We Keep Coding

Android: I am having trouble opening the UI from MainActivity after creating intent [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 4 years ago.
I am having trouble accessing my UIs from MainActivity after creating the Intent methods.My app crashes when I select the SelectPLayer and SelectPLayer2 activities from my MainActivity. I am also having trouble getting the Clickable ListViews to go to the specified TextView in GameEmulator.
//MainActivity.java
//Class to select player 1
public class SelectPlayer extends Activity {
//Public static array list with adapter to crete the array and reference for listview being sent by intent from AddPLayer class
public static ArrayList<String> list = new ArrayList<>();
public static ArrayAdapter<String> adapter;
ListView selectView;
TextView title;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.selectplayer);
//Identify selectview ListView
selectView = findViewById(R.id.selectview) ;
selectView.setClickable(true);
selectView.setVisibility(View.VISIBLE);
//Using adapter for ListView menu
adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,list);
selectView.setAdapter(adapter);
selectView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String item =(String) parent.getItemAtPosition(position); // finding the item which has been clicked by the user
Intent intent = new Intent(SelectPlayer.this, GameEmulator.class); //starting an intent to call GameEmulator Activity
intent.putExtra(GameEmulator.value, item);// Putting the value clicked by user in intent
startActivity(intent); // starting GameEmulator Activity
}
});
//Using intent to retrieve string from AddPlayer Activity
Intent i = getIntent();
String data = i.getExtras().getString("text_key");
list.add(data);
changeList();
}
public static void changeList()
{
adapter.notifyDataSetChanged();
}
}
//Addplayer.java
import android.app.Activity;
import android.view.View;
import android.widget.EditText;
import android.os.Bundle;
import android.widget.Button;
import android.content.Intent;
//Addplayer class to add players using intent to separate activities
public class AddPlayer extends Activity{
//Declare buttons and edittext
Button listButtonplayer1;
Button listButtonplayer2;
EditText playerIn;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.playerinput);
//Identify buttons and editext
playerIn = (EditText) findViewById(R.id.inputname);
listButtonplayer1 = (Button)findViewById(R.id.addbutton);
listButtonplayer1.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//Using intent to send input to SelectPLayer Class
Intent i = new Intent(AddPlayer.this,SelectPlayer.class);
//Using string text_key to get and send string through intent
i.putExtra("text_key", playerIn.getText().toString());
//Start intent activity
startActivity(i);
}
});
//Second button I am trying to use for SelectPLayer2 activity only.
listButtonplayer2 = (Button)findViewById(R.id.addbutton2);
listButtonplayer2.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
//Using intent to send input to SelectPLayer2 Class
Intent in = new Intent(AddPlayer.this, SelectPlayer2.class);
in.putExtra("text_key", playerIn.getText().toString());
startActivity(in);
}
});
}
}
Selectplayer1.java
//Class to select player 1
public class SelectPlayer extends Activity {
//Public static array list with adapter to crete the array and reference for listview being sent by intent from AddPLayer class
public static ArrayList<String> list = new ArrayList<>();
public static ArrayAdapter<String> adapter;
ListView selectView;
TextView title;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.selectplayer);
//Identify selectview ListView
selectView = findViewById(R.id.selectview) ;
selectView.setClickable(true);
selectView.setVisibility(View.VISIBLE);
//Using adapter for ListView menu
adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,list);
selectView.setAdapter(adapter);
selectView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String item =(String) parent.getItemAtPosition(position); // finding the item which has been clicked by the user
Intent intent = new Intent(SelectPlayer.this, GameEmulator.class); //starting an intent to call GameEmulator Activity
intent.putExtra(GameEmulator.value, item);// Putting the value clicked by user in intent
startActivity(intent); // starting GameEmulator Activity
}
});
//Using intent to retrieve string from AddPlayer Activity
Intent i = getIntent();
String data = i.getExtras().getString("text_key");
list.add(data);
changeList();
}
public static void changeList()
{
adapter.notifyDataSetChanged();
}
}
//Selectplayer2.java
//Class to select player 2
public class SelectPlayer2 extends Activity {
//Public static array list with adapter to crete the array and reference for listview being sent by intent from AddPLayer class
public static ArrayList<String> list1 = new ArrayList<>();
public static ArrayAdapter<String> adapter1;
ListView selectView2;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.selectplayer2);
selectView2 = (ListView) findViewById(R.id.selectview1);
selectView2.setClickable(true);
selectView2.setVisibility(View.VISIBLE);
//Using adapter for ListView menu
adapter1 = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,list1);
selectView2.setAdapter(adapter1);
selectView2.setOnItemClickListener(new AdapterView.OnItemClickListener() {
#Override
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
String item =(String) parent.getItemAtPosition(position); // finding the item which has been clicked by the user
Intent in = new Intent(SelectPlayer2.this, GameEmulator.class); //starting an intent to call GameEmulator Activity
in.putExtra(GameEmulator.value, item);// Putting the value clicked by user in intent
startActivity(in); // starting GameEmulator Activity
}
});
//Using intent to retrieve string from AddPlayer Activity
Intent in = getIntent();
String data = in.getExtras().getString("text_key");
list1.add(data);
changeList();
}
public static void changeList()
{
adapter1.notifyDataSetChanged();
}
}
I have seperate static array lists, but the listview clickables are still showing on both textviews in the GameEmulator class. Here is my error log trying to click the button for SelectPLayer UI:
07-17 23:41:37.296 13468-13468/com.example.ryan_.ryansplayersapp E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.ryan_.ryansplayersapp, PID: 13468
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.ryan_.ryansplayersapp/com.example.ryan_.ryansplayersapp.SelectPlayer}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6494)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.os.Bundle.getString(java.lang.String)' on a null object reference
at com.example.ryan_.ryansplayersapp.SelectPlayer.onCreate(SelectPlayer.java:47)
at android.app.Activity.performCreate(Activity.java:7009)
at android.app.Activity.performCreate(Activity.java:7000)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2731)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856) 
at android.app.ActivityThread.-wrap11(Unknown Source:0) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:164) 
at android.app.ActivityThread.main(ActivityThread.java:6494) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807) 

