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how to fix android app crashing on startup? [duplicate]

This question already has answers here:
Null pointer Exception - findViewById()
(12 answers)
Closed 4 months ago.
i'm a begginner developer and the app in question is a test app for an api, from jkutner's tutorial on github. it is crashing as soon as it opens, which is weird, because i've used this exact same code at least thrice and it used to work. i'll leave the code and the logcat below, thank you in advance for your help!
MainActivity
package com.example.myapplication;
import androidx.appcompat.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import java.util.List;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;
public class MainActivity extends AppCompatActivity
{
final EditText isbnInput = (EditText) findViewById(R.id.isbnInput);
final TextView textView = (TextView) findViewById(R.id.textView);
final Button button = (Button) findViewById(R.id.button);
#Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Retrofit retrofit = new Retrofit.Builder()
.baseUrl("https://venusdove.herokuapp.com")
.addConverterFactory(GsonConverterFactory.create())
.build();
final BookService service = retrofit.create(BookService.class);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Book book = new Book(isbnInput.getText().toString());
Call<Book> createCall = service.create(book);
createCall.enqueue(new Callback<Book>() {
#Override
public void onResponse(Call<Book> _, Response<Book> resp) {
Book newBook = resp.body();
textView.setText("Created Book with ISBN: " + newBook.isbn);
}
#Override
public void onFailure(Call<Book> _, Throwable t) {
t.printStackTrace();
textView.setText(t.getMessage());
}
});
}
});
}
}
Book class
package com.example.myapplication;
import com.google.gson.annotations.SerializedName;
public class Book
{
#SerializedName("id")
int id;
#SerializedName("isbn")
String isbn;
public Book(int id, String isbn) {
this.id = id;
this.isbn = isbn;
}
public Book(String isbn) {
this.isbn = isbn;
}
}
BookService class
package com.example.myapplication;
import java.util.List;
import retrofit2.Call;
import retrofit2.http.Body;
import retrofit2.http.GET;
import retrofit2.http.POST;
import retrofit2.http.Path;
public interface BookService
{
#GET("books")
Call<List<Book>> all();
#GET("books/{isbn}")
Call<Book> get(#Path("isbn") String isbn);
#POST("books/new")
Call<Book> create(#Body Book book);
}
logcat
2022-10-19 08:56:03.651 8041-8041/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 8041
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.myapplication/com.example.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2679)
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 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:152)
at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:157)
at android.content.Context.obtainStyledAttributes(Context.java:655)
at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:852)
at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:819)
at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:640)
at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:261)
at com.example.myapplication.MainActivity.<init>(MainActivity.java:22)
at java.lang.Class.newInstance(Native Method)
at android.app.Instrumentation.newActivity(Instrumentation.java:1174)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2669)
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)

You need to "find" view after they are created.
EditText isbnInput;
TextView textView;
Button button;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
isbnInput = (EditText) findViewById(R.id.isbnInput);
textView = (TextView) findViewById(R.id.textView);
button = (Button) findViewById(R.id.button);
}

It is because of findViewById. You should call it inside OnCreate. Because it needs View that it is being called from to be initialized.
private EditText isbnInput;
private TextView textView;
private Button button;
#Override
protected void onCreate(Bundle savedInstanceState)
{
isbnInput = (EditText) findViewById(R.id.isbnInput);
textView = (TextView) findViewById(R.id.textView);
button = (Button) findViewById(R.id.button);

