Develop Reference

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>

Firing an action to be executed when a button is pressed

Just started learning Java for application development through Android Studio. Creating an application that collects the user's inputs of which include their Name and Age of which when a Submition button is clicked the output is a string based on their Age range. code below:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Adding Action to the Button
Button BtnSubmit = findViewById(R.id.BtnSubmit);
BtnSubmit.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String TbName = "";
int TbAge =0;
String TxtOuput;
if (TbAge>0 && TbAge<=18)
{
TxtOuput = TbName + ("You Are Still A Child");
}
else if(TbAge>18 && TbAge<=64)
{
TxtOuput = TbName + ("You Are Grown");
}
else if(TbAge>64)
{
TxtOuput = TbName + ("You Are About To Die") + ("R.I.P");
}
}
});
}
}
Tried various methods from google, youtube and other sources but the application will not still execute an output.
Application layout/blueprint:

You are not getting your text fields values in a variable anywhere in code you have shared. Similarly you are not setting those values back to Status text field as well.
So it should be something like this:
If I assume you have firstEditText EditText View for name, secondEditText for age, and resultTextView for status, then your code would be something like below:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Adding Action to the Button
Button BtnSubmit = (Button)findViewById(R.id.BtnSubmit);
EditText firstEditText = (EditText) findViewById(R.id.firstEditText);
EditText secondEditText = (EditText) findViewById(R.id.secondEditText);
TextView resultTextView = (TextView) findViewById(R.id.resultTextView);
BtnSubmit.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String TbName = firstEditText.getText();
int TbAge = Integer.parseInt(secondEditText.getText().toString());
String TxtOuput;
if (TbAge>0 && TbAge<=18)
{
TxtOuput = TbName + ("You Are Still A Child");
}
else if(TbAge>18 && TbAge<=64)
{
TxtOuput = TbName + ("You Are Grown");
}
else if(TbAge>64)
{
TxtOuput = TbName + ("You Are About To Die") + ("R.I.P");
}
resultTextView.setText(TxtOuput);
}
});
}
}
Try this and let me know

AS per your question, you want user to add his name and age in the editText fields. When clicked on SUBMIT button, that entered data should be displayed on the next screen(activity).
To achieve this:
use 2 editText fields and 1 button in your xml layout file.
Problem:
You have added only button view in your layout file and not the editText.
Let me know if you want the code for the same then.

Best and easy way of using onclick listener,
In your xml layout,
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
xmlns:app="http://schemas.android.com/apk/res-auto"
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".activity.MainActivity">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:onclick="goToMethod"/>
</LinearLayout>
In your activity,
class MainActivity extends Activity{
public void goToMethod(View view){
//do your code here
}
}
Note: In tools:context you should mention the activity where you are using layout and onclick

How to validate decimal input not allowing alone "." and empty field?

I'm writing a calculator on Android Studio, in Java, and the app crashes if the user call the result with a dot "." alone or let the EditText field in blank.
I'm looking for a solution for not allowing these two conditions happening, together or individualy, in each of the three fields.
I've already tried TextWatcher and if/else but without success.
The .xml file where the editText field are designed is already set for decimalNumber.
I've already tried this:
if(myfieldhere.getText().toString().equals(".")){myfieldhere.setText("0");}
For each "valor line" and else for the "finalresult" line if everything is fine. Both inside the setOnClickListener block. This is my code:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.peso_layout);
result = findViewById(R.id.layresult);
conc = findViewById(R.id.layconc);
dose = findViewById(R.id.laydose);
peso = findViewById(R.id.laypeso);
calc = findViewById(R.id.laycalcpeso);
calc.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
float valor1 = Float.parseFloat(peso.getText().toString());
float valor2 = Float.parseFloat(conc.getText().toString());
float valor3 = Float.parseFloat(dose.getText().toString());
float finalresult = valor1 * valor2 * valor3;
result.setText("The result is: " + finalresult);
}
});
}
The ideal output should be the app not crashing if these two conditions happen and sending an error message to the user that input is invalid.
What i'm receiving is the app crashing.
Thank you very much. I'm very beginner in Java and I'm few days struggling with this.

Dear Friend, Your directly trying to convert string input into float and then after your check value but do your code like Below.
public class MainActivity extends AppCompatActivity implements View.OnClickListener {
EditText edt1,edt2;
TextView txtans;
Button btnsum;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
edt1=findViewById(R.id.edt1);
edt2=findViewById(R.id.edt2);
txtans=findViewById(R.id.txtans);
btnsum=findViewById(R.id.btnsum);
btnsum.setOnClickListener(this);
}
#Override
public void onClick(View v) {
if(v.getId()==R.id.btnsum){
float n1,n2;
String value1=edt1.getText().toString();
String value2=edt2.getText().toString();
if(value1.equals("") || value1.equals(".")){
n1=0;
}else {
n1= Float.parseFloat(value1);
}
if(value2.equals("")|| value2.equals(".")){
n2=0;
}else{
n2= Float.parseFloat(value2);
}
float ans=n1+n2;
txtans.setText(ans+"");
}
}
}
See In above code, First get value from edittext and then check wheather it contain null or "." inside it. if it contains then store 0.0 value in some variable. then after make sum and display in textbox.

calc.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
String myvalor = myfieldhere.getText().toString();
if(myvalor.equals(".") || myvalor.isEmpty())
{
// toast error : incorrect value
return;
}
try
{
float valor1 = Float.parseFloat(peso.getText().toString());
float valor2 = Float.parseFloat(conc.getText().toString());
float valor3 = Float.parseFloat(dose.getText().toString());
float finalresult = valor1 * valor2 * valor3;
result.setText("The result is: " + finalresult);
}
catch(Exception exp){// toast with exp.toString() as message}
}
});

use TextUtils for check empty String its better
if(TextUtils.isEmpty(peso.getText().toString())||
TextUtils.isEmpty(conc.getText().toString())||
TextUtils.isEmpty(dose.getText().toString())){
return;
}

How to update method to return updated information from textwatcher after pressing button

I have declared my variable, 'changed' too null so that I can check if it changes when the edittext is changed,
The problem I think is, when I press either the save button or the cancel button, it will always produce the value null, as upon clicking the button it is still null. However, I thought that the textwatcher would listen to the EditText and even if nothing was changed in the EditText it would by default change the SetChanged() to false as it provided "live updates", however clearly this isn't the case, am I doing something wrong? or am I supposed to approach it in a different way?, is there some way of refreshing it?
Advise would be greatly appreciated.
(P.S Some code was deleted to reduce the size and make it look easy on the eye, so excuse me for any missing braces. Furthermore, the activity does run properly as it shows the layout.However upon pressing any of the buttons it causes it to crash.)
public class EditNewItemActivity extends AppCompatActivity{
private Boolean changed = null;
private TextView title,content;
private Button saveBtn,cancelBtn;
private String date;
private int id;
#Override
protected void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_edit_item);
title = (TextView) findViewById(R.id.editItemTitle);
content = (TextView) findViewById(R.id.editItemDescription);
saveBtn = (Button) findViewById(R.id.editItemSaveBtn);
cancelBtn = (Button) findViewById(R.id.editItemCancelBtn);
Bundle extras = getIntent().getExtras();
title.setText(extras.getString("title"));
content.setText(extras.getString("content"));
date = extras.getString("date");
id = extras.getInt("id");
GenericTextWatcher textWatcher = new GenericTextWatcher();
title.addTextChangedListener(textWatcher);
content.addTextChangedListener(textWatcher);
ClickEvent clickEvent = new ClickEvent();
saveBtn.setOnClickListener(clickEvent);
cancelBtn.setOnClickListener(clickEvent);
}
private class ClickEvent implements View.OnClickListener{
#Override
public void onClick(View v) {
switch (v.getId()){
case R.id.editItemSaveBtn:
save();
break;
case R.id.editItemCancelBtn:
cancel();
break;
}
}
}
private void cancel() {
if (getChanged() == null){
//This was used to simply verify that getchanged was still null.
}
if (title.getText().toString() != "" || content.getText().toString() != ""){
if (getChanged() == false) {
// if nothing has been changed let it cancel etc
}else {
}
}
}
private void save() {
if (tempTitle != "" || tempContent != "") {
if(getChanged() == true){
}
}
public Boolean getChanged() {
return changed;
}
public void setChanged(Boolean changed) {
this.changed = changed;
}
private class GenericTextWatcher implements TextWatcher{
#Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
Log.v("Beforetext:", s.toString());
EditNewItemActivity editItem = new EditNewItemActivity();
editItem.setChanged(false);
}
#Override
public void afterTextChanged(Editable s) {
Log.v("afterTextChanged:", s.toString());
EditNewItemActivity editItem = new EditNewItemActivity();
editItem.setChanged(true);
Log.v("Status:", editItem.getChanged().toString());
}
}

You had change the changed. But which you changed is in your new EditNewItemActivity not in your current page.
This is where you made mistake (beforeTextChanged and afterTextChanged in your GenericTextWatcher):
EditNewItemActivity editItem = new EditNewItemActivity();
editItem.setChanged(false); //or true
You should just call:
setChanged(false); // or true
In fact, you should not new an activity yourself, activity must be create by the Android Framework so that it can be managed by the system.

Changing textview on edittext ( when possible without a button)

I'm kinda new to java programming for android, so if i make stupid mistakes, i'm sorry.
So basically, what i wanna make is an app where if you type in the answer correctly, the next textview is gonna be displayed. And when the next textView is displayed, you're needing to give a answer to that textView, when the answer is given correctly. The textview changes again. And so on.
Does anybody have an idea how to do this?
If you don't undarstand what im saying, here is a example:
public class Game extends AppCompatActivity {
public static EditText editText_ans;
public static TextView textView_1;
String enteredText = editText.getText().toString();
If(enteredText = 3 && textView_1 = #string/1+2){
setText.textView_1(#string/3+4)
}
If(enteredText = 7 && textView_1 = #string/3+4){
setText.textView_1("100 - 23")
I'm really stuck and i hope that you guys wanna help me.

If you wanted to change the view without button you can use method addTextChangeListner() which will notify you when when the text hasbeen change for particular edittext.
edittext.addTextChangedListener(textWatcher);
private final TextWatcher textWatcher = new TextWatcher() {
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}
public void onTextChanged(CharSequence s, int start, int before, int count) {
textView.setVisibility(View.VISIBLE);
}
public void afterTextChanged(Editable s) {
if (s.length() == 0) {
textView.setVisibility(View.GONE);
} else{
textView.setText("You have entered : " + editText.getText());
}
}
};

int x=0; //to keep track of qustions
private List<String> mQuestionList=new ArrayList<>(); //array of question
private List<String> mAnswerList=new ArrayList<>(); //array of question answer
displayquestion.settext(mQuestionList.get(x);//displayquestion is textview
//nextquestion is the button when user click it will first check answer and than move to next question if answer is correct
nextquestion.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String answer=editText.getText().toString();
if(answer.equal(mAnswerList.get(x)){
x=x+1;
displayquestion.settext(mQuestionList.get(x); //answer is correct display next quesion
}else{
//wrong answer
}
}
});