String data = i.getExtras().getString("text_key");
Your getExtras() is returning null. Make sure you initialise your intent properly.

App crashes when launching another activity

I searched everywhere for a solution to my problem, but couldn't get one.So, the problem is I want to launch another activity called FifthActivity from my MainActivity via the button but my activity keeps crashing. I checked the logcat and found this -
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.india.chemistry/com.example.india.chemistry.FifthActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
Below is my mainActivity java file.
package com.example.india.chemistry;
public class MainActivity extends AppCompatActivity {
private static boolean isRunning = false;
private Toolbar toolbar;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if(!isRunning)
{
isRunning = true;
startActivity(new Intent(this, Intro.class));//Play your video here
}
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void part_a( View View){
Intent intent1 = new Intent("com.example.india.chemistry.Second_Activity");
startActivity(intent1);
}
public void part_b( View View) {
Intent intent2 = new Intent("com.example.india.chemistry.ThirdActivity");
startActivity(intent2);
}
public void formulas( View View) {
Intent intent4 = new Intent(this,FifthActivity.class);
startActivity(intent4);
}
}
Below is my FifthActivity.java file.
package com.example.india.chemistry;
public class FifthActivity extends ActionBarActivity {
final Animation shake = AnimationUtils.loadAnimation(getApplicationContext(),
R.anim.shake);
final Animation bounce = AnimationUtils.loadAnimation(getApplicationContext(),R.anim.bounce);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_fifth);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.menu_fifth, menu);
return true;
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
int id = item.getItemId();
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
public void nernst(View View) {
Intent intentf1 = new Intent("com.example.india.chemistry.nernst_activity");
startActivity(intentf1);
}
public void waterhardness(View View) {
Intent intentf2 = new Intent("com.example.india.chemistry.WaterHardness");
startActivity(intentf2);
}
public void determinationOfCao(View view) {
Intent intentf3 = new Intent("com.example.india.chemistry.CementCao");
startActivity(intentf3);
}
public void COD_waste_water(View view) {
Intent intentf4 = new Intent("com.example.india.chemistry.COD");
startActivity(intentf4);
}
public void C_in_B(View view) {
Intent intentf5 = new Intent("com.example.india.chemistry.Copper_in_Brass");
startActivity(intentf5);
}
public void alkalinity(View view) {
Intent intentf6 = new Intent("com.example.india.chemistry.Alkalinity");
startActivity(intentf6);
}
public void haematite_ore(View view) {
Intent intentf7 = new Intent("com.example.india.chemistry.HaemetiteOre");
startActivity(intentf7);
}
public void colourimetry_copper(View view) {
Intent intentf8 = new Intent("com.example.india.chemistry.Colourimetric_Copper");
startActivity(intentf8);
}
public void potentiometry_fas(View view) {
Intent intentf9 = new Intent("com.example.india.chemistry.Potentiometry_fas");
startActivity(intentf9);
}
public void conductometry(View view) {
Intent intentf10 = new Intent("com.example.india.chemistry.Conductometry");
startActivity(intentf10);
}
public void pka(View view) {
Intent intentf11 = new Intent("com.example.india.chemistry.pka");
startActivity(intentf11);
}
}
Below is the logcat.
10-14 17:13:58.145 15430-15430/com.example.india.chemistry E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.india.chemistry, PID: 15430 java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.india.chemistry/com.example.india.chemistry.FifthActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2420)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2569)
at android.app.ActivityThread.access$900(ActivityThread.java:150)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1399)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:168)
at android.app.ActivityThread.main(ActivityThread.java:5885)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:797)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:687)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.Context android.content.Context.getApplicationContext()' on a null object reference
at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:107)
at com.example.india.chemistry.FifthActivity.<init>(FifthActivity.java:21)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1085)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2410)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2569) 
at android.app.ActivityThread.access$900(ActivityThread.java:150) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1399) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:168) 
at android.app.ActivityThread.main(ActivityThread.java:5885) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:797) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:687) 
Please help me.

