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App keeps crashing when ListView item is clicked on

Hello I am new to Java and coding in general.
I am using a ListView to display different sets of words which are stored in array. Clicking an item in the list will display the words in the array according to which item has been clicked. I have added the lines of the code that display the text and display a hint into an if statement and now my app keeps crashing when I click on the item 0.
Could someone please give me some advice?
Here is my code :
package com.example.anotherapp;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import java.util.ArrayList;
public class MainActivity extends AppCompatActivity {
int i = -1;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
chooseGame();
}
public void chooseGame() {
final ArrayList<String> arrayList = new ArrayList<String>();
final TextView wordTextView = findViewById(R.id.wordTextView);
final EditText editTextView = findViewById(R.id.enterEditText);
final Button nextButton = findViewById(R.id.nextButton);
ArrayList<String> gamesArrayList = new ArrayList<String>();
gamesArrayList.add("A Vegan's Worst Nightmare");
gamesArrayList.add("The Wet Floor Sign");
gamesArrayList.add("The Meaning of life");
gamesArrayList.add("Campfire Story");
gamesArrayList.add("The Crocobearamouse");
final ListView gamesListView = findViewById(R.id.gamesListView);
ArrayAdapter<String> arrayAdapter = new ArrayAdapter<String>(
this,
android.R.layout.simple_list_item_1,
gamesArrayList);
gamesListView.setAdapter(arrayAdapter);
gamesListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
if (position == 0) {
gamesListView.setVisibility(View.INVISIBLE);
editTextView.setVisibility((View.VISIBLE));
wordTextView.setVisibility((View.VISIBLE));
nextButton.setVisibility(View.VISIBLE);
String[] zeroArray = {"Food", "Adjective", "Proper Noun", "Name"};
String displayHint = "";
String displayText = "";
displayText = enterWord() + zeroArray[i];
displayHint = zeroArray[i];
wordTextView.setText(displayText);
editTextView.setHint(displayHint);
}
}
}
);
}
public String enterWord() {
String[] zeroArray = {"Food", "Adjective", "Proper Noun", "Name"};
String entry;
if (zeroArray[i].equals("Adjective")) {
entry = "Enter an ";
} else {
entry = "Enter a ";
}
return entry;
}
public void nextWord(View view) {
i++;
}
}

Your variable i start from -1, and your codes call array[i], I think it is main reason to make your app crash

Adapter not working inside asyncTask when notifyDataSetChanged?

