Unable to start activity ComponentInfo java.lang.NullPointerException: Attempt to invoke virtual method on a null object reference

Question

I'm trying to change to another activity with a button. The second activity (called capturar) takes a picture and saves it on the gallery. But, for some reason, every time I try to change to that activity with the button, it crashes, I know the problem is on the capturar's code, because If I comment all of the code, it works.

I'm gonna put a picture of my main activity code (where I try to change to the other activity with an intent) and the code of my Capturar activity where I try to take a picture and save it.

Main Activity:

package com.iris.phototask;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import android.app.Activity;
import android.content.Intent;
import android.media.Image;
import android.os.Bundle;
import android.provider.MediaStore;
import android.view.View;
import android.widget.Button;
import android.widget.ImageButton;
import android.widget.Toast;

public class MainActivity extends AppCompatActivity {


    //Declaramos las variables
    public Button btnHorario;
    public Button Galeria;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        //Asignamos el componente al que corresponde la variable
        btnHorario = (Button) findViewById(R.id.buttonHorario);
        ImageButton imgButtonCamara = findViewById(R.id.imageButtonCamera);
        Galeria = (Button) findViewById(R.id.buttonGaleria);


        //Creamos un onClickListener para generar un cambio de actividad al pulsar el botón
       btnHorario.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                //Creamos un Intent que nos cambie de ventana
                Intent intent = new Intent (MainActivity.this, Horario.class);
                startActivity(intent);

            }
        });

        imgButtonCamara.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                //Creamos un Intent que nos cambie de ventana
                Intent intent = new Intent (MainActivity.this, Capturar.class);
                startActivity(intent);

            }
        });
    }
}

Main Activiry xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity">

    <Button
        android:id="@+id/buttonGaleria"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginBottom="30dp"
        android:background="#8BC34A"
        android:text="Galeria"
        app:layout_constraintBottom_toTopOf="@+id/buttonHorario"
        app:layout_constraintEnd_toEndOf="@+id/buttonHorario"
        app:layout_constraintStart_toStartOf="@+id/buttonHorario"
        app:layout_constraintTop_toBottomOf="@+id/imageButtonCamera" />

    <Button
        android:id="@+id/buttonHorario"
        android:layout_width="128dp"
        android:layout_height="0dp"
        android:layout_marginBottom="234dp"
        android:background="#8BC34A"
        android:text="Horario"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toBottomOf="@+id/buttonGaleria" />

    <ImageButton
        android:id="@+id/imageButtonCamera"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginTop="175dp"
        android:layout_marginEnd="1dp"
        android:layout_marginBottom="32dp"
        android:background="#8BC34A"
        android:contentDescription="@string/app_name"
        app:layout_constraintBottom_toTopOf="@+id/buttonGaleria"
        app:layout_constraintEnd_toEndOf="@+id/buttonGaleria"
        app:layout_constraintStart_toStartOf="@+id/buttonHorario"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@android:drawable/ic_menu_camera" />


</androidx.constraintlayout.widget.ConstraintLayout>

Capturar Activity

package com.iris.phototask;

import androidx.appcompat.app.AppCompatActivity;
import androidx.core.content.FileProvider;

import android.content.Context;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.net.Uri;
import android.os.Bundle;
import android.os.Environment;
import android.provider.ContactsContract;
import android.provider.MediaStore;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.util.UUID;

public class Capturar extends AppCompatActivity {

    //Declaración de variables
    private static final String TAG = "CapturePicture";
    static final int REQUEST_PICTURE_CAPTURE = 1; //Código para referirnos a request capture
    private ImageView Imagen; //Declaramos el imageview que tenemos en el xml
    private String deviceIdentifier;
    String currentPhotoPath; //Un string donde guardaremos el url de la foto
    Uri photoURI; //El uri de la foto


    @Override
    protected void onCreate(Bundle savedInstanceState) {// ************************************************* INICIA ON CREATE PRINCIPAL ********************************************************
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_capturar);

        Imagen = findViewById(R.id.imageViewImagen);

        Button guardarButton = findViewById(R.id.buttonGuardar);
        Button captureButton = findViewById(R.id.buttonCapture);

        captureButton.setOnClickListener(buttonCapture);
        guardarButton.setOnClickListener(buttonGuardar);

        //Si no se habilitó la cámara, deshabilitar el botón de capturar
        if (!getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA)){
            captureButton.setEnabled(false);
        }

        findViewById(R.id.save_local).setOnClickListener(buttonGuardar);

        getInstallationIdentifier();
    }// *************************************************************************************************** TERMINA ON CREATE PRINCIPAL *********************************************************

    //Si se habilitó la cámara y se pulsa el botón para capturar foto, llamamos al intent que toma la foto, declarado más adelante
    private View.OnClickListener buttonCapture = new View.OnClickListener(){
        @Override
        public void onClick(View view){

            if (getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA)){
                dispatchTakePictureIntent();
            }

        }
    };

    //Creamos una función que genera un intent que solicita IMAGE_CAPTURE

    private void dispatchTakePictureIntent(){
        Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE);

        //Asegurarse de que hay un camera activity para manejar el intent
        if(takePictureIntent.resolveActivity(getPackageManager())!=null){//Inicia if