You can't call getApplicationContext(result in null) before oncreate because activity has not been created properly yet so you need to call this once your oncreate has been executed or after the super call .
The super call of onCreate fetches the application context for your activity.
Solution :
So either put your code inside oncreate or create a function and call it from inside oncreate after the super call.
Note : you will have to avoid final to make your identifiers global because the lazy initialization with final only works with constructors but don't worry , onCreate gets executed once when your activity is created or recreated.

Try this and let me know if problem solved or not.....
Animation shake,bounce;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_fifth);
shake = AnimationUtils.loadAnimation(getApplicationContext(),R.anim.shake);
bounce = AnimationUtils.loadAnimation(getApplicationContext(),R.anim.bounce);
}

You need to add the activity in your manifest file, under application. Whenever you create a new activity add it to manifest file.
<application
...
<activity
android:name=". FifthActivity"
android:label="Fifth" />
...
</application>
Hope this helps.

try this:
public class FifthActivity extends ActionBarActivity {
Animation shake,bounce;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_fifth);
shake = AnimationUtils.loadAnimation(getApplicationContext(),
R.anim.shake);
bounce = AnimationUtils.loadAnimation(getApplicationContext(),R.anim.bounce);
}

Your view has not yet been created, move :
shake = AnimationUtils.loadAnimation(getApplicationContext(),R.anim.shake);
bounce = AnimationUtils.loadAnimation(getApplicationContext(),R.anim.bounce);
To your oncreate method.

stack trace's first line gives Detailed information : getApplicationContext()' on a null object reference.Means Activity was not created,it's return null Context. You make a both animation's Object Globally. try to edit your code this way.
public class FifthActivity extends ActionBarActivity {
Animation shake,bounce;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_fifth);
shake = AnimationUtils.loadAnimation(getApplicationContext(),
R.anim.shake);
bounce = AnimationUtils.loadAnimation(getApplicationContext(),R.anim.bounce);
}
}

NullPointerException using fragment transactions [duplicate]

