Develop Reference

How to Randomized the questions and answer at once in quiz app multiple choices using Android Studio?

Here is the code of Question and Answer
public class QuestionAnswer {
public static String[] question ={
"Who invented C++ ?",
"Which is not the programming language ?",
"What is C++ ?",
"Which of the following is the correct syntax of including a user defined header files in C++ ?",
};
public static String[][] choices ={
{"Dennis Retchie","Ken Thompson","Brian Kernighan","Bjarne Stroustrup"},
{"Java","C++","Notepad++","Python"},
{"C++ is an object oriented programming language"
,"C++ is a procedural programming language"
,"C++ supports both procedural and object oriented programming language"
,"C++ is a functional programming language"},
{"#include [userdefined]","#include <userdefined.h>","#include “userdefined”","#include <userdefined>"},
};
public static String correctAnswer[]={
"Bjarne Stroustrup",
"Notepad++",
"C++ supports both procedural and object oriented programming language",
"#include “userdefined”",
};
}
Here is the code in Quiz
public class Quiz extends AppCompatActivity implements View.OnClickListener {
TextView totalQuestion_tv, question_tv,score_tv;
Button ansA, ansB, ansC, ansD, submitBtn,stopBtn;
int score;
int totalQuestion = QuestionAnswer.question.length;
int currentQuestionIndex = 0;
String selectedAnswer = "";
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_quiz);
getSupportActionBar().setDisplayHomeAsUpEnabled(false);
totalQuestion_tv = findViewById(R.id.total_question);
question_tv = findViewById(R.id.question);
score_tv = findViewById(R.id.my_score);
ansA = findViewById(R.id.ans_A);
ansB = findViewById(R.id.ans_B);
ansC = findViewById(R.id.ans_C);
ansD = findViewById(R.id.ans_D);
submitBtn = findViewById(R.id.submit_btn);
stopBtn = findViewById(R.id.stop_btn);
ansA.setOnClickListener(this);
ansB.setOnClickListener(this);
ansC.setOnClickListener(this);
ansD.setOnClickListener(this);
submitBtn.setOnClickListener(this);
stopBtn.setOnClickListener(this);
stopBtn.setBackgroundColor(Color.RED);
totalQuestion_tv.setText("Total Question: "+totalQuestion);
loadNewQuestion();
}
#Override
public void onClick(View v) {
ansA.setBackgroundColor(Color.WHITE);
ansB.setBackgroundColor(Color.WHITE);
ansC.setBackgroundColor(Color.WHITE);
ansD.setBackgroundColor(Color.WHITE);
Button click_btn = (Button) v;
if(click_btn.getId()==R.id.submit_btn){
if(selectedAnswer.equals(correctAnswer[currentQuestionIndex])) {
score++;
}
score_tv.setText("Score: "+score);
currentQuestionIndex++;
loadNewQuestion();
}
else if(click_btn.getId() == R.id.stop_btn){
new AlertDialog.Builder(this)
.setTitle(" Quit Quiz ")
.setMessage("Are you sure you want to quit ?")
.setPositiveButton("Quit",((dialogInterface, x) -> finishQuiz()))
.setNegativeButton("Cancel",((dialogInterface, x) -> loadNewQuestion()))
.setCancelable(false)
.show();
}
else{
selectedAnswer = click_btn.getText().toString();
click_btn.setBackgroundColor(Color.CYAN);
}
}
private void loadNewQuestion() {
ranDomized();
if(currentQuestionIndex==totalQuestion){
finishQuiz();
return;
}
question_tv.setText(question[currentQuestionIndex]);
ansA.setText(choices[currentQuestionIndex][0]);
ansB.setText(choices[currentQuestionIndex][1]);
ansC.setText(choices[currentQuestionIndex][2]);
ansD.setText(choices[currentQuestionIndex][3]);
}
void ranDomized(){
//Collections.shuffle(Arrays.asList(choices[currentQuestionIndex]));
Collections.shuffle(Arrays.asList(question));
choices.equals(question);
}
void finishQuiz() {
String passStatus = "";
if(score > totalQuestion*0.60){
passStatus = "Passed";
}else{
passStatus = "Failed";
}
score = 0;
new AlertDialog.Builder(this)
.setTitle(passStatus)
.setMessage("Score is: "+score+" out of "+ totalQuestion)
.setPositiveButton("Restart",((dialogInterface, i) -> restartQuiz()))
.setNegativeButton("Exit",((dialogInterface, i) -> finish()))
.setCancelable(false)
.show();
}
void restartQuiz() {
score = 0;
currentQuestionIndex = 0;
loadNewQuestion();
}
void correctAns(){
currentQuestionIndex++;
score_tv.setText("Score: "+score);
loadNewQuestion();
}
}
void ranDomized(){
//Collections.shuffle(Arrays.asList(choices[currentQuestionIndex]));
Collections.shuffle(Arrays.asList(question));
choices.equals(question);
}
I'm trying this code to randomized the questions, The question is randomly generates but not the choices, What I want is whatever the questions is, its choices will follow concurrently.
For Example:
If question number 3 will generate the choices of question in number 3 will follow
How can I do that Please Help, Thank you

