static final int FLAGS_IN_QUIZ = 10;

    List<String> fileNameList;          // flag file names
    List<String> quizCountriesList;     // countries in current quiz
    Set<String> regionsSet;             // world regions in current quiz
    String correctAnswer;               // correct country for the correct flag
    int totalGuesses;                   // number of guesses made
    int correctAnswers;                 // number of correct guesses
    int guessRows;                      // number of rows displaying guess buttons
    SecureRandom random;                // used to randomize the quiz
    Handler handler;                    // used to delay loading next flag (android.os)
    Animation shakeAnimation;           // animation for incorrect guess
    
    LinearLayout quizLinearLayout;      // layout that contains the quiz               
    TextView questionNumberTextView;   // shows current question #                    
    ImageView flagImageView;            // displays a flag                             
    LinearLayout[] guessLinearLayouts;  // rows of answer buttons                      
    TextView answerTextView;            // displays correct answer                     


************************************************************************
MainActivityFragment.java - fields
************************************************************************
    private List<String> fileNameList;          // flag file names                             
    private List<String> quizCountriesList;     // countries in current quiz                   
    private Set<String> regionsSet;             // world regions in current quiz               
    private String correctAnswer;               // correct country for the correct flag        
    private int totalGuesses;                   // number of guesses made                      
    private int correctAnswers;                 // number of correct guesses                   
    private int guessRows;                      // number of rows displaying guess buttons     
    private SecureRandom random;                // used to randomize the quiz                  
    private Handler handler;                    // used to delay loading next flag (android.os)
    private Animation shakeAnimation;           // animation for incorrect guess               
                                                                                               
    private LinearLayout quizLinearLayout;      // layout that contains the quiz               
    private TextView questionNumberTextView;   // shows current question #                    
    private ImageView flagImageView;            // displays a flag                             
    private LinearLayout[] guessLinearLayouts;  // rows of answer buttons                      
    private TextView answerTextView;            // displays correct answer                     


************************************************************************
MainActivityFragment.java - onCreateView()
************************************************************************
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        super.onCreateView(inflater, container, savedInstanceState);
        View view = inflater.inflate(R.layout.fragment_main, container, false);

        fileNameList = new ArrayList<>();
        quizCountriesList = new ArrayList<>();
        random = new SecureRandom();
        handler = new Handler();

        // load the shake animation that's used for incorrect answers
        shakeAnimation = AnimationUtils.loadAnimation(getActivity(), R.anim.incorrect_shake);
        shakeAnimation.setRepeatCount(3);  // animation repeats 3 times

        // get references to GUI components
        quizLinearLayout = (LinearLayout) view.findViewById(R.id.quizLinearLayout);
        questionNumberTextView = (TextView) view.findViewById(R.id.questionNumberTextView);
        flagImageView = (ImageView) view.findViewById(R.id.flagImageView);
        guessLinearLayouts = new LinearLayout[4];
        guessLinearLayouts[0] = (LinearLayout) view.findViewById(R.id.row1LinearLayout);
        guessLinearLayouts[1] = (LinearLayout) view.findViewById(R.id.row2LinearLayout);
        guessLinearLayouts[2] = (LinearLayout) view.findViewById(R.id.row3LinearLayout);
        guessLinearLayouts[3] = (LinearLayout) view.findViewById(R.id.row4LinearLayout);
        answerTextView = (TextView) view.findViewById(R.id.answerTextView);
        
        // configure listeners for the guess buttons
        for (LinearLayout row : guessLinearLayouts) {
            for (int column = 0; column < row.getChildCount(); column++) {
                Button button = (Button) row.getChildAt(column);
                button.setOnClickListener(guessButtonListener);
            }
        }
        
        // set questionNumberTextView's text
        questionNumberTextView.setText(getString(R.string.question, 1, FLAGS_IN_QUIZ));
        return view;
    }



************************************************************************
MainActivityFragment.java - updateGuessRows()
************************************************************************
    // update guessRows based on value in sharedPreferences
    public void updateGuessRows(SharedPreferences sharedPreferences) {
        // get the number of guess buttons that should be diplayed
        String choices = sharedPreferences.getString(MainActivity.CHOICES, null);
        guessRows = Integer.parseInt(choices) / 2;

        // hide all quests button LinearLayout
        for (LinearLayout layout : guessLinearLayouts) {
            layout.setVisibility(View.GONE);
        }

        // display appropriate guess button LinearLayout
        for (int row = 0; row < guessRows; row++) {
		guessLinearLayouts[row].setVisibility(View.VISIBLE);
        }
    }



************************************************************************
MainActivityFragment.java - updateRegions()
************************************************************************
    // update world regions for quiz based on values in SharedPrefences
    public void updateRegions(SharedPreferences sharedPreferences) {
        regionsSet = sharedPreferences.getStringSet(MainActivity.REGIONS, null);
    }