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 6 years ago.
I'm starting with android and just getting crazy with the implements of multiple fragments.
I have two fragments in my MainActivity: QuestionDetail and QuestionListFragment.
When I use a fragment transactions to replace the QuestionDetail fragment when someone click in one of the QuestionListFragment options I get a NullPointerException error.
I have been trying to fix this issue for hours. Any help is greatly appreciated.
QuestionDetail
public class QuestionListFragment extends Fragment{
private RecyclerView recView;
public static QuestionAdapter adapter;
private QuestionListener listener;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.fragment_question_list, container, false);
recView = (RecyclerView) v.findViewById(R.id.recView);
return v;
}
#Override
public void onActivityCreated(#Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
LinearLayoutManager layoutManager = new LinearLayoutManager(getActivity());
layoutManager.setOrientation(LinearLayoutManager.VERTICAL);
recView.setLayoutManager(layoutManager);
adapter = new QuestionAdapter(QuestionCatalog.getQuestionCatalog().getQuestionList().getList());
adapter.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
if (listener!=null) {
listener.onQuestionListener(adapter.getItem(recView.getChildAdapterPosition(v)));
}
}
});
recView.setAdapter(adapter);
}
public interface QuestionListener {
void onQuestionListener(Question q);
}
public void setQuestionListener(QuestionListener listener) {
this.listener=listener;
}
QuestionDetail
public class QuestionDetail extends Fragment {
// We use an ID to know which Question we're using
private long questionId;
public QuestionDetail() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
return inflater.inflate(R.layout.fragment_question_detail, container, false);
}
#Override
public void onStart() {
super.onStart();
//Fragments don’t include findViewById(). To get a reference to a view, we use getView()
View view = getView();
if (view != null) {
TextView title = (TextView) view.findViewById(R.id.textQuestion);
Question question = QuestionCatalog.getQuestionCatalog().getQuestionList().getList().get((int) questionId);
title.setText(question.getName());
TextView kind = (TextView) view.findViewById(R.id.textKind);
kind.setText(question.getKind());
}
}
public void showDetails(String texto) {
TextView txtName = (TextView)getView().findViewById(R.id.textQuestion);
TextView txtKind = (TextView)getView().findViewById(R.id.textKind);
txtName.setText(texto);
txtKind.setText(texto);
}
}
MainActivity
public class MainActivity extends AppCompatActivity implements QuestionListFragment.QuestionListener {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
QuestionListFragment frg =(QuestionListFragment)getFragmentManager().findFragmentById(R.id.listFragment);
frg.setQuestionListener(this);
}
#Override
public void onQuestionListener(Question q) {
Toast.makeText(this, "num: " + q.getName(),
Toast.LENGTH_LONG).show();
FragmentTransaction t = getSupportFragmentManager().beginTransaction();
QuestionDetail f1 = new QuestionDetail();
f1.showDetails(q.getName());
t.replace(R.id.detailFragment,f1);
t.addToBackStack(null);
t.commit();
}
stacktrace
08-04 09:54:11.914 22277-22277/com.hfad.predictandwin E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.NullPointerException
at com.hfad.predictandwin.Fragments.QuestionDetail.showDetails(QuestionDetail.java:50)
at com.hfad.predictandwin.MainActivity.onQuestionListener(MainActivity.java:34)
at com.hfad.predictandwin.Fragments.QuestionListFragment$1.onClick(QuestionListFragment.java:55)
at com.hfad.predictandwin.QuestionAdapter.onClick(QuestionAdapter.java:61)
at android.view.View.performClick(View.java:4475)
at android.view.View$PerformClick.run(View.java:18786)
at android.os.Handler.handleCallback(Handler.java:730)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:176)
at android.app.ActivityThread.main(ActivityThread.java:5419)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1046)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:862)
at dalvik.system.NativeStart.main(Native Method)

First, don't use getView() in onStart() - You shouldn't have a view to get at that point. Second, you shouldn't be calling methods directly on the Fragment instances from elsewhere, in your case f1.showDetails(q.getName());. There, again, the Fragment has no View. Please see Best practice for instantiating a new Android Fragment for how to pass arguments into Fragment before you load it into the FragmentManager.
Next point - you should initialize your views using findViewById inside of onCreateView just like you did for the other Fragment class. For example,
private TextView txtName, txtKind;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View rootView = inflater.inflate(R.layout.fragment_question_detail, container, false);
txtName = (TextView) rootView.findViewById(R.id.textQuestion);
txtKind = (TextView) rootView.findViewById(R.id.textKind);
// TODO: Read the link how to use these
Bundle arguments = getArguments();
Question question = QuestionCatalog.getQuestionCatalog()
.getQuestionList().getList().get((int) questionId);
showQuestion(question);
return view;
}
private void showQuestion(Question q) {
txtName.setText(q.getName());
txtKind.setText(q.getKind());
}

in QuestionListFragment:
We set click listener for recView, not adapter. You should replace adapter.setOnClickListener with
recView.addOnItemTouchListener(new RecyclerTouchListener(getApplicationContext(), recView, new ClickListener() {
#Override
public void onClick(View view, int position) {
// do something with position.
}
#Override
public void onLongClick(View view, int position) {
}
}));
in QuestionDetail:
questionId wasn't initialized but you have use it in this line:
Question question = QuestionCatalog.getQuestionCatalog().getQuestionList().getList().get((int) questionId);

