NullPointerException while using getApplicationContext()

Question

I'm writing my first Android application and I still cannot deal with this error:

01-29 23:28:06.503 2135-2135/com.example.centrum.doradcazakupuv1 E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.centrum.doradcazakupuv1, PID: 2135
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.centrum.doradcazakupuv1/com.example.centrum.doradcazakupuv1.StronaGlowna}: 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: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.content.Context android.content.Context.getApplicationContext()' on a null object reference
    at android.content.ContextWrapper.getApplicationContext(ContextWrapper.java:107)
    at com.example.centrum.doradcazakupuv1.StronaGlowna.<init>(StronaGlowna.java:63)
    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)

My code is:

package com.example.centrum.doradcazakupuv1;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.CheckBox;
import android.widget.Toast;

import com.google.zxing.integration.android.IntentIntegrator;
import com.google.zxing.integration.android.IntentResult;


public class StronaGlowna extends AppCompatActivity {

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

    boolean cSoja = false;
    boolean cOA = false;
    boolean cWege = false;
    boolean cFullWege = false;
    IntentResult wr;

    String wynik;


    public void onCheckBoxClicked(View view) {
        boolean checked = ((CheckBox) view).isChecked();
        switch (view.getId()) {
            case R.id.soja:
                if (checked) {
                    cSoja = true;
                } else {
                    cSoja = false;
                }
                break;
            case R.id.oa:
                if (checked) {
                    cOA = true;
                } else {
                    cOA = false;
                }
                break;
            case R.id.wege:
                if (checked) {
                    cWege = true;
                } else {
                    cWege = false;
                }
                break;
            case R.id.fullWege:
                if (checked) {
                    cFullWege = true;
                } else {
                    cFullWege = false;
                }
                break;
        }
    }

    public int bts(boolean p) {
        if (p) return 1;
        else return 0;
    }


    public class ScanActivity extends Activity {
        public void onActivityResult(int requestCode, int resultCode, Intent intent) {
            IntentResult scanningResult = IntentIntegrator.parseActivityResult(requestCode, resultCode, intent);
            wr = scanningResult;
        }

        protected void onCreate(Bundle icicle) {
            super.onCreate(icicle);
            setContentView(R.layout.activity_strona_glowna);
            final Button button = (Button) findViewById(R.id.button);
            button.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                    // moja akcja;
                    IntentIntegrator Skaner = new IntentIntegrator(new ScanActivity());
                    Skaner.initiateScan();
                    wynik = wr.getContents();
                    int[] tablica = new int[4];
                    for (int i = 0; i < 4; i++) {
                        tablica[i] = wynik.charAt(i) - 48;
                    }
                    boolean fTest = true;
                    if (tablica[0] != bts(cSoja)) fTest = false;
                    else if (tablica[1] != bts(cOA)) fTest = false;
                    else if (tablica[2] != bts(cWege)) fTest = false;
                    else if (tablica[3] != bts(cFullWege)) fTest = false;
                    final Toast fail = Toast.makeText(getApplicationContext(), "Ten produkt nie odpowiada twoim preferencjom", Toast.LENGTH_SHORT);
                    final Toast good = Toast.makeText(getApplicationContext(), "Możesz to zjeść", Toast.LENGTH_SHORT);
                    if (fTest) good.show();
                    else fail.show();

                    // koniec akcji
                }
            });
        }
    }
}

Are there also any tips for solving such problems in general?

You should try using `this` instead of application context. – David Medenjak Jan 30 '16 at 00:34 — David Medenjak, Jan 30 '16 at 00:34

score 0 · Answer 1 · answered Jan 30 '16 at 00:48

Change:

final Toast fail = Toast.makeText(getApplicationContext(), "Ten produkt nie odpowiada twoim preferencjom", Toast.LENGTH_SHORT);
final Toast good = Toast.makeText(getApplicationContext(), "Możesz to zjeść", Toast.LENGTH_SHORT);

to

final Toast fail = Toast.makeText(ScanActivity.this, "Ten produkt nie odpowiada twoim preferencjom", Toast.LENGTH_SHORT);
final Toast good = Toast.makeText(ScanActivity.this, "Możesz to zjeść", Toast.LENGTH_SHORT);

and avoid using nested class which extends Activity.

score 0 · Answer 2 · answered Jan 30 '16 at 01:19

Exactly what Damian Kozlak said. Change the getApplicationContext() to ScanActivity.this

Why? Because when you call getApplicationContext() you are calling the context of the StronaGlowna Activity and not the ScanActivity context.

And yes, try to avoid nested classes which extends Activity. Is not a good practice because it may create conflicts and cause problems

NullPointerException while using getApplicationContext()

2 Answers2