Develop Reference

nullpointerexception error I do now know how to fix

where is error? how can I fix it? layout is true error in 24th line that
kaleciKayit.setOnClickListener(new View.OnClickListener() {
here is my all codes
public class oyuncuAdlariActivity extends AppCompatActivity {
Button kaleciKayit;
Button oyuncuKayit;
EditText isimGiris;
String isimGirisString;
int kaleciSayisi = 0;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_oyuncu_adlari);
kaleciKayit = (Button) findViewById(R.id.kaleciButton);
oyuncuKayit = (Button) findViewById(R.id.oyuncuButton);
isimGiris = (EditText) findViewById(R.id.isimGir);
kaleciKayit.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
kaleciSayisi++;
isimGirisString = isimGiris.getText().toString();
if (isimGirisString.isEmpty()){
Toast toast1 = Toast.makeText(getApplicationContext(),getApplicationContext().getString(R.string.isimBos), Toast.LENGTH_SHORT);
toast1.show();
}
else if (kaleciSayisi >2)
kaleciKayit.setEnabled(false);
}
});
}
}

First of all, I will recommend setting the objects in a class to private. I think the problem is that maybe you are assigning the id of the wrong widget? check the FindViewByID again.
The other 3 possibilities that I can think about are-
The problem is in the first activity(In this case I ask you to post here the content of the first activity)
The setContentView method points at a wrong XML file.
Your AVD ran out of memory and you need to add more to it in the AVD Manager tool.

Change MainActivity to this,
public class MainActivity extends AppCompatActivity {
Button devamButton;
EditText takim1, takim2;
String takimTextA;
String takimTextB;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
devamButton = findViewById(R.id.devamButton);
takim1 = findViewById(R.id.takimB);
takim2 = findViewById(R.id.takimA);
devamButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
takimTextA = takim1.getText().toString();
takimTextB = takim2.getText().toString();
if (takimTextA.equals(takimTextB)) {
Toast toast1 = Toast.makeText(getApplicationContext(),getApplicationContext().getString(takimAyniOlmaz), Toast.LENGTH_SHORT);
toast1.show();
} else if (takimTextA.isEmpty() || takimTextB.isEmpty()) {
Toast toast2 = Toast.makeText(getApplicationContext(), getApplicationContext().getString(R.string.takimBosBirakma), Toast.LENGTH_SHORT);
toast2.show();
} else {
activityGecis1(v);
}
}
});
}
private void activityGecis1(View v) {
Intent gecis1 = new Intent(v.getContext(), oyuncuAdlariActivity.class);
startActivity(gecis1);
}
Since you are calling inside onclicklistener maybe this in intent may point to that functions class.