Based on stacktrace and your code (not sure which one is line #50 in your QuestionDetail) ether txtName or txtKind evaluates to null (maybe both), so for whatever reason getView().findViewById(R.id.textQuestion) returns null. Probably because getView() in that call doesn't get you a parent view of the TextView in question

To Do app crash

I'm trying to make a To Do app in android studio. But as soon as I click on add-button (+ in top right corner) the app crashes. I am very new to java and android studio but I think the problem may lay in "saveListInfo()" but I can't figure out how to fix it...
Code from EditedActivity.java:
public class EditedActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_edited);
String name;
name = getIntent().getStringExtra("theName");
EditText editList = (EditText) findViewById(R.id.editText);
editList.setText(name);
}
private void saveListInfo() {
EditText editList = (EditText) findViewById(R.id.editText);
String name = editList.getText().toString();
Bundle listBundle = new Bundle();
listBundle.putString("name", name);
Intent finalIntent = new Intent(this, MainActivity.class);
finalIntent.putExtras(listBundle);
setResult(RESULT_OK, finalIntent);
}
Button addBtn = (Button) findViewById(R.id.add_btn);
{
addBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
saveListInfo();
}
});
}
}
Code from MainActivity.java:
public class MainActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
}
#Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.menu, menu);
return super.onCreateOptionsMenu(menu);
}
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.action_add_task:
saveTodoInfo();
}
return true;
}
private void saveTodoInfo(){
TextView nameView = (TextView) findViewById(R.id.action_add_task);
String name = nameView.getText().toString();
Intent myIntent = new Intent(this, EditedActivity.class);
myIntent.putExtra("theName", name);
startActivityForResult(myIntent, 0);
}
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
super.onActivityResult(requestCode, resultCode, data);
if (requestCode == 0){
if(resultCode == RESULT_OK){
Bundle ListBundle = data.getExtras();
String name = ListBundle.getString("theName");
updateToDo(name);
}
}
}
private void updateToDo(String name){
TextView nameView = (TextView) findViewById(R.id.action_add_task);
nameView.setText(name);
}
}
This is the error I get when clicking the add-button:
02-12 16:07:40.553 1410-1410/com.carpe_diem.anitas_todolist
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.carpe_diem.anitas_todolist, PID: 1410
java.lang.RuntimeException: Unable to instantiate activity
ComponentInfo{com.carpe_diem.anitas_todolist/com.carpe_diem.anitas_todolist.EditedActivity}:
java.lang.NullPointerException: Attempt to invoke virtual method
'android.view.View android.view.Window.findViewById(int)' on a null
object reference
at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2327)
at
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476)
at android.app.ActivityThread.-wrap11(ActivityThread.java)
at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual
method 'android.view.View android.view.Window.findViewById(int)' on a
null object reference
at android.app.Activity.findViewById(Activity.java:2090)
at
com.carpe_diem.anitas_todolist.EditedActivity.(EditedActivity.java:40)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1067)
at
android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2317)
at
android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2476) 
at android.app.ActivityThread.-wrap11(ActivityThread.java) 
at
android.app.ActivityThread$H.handleMessage(ActivityThread.java:1344) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:148) 
at android.app.ActivityThread.main(ActivityThread.java:5417) 
at java.lang.reflect.Method.invoke(Native Method) 
at
com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)