Android chat app keeps on crashing when I run it

I have just begun writing some code for my Chat app after days of planning but the problem is that keeps on crashing right after the Gradle Build has finished and the app is installed on my device. I have created a button that is expected to open a new activity but instead of doing so it crashes. Everything works before I have written any code, the app opens and logcat doesn't show any errors. Here is the error:
2022-08-10 19:26:48.372 15348-15348/? E/e.myapplicatio: Unknown bits set in runtime_flags: 0x40000000
2022-08-10 19:26:48.391 15348-15348/? E/RefClass: java.lang.reflect.InvocationTargetException
2022-08-10 19:26:48.474 15348-15348/com.example.myapplication E/Perf: perftest packageName : com.example.myapplication App is allowed to use Hide APIs
2022-08-10 19:26:48.515 15348-15374/com.example.myapplication E/libEGL: Invalid file path for libcolorx-loader.so
2022-08-10 19:26:48.528 15348-15348/com.example.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.myapplication, PID: 15348
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.myapplication/com.example.myapplication.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3628)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3887)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:140)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:100)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2317)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:263)
at android.app.ActivityThread.main(ActivityThread.java:8292)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:612)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1006)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference
at android.content.ContextWrapper.getApplicationInfo(ContextWrapper.java:183)
at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:174)
at android.content.Context.obtainStyledAttributes(Context.java:744)
at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:848)
at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:815)
at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:640)
at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:259)
at com.example.myapplication.MainActivity.<init>(MainActivity.java:12)
at java.lang.Class.newInstance(Native Method)
at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
at android.app.Instrumentation.newActivity(Instrumentation.java:1254)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3616)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3887) 
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:140) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:100) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2317) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:263) 
at android.app.ActivityThread.main(ActivityThread.java:8292) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:612) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1006) 
I tried following some other suggestions but they didn't work. Here's the snippet of my code:
package com.example.myapplication;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.view.View;
import android.widget.Button;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity {
public Button signUp = findViewById(R.id.signUpBtn);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
signUp.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
openActivity();
}
});
}
public void openActivity(){
Intent intent = new Intent(this, LoginActivity.class);
startActivity(intent);
}
}

You can not use findViewById() outside of onCreate() like this and if you really wanna do that, do it by creating a new method for setting up IDs and then add that method in onCreate().
this code will do the work now:
package com.example.myapplication;
import androidx.appcompat.app.AppCompatActivity;
import android.content.Intent;
import android.view.View;
import android.widget.Button;
import android.os.Bundle;
public class MainActivity extends AppCompatActivity {
public Button signUp;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
signUp = findViewById(R.id.signUpBtn);
signUp.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
openActivity();
}
});
}
public void openActivity(){
Intent intent = new Intent(this, LoginActivity.class);
startActivity(intent);
}
}