Quiz app not showing dialog in last question

So when the last question is asked on the quiz, it doesn't show the dialog box if it is correct or not. And by the results screen the last question is always considered as 'correct'
public class MainGameActivity extends AppCompatActivity {
FButton buttonA, buttonB, buttonC, buttonD;
Button pause;
TextView questionText, triviaQuizText, timeText, resultText, coinText;
TriviaQuizHelper triviaQuizHelper;
TriviaQuestion currentQuestion;
MediaPlayer mysong;
List<TriviaQuestion> list;
int qid = 0;
int timeValue = 20;
int coinValue = 0;
CountDownTimer countDownTimer;
Typeface tb, sb;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_game_main);
mysong = MediaPlayer.create(MainGameActivity.this,R.raw.hs);
mysong.start();
int media_length;
//Initializing variables
questionText = (TextView) findViewById(R.id.triviaQuestion);
pause = (Button) findViewById(R.id.pause);
buttonA = (FButton) findViewById(R.id.buttonA);
buttonB = (FButton) findViewById(R.id.buttonB);
buttonC = (FButton) findViewById(R.id.buttonC);
buttonD = (FButton) findViewById(R.id.buttonD);
triviaQuizText = (TextView) findViewById(R.id.triviaQuizText);
timeText = (TextView) findViewById(R.id.timeText);
resultText = (TextView) findViewById(R.id.resultText);
coinText = (TextView) findViewById(R.id.coinText);
pause.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
pausedialog();
}
});
//Setting typefaces for textview and buttons - this will give stylish fonts on textview and button etc
tb = Typeface.createFromAsset(getAssets(), "fonts/TitilliumWeb-Bold.ttf");
sb = Typeface.createFromAsset(getAssets(), "fonts/shablagooital.ttf");
triviaQuizText.setTypeface(sb);
questionText.setTypeface(tb);
buttonA.setTypeface(tb);
buttonB.setTypeface(tb);
buttonC.setTypeface(tb);
buttonD.setTypeface(tb);
timeText.setTypeface(tb);
resultText.setTypeface(sb);
coinText.setTypeface(tb);
//Our database helper class
triviaQuizHelper = new TriviaQuizHelper(this);
//Make db writable
triviaQuizHelper.getWritableDatabase();
//It will check if the ques,options are already added in table or not
//If they are not added then the getAllOfTheQuestions() will return a list of size zero
if (triviaQuizHelper.getAllOfTheQuestions().size() == 0) {
//If not added then add the ques,options in table
triviaQuizHelper.allQuestion();
}
//This will return us a list of data type TriviaQuestion
list = triviaQuizHelper.getAllOfTheQuestions();
//Now we gonna shuffle the elements of the list so that we will get questions randomly
Collections.shuffle(list);
//currentQuestion will hold the que, 4 option and ans for particular id
currentQuestion = list.get(qid);
//countDownTimer
countDownTimer = new CountDownTimer(22000, 1000) {
public void onTick(long millisUntilFinished) {
//here you can have your logic to set text to timeText
timeText.setText(String.valueOf(timeValue) + "\"");
//With each iteration decrement the time by 1 sec
timeValue -= 1;
//This means the user is out of time so onFinished will called after this iteration
if (timeValue == -1) {
//Since user is out of time setText as time up
// resultText.setText(getString(R.string.timeup));
timeUp();
//Since user is out of time he won't be able to click any buttons
//therefore we will disable all four options buttons using this method
// disableButton();
}
}
//Now user is out of time
public void onFinish() {
//We will navigate him to the time up activity using below method
//timeUp();
}
}.start();
//This method will set the que and four options
updateQueAndOptions();
}
public void updateQueAndOptions() {
//This method will setText for que and options
questionText.setText(currentQuestion.getQuestion());
buttonA.setText(currentQuestion.getOptA());
buttonB.setText(currentQuestion.getOptB());
buttonC.setText(currentQuestion.getOptC());
buttonD.setText(currentQuestion.getOptD());
timeValue = 20;
//Now since the user has ans correct just reset timer back for another que- by cancel and start
countDownTimer.cancel();
countDownTimer.start();
//set the value of coin text
coinText.setText(String.valueOf(coinValue));
//Now since user has ans correct increment the coinvalue
coinValue++;
}
public void buttonA(View view) {
Button button = (Button) view;
buttonPressed(button);
}
public void buttonB(View view) {
Button button = (Button) view;
buttonPressed(button);
}
public void buttonC(View view) {
Button button = (Button) view;
buttonPressed(button);
}
public void buttonD(View view) {
Button button = (Button) view;
buttonPressed(button);
}
public void buttonPressed(Button button) {
if (qid < list.size() - 1) {
disableButton();
if (button.getText().equals(currentQuestion.getAnswer())) {
correctDialog();
} else {
incorrectDialog();
coinValue--;
}
} else {
gameWon();
}
}
//This method will navigate from current activity to GameWon
public void gameWon() {
Intent intent = new Intent(this, GameWon.class);
intent.putExtra("score", coinValue);
startActivity(intent);
finish();
}
//This method is called when user ans is wrong
//this method will navigate user to the activity PlayAgain
public void gameLostPlayAgain() {
Intent intent = new Intent(this, PlayAgain.class);
startActivity(intent);
finish();
}
//This method is called when time is up
//this method will navigate user to the activity Time_Up
public void timeUp() {
Intent intent = new Intent(this, Time_Up.class);
startActivity(intent);
finish();
}
//If user press home button and come in the game from memory then this
//method will continue the timer from the previous time it left
#Override
protected void onRestart() {
super.onRestart();
mysong.getCurrentPosition();
mysong.start();
countDownTimer.start();
}
//When activity is destroyed then this will cancel the timer