You can create a new array that contains indexes and shuffle it. Then use those indexes to reference both arrays.
List<Integer> indices = Arrays.asList(0, 1, 2);
Collections.shuffle(indices);
String question = questions[indices.get(0)];
String answer = answers[indices.get(0)];

Android: How to run a loop controlled by one button (start/pause)

I am working on a program in java (android) I would like it to start and continue asking questions, upon button click, until the user is prompted for input, once input is received the program should resume asking the questions. The program should pause when the button is clicked again.
I am new to OOP and self taught. I thought that a thread was going to be the most practical way to solve the issue. I cannot get the program to both loop and allow user input. When trying to use HandlerThread I loose the ability to input data in the EditText. Could someone help with getting this loop to run on start click and loop after input?
I have a functional program that works when the button is cycled:
Main layout begins with "START" button, on click the start button turns to "PAUSE" and a seperate repeat button is made visible (and functional).
The values are generated, the question is asked, and the user is prompted by popping up the soft keyboard and setting the cursor in the EditText field.
Once an answer is received and the "enter/done" keyboard button is clicked, the answer will be evaluated against the saved values. But I cannot get the program to loop, or if I get it to loop it skips input completely and continues to as questions with no time for input.
Please direct me on code cleanliness if needed, I want to learn what I am doing incorrectly.
MAIN.java
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.speech.tts.TextToSpeech;
import android.text.TextUtils;
import android.view.KeyEvent;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
import java.util.Locale;
public class MainActivity extends AppCompatActivity {
// Create appropriate objects for buttons, edit text, and text to speech
TextToSpeech tts;
EditText txt;
Button sbtn, rbtn;
// Array and int to store numbers
int[] num;
int added = 0;
// Boolean to check if questions is running
public boolean isRunning;
// Variables for random number range. TODO(Put into switch statement and list to select 1, 10, or 100s)
static int maxNum = 100;
static int minNum = 10;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Initializing buttons and others
txt = findViewById(R.id.ans);
sbtn = findViewById(R.id.strButton);
rbtn = findViewById(R.id.rptButton);
rbtn.setVisibility(View.INVISIBLE);
// Initialize text to speech engine
tts = new TextToSpeech(getApplicationContext(), new TextToSpeech.OnInitListener() {
#Override
public void onInit(int status) {
if (status != TextToSpeech.ERROR) {
tts.setLanguage(Locale.ENGLISH);
}
}
});
// Start button click listener
sbtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
if (!isRunning) {
// Show repeat button, hide start and show pause
rbtn.setVisibility(View.VISIBLE);
sbtn.setText("Pause");
process();
isRunning = true;
} else {
sbtn.setText("Start");
rbtn.setVisibility(View.GONE);
isRunning = false;
}
}
});
// Repeat button click listener
rbtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
// Repeat recently generated numbers
Utilities.speakNums(num[0], num[1], tts);
}
});
}
public void onPause() {
if (tts != null) {
tts.stop();
tts.shutdown();
}
super.onPause();
}
// Get input and compare with stored values, announce if user answer is correct or incorrect
public void submitAns() {
txt.setOnKeyListener(new View.OnKeyListener() {
public boolean onKey(View v, int keyCode, KeyEvent event) {
// If the event is a key-down event on the "enter/done" button
if ((event.getAction() == KeyEvent.ACTION_DOWN) &&
(keyCode == KeyEvent.KEYCODE_ENTER)) {
// Check to make sure the text field is not empty
if (TextUtils.isEmpty(txt.getText().toString())) {
Toast.makeText(MainActivity.this, "Enter a Number!", Toast.LENGTH_SHORT).show();
return false;
}
int intValue = Integer.parseInt(txt.getText().toString());
if (added == intValue) {
Toast.makeText(MainActivity.this, "Correct", Toast.LENGTH_SHORT).show();
tts.speak("Correct", TextToSpeech.QUEUE_ADD, null, null);
} else {
Toast.makeText(MainActivity.this, added + " is the Correct Answer!", Toast.LENGTH_SHORT).show();
tts.speak("Incorrect", TextToSpeech.QUEUE_FLUSH, null, null);
Utilities.speakAns(added, tts);
tts.speak("is the Correct answer", TextToSpeech.QUEUE_ADD, null, null);
}
txt.setText("");
return true;
}
return false;
}
});
}
public void process() {
num = Utilities.askQuestion(minNum, maxNum, tts);
added = Utilities.add(num[0], num[1]);
Utilities.focus(txt, getApplicationContext());
submitAns();
}
}
UTILITIES.java
import android.content.Context;
import android.speech.tts.TextToSpeech;
import android.view.inputmethod.InputMethodManager;
import android.widget.EditText;
import java.util.Random;
public class Utilities {
// Function to generate random numbers in range
public static int randomGen(int minNum, int maxNum) {
final Random randNum = new Random();
return randNum.nextInt(maxNum - minNum) + minNum;
}
public static int add(int num1, int num2) {
return num1 + num2;
}
public static int sub(int num1, int num2) {
return num1 - num2;
}
// Speak individual numbers with operator in between speech
public static void speakNums(int r1, int r2, TextToSpeech tts) {
String toSpeak = Integer.toString(r1);
String nexToSpeak = Integer.toString(r2);
tts.speak(toSpeak, TextToSpeech.QUEUE_ADD, null, null);
tts.speak("Plus", TextToSpeech.QUEUE_ADD, null, null);
tts.speak(nexToSpeak, TextToSpeech.QUEUE_ADD, null, null);
}
// Speak answer
public static void speakAns(int a, TextToSpeech tts) {
String sumSpeak = Integer.toString(a);
tts.speak(sumSpeak, TextToSpeech.QUEUE_ADD, null, null);
}
// Request focus so that keyboard pops up as generate button is tapped
public static void focus(EditText txt, Context context) {
txt.requestFocus();
InputMethodManager imm = (InputMethodManager) context.getSystemService(Context.INPUT_METHOD_SERVICE);
imm.showSoftInput(txt, InputMethodManager.SHOW_IMPLICIT);
}
// Generate question, speak question, and return array of random numbers for other operations
public static int[] askQuestion(int minNum, int maxNum, TextToSpeech tts) {
int r1 = randomGen(minNum, maxNum);
int r2 = randomGen(minNum, maxNum);
speakNums(r1, r2, tts);
return new int[] { r1, r2};
}
}