i've got problem when trying to implement loadmore, exactly problem is adapter.notifyDataSetChanged inside AsyncTask. i trying to implement from this tuts https://github.com/shontauro/android-pulltorefresh-and-loadmore
, this tuts try implementing using extend ListActivity in Class, but i'm using extend Fragment, anyway this code is working, but just data not updated when trying to get data from loadmore. i'm sorry if my language is bad :)
this is my class :
import android.content.Intent;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.support.v4.view.PagerAdapter;
import android.support.v4.view.ViewPager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.BaseAdapter;
import android.widget.ListView;
import android.widget.TextView;
import com.bye.swipetab.adapter.ViewPagerAdapter;
import com.viewpagerindicator.CirclePageIndicator;
import com.viewpagerindicator.UnderlinePageIndicator;
import java.util.Arrays;
import java.util.LinkedList;
public class Tour extends Fragment {
private static final String TAG = Tour.class.getSimpleName();
View myView;
private String[] values ;
private static final String brand_value = "brand_value";
// Array of strings...
String[] mobileArray = {"Android","IPhone","WindowsMobile","Blackberry","WebOS"};
// list with the data to show in the listview
private LinkedList<String> mListItems;
// The data to be displayed in the ListView
private String[] mNames = { "Fabian", "Carlos", "Alex", "Andrea", "Karla",
"Freddy", "Lazaro", "Hector", "Carolina", "Edwin", "Jhon",
"Edelmira", "Andres" };
// Declare Variables
ViewPager viewPager;
PagerAdapter vAdapter;
String[] rank;
String[] country;
String[] population;
int[] flag;
UnderlinePageIndicator mIndicator;
ListView listView;
ArrayAdapter adapter;
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
myView = inflater.inflate(R.layout.tour_layout, null);
View header = inflater.inflate(R.layout.tour_header_layout, null);
//View footer = inflater.inflate(R.layout.tour_footer_layout, null);
listView = (ListView) myView.findViewById(android.R.id.list);
listView.addHeaderView(header, null, false); // header will not be clickable
mListItems = new LinkedList<String>();
mListItems.addAll(Arrays.asList(mNames));
adapter = new ArrayAdapter<String>(getActivity(), R.layout.tour_listview, R.id.MobileArray, mNames);
listView.setAdapter(adapter);
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
// When clicked, show a toast with the TextView text
String brand_text = ((TextView) view.findViewById(R.id.MobileArray)).getText().toString();
//Toast.makeText(getApplicationContext(),brand_text, Toast.LENGTH_SHORT).show();
// Starting single contact activity
Intent in = new Intent(getActivity(), TourActivity.class);
in.putExtra(brand_value, brand_text);
in.addFlags(Intent.FLAG_ACTIVITY_NO_ANIMATION);
startActivity(in);
}
});
population = new String[] {
"1,354,040,000",
"1,210,193,422",
"315,761,000",
"315,123,000",
"363,752,000" };
flag = new int[] {
R.drawable.offline_ide_4,
R.drawable.offline_ide_1,
R.drawable.offline_ide_2,
R.drawable.offline_ide_3,
R.drawable.offline_ide_5 };
// Locate the ViewPager in viewpager_main.xml
viewPager = (ViewPager) myView.findViewById(R.id.pager);
// Pass results to ViewPagerAdapter Class
vAdapter = new ViewPagerAdapter(getContext(), rank, country, population, flag);
// Binds the Adapter to the ViewPager
viewPager.setAdapter(vAdapter);
CirclePageIndicator indicator = (CirclePageIndicator)myView.findViewById(R.id.indicator);
indicator.setViewPager(viewPager);
final float density = getResources().getDisplayMetrics().density;
indicator.setRadius(5 * density);
//indicator.setBackgroundColor(0x7f0c006a);
//indicator.setPageColor(R.color.black);
//indicator.setFillColor(R.color.tab_bg_yellow_deep);
//indicator.setStrokeColor(R.color.tab_bg_yellow_deep);
//indicator.setStrokeWidth(2 * density);
// set a listener to be invoked when the list reaches the end
((LoadMoreListView) listView)
.setOnLoadMoreListener(new LoadMoreListView.OnLoadMoreListener() {
public void onLoadMore() {
// Do the work to load more items at the end of list
// here
new LoadDataTask().execute();
}
});
return myView;
}
private class LoadDataTask extends AsyncTask<Void, Void, Void> {
#Override
protected Void doInBackground(Void... params) {
if (isCancelled()) {
return null;
}
// Simulates a background task
try {
Thread.sleep(1000);
} catch (InterruptedException e) {
}
for (int i = 0; i < mobileArray.length; i++) {
mListItems.add(mobileArray[i]);
}
return null;
}
#Override
protected void onPostExecute(Void result) {
mListItems.add("Added after load more");
// We need notify the adapter that the data have been changed
adapter.notifyDataSetChanged();
// Call onLoadMoreComplete when the LoadMore task, has finished
((LoadMoreListView) listView).onLoadMoreComplete();
super.onPostExecute(result);
}
#Override
protected void onCancelled() {
// Notify the loading more operation has finished
((LoadMoreListView) listView).onLoadMoreComplete();
}
}
}
please tell me why this is not working ?

mListItems is not used for anything.
mNames is the one linked to the adapter, not mListItems which you are filling in the AsyncTask, may be you should review that.
mListItems.addAll(Arrays.asList(mNames));
adapter = new ArrayAdapter<String>(getActivity(), R.layout.tour_listview, R.id.MobileArray, mNames);
and then you do
for (int i = 0; i < mobileArray.length; i++) {
mListItems.add(mobileArray[i]);
}