By the logs, we can see that you crash is happening in following line:
java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.Window.findViewById(int)' on a null object reference at
android.app.Activity.findViewById(Activity.java:2090) at
com.carpe_diem.anitas_todolist.EditedActivity.(EditedActivity.java:40)
...
After checking your code, I can find in line 40 (EditedActivity.java:40) that following code is outside of any method or function.
Button addBtn = (Button) findViewById(R.id.add_btn);
{
addBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
saveListInfo();
}
});
}
So, you have to move the lines above to onCreate() method.
EditedActivity.java
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_edited);
String name;
name = getIntent().getStringExtra("theName");
EditText editList = (EditText) findViewById(R.id.editText);
editList.setText(name);
Button addBtn = (Button) findViewById(R.id.add_btn);
addBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
saveListInfo();
}
});
}
Root Cause
If you leave the line below outside of any method, it will run during object instantiation.
Button addBtn = (Button) findViewById(R.id.add_btn);
However, during object creation, the view was not created yet. So, findViewById wont find anything and will return null. Thus, that CRASH (or Force Close) will happen.
Solution
So, make sure to add findViewById() inside a method which is called after the view was already created (otherwise, it will never find the view).
As you can see, I suggested to add at onCreate() method after setContentView(R.layout.activity_edited) (which is responsible to add the objects to VIEW).
After that line, findViewById() will be able to find the views (if you add them in the layout, of course).

Remove the brackets around this code
{
addBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
saveListInfo();
}
});
}
Should look like this
Button addBtn = (Button) findViewById(R.id.add_btn);
addBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
saveListInfo();
}
});
If you want to know why the crash happened, you can read more about What is an initialization block?

Create Custom AlertDialog requestFeature exception [duplicate]