Nullable problem with Intents with extras

I am learning how to develop for Android (and development in general). I am trying to create a Quiz App, so I can learn the basics.
While trying to use an Intent to go to another class with an extra variable on it, I found this problem (which I think is pretty usual): My app crashes when I go to the next Activity.
This is the code in the activity that gets the username ("usuario and nomeUsuario"):
package com.isa56.quiz2;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import androidx.appcompat.app.AppCompatActivity;
public class HomeActivity extends AppCompatActivity {
public EditText usuario;
public EditText senha;
public Button botaoLogin;
public String nomeUsuario;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
botaoLogin = findViewById(R.id.botaoLogin);
senha = findViewById(R.id.senha);
usuario = findViewById(R.id.usuario);
nomeUsuario = usuario.getText().toString();
Log.d("nome de usuario", nomeUsuario);
botaoLogin.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
Intent i = new Intent(HomeActivity.this, FirstQuestionActivity.class);
i.putExtra("nome", nomeUsuario);
startActivity(i);
}});
}
}
And this is the code on the SecondQuestionActivity:
package com.isa56.quiz2;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import androidx.appcompat.app.AppCompatActivity;
public class FirstQuestionActivity extends AppCompatActivity {
public Button prox1;
public Button respUm1;
public Button respUm2;
public TextView texto1;
public int pontuacao = 0;
Intent i = getIntent();
String nome = i.getStringExtra("nome");
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_firstquestion);
prox1 = findViewById(R.id.prox1);
respUm1 = findViewById(R.id.botao1a);
respUm2 = findViewById(R.id.botao1b);
texto1 = findViewById(R.id.texto1);
respUm1.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
texto1.setText("Resposta errada!");
respUm1.setEnabled(false);
respUm2.setEnabled(false);
prox1.setEnabled(true);
}});
respUm2.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
texto1.setText("Resposta certa!");
respUm2.setEnabled(false);
respUm1.setEnabled(false);
pontuacao += 1;
prox1.setEnabled(true);
}});
prox1.setOnClickListener(new View.OnClickListener(){
#Override
public void onClick(View v) {
Intent i = new Intent(FirstQuestionActivity.this, SecondQuestionActivity.class);
i.putExtra("pontos", pontuacao);
i.putExtra("nome", nome);
startActivity(i);
}
});
}
}
What is wrong with it? How can I prevent it?
Thank you!
P.S.: I am not used to forum or development in general, so I might have done this wrongly. I'm sorry.
Edit: Also, if anyone wanna take a look at the whole project, it's here.
Edit2: This is the Logcat output:
2020-11-13 21:05:18.531 7517-7517/com.isa56.quiz2 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.isa56.quiz2, PID: 7517
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.isa56.quiz2/com.isa56.quiz2.FirstQuestionActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Intent.getStringExtra(java.lang.String)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3365)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:223)
at android.app.ActivityThread.main(ActivityThread.java:7656)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Intent.getStringExtra(java.lang.String)' on a null object reference
at com.isa56.quiz2.FirstQuestionActivity.<init>(FirstQuestionActivity.java:18)
at java.lang.Class.newInstance(Native Method)
at android.app.AppComponentFactory.instantiateActivity(AppComponentFactory.java:95)
at androidx.core.app.CoreComponentFactory.instantiateActivity(CoreComponentFactory.java:45)
at android.app.Instrumentation.newActivity(Instrumentation.java:1253)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3353)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3601) 
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:85) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2066) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:223) 
at android.app.ActivityThread.main(ActivityThread.java:7656) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:592) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:947) 

Keep these lines inside onCreate() method.
Intent i = getIntent();
String nome = i.getStringExtra("nome");