"Real time" answer in a conversion program

How to code in java for real time output which displayed on the screen,as soon as user inputs some value with keyboard, with out a calculate button in activity in a simple conversion program? I have given the code below. In that it takes one input value and "FROM" and "TO" to convert the value and showed in the display with press of "calculate" button
Now I want to eliminate the "calculate" button and as soon as user inputs the numbers want to show the answer to the display
My code given below. Please let me know any additional information required
package sujaynambiar.textilecalculation;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
import java.util.ArrayList;
import java.util.List;
public class LengthConverter extends AppCompatActivity {
private Spinner spinner11, spinner21;
private EditText from;
private TextView to;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.lenght_converter);
Button btnSubmit = (Button) findViewById(R.id.btnSubmit1);
from = (EditText) findViewById(R.id.InputEditText1);
to = (TextView) findViewById(R.id.OutputTextView1);
spinner11 = (Spinner) findViewById(R.id.spinner11);
List<String> list1 = new ArrayList<String>();
list1.add("Kilometer");
list1.add("Meter");
list1.add("Centimeter");
list1.add("Millimeter");
list1.add("Feet");
list1.add("Yard");
list1.add("Inch");
list1.add("Mile");
ArrayAdapter<String> dataAdapter1 = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, list1);
dataAdapter1.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner11.setAdapter(dataAdapter1);
spinner21 = (Spinner) findViewById(R.id.spinner21);
List<String> list2 = new ArrayList<String>();
list2.add("Kilometer");
list2.add("Meter");
list2.add("Centimeter");
list2.add("Millimeter");
list2.add("Feet");
list2.add("Yard");
list2.add("Inch");
list2.add("Mile");
ArrayAdapter<String> dataAdapter2 = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, list2);
dataAdapter2.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner21.setAdapter(dataAdapter2);
}
public void onClick(View v)
{
int index1 = spinner11.getSelectedItemPosition();
int index2 = spinner21.getSelectedItemPosition();
double value = 0;
if (from.getText().toString().isEmpty())
Toast.makeText(getApplicationContext(), getResources().getString(R.string.toastmessage1),
Toast.LENGTH_LONG).show();
else {
value = Double.parseDouble(from.getText().toString());
}
//From Kilometer
if (index1 == 0 && index2 == 0 )//N
{
double result = value*1;
to.setText(result+"");
}

You are looking for a text change listener.
from.addTextChangedListener(new TextWatcher() {
#Override
public void beforeTextChanged(CharSequence s, int start, int count, int after) {
}
#Override
public void onTextChanged(CharSequence s, int start, int before, int count) {
calculateNewResult(s);
}
#Override
public void afterTextChanged(Editable s) {
}
});
You may also want to use an item select listener on the spinners.
mySpinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
#Override
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
updateTheCalculation();
}
#Override
public void onNothingSelected(AdapterView<?> parent) {
}
});

Error "must implement the inherited abstract method"

The error is solved and the app runs. The problem is how do i add a listener to the amound field in the app aswell? As the app is now it just sums up for ex "sek 1" + "usd 6.69" = "7.69".
Any good ideas how to make this work?
And here is my code:
package com.example.currencyconverter;
import android.app.Activity;
import android.os.Bundle;
import android.view.Menu;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Spinner;
import android.widget.TextView;
public class MainActivity extends Activity {
private String [] currency_name;
private ArrayAdapter<String> adapter;
private Spinner spin1, spin2;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
setUpTheSpinners();
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
return true;
}
private void setUpTheSpinners() {
currency_name = getResources().getStringArray(R.array.currency_name);
adapter= new ArrayAdapter<String>(this, android.R.layout.simple_spinner_item, currency_name);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
OnItemSelectedListener listener = new CurrencySelectedListener();
spin1 = (Spinner)findViewById(R.id.spinner1);
spin1.setAdapter(adapter);
spin1.setOnItemSelectedListener(listener);
spin2 = (Spinner)findViewById(R.id.spinner2);
spin2.setAdapter(adapter);
spin2.setOnItemSelectedListener(listener);
}
private void calculateSum() {
String [] rates = getResources().getStringArray(R.array.currency_rate);
int index1 = spin1.getSelectedItemPosition();
int index2 = spin2.getSelectedItemPosition();
double rate1 = Double.parseDouble( rates[index1] );
double rate2 = Double.parseDouble( rates[index2] );
double totalRate = rate1 + rate2;
TextView totalRateText = (TextView)findViewById(R.id.textView4);
totalRateText.setText("" + totalRate);
}
private class CurrencySelectedListener implements OnItemSelectedListener {
public void onItemSelected(AdapterView<?> parent, View view, int pos, long id) {
calculateSum();
}
public void onNothingSelected(AdapterView<?> parent) {
}
}
}