#Override
protected void onStop() {
super.onStop();
countDownTimer.cancel();
}
//This will pause the time/
#Override
protected void onPause() {
super.onPause();
mysong.pause();
countDownTimer.cancel();
}
//On BackPressed
#Override
public void onBackPressed() {
Intent intent = new Intent(this, HomeScreen.class);
startActivity(intent);
finish();
}
//This dialog is show to the user after he ans correct
public void correctDialog() {
final Dialog dialogCorrect = new Dialog(MainGameActivity.this);
dialogCorrect.requestWindowFeature(Window.FEATURE_NO_TITLE);
if (dialogCorrect.getWindow() != null) {
ColorDrawable colorDrawable = new ColorDrawable(Color.TRANSPARENT);
dialogCorrect.getWindow().setBackgroundDrawable(colorDrawable);
}
dialogCorrect.setContentView(R.layout.dialog_correct);
dialogCorrect.setCancelable(false);
dialogCorrect.show();
//Since the dialog is show to user just pause the timer in background
onPause();
onRestart();
TextView correctText = (TextView) dialogCorrect.findViewById(R.id.correctText);
FButton buttonNext = (FButton) dialogCorrect.findViewById(R.id.dialogNext);
//Setting type faces
correctText.setTypeface(sb);
buttonNext.setTypeface(sb);
//OnCLick listener to go next que
buttonNext.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
//This will dismiss the dialog
dialogCorrect.dismiss();
//it will increment the question number
qid++;
//get the que and 4 option and store in the currentQuestion
currentQuestion = list.get(qid);
//Now this method will set the new que and 4 options
updateQueAndOptions();
//reset the color of buttons back to white
resetColor();
//Enable button - remember we had disable them when user ans was correct in there particular button methods
enableButton();
}
});
}
//INCORRECT//////////////////////////////////////////////////////////////
public void incorrectDialog() {
final Dialog incorrectDialog = new Dialog(MainGameActivity.this);
incorrectDialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
if (incorrectDialog.getWindow() != null) {
ColorDrawable colorDrawable = new ColorDrawable(Color.TRANSPARENT);
incorrectDialog.getWindow().setBackgroundDrawable(colorDrawable);
}
incorrectDialog.setContentView(R.layout.dialog_incorrect);
incorrectDialog.setCancelable(false);
incorrectDialog.show();
//Since the dialog is show to user just pause the timer in background
onPause();
onRestart();
TextView IncorrectText = (TextView) incorrectDialog.findViewById(R.id.IncorrectText);
FButton buttonNext = (FButton) incorrectDialog.findViewById(R.id.dialogNext);
//Setting type faces
IncorrectText.setTypeface(sb);
buttonNext.setTypeface(sb);
//OnCLick listener to go next que
buttonNext.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
//This will dismiss the dialog
incorrectDialog.dismiss();
//it will increment the question number
qid++;
//get the que and 4 option and store in the currentQuestion
currentQuestion = list.get(qid);
//Now this method will set the new que and 4 options
updateQueAndOptions();
//reset the color of buttons back to white
resetColor();
//Enable button - remember we had disable them when user ans was correct in there particular button methods
enableButton();
}
});
}
//This method will make button color white again since our one button color was turned green
public void resetColor() {
buttonA.setButtonColor(ContextCompat.getColor(getApplicationContext(),R.color.white));
buttonB.setButtonColor(ContextCompat.getColor(getApplicationContext(),R.color.white));
buttonC.setButtonColor(ContextCompat.getColor(getApplicationContext(),R.color.white));
buttonD.setButtonColor(ContextCompat.getColor(getApplicationContext(),R.color.white));
}
//This method will disable all the option button
public void disableButton() {
buttonA.setEnabled(false);
buttonB.setEnabled(false);
buttonC.setEnabled(false);
buttonD.setEnabled(false);
}
//This method will all enable the option buttons
public void enableButton() {
buttonA.setEnabled(true);
buttonB.setEnabled(true);
buttonC.setEnabled(true);
buttonD.setEnabled(true);
}
public void pausedialog()
{
final Dialog pausedialog = new Dialog(MainGameActivity.this);
pausedialog.requestWindowFeature(Window.FEATURE_NO_TITLE);
if (pausedialog.getWindow() != null) {
ColorDrawable colorDrawable = new ColorDrawable(Color.TRANSPARENT);
pausedialog.getWindow().setBackgroundDrawable(colorDrawable);
}
pausedialog.setContentView(R.layout.activity_dialog_pause);
pausedialog.setCancelable(false);
pausedialog.show();
//Since the dialog is show to user just pause the timer in background
onPause();
Button resume = (FButton) pausedialog.findViewById(R.id.resume);
Button menu = (FButton) pausedialog.findViewById(R.id.menu);
Button music = (FButton) pausedialog.findViewById(R.id.music);
resume.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
//This will dismiss the dialog
pausedialog.dismiss();
onRestart();
}
});
menu.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
Intent intent2 = new Intent(MainGameActivity.this,HomeScreen.class);
// mysong.release();
// finish();
startActivity(intent2);
finish();
}
});
}
}
EDIT: posted the full code. I tried understanding it again but I don't know what to do anymore this may be the only problem I have left other than inserting images (that's another problem for now I wanna finish this)
EDIT: I tried fixing the if statements like this:
if (button.getText().equals(currentQuestion.getAnswer())) {
correctDialog();
} else {
incorrectDialog();
coinValue--;
}
if (qid < list.size() - 1) {
disableButton();
} else
{
gameWon();
}
It works now, the last answer is now also registered if right or wrong BUT the dialog box flashes for a split second and automatically goes to the results screen.

Why doesn't the intent of the button work

In my Code I have an Intent to an other Activity but when I use my Phone to test it nothing appears. The program doesn't crashes or something like that. It simply does nothing. I have another Intent and this works perfectly. I don't know what the problem is.
I am using the onClick feature on the xml file
On the Main Activity:
public class MainActivity extends AppCompatActivity {
private Object TextView;
int eggcounter;
Button b1;
android.widget.TextView textClicks;
private Object SafeBrowsingResponse;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final Button b1 = findViewById(R.id.b1);
eggcounter = 100;
final ImageButton ImgButton = findViewById(R.id.eggBtn);
ImgButton.setOnClickListener(
new View.OnClickListener() {
public void onClick(View view) {
eggcounter = eggcounter - 1;
updateEgg();
if (eggcounter < 80) {
ImgButton.setImageResource(R.drawable.egg_2);
if (eggcounter < 60){
ImgButton.setImageResource(R.drawable.egg_3);
if (eggcounter < 40) {
ImgButton.setImageResource(R.drawable.egg_4);
if (eggcounter < 15) { ImgButton.setImageResource(R.drawable.egg_5);
if (eggcounter <= 0) {
b1.setVisibility(View.VISIBLE);
ImgButton.setImageResource(R.drawable.egg_ende);
b1.setOnClickListener(
new View.OnClickListener() {
public void onClick(View view) {
}
}
);
}
}
}
}
}
}
}
);
}
public void updateEgg() {
textClicks = (TextView) findViewById(R.id.textScore);
textClicks.setText(eggcounter + " ");
}
public void backstartseite(View view) {
Intent back = new Intent(this, Startseite.class);
startActivity(back);
}
public void ende (View view) {
Intent e = new Intent(this, Ende.class);
startActivity(e);
}
}

You are never calling backStartSeite or ende therefore no Intent fires.
Also don't set the onClickListener of b1 inside another onClickListener (your listener for b1 will only be able to handle click events once the other button has been clicked already - this would confuse users).
If you want your Intent to work, call either startSeite or ende in the outer onClickListener.

How to implement "turn off music" button Android

I want to add a button in my application that turns off the music but I don't know how to approach it, I have an idea but I'm sure it's far from best so I want to consult with you. The situation is as follows:
public class MainActivity extends Activity implements OnClickListener {
MediaPlayer easysong;
MediaPlayer normalsong;
MediaPlayer hardsong;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.land_main);
mContext = this;
restartButton = (Button)findViewById(R.id.restartButton);
restartButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
easysong = MediaPlayer.create(MainActivity.this, R.raw.arideniro);
normalsong = MediaPlayer.create(MainActivity.this, R.raw.junior);
hardsong = MediaPlayer.create(MainActivity.this, R.raw.ketsathis);
counter = 101;
i = 500 - dif;
new Thread(new Runnable() {
public void run() {
if(i==500){
easysong.start();}
else if(i==375){
normalsong.start();
}else if(i==250){
hardsong.start();
}
while (counter > 0) {
try {
Thread.sleep(i);
} catch (InterruptedException e) {
e.printStackTrace();
}
counter--;
runOnUiThread(new Runnable() {
#Override
public void run() {
scoreText.setText(Integer.toString(counter));
}
});
if(i>150){
i/=1.01;}
else if(i>90-(dif/10)){
i-=1;
}
}if (counter==0) {
mChronometer.stop();
if(easysong.isPlaying()) {
easysong.stop();
easysong.release();
easysong = null;
}else if(normalsong.isPlaying()){
normalsong.stop();
normalsong.release();
normalsong = null;
}else if(hardsong.isPlaying()){
hardsong.stop();
hardsong.release();
hardsong = null;
}
This is the main class of my app where the mediaplayer is used, now I deleted much of the code because it was irrelevant to the mediaplayer and the question, so don't look for the missing brackets and such. And this here is the main menu class where the Switch that will turn on and off the music will be located:
public class MainMenu extends Activity{
private Button easy;
private Button normal;
private Button hard;
private Button scores;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main_menu);
easy = (Button) findViewById(R.id.btn_easy);
scores = (Button) findViewById(R.id.btn_highscores);
easy.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
dif = 0;
startGame();
}
});
}
public void startGame() {
Intent intent = new Intent(MainMenu.this, MainActivity.class);
startActivity(intent);
}
So my idea is simnple, to add a variable in MainActivity like "int p;" and from the MainMenu class to change it's state between 0 and 1, then I will add around each line that starts music an if(p==1) but is this a good approach ? Also I would like the value of the int to be saved when the app is closed

Destroy data on pressing back button in android

I have few activity files that contains almost same code as shown below. Well i have not included onDestroy and finish() method in all of my activity files, before moving forward i want to be sure of the code posted below.
public class Three extends AppCompatActivity {
Button forwardB,backwardB,homeB;
TextView textView2,textView4,textView5;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.one);
//Place advertisement here
AdView adView = (AdView) findViewById(R.id.adView);
AdRequest adRequest = new AdRequest.Builder()
.build();
adView.loadAd(adRequest);
//
//find widget by Id
forwardB = (Button) findViewById(R.id.forwardB);
backwardB = (Button) findViewById(R.id.backwardB);
homeB = (Button) findViewById(R.id.homeB);
textView2= (TextView) findViewById(R.id.textView2);
textView4 = (TextView) findViewById(R.id.textView4);
textView5 = (TextView) findViewById(R.id.textView5);
textView5.setText("3/50");
//set text inside textView3 and textView4
textView2.setText("Apfel");textView4.setText("apple");
//set on click listener for forward,backward and home button
forwardB.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent i = new Intent(getApplicationContext(), Two.class);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
startActivity(i);
finish();
}
});
homeB.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent i = new Intent(getApplicationContext(), MainActivity.class);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
startActivity(i);
finish();
}
});
backwardB.setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
Intent i = new Intent(getApplicationContext(), Four.class);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_CLEAR_TASK);
startActivity(i);
finish();
}
});
}
#Override
protected void onDestroy() {
super.onDestroy();
}
}
After running the application i found a serious issue with data,it looks like android keeps data in background. How can i avoid this?
Everytime i run app and check the data it seems to be increasing.
Well this is my MainActivity.java:
public class MainActivity extends Activity {
Button btnflashcards;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRequestedOrientation(ActivityInfo.SCREEN_ORIENTATION_PORTRAIT);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.activity_main);
//create widget ids that are usable forw rest of the code
btnflashcards = (Button) findViewById(R.id.btnflashcards);
}
//on flash card button click
public void findFlashCards(View v){
Intent i = new Intent(this, FlashCardSelection.class);
startActivity(i);
}
#Override
public void onBackPressed() {
Intent intent = new Intent(Intent.ACTION_MAIN);
intent.addCategory(Intent.CATEGORY_HOME);
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
startActivity(intent);
}
#Override
protected void onDestroy() {
super.onDestroy();
}
}

You will need to explicitly clear the application's user data every time you exit the aplication or at any point of time you want to during the use of your app.
Use this: ActivityManager's clearApplicationUserData() method
As per documentation this will:
Permits an application to erase its own data from disk. This is
equivalent to the user choosing to clear the app's data from within
the device settings UI. It erases all dynamic data associated with the
app -- its private data and data in its private area on external
storage -- but does not remove the installed application itself, nor
any OBB files.

Give something like this a shot
import java.io.File;
import android.app.Activity;
import android.content.Context;
import android.os.Bundle;
public class HelloWorld extends Activity {
/** Called when the activity is first created. */
#Override
public void onCreate(Bundle *) {
super.onCreate(*);
setContentView(R.layout.main);
}
#Override
protected void onStop(){
super.onStop();
}
//Fires after the OnStop() state
#Override
protected void onDestroy() {
super.onDestroy();
try {
trimCache(this);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public static void trimCache(Context context) {
try {
File dir = context.getCacheDir();
if (dir != null && dir.isDirectory()) {
deleteDir(dir);
}
} catch (Exception e) {
// TODO: handle exception
}
}
public static boolean deleteDir(File dir) {
if (dir != null && dir.isDirectory()) {
String[] children = dir.list();
for (int i = 0; i < children.length; i++) {
boolean success = deleteDir(new File(dir, children[i]));
if (!success) {
return false;
}
}
}
// The directory is now empty so delete it
return dir.delete();
}
}