            //Creamos el archivo a donde la foto irá
            File photoFile = null;

            try{//Inicia Try Catch
                //Llamammos a la función para crear la foto
                photoFile = createImageFile();
            }catch (IOException ex){
                //Un error ocurrió al crear el archivo
            }//Termina catch

            //Si foto file es diferente de nulo
            if (photoFile != null){//Empieza if 2
                photoURI = FileProvider.getUriForFile(this,"com.example.android.fileprovider",photoFile);
                takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, photoURI);
                startActivityForResult(takePictureIntent,REQUEST_PICTURE_CAPTURE);
            }//Termina if 2
        }//Termina if
    }

    private File createImageFile() throws IOException {//Creamos la función que generará la imagen

        File storageDir = getExternalFilesDir(Environment.DIRECTORY_PICTURES);

        //SI no existe en directorio para almacenarlo, lo crea.
        if (!storageDir.exists())
                storageDir.mkdir();

        File Imagen = File.createTempFile(
                "2019",".jpeg",storageDir
        );

        currentPhotoPath = Imagen.getAbsolutePath();
        return Imagen;
    }//Termina función para crear la imagen

    @Override
    protected void onActivityResult(int requestCode, int resultCode, Intent data){//Función de iniciar el INTENT con resultados

        if (requestCode == REQUEST_PICTURE_CAPTURE && resultCode == RESULT_OK){//Inicia if

            Bitmap bitmap;

            try {
                bitmap = MediaStore.Images.Media.getBitmap(getContentResolver(),photoURI);
                Imagen.setImageBitmap(bitmap);
            }catch (FileNotFoundException e){
                e.printStackTrace();
            }catch (IOException e){
                e.printStackTrace();
            }
        }//Termina if
    }//Termina función de iniciar el INTENT con resultados

    //AL presionar el botón guardar la intentaremos guardar en la librería
    private View.OnClickListener buttonGuardar = new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            try{
                addToGallery();
            }catch (IOException e){
                e.printStackTrace();
            }
        }
    };

    //Iniciamos la función de añadir a la galería
    private void addToGallery() throws IOException{

        Intent mediaScanIntent = new Intent (Intent.ACTION_MEDIA_SCANNER_SCAN_FILE);
        File f = new File (currentPhotoPath);
        Uri contentUri = Uri.fromFile(f);
        mediaScanIntent.setData(contentUri);
        this.sendBroadcast(mediaScanIntent);
        notifyMediaStoreScanner(f); //función
    }

    public final void notifyMediaStoreScanner (final File file){

        try{
            MediaStore.Images.Media.insertImage(this.getContentResolver(),file.getAbsolutePath(), file.getName(),null);
            this.sendBroadcast(new Intent (Intent.ACTION_MEDIA_SCANNER_SCAN_FILE, Uri.fromFile(file)));
        }catch (FileNotFoundException e){
            e.printStackTrace();
        }
    }

    protected synchronized String getInstallationIdentifier(){

        if(deviceIdentifier == null){
            SharedPreferences sharedPref = this.getSharedPreferences("DEVICE_ID", Context.MODE_PRIVATE);
            deviceIdentifier = sharedPref.getString("DEVICE_ID", null);

            if(deviceIdentifier == null){
                deviceIdentifier = UUID.randomUUID().toString();
                SharedPreferences.Editor editor = sharedPref.edit();
                editor.putString("DEVICE_ID",deviceIdentifier);
                editor.commit();
            }
        }
        return deviceIdentifier;
    }

}

Capturar xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".Capturar">

    <ImageView
        android:id="@+id/imageViewImagen"
        android:layout_width="0dp"
        android:layout_height="0dp"
        android:layout_marginStart="45dp"
        android:layout_marginTop="73dp"
        android:layout_marginEnd="45dp"
        android:layout_marginBottom="73dp"
        app:layout_constraintBottom_toTopOf="@+id/buttonCapture"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent"
        app:srcCompat="@android:drawable/ic_menu_gallery" />

    <Button
        android:id="@+id/buttonCapture"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginStart="51dp"
        android:text="Capturar"
        android:background="#8BC34A"
        app:layout_constraintBottom_toBottomOf="@+id/buttonGuardar"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="@+id/buttonGuardar" />

    <Button
        android:id="@+id/buttonGuardar"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginEnd="52dp"
        android:layout_marginBottom="78dp"
        android:text="Guardar"
        android:background="#8BC34A"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent" />
</androidx.constraintlayout.widget.ConstraintLayout>

Console:

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.iris.phototask, PID: 6499
    java.lang.RuntimeException: Unable to start activity ComponentInfo{com.iris.phototask/com.iris.phototask.Capturar}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2946)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3081)
        at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1831)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:201)
        at android.app.ActivityThread.main(ActivityThread.java:6810)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873)
     Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.View.setOnClickListener(android.view.View$OnClickListener)' on a null object reference
        at com.iris.phototask.Capturar.onCreate(Capturar.java:54)
        at android.app.Activity.performCreate(Activity.java:7224)
        at android.app.Activity.performCreate(Activity.java:7213)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1272)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2926)

Thanks a lot, I hope I explained myself.

Answer 1

The null pointer exception is caused because of the following line

findViewById(R.id.save_local).setOnClickListener(buttonGuardar);

as it cant find id save_local