Null pointer exception while using Parcelable

I have made a java class 'store' which simply stores the values that I give through 2 spinners n one edittext...I pass the object of this class using parcelable to the intermediate class Spinpizza.java followed by Bill.java....It is showing the correct output till SpinPizza..(displays the values entered through spinner n edittext) but it gives NULL POINTER EXCEPTION IN Bill.java :-( Please help me...I m stuck with this for over 4 days..
Here is my code...
Store.java
package com.Lak;
import android.os.Parcel;
import android.os.Parcelable;
public class store implements Parcelable {
/**
*
*/
private static final long serialVersionUID = 1L;
private String pizzaname;
private String pizzasize;
private int n;
public void setOrder(String name,String size,int qty)
{
pizzaname = name;
pizzasize = size;
n = qty;
}
public String getPizzaName()
{
return pizzaname;
}
public int getQuantity()
{return n;}
public String getPizzaSize() {
// TODO Auto-generated method stub
return pizzasize;
}
public int describeContents() {
// TODO Auto-generated method stub
return 0;
}
#SuppressWarnings("rawtypes")
public static final Parcelable.Creator CREATOR = new Parcelable.Creator() {
public store createFromParcel(Parcel in) {
return new store(in);
}
public store[] newArray(int size) {
return new store[size];
}
};
public void writeToParcel(Parcel dest, int flags) {
dest.writeInt(n);
dest.writeString(pizzaname);
dest.writeString(pizzasize);
}
public store()
{}
public store(Parcel source){
/*
* Reconstruct from the Parcel
*/
n = source.readInt();
pizzaname = source.readString();
pizzasize = source.readString();
}
/** Called when the activity is first created. */
}
(SpinPizza.java)
package com.Lak;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.view.View.OnKeyListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
public class SpinPizza extends Activity{
/**
*
*/
private static final long serialVersionUID = 1L;
store B[]= new store[10];
Spinner s=null,s1=null;
EditText edittext=null;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.drop);
s = (Spinner) findViewById(R.id.spinner);
ArrayAdapter<?> adapter = ArrayAdapter.createFromResource(
this, R.array.pizzaarray, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
s.setAdapter(adapter);
s1 = (Spinner) findViewById(R.id.spinner1);
ArrayAdapter<?> adapter1 = ArrayAdapter.createFromResource(
this, R.array.sizearray, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
s1.setAdapter(adapter1);
edittext = (EditText) findViewById(R.id.edittext);
edittext.setOnKeyListener(new OnKeyListener() {
public boolean onKey(View v, int keyCode, KeyEvent event) {
// If the event is a key-down event on the "enter" button
if ((event.getAction() == KeyEvent.ACTION_DOWN) &&
(keyCode == KeyEvent.KEYCODE_ENTER || keyCode == KeyEvent.KEYCODE_DPAD_CENTER)) {
// Perform action on key press
int i=0;
B[i]=new store();
int n=Integer.parseInt(edittext.getText().toString());
B[i].setOrder(s.getSelectedItem().toString(), s1.getSelectedItem().toString(),n );
TextView objText=(TextView) findViewById(R.id.pl);
TextView objText1=(TextView) findViewById(R.id.pl2);
objText.setText(B[i].getPizzaName());
objText1.setText(B[i].getPizzaSize());
i++;
Toast.makeText(SpinPizza.this, edittext.getText(), Toast.LENGTH_SHORT).show();
return true;
}
return false;
}
});
Button next1 = (Button) findViewById(R.id.bill);