If you want to have a repeating/infinite series of events that involve user interaction (like answering a question) you should set it up as a series of chained events rather than trying to use an actual code loop or handler thread.
An example of how this could be set up is:
Generate a question to show (e.g. "What is 12 + 54?")
When the user is done answering, call a "submit" method that checks their answer and either shows an error or generates a new question to show.
Repeat the cycle above for as long as you want. No loops or handler threads are needed for this.
In terms of architecture, separating out as much of the question-generation and answer-processing logic into a ViewModel will help you tremendously, then the activity can just observe the relevant state in the view model (like what question to show).
Here is a simple example based on the description and example code you provided. There is a ViewModel that handles creating a question, checking the answer, and advancing to a new question, and an Activity that observes the relevant state from the ViewModel. Try it out in a blank app project to understand how it works.
ViewModel
public class MainViewModel extends ViewModel {
// Error string to observe - to show an error message or toast
private final MutableLiveData<String> error = new MutableLiveData<>("");
LiveData<String> getError() {
return error;
}
// Current question to show
private final MutableLiveData<String> question = new MutableLiveData<>("");
LiveData<String> getQuestion() {
return question;
}
// Text to show on the start/pause button
private final MutableLiveData<String> startPauseButton = new MutableLiveData<>("START");
LiveData<String> getStartPauseButton() {
return startPauseButton;
}
// private internal state, e.g. current question,
// expected answer, play/pause state
private int expected = 0;
private String current_question = "";
private boolean playing = false;
private final Random random = new Random();
private final int minNum = 10;
private final int maxNum = 100;
private int getNumber() {
return random.nextInt(maxNum - minNum) + minNum;
}
// Process a user's answer, and either show an error
// message or generate a new question to show
void submitAnswer(String ans) {
try {
int a = Integer.parseInt(ans);
if( a == expected ) {
generateNewQuestion();
question.postValue(current_question);
}
else {
error.postValue("Incorrect answer, try again");
}
}
catch (NumberFormatException e) {
error.postValue("Not a number - enter a number");
}
}
private void generateNewQuestion() {
int a = getNumber();
int b = getNumber();
expected = a + b;
current_question = "What is " + a + " + " + b + "?";
}
void clearError() {
error.postValue("");
}
// Called when the user clicks the play/pause button
void clickStartPause() {
playing = !playing;
if( playing ) {
startPauseButton.postValue("PAUSE");
question.postValue(current_question);
}
else {
startPauseButton.postValue("START");
question.postValue("");
}
}
public MainViewModel() {
generateNewQuestion();
}
}
Activity
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
TextView question = findViewById(R.id.question);
EditText answer = findViewById(R.id.answer);
Button start = findViewById(R.id.start);
Button submit = findViewById(R.id.submit);
question.setVisibility(View.GONE);
answer.setVisibility(View.GONE);
submit.setVisibility(View.GONE);
MainViewModel model = new ViewModelProvider(this).get(MainViewModel.class);
// Observe the current question, and if it is blank
// hide the question/answer/submit views
final Observer<String> questionObserver = questionTxt -> {
if( questionTxt == null || questionTxt.isEmpty() ) {
question.setVisibility(View.GONE);
answer.setVisibility(View.GONE);
submit.setVisibility(View.GONE);
}
else {
question.setVisibility(View.VISIBLE);
answer.setVisibility(View.VISIBLE);
submit.setVisibility(View.VISIBLE);
question.setText(questionTxt);
}
};
// Observe the error state, if it is non-blank show
// a toast then reset the state (so the toast only shows once)
final Observer<String> errorObserver = errorText -> {
if( errorText != null && !errorText.isEmpty() ) {
Toast.makeText(this, errorText, Toast.LENGTH_LONG).show();
model.clearError();
}
};
model.getError().observe(this, errorObserver);
model.getQuestion().observe(this, questionObserver);
model.getStartPauseButton().observe(this, start::setText);
submit.setOnClickListener(v -> {
model.submitAnswer(answer.getText().toString());
answer.setText("");
});
start.setOnClickListener(v -> model.clickStartPause());
}
XML
<androidx.constraintlayout.widget.ConstraintLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:layout_width="match_parent"
android:layout_height="wrap_content">
<TextView
android:id="#+id/question"
android:layout_width="0dp"
android:layout_height="wrap_content"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toTopOf="parent"/>
<EditText
android:id="#+id/answer"
android:hint="Answer"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="#id/question"
android:layout_width="0dp"
android:layout_height="wrap_content" />
<Button
android:id="#+id/start"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Start"
app:layout_constraintStart_toStartOf="parent"
app:layout_constraintTop_toBottomOf="#id/answer"/>
<Button
android:id="#+id/submit"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Submit"
app:layout_constraintEnd_toEndOf="parent"
app:layout_constraintTop_toBottomOf="#id/answer"/>
</androidx.constraintlayout.widget.ConstraintLayout>