NullPointerException: Attempt to invoke virtual method setLayoutManager on a null object reference [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 doing a challenge from Treehouse and they have given some initial project files to follow along. The problem is they're 2 years old and a lot of the code is outdated. I changed as much as I could, but apparently there still are some problems.
I try to run this code and it says it can't invoke setLayoutManager() on a null object reference. How can the object be null if I initialise it right before?
private void populate() {
StaggeredGridLayoutManager lm = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
mAlbumList.setLayoutManager(lm);
This is all the code in the file.
package com.teamtreehouse.albumcover;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.StaggeredGridLayoutManager;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import butterknife.BindView;
import butterknife.ButterKnife;
public class AlbumListActivity extends Activity {
#BindView(R.id.album_list) RecyclerView mAlbumList;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_album_list);
initTransitions();
ButterKnife.bind(this);
populate();
}
private void initTransitions() {
getWindow().setExitTransition(null);
getWindow().setReenterTransition(null);
}
interface OnVHClickedListener {
void onVHClicked(AlbumVH vh);
}
static class AlbumVH extends RecyclerView.ViewHolder implements View.OnClickListener {
private final OnVHClickedListener mListener;
#BindView(R.id.album_art)
ImageView albumArt;
public AlbumVH(View itemView, OnVHClickedListener listener) {
super(itemView);
ButterKnife.bind(this, itemView);
itemView.setOnClickListener(this);
mListener = listener;
}
#Override
public void onClick(View v) {
mListener.onVHClicked(this);
}
}
private void populate() {
StaggeredGridLayoutManager lm = new StaggeredGridLayoutManager(2, StaggeredGridLayoutManager.VERTICAL);
mAlbumList.setLayoutManager(lm);
final int[] albumArts = {
R.drawable.mean_something_kinder_than_wolves,
R.drawable.cylinders_chris_zabriskie,
R.drawable.broken_distance_sutro,
R.drawable.playing_with_scratches_ruckus_roboticus,
R.drawable.keep_it_together_guster,
R.drawable.the_carpenter_avett_brothers,
R.drawable.please_sondre_lerche,
R.drawable.direct_to_video_chris_zabriskie };
RecyclerView.Adapter adapter = new RecyclerView.Adapter<AlbumVH>() {
#Override
public AlbumVH onCreateViewHolder(ViewGroup parent, int viewType) {
View albumView = getLayoutInflater().inflate(R.layout.album_grid_item, parent, false);
return new AlbumVH(albumView, new OnVHClickedListener() {
#Override
public void onVHClicked(AlbumVH vh) {
int albumArtResId = albumArts[vh.getLayoutPosition() % albumArts.length];
Intent intent = new Intent(AlbumListActivity.this, AlbumDetailActivity.class);
intent.putExtra(AlbumDetailActivity.EXTRA_ALBUM_ART_RESID, albumArtResId);
startActivity(intent);
}
});
}
#Override
public void onBindViewHolder(AlbumVH holder, int position) {
holder.albumArt.setImageResource(albumArts[position % albumArts.length]);
}
#Override
public int getItemCount() {
return albumArts.length * 4;
}
};
mAlbumList.setAdapter(adapter);
}
}
This is the exception:
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.jimulabs.googlemusicmock, PID: 30956
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.jimulabs.googlemusicmock/com.teamtreehouse.albumcover.AlbumListActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$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$MethodAndArgsCaller.run(RuntimeInit.java:438)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at com.teamtreehouse.albumcover.AlbumListActivity.populate(AlbumListActivity.java:59)
at com.teamtreehouse.albumcover.AlbumListActivity.onCreate(AlbumListActivity.java:27)
at android.app.Activity.performCreate(Activity.java:6999)
at android.app.Activity.performCreate(Activity.java:6990)
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) 

Just a simple solution to this problem is, init your mAlbumLayout and pass it as a parameter in the populate() method. This will prevent it from getting null.

Android error, Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference

My app is crashing every time, I couldn't find any solution for the issue.
The code is:
package com.example.juan.sem4;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;
public class Registrarse extends AppCompatActivity {
EditText txtNom, txtCor, txtPas;
Button btnRegistrarse;
BD_Usuarios bd=new BD_Usuarios(this,"BD1",null,1);
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_registrarse);
txtNom=(EditText)findViewById(R.id.txtRegNom);
txtCor=(EditText)findViewById(R.id.txtRegCor);
txtPas=(EditText)findViewById(R.id.txtPas);
btnRegistrarse=(Button)findViewById(R.id.btnRegistrarse);
btnRegistrarse.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
bd.abrir();
bd.registrarUsu(txtNom.getText().toString(),txtCor.getText().toString(),txtPas.getText().toString());
bd.cerrar();
txtCor.setText("");
txtNom.setText("");
txtPas.setText("");
txtNom.findFocus();
Toast.makeText(getApplicationContext(),"Se registro con exito",Toast.LENGTH_LONG).show();
finish();
}
});
}
}
The LOGCAT shows the following problem:
java.lang.NullPointerException: Attempt to invoke virtual method 'android.text.Editable android.widget.EditText.getText()' on a null object reference
at com.example.juan.sem4.Registrarse$1.onClick(Registrarse.java:32)
at android.view.View.performClick(View.java:5637)
at android.view.View$PerformClick.run(View.java:22429)
at android.os.Handler.handleCallback(Handler.java:751)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:154)
at android.app.ActivityThread.main(ActivityThread.java:6119)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)
It seems that the issue is on the line 32 which is:
bd.registrarUsu(txtNom.getText().toString(),txtCor.getText().toString(),txtPas.getText().toString());
But honestly I can't see the problem in it.