next1.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent myIntent = new Intent(view.getContext(), Bill.class);
for(int i =0;i<B.length;i++)
{
myIntent.putExtra("myclass"+i,B[i]);
}
myIntent.putExtra("length",B.length);
startActivityForResult(myIntent, 0);
}
});
}
}
(Bill.java)
package com.Lak;
import android.app.Activity;
import android.os.Bundle;
import android.view.ViewGroup.LayoutParams;
import android.widget.TableLayout;
import android.widget.TableRow;
import android.widget.TextView;
public class Bill extends Activity {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.setContentView(R.layout.calc);
store B[] = new store[10];
Bundle bj=getIntent().getExtras();
int length = bj.getInt("length");
for(int i = 0 ;i<length;i++)
{
B[i] = (store)bj.getParcelable("myClass"+i);
}
// B = (store[]) bj.get("myClass");
/* Find Tablelayout defined in main.xml */
TableLayout tl = (TableLayout)findViewById(R.id.myTable);
/* Create a new row to be added. */
TableRow tr = new TableRow(this);
tr.setLayoutParams(new LayoutParams(
LayoutParams.FILL_PARENT,
LayoutParams.WRAP_CONTENT));
/* Create TEXTVIEWS to be the row-content. */
for(int i=0;i<length;i++)
{ TextView b = new TextView(this);
b.setText(B[i].getPizzaName()); // NULL POINTER EXCEPTION :(
TextView b1 = new TextView(this);
b1.setText(B[i].getPizzaSize());
TextView b2 = new TextView(this);
b2.setText(B[i].getQuantity());
b.setLayoutParams(new LayoutParams(
LayoutParams.FILL_PARENT,
LayoutParams.WRAP_CONTENT));
b1.setLayoutParams(new LayoutParams(
LayoutParams.FILL_PARENT,
LayoutParams.WRAP_CONTENT));
b2.setLayoutParams(new LayoutParams(
LayoutParams.FILL_PARENT,
LayoutParams.WRAP_CONTENT));
/* Add TextViews to row. */
tr.addView(b);
tr.addView(b1);
tr.addView(b2);
/* Add row to TableLayout. */
tl.addView(tr,new TableLayout.LayoutParams(
LayoutParams.FILL_PARENT,
LayoutParams.WRAP_CONTENT));
}}
}

Well, if this line is throwing the exception:
b.setText(B[i].getPizzaName());
Then the options are:
b is null (definitely not; it's assigned a non-null value in the previous line)
B is null
B[i] is null
My money's on the last one. Here's how you initialize the array:
for(int i = 0 ;i<length;i++)
{
B[i] = (store)bj.getParcelable("myClass"+i);
}
Is there anything to say that getParcelable won't return null?
From the documentation for Bundle.getParcelable():
Returns the value associated with the given key, or null if no mapping of the desired type exists for the given key or a null value is explicitly associated with the key.
So my guess is that getParcelable is returning null. Now you need to find out why, and fix it. I'd also suggest using more conventional and descriptive names for your classes and variables.

Very old question indeed, but I got here in 2018 via a simple search and am using Kotlin so am gonna answer this for the future.
you can't actually do pacel on a final\val fields as the Parcelable interface can't write and re-write the values in it, either drop the final\val fields or don't incorporate them with your parceling scenarios.

This post is old, but the most common problem here is implementing the Parcelable interface for your class and then touching the fields and the methods, which may require you to re-implement the Parcelable interface or just add the missing.
I recommend you to install the Parcelable plugin for Android Studio or Eclipse and recreate the boiler plate.