************************************************************************
MainActivityFragment.java - resetQuiz()
************************************************************************
    // set up and start the next quiz
    public void resetQuiz() {
        // use AssetManager to get image file names for enabled regions
        AssetManager assets = getActivity().getAssets();
        fileNameList.clear();   // empty list of already used image file names

        try {
            // loop through each region
            for (String region : regionsSet) {
                // get a list of all flag image files in this region
                String[] paths = assets.list(region);

                for (String path : paths) {
                    fileNameList.add(path.replace(".png", ""));
                }
            }
        } catch (IOException e) {
            Log.e(LOG_TAG, "Error loading image file names", e);
        }

        correctAnswers = 0;         // reset the number of correct answers made
        totalGuesses = 0;           // reset the total number of guesses the user mode
        quizCountriesList.clear();  // clear prior list of quiz countries

        int flagCounter = 1;
        int numberOfFlags = fileNameList.size();

        // add FLAGS_IN_QUIZ random file names to the quizCountriesList
        while (flagCounter <= FLAGS_IN_QUIZ) {
            int randomIndex = random.nextInt(numberOfFlags);

            // get the random file name
            String filename = fileNameList.get(randomIndex);

            // if the region is enabled and it hasn't already been chosen
            if (!quizCountriesList.contains(filename)) {
                quizCountriesList.add(filename);
                flagCounter++;
            }
        }

        loadNextFlag();  // start the quiz by loading the first flag
    }


************************************************************************
MainActivityFragment.java - loadNextFlag()
************************************************************************
    // after the user guesses a correct flag, load the next flag
    private void loadNextFlag() {
        // get file name of the next flag and remove it from the list
        String nextImage = quizCountriesList.remove(0);
        correctAnswer = nextImage;      // update the correct answer
        answerTextView.setText("");     // clear answerTextView

        // display current question number
        questionNumberTextView.setText(getString(
                R.string.question, (correctAnswers + 1), FLAGS_IN_QUIZ));

        // extract the region from the next image's name
        String region = nextImage.substring(0, nextImage.indexOf('-'));

        // use AssetManager to load next image from assets folder
        AssetManager assets = getActivity().getAssets();

        // get an InputStream to the asset representing the next flag
        // and try to use the InputStream
        try (InputStream stream = assets.open(region + "/" + nextImage + ".png")) {
            // load the asset as a Drawable and display on the flagImageView
            Drawable flag = Drawable.createFromStream(stream, nextImage);
            flagImageView.setImageDrawable(flag);

            animate(false);                     // animate the flag onto the screen
        } catch (IOException e) {
            Log.e(LOG_TAG, "Error loading " + nextImage, e);
        }

        Collections.shuffle(fileNameList);      // shuffle file names

        // put the correct answer at the end of fileNameList
        int correct = fileNameList.indexOf(correctAnswer);
        fileNameList.add(fileNameList.remove(correct));

        // add 2, 4, 6 or 8 guess Buttons based on the value
        for (int row = 0; row < guessRows; row++) {
            // place Buttons in currentTableRow
            for (int column = 0; column < guessLinearLayouts[row].getChildCount(); column++) {
                // get reference to Button to configure
                Button newGuessButton = (Button) guessLinearLayouts[row].getChildAt(column);
                newGuessButton.setEnabled(true);

                // get country name and set is as newGuessButton's text
                String fileName = fileNameList.get((row * 2) + column);
                newGuessButton.setText(getCountryName(fileName));
            }
        }

        // randomly replace one Button with the correct answer
        int row = random.nextInt(guessRows);                // pick random row
        int column = random.nextInt(2);                     // pick random column
        LinearLayout randomRow = guessLinearLayouts[row];   // get the row
        String countryName = getCountryName(correctAnswer);
        ((Button) randomRow.getChildAt(column)).setText(countryName);
    }



************************************************************************
MainActivityFragment.java - getCountryName()
************************************************************************
    private String getCountryName(String name) {
        return name.substring(name.indexOf('-') + 1).replace('_', ' ');
    }


************************************************************************
MainActivityFragment.java - animate()
************************************************************************
    // animates the entire quizLinearLayout on or off screen
    private void animate(boolean animateOut) {
        // prevent animation into the UI for the first flag
        if (correctAnswers == 0) {
            return;
        }
        
        // calcualte center x and center y
        int centerX = (quizLinearLayout.getLeft() + quizLinearLayout.getRight()) / 2;
        int centerY = (quizLinearLayout.getTop() + quizLinearLayout.getBottom()) / 2;
        
        // calculate animation radius
        int radius = Math.max(quizLinearLayout.getWidth(), quizLinearLayout.getHeight());
        