This question already has answers here:
android.util.AndroidRuntimeException: requestFeature() must be called before adding content
(12 answers)
Closed 8 years ago.
I'm trying to create my own custom AlertDialog in a DialogFragment for a simple alarm clock application, and the code for the onCreateDialog method is below.
public class CreateAlarmSetting extends DialogFragment implements View.OnClickListener, AlertDialog.OnClickListener, TimePicker.OnTimeChangedListener, NumberPicker.OnValueChangeListener {
/*
the isEdit variable is set to true when an existing alarm time is clicked, this will add the
"delete" button to the dialog, to possibly delete the item from the listview
*/
private boolean isEdit = false;
public static final String ISEDIT_PARAM = "isEdit";
public static final String ALARMSETTING_PARAM = "AlarmSetting";
public AlarmSetting alarmSetting;
private TimePicker timePicker;
private NumberPicker numberPicker;
//private Button cancelButton, createButton, deleteButton;
//View of the dialog layout that will be inflated
private View main;
private OnFragmentInteractionListener mListener;
public CreateAlarmSetting() {
}
/*
Below are a few of the Fragment lifecycle methods
*/
public void setArguments(Bundle bundle) {
isEdit = bundle.getBoolean(ISEDIT_PARAM);
alarmSetting = (AlarmSetting) bundle.get(ALARMSETTING_PARAM);
}
#Override
public void onCreate(Bundle savedInstanceState) {
getActivity().requestWindowFeature(Window.FEATURE_ACTION_BAR);
super.onCreate(savedInstanceState);
/*
Not doing anything yet, because findViewById() doesn't work at this point in the lifecycle
*/
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
// TODO: check if this is to edit a current alarmSetting and add the save button and delete button
main = inflater.inflate(R.layout.fragment_create_alarm_setting, null);
//Initialize views and their listeners
timePicker = (TimePicker) main.findViewById(R.id.alarm_fragment_dialog_timepicker);
numberPicker = (NumberPicker) main.findViewById(R.id.alarm_fragment_dialog_numberpicker);
// cancelButton = (Button) main.findViewById(R.id.alarm_fragment_dialog_cancel_button);
// createButton = (Button) main.findViewById(R.id.alarm_fragment_dialog_create_button);
timePicker.setOnTimeChangedListener(this);
numberPicker.setOnValueChangedListener(this);
//cancelButton.setOnClickListener(this);
//createButton.setOnClickListener(this);
numberPicker.setMaxValue(45);
numberPicker.setMinValue(0);
//create display based on given parameters
/*
if (isEdit) {
// ViewGroup parent= (ViewGroup) main.findViewById(R.id.alarm_fragment_dialog_button_container);
deleteButton= (Button) main.findViewById(R.id.alarm_fragment_dialog_delete_button);
deleteButton.setText("Delete");
deleteButton.getLayoutParams().height= LinearLayout.LayoutParams.WRAP_CONTENT;
deleteButton.getLayoutParams().width= LinearLayout.LayoutParams.WRAP_CONTENT;
deleteButton.setOnClickListener(this);
createButton.setText("Save");
//TODO: Set Display Settings to current alarm settings, includes having cancel, delete, save buttons
timePicker.setCurrentHour(alarmSetting.getHours());
timePicker.setCurrentMinute(alarmSetting.getMinutes());
//Replace create button with the save add the delete button
ViewGroup parent= (ViewGroup) main.findViewById(R.id.alarm_fragment_dialog_button_container);
ViewGroup v=(ViewGroup) edit.findViewById(R.id.miscellaneous_items_container);
//v.removeView(edit.findViewById(R.id.alarm_fragment_dialog_delete_button));
parent.addView(edit.findViewById(R.id.alarm_fragment_dialog_delete_button), 1);
//Replace create button with save button
parent = (ViewGroup) createButton.getParent();
int index = parent.indexOfChild(createButton);
parent.removeView(createButton);
parent.addView(parent.findViewById(R.id.alarm_fragment_dialog_save_button), index);
}*/
return main;
}
#Override
public Dialog onCreateDialog(Bundle savedInstanceState) {
super.onCreateDialog(savedInstanceState);
if (main == null) {
main = getActivity().getLayoutInflater().inflate(R.layout.fragment_create_alarm_setting, null);
}
AlertDialog.Builder builder = new AlertDialog.Builder(getActivity());
builder.setView(main);
builder.setNegativeButton("Cancel", this);
builder.setPositiveButton("Create", this);
builder.setTitle("Create a new Alarm Setting");
AlertDialog alertDialog=builder.create();
//show or create?
return alertDialog;
}
// TODO: Rename method, update argument and hook method into UI event
public void onButtonPressed(Uri uri) {
if (mListener != null) {
mListener.onFragmentInteraction(uri);
}
}
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
mListener = (OnFragmentInteractionListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement OnFragmentInteractionListener");
}
}
#Override
public void onDetach() {
super.onDetach();
mListener = null;
}
/*
Below are listeners for the actions in the dialog
*/
#Override
public void onClick(DialogInterface dialogInterface, int id) {
switch (id) {
case DialogInterface.BUTTON_NEGATIVE:
case DialogInterface.BUTTON_NEUTRAL:
case DialogInterface.BUTTON_POSITIVE:
}
}
#Override
public void onValueChange(NumberPicker picker, int val, int num) {
//Do something
}
#Override
public void onTimeChanged(TimePicker picker, int hours, int minutes) {
if (alarmSetting != null) {
alarmSetting.setHours(hours);
alarmSetting.setMinutes(minutes);
} else alarmSetting = new AlarmSetting(hours, minutes, false);
}
#Override
public void onClick(View v) {
//do stuff for each button
switch (v.getId()) {
}
}
When I run this code in the emulator, I receive an exception saying
01-22 20:32:39.489 1883-1883/com.stanfordude.ryan.snooze E/AndroidRuntime﹕ FATAL EXCEPTION: main
android.util.AndroidRuntimeException: requestFeature() must be called before adding content
at com.android.internal.policy.impl.PhoneWindow.requestFeature(PhoneWindow.java:215)
at com.android.internal.app.AlertController.installContent(AlertController.java:234)
at android.app.AlertDialog.onCreate(AlertDialog.java:336)
at android.app.Dialog.dispatchOnCreate(Dialog.java:351)
at android.app.Dialog.show(Dialog.java:256)
at android.app.DialogFragment.onStart(DialogFragment.java:490)
at android.app.Fragment.performStart(Fragment.java:1570)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:863)
at android.app.FragmentManagerImpl.moveToState(FragmentManager.java:1035)
at android.app.BackStackRecord.run(BackStackRecord.java:635)
at android.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1397)
at android.app.FragmentManagerImpl$1.run(FragmentManager.java:426)
at android.os.Handler.handleCallback(Handler.java:615)
at android.os.Handler.dispatchMessage(Handler.java:92)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
How do I fix this?
Btw, sorry for my messy code and comments, I'm new to java

Its not the code as I can see from the error, its the requestWindowsFeature or something you have called before setContentView on the top. You should call the request before setting the contentView like this :
super.onCreate(savedInstanceState);
// Hiding title bar using code
requestWindowFeature(Window.FEATURE_NO_TITLE);
// Hiding status bar using code
getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
WindowManager.LayoutParams.FLAG_FULLSCREEN);
setContentView(R.layout.activity_main);