Firebase Realtime Database - Data from Code doesn't "reach" the database

I'm working with Firebase's realtime database in order to make a recipe application in android studio. The code runs fine and nothing crashes, but every time it's supposed to send information to the database, it does not. I attempted to create a shell for it to put data into, and instead, I saw it erase it once it got past the part where it was supposed to send the data. I've done all the required imports, implementations and dependencies according to their documentation, as well as wrote the code according to it too, but it doesn't seem to work.
Firebase Realtime Database before I send data, plus rules screenshot:
Firebase RD before
Firebase RD rules
After it runs the logic to send the data, I see it go red and disappear, like it was deleted, and nothing is left behind.
Here is my HomeScreen.java code:
package com.capteamfour.recipeappdatabase;
import android.content.Intent;
import android.os.Bundle;
import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import androidx.appcompat.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.TextView;
public class HomeScreen extends AppCompatActivity {
final FirebaseDatabase mDatabase = FirebaseDatabase.getInstance();
DatabaseReference mDatabaseUsers = mDatabase.getReference("USERS");
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_home_screen);
newUser(FirebaseAuth.getInstance().getCurrentUser().getDisplayName(),
FirebaseAuth.getInstance().getCurrentUser().getEmail());
String username = FirebaseAuth.getInstance().getCurrentUser().getDisplayName();
String email = FirebaseAuth.getInstance().getCurrentUser().getEmail();
TextView userWelcome = (TextView) findViewById(R.id.userWelcome);
FloatingActionButton addRecipe = (FloatingActionButton) findViewById(R.id.addRecipeButton);
ImageButton userProfile = (ImageButton) findViewById(R.id.userProfileButton);
// Welcomes the current user
userWelcome.setText("Welcome, " + username + "!");
// Creates a listener for the "add recipe" button; takes user to recipe form activity
addRecipe.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent toRecipeForm = new Intent(HomeScreen.this, recipeForm.class);
startActivity(toRecipeForm);
}
});
// Creates a listener for the "user Profile Button" button; takes user to profile activity
userProfile.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Intent ToProfile = new Intent(HomeScreen.this, Profile.class);
startActivity(ToProfile);
}
});
}
public void newUser(String name, String email)
{
userProfile user = new userProfile(name, email);
System.out.println("This is what I need to send: " + mDatabaseUsers.setValue(user));
mDatabaseUsers.setValue(user);
}
}
I declare a database instance and create a reference to the USERS path as global variables, and then made a function newUser(String name, String email) that creates an instance of a userProfile() class for me and is supposed to then send it to the database using the next line (the Sys.out was me trying to see what it was attempting to send if anything at all).
userProfile class code:
package com.capteamfour.recipeappdatabase;
import com.google.firebase.database.IgnoreExtraProperties;
import java.util.ArrayList;
import java.util.List;
#IgnoreExtraProperties
public class userProfile {
private String username;
private String email;
private List<Recipe> subRecipes = new ArrayList<>();
// Not yet implemented
private List<Recipe> favRecipes = new ArrayList<>();
private List<Recipe> savedRecipes = new ArrayList<>();
// A user profile will include their name, the recipes they've submitted, as well as recipes they've
// favorited or saved to their profile. Saved recipes are private to the user.
public userProfile() {
// Default constructor for DataSnapshot.getValue(userProfile.class) calls
}
public userProfile(String usernameIn, String emailIn)
{
this.username = username;
this.email = email;
}
public String getUsername () {
return this.username;
}
public String getEmail() {
return this.email;
}
/*
Each of these add functions will check the length of the given array and either
add to the end of it if there's already results, or just adds it on the empty array.
Example: array empty, then array[0] = recipe
array has values, then array[length + 1] = recipe
*/
public void addSubRecipe (Recipe recipe) {
int size = this.subRecipes.size();
if (size == 0) {
subRecipes.add(recipe);
}
else {
subRecipes.add(size+1, recipe);
}
}
public List<Recipe> getSubRecipes() {
return subRecipes.subList(0, (subRecipes.size()));
}
/*
These are commented out to prevent additional bugs and confusion while they're not implemented
public void addSavedRecipe (Recipe recipe) {
int size = this.savedRecipes.size();
if (size == 0) {
savedRecipes.add(recipe);
}
else {
savedRecipes.add(size + 1, recipe);
}
}
public List<Recipe> getSavedRecipes() {
return this.savedRecipes.subList(0, (subRecipes.size() + 1));
}
/*public void addFavRecipe (Recipe recipe) {
int size = this.favRecipes.size();
if (size == 0) {
favRecipes.add(recipe);
}
else {
favRecipes.add(size + 1, recipe);
}
}
public List<Recipe> getFavRecipes() {
return this.favRecipes.subList(0, (subRecipes.size() + 1));
}*/
}
In this class, I made sure to have an empty constructor with additional constructors and the usual get/set functions so that the database could work with it.
I appreciate any and all pointers that anyone could provide on how to fix this issue. This is for my college capstone course, and it's holding us up quite drastically for what appears to be no good reason. Thanks everyone.

Have at least one item selected in Android MultiSelectListPreference

I have search now for hours through the internet and have found nothing substantial so far. The thing that I want to do is a multi choice preference view, that disables the last item and reenables it, if it is not alone anymore.
I through so far about taking the super class force read the private variables in there to write my own onPrepareDialogBuilder(AlertDialog.Builder builder). Which is configuring its own OnMultiChoiceClickListener that jumps in, in the moment where has only one item left. The problem here is, that I use a bad practice force read of a private variable and that I have so far no idea how to get the checkbox item and how to disable it. But I think looking even deeper into the Android SDK will solve this problem.
At the end, if nothing works, solving the problem with doing an overwrite the OnPreferenceChangeListener to display a toast if the user has less than one item selected. But user friendliness is a high value, that needs to be earned and that often isn't easy.
Thx.
import android.content.Context;
import android.preference.MultiSelectListPreference;
import android.util.AttributeSet;
import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import georg.com.flironetest_01.Variables.Units;
/**
* Created by Georg on 16/03/16.
*/
public class UnitMultipleSelectorPreference extends MultiSelectListPreference {
public UnitMultipleSelectorPreference(Context context, AttributeSet attrs) {
super(context, attrs);
List<CharSequence> humanU = new ArrayList<>();
List<CharSequence> machineU = new ArrayList<>();
Units[] all = Units.values(); // Units is a enum with a rewriten to string statement.
for (Units elem : all) {
humanU.add(elem.toString());
machineU.add(elem.name());
}
setEntries(humanU.toArray(new CharSequence[humanU.size()]));
setEntryValues(machineU.toArray(new CharSequence[machineU.size()]));
Set<String> mU = new HashSet<>();
mU.add(Units.C.name());
mU.add(Units.K.name());
setDefaultValue(mU);
}
}

Okay. To answer my own question here after the motto "self is the man": I ended up with programming my own preference panel. Below is the code. If somebody likes to look over it and give some times how to make it even more stable: feel free.
But to sum up what I did: I created my own ArrayAdapter. But DialogPreference didn't allowed me to create my own multi selector. You need to change the final dialog fragment to create a working multi selector list (see here: https://stackoverflow.com/a/17907379/5759814). That is not an easy task if you work with the DialogPreferences. The reason is these few amounts of code:
/**
* Shows the dialog associated with this Preference. This is normally initiated
* automatically on clicking on the preference. Call this method if you need to
* show the dialog on some other event.
*
* #param state Optional instance state to restore on the dialog
*/
protected void showDialog(Bundle state) {
Context context = getContext();
mWhichButtonClicked = DialogInterface.BUTTON_NEGATIVE;
mBuilder = new AlertDialog.Builder(context)
.setTitle(mDialogTitle)
.setIcon(mDialogIcon)
.setPositiveButton(mPositiveButtonText, this)
.setNegativeButton(mNegativeButtonText, this);
View contentView = onCreateDialogView();
if (contentView != null) {
onBindDialogView(contentView);
mBuilder.setView(contentView);
} else {
mBuilder.setMessage(mDialogMessage);
}
onPrepareDialogBuilder(mBuilder);
getPreferenceManager().registerOnActivityDestroyListener(this);
// Create the dialog
final Dialog dialog = mDialog = mBuilder.create();
if (state != null) {
dialog.onRestoreInstanceState(state);
}
if (needInputMethod()) {
requestInputMethod(dialog);
}
dialog.setOnDismissListener(this);
dialog.show();
}
As you can see here is a method triggered to change my dialog builder with onPrepareDialogBuilder, but it doesn't seem like that there is any other function triggered afterwards, that would allow me to change the dialog directly after its creation. And the second idea of changing the onPrepareDialogBuilder so that I can init everything there, doesn't really help, because I end up with displayed dialog windows. That lead me to my decision of creating my completely own Preference class. With that decision I loose all those nice prepared functions like onRestoreInstanceState and Co, but I now have an application with a much more persistent flow, that doesn't do any stupid things when I select zero units for my thermal view.
Below the non commented code. I'm sorry, but I think its simple enough for everybody who landing here.
import android.app.AlertDialog;
import android.content.Context;
import android.content.DialogInterface;
import android.content.SharedPreferences;
import android.preference.Preference;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
import android.widget.AbsListView;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Set;
import georg.com.flironetest_01.Variables.Units;
/**
* Created by Georg on 16/03/16.
*/
public class UnitMultipleSelectorPreference extends Preference implements DialogInterface.OnClickListener, Preference.OnPreferenceClickListener {
String[] human_entries = null;
String[] machine_entries = null;
public SharedPreferences prev;
public UnitMultipleSelectorPreference(Context context, AttributeSet attrs) {
super(context, attrs);
prev = getSharedPreferences();
List<String> humanU = new ArrayList<>();
List<String> machineU = new ArrayList<>();
Units[] all = Units.values();
for (Units elem : all) {
humanU.add(elem.toString());
machineU.add(elem.name());
}
human_entries = humanU.toArray(new String[humanU.size()]);
machine_entries = machineU.toArray(new String[machineU.size()]);
Set<String> mU = new HashSet<>();
mU.add(Units.C.name());
mU.add(Units.K.name());
setDefaultValue(mU);
setOnPreferenceClickListener(this);
}
boolean[] selected = new boolean[0];
protected void onPrepareDialogBuilder(AlertDialog.Builder builder) {
if (prev == null)
return;
if (human_entries == null || machine_entries == null || human_entries.length != machine_entries.length ) {
throw new IllegalStateException(
"ListPreference requires an entries array and an entryValues array which are both the same length");
}
selected = new boolean[human_entries.length];
for (int i = 0; i < human_entries.length; i++)
selected[i] = prefSet.contains(machine_entries[i]);
String[] stringObj = new String[human_entries.length];
int i = 0;
for(CharSequence ch : human_entries)
stringObj[i++] = ch.toString();
builder.setAdapter(new MyAdapter(getContext(), android.R.layout.simple_list_item_multiple_choice, stringObj), new DialogInterface.OnClickListener() {
#Override
public void onClick(DialogInterface dialog, int which) {
}
});
AlertDialog mDialog = builder.create();
mDialog.getListView().setChoiceMode(AbsListView.CHOICE_MODE_MULTIPLE);
mDialog.getListView().setItemsCanFocus(false);
mDialog.getListView().setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// Manage selected items here
ListView mParent = (ListView)parent;
if (mParent.getCheckedItemCount() >= 1)
selected[position] = mParent.isItemChecked(position);
if (mParent.getCheckedItemCount() == 0)
mParent.setItemChecked(position, true);
}
});
mDialog.show();
i = 0;
for (boolean select : selected)
mDialog.getListView().setItemChecked(i++, select);
}
#Override
public boolean onPreferenceClick(Preference preference) {
AlertDialog.Builder mBuilder = new AlertDialog.Builder(getContext());
mBuilder.setTitle(getTitle())
.setPositiveButton(android.R.string.ok, this)
.setNegativeButton(android.R.string.cancel, this);
onPrepareDialogBuilder(mBuilder);
return true;
}
#Override
public void onClick(DialogInterface dialog, int which) {
Toast.makeText(getContext(), "W:"+which + " | " + Arrays.toString(selected), Toast.LENGTH_SHORT).show();
switch (which) {
case -1:
if (isPersistent()) {
prefSet = new HashSet<>();
for (int i = 0; i < selected.length; i++) {
if (selected[i])
prefSet.add(machine_entries[i]);
}
getEditor().putStringSet(getKey(), prefSet).apply();
Toast.makeText(getContext(), "W:"+which + " | " + getSharedPreferences().getStringSet(getKey(),null).toString(), Toast.LENGTH_SHORT).show();
}
return;
}
}
public class MyAdapter extends ArrayAdapter<String> {
public MyAdapter(Context context, int textViewResourceId, String[] objects) {
super(context, textViewResourceId, objects);
}
#Override
public boolean isEnabled(int n) {
return true;
}
}
Set<String> prefSet;
#Override
protected void onSetInitialValue(boolean restorePersistedValue, Object defaultValue) {
super.onSetInitialValue(restorePersistedValue, defaultValue);
prev = getSharedPreferences();
if(restorePersistedValue) {
prefSet = prev.getStringSet(getKey(), new HashSet<String>());
} else {
try {
prefSet = (Set<String>)defaultValue;
if(isPersistent())
getEditor().putStringSet(getKey(), prefSet);
} catch (ClassCastException e) {
Log.e("ERROR_CAST", "Error casting the default value to Set<String>.");
}
}
}
}

A really simple solution is to set a setOnPreferenceChangeListener and just return false if the new value would be empty.
All of the code is put into onCreatePreferences.
MultiSelectListPreference infoPreference = findPreference("information");
infoPreference.setOnPreferenceChangeListener(new Preference.OnPreferenceChangeListener() {
#Override
public boolean onPreferenceChange(Preference preference, Object newValue) {
if (size(newValue) == 0){
return false;
}
return true;
}
});

NullPointerException after changing class ( Code worked before )

I'm doing basic calculator for Android in Java. My calculator worked but i had all code in one class. Then i wanted to make code more readable and i created another Calculation class and i put calculation code in there. And now for some reason my app crashes. LogCat says: NullPointerException. (My app starts fine and then when i choose desirable currency to convert and when i click on ImageButton(convert) then app crashes). Here is my code:
CroToEu class:
package com.eu.calculator;
import android.app.Activity;
import android.os.Bundle;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageButton;
import android.widget.TextView;
public class CroToEur extends Activity {
TextView resultView;
#Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.cro_to_eur);
final ImageButton convert = (ImageButton) findViewById(R.id.converButton);
convertButton(convert);
}
private void convertButton(final ImageButton convert) {
resultView = (TextView) findViewById(R.id.resultView);
convert.setOnTouchListener(new View.OnTouchListener() {
#Override
public boolean onTouch(View v, MotionEvent event) {
Calculate now = new Calculate();
now.croToEu();
if(event.getAction() == MotionEvent.ACTION_DOWN) {
convert.setImageResource(R.drawable.convert_button_ontouch);
checkForEmptyEntry();
} else if (event.getAction() == MotionEvent.ACTION_UP) {
convert.setImageResource(R.drawable.convert_button);
}
return false;
}
private void checkForEmptyEntry() {
if(Calculate.HRKfield.getText() == null || "".equals(Calculate.HRKfield.getText().toString())) {
resultView.setText("You left empty field");
} else {
resultView.setText(Calculate.HRKfield.getText()+" HRK = "+Calculate.fixDecimal+" EUR");
}
}
});
}
}
And my calculation class:
package com.eu.calculator;
import java.math.BigDecimal;
import android.app.Activity;
import android.widget.EditText;
public class Calculate extends Activity {
public static EditText HRKfield; //S tem dobimo vrednost iz polja edittext
public static double EUR = 0.133;//drži vrednost
public static Double HRK; // Možnost uporabe double za parsing
public static double result; // rezultat
public static BigDecimal fixDecimal; // rezultat pretvori na decimalko
public BigDecimal croToEu() {
HRKfield = (EditText) findViewById(R.id.enterField);
try {
HRK = Double.parseDouble(HRKfield.getText().toString()); //tukaj dobimo čisto številko, ki jo uporabnik vnese v polje
result = HRK * EUR;
fixDecimal = new BigDecimal(result);
fixDecimal = fixDecimal.setScale(2, BigDecimal.ROUND_HALF_UP);
} catch (NumberFormatException e) {
}
return fixDecimal;
}
}

Don' t extend Calculate class with Activity . Remove extends Activity in Calculate class

If you are trying to just create a helper class whcih does the calculation for you then don't extend Activity on your Calculate class. Instead get your croToEu method to return a variable and call this from the other class as follows.
Calculate now = new Calculate();
BigDecimal val = now.croToEu();
Id actually have the caluclate class as follows
public abstract class Calculate {
public static final double EUR = 0.133;//drži vrednost
public static BigDecimal croToEu(double hrkValue) {
BigDecimal fixDecimal = new BigDecimal(hrkValue * EUR);
fixDecimal = fixDecimal.setScale(2, BigDecimal.ROUND_HALF_UP);
return fixDecimal;
}
}
Then in your main activity class call
BigDecimal val = Calculate.croToEu(hrkValue);

if(Calculate.HRKfield.getText() == null || "
this is wrong to get the view of other activity .........
you are in CroToEur and your acessing the HRKfield of Calculate activity which will be null
So should pass the data from CroToEur activity to Calculate activity using intent and set that in HRKfield in onCreate of CroToEur

You are missing your onCreate() method and even setContentView in Calculate.class and so it cannot find your edittext HRKfield, and so it is throwing NullpointerException