Database Error: "NullPointerException: Attempt to invoke virtual method getApplicationInfo()... on a null object reference"

Question

I'm building a simple multi-activity list app to practice with SQLite. I was trying to get the strings from the database to display in the listview when this started. I'm getting the error

java.lang.NullPointerException: Attempt to invoke virtual method 'android.content.pm.ApplicationInfo android.content.Context.getApplicationInfo()' on a null object reference

Here the code

public class MainActivity extends AppCompatActivity {
    SharedPreferences sharedPreferences;
    ArrayList<String> listItem;
    ArrayAdapter adapter;
    ListView lv = (ListView) findViewById(R.id.list_view);
    DatabaseHelper db = new DatabaseHelper(this);
    Context context;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        listItem = new ArrayList<>();
        viewData();
        context = this;

        FloatingActionButton fab = findViewById(R.id.fab);
        fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                startActivity(new Intent(MainActivity.this, textInput.class));
            }
        });
    }

    // cast from sql database to the listview
    private void viewData() {
        Cursor res = db.viewData();

        if (res.getCount() == 0 ){
            Toast.makeText(this,"No Data!",Toast.LENGTH_SHORT).show();
        }
        else{
            while (res.moveToNext()){
                listItem.add(res.getString(1));
            }
            adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1,listItem);
            lv.setAdapter(adapter);
        }
    }
}

This is the Database Helper:

public class DatabaseHelper extends SQLiteOpenHelper {
public static final String DATABASE_NAME = "item.db";
public static final String TABLE_NAME = "item_table";
public static final String ID = "item_id";
public static final String NAME = "item_name";
public static final String PRICE = "item_price";
public static final String URL = "item_url";

public DatabaseHelper(@Nullable Context context) {
    super(context, DATABASE_NAME, null, 1);
}

@Override
public void onCreate(SQLiteDatabase db) {
    db.execSQL("create table " + TABLE_NAME +" ( item_id INTEGER PRIMARY 
KEY AUTOINCREMENT,item_name TEXT,item_price INTEGER,item_url TEXT) ");
}

@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
    db.execSQL("DROP TABLE IF EXISTS "+TABLE_NAME);
    onCreate(db);
}