        Animator animator;
        
        // if the quizLinearLayout should animate out rathe than in
        if (animateOut) {
            // create circular reveal animation
            animator = ViewAnimationUtils.createCircularReveal(
                    quizLinearLayout, centerX, centerY, radius, 0);
            animator.addListener(new AnimatorListenerAdapter() {
                // called when the animation finishes
                @Override
                public void onAnimationEnd(Animator animation) {
                    loadNextFlag();
                }
            });
        } else { // if the quizLinearLayout should animate in
            animator = ViewAnimationUtils.createCircularReveal(
                    quizLinearLayout, centerX, centerY, 0, radius);
        } 
        animator.setDuration(500); // set animation duration to 500ms
        animator.start();
    }



************************************************************************
MainActivityFragment.java - guessButtonListener()
************************************************************************
    // called when a guess Button is touched
    private View.OnClickListener guessButtonListener = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            Button guessButton = (Button) v;
            String guess = guessButton.getText().toString();
            String answer = getCountryName(correctAnswer);
            totalGuesses++; // increment number of guesses the user has made

            if (guess.equals(answer)) {     // if the guess is correct
                correctAnswers++;           // increment the number of correct answers

                // display correct answer in green text
                answerTextView.setText(answer + "!");
                answerTextView.setTextColor(getResources()
                        .getColor(R.color.correct_answer, getContext().getTheme())
                );

                disableButtons();           // disable all guess Buttons

                // if the user has correctly identified FLAGS_IN_QUIZ flags
                if (correctAnswers == FLAGS_IN_QUIZ) {
                    // DialogFragment to display quiz stats and start new quiz
                    DialogFragment quizResults =
                            new DialogFragment() {
                                // create an AlertDialog and return it

                                @NonNull
                                @Override
                                public Dialog onCreateDialog(Bundle bundle) {
                                    AlertDialog.Builder builder
                                            = new AlertDialog.Builder(getActivity());
                                    builder.setMessage(getString(R.string.results,
                                            totalGuesses,
                                            (1000 / (double) totalGuesses)));

                                    // "Reset Quiz" Button
                                    builder.setPositiveButton(R.string.reset_quiz,
                                            new DialogInterface.OnClickListener() {
                                                @Override
                                                public void onClick(DialogInterface dialog, int id) {
                                                    resetQuiz();
                                                }
                                            });
                                    return builder.create();
                                }
                            };

                    // use FragmentManager to display the DialogFragment
                    quizResults.setCancelable(false);
                    quizResults.show(getFragmentManager(), "quiz results");
                } else {    // answer is correct but quiz is not over
                    // load the next flag after a 2-second delay
                    handler.postDelayed(
                            new Runnable() {
                                @Override
                                public void run() {
                                    animate(true);  // animate the flag off the screen
                                }
                            }, 2000);       // 2000 milliseconds for 2-second delay
                }
            } else { // answer was incorrect
                flagImageView.startAnimation(shakeAnimation);   // play shake

                // display "Incorrect!" in red
                answerTextView.setText(R.string.incorrect_answer);
                answerTextView.setTextColor(getResources().getColor(
                        R.color.incorrect_answer, getContext().getTheme()));
                guessButton.setEnabled(false);  // disable incorrect answer
            }
        }
    };



************************************************************************
MainActivityFragment.java - disableButtons()
************************************************************************
    // utility method that disables all answer buttons
    private void disableButtons() {
        for (int row = 0; row < guessRows; row++) {
            LinearLayout guessRow = guessLinearLayouts[row];
            for (int i = 0; i < guessRow.getChildCount(); i++) {
                guessRow.getChildAt(i).setEnabled(false);
            }
        }
    }



************************************************************************
SettingsActivity.java
************************************************************************
public class SettingsActivity extends AppCompatActivity {
    // inflates the GUI, displays Toolbar and adds "up" button
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_settings);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    }
}



************************************************************************
SettingsActivityFragment.java 
************************************************************************
public class SettingsActivityFragment extends PreferenceFragment {
    // creates preferences GUI from preferences.xml file in res/xml
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        addPreferencesFromResource(R.xml.preferences); // load from xml
    }
}



************************************************************************
AndroidManifest.xml
************************************************************************
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="at.htl.flagquiz">

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:launchMode="singleTop"
            android:theme="@style/AppTheme.NoActionBar">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
        <activity
            android:name=".SettingsActivity"
            android:label="@string/title_activity_settings"
            android:parentActivityName=".MainActivity"
            android:theme="@style/AppTheme.NoActionBar">
            <meta-data
                android:name="android.support.PARENT_ACTIVITY"
                android:value="at.htl.flagquiz.MainActivity" />
        </activity>
    </application>

</manifest>


************************************************************************

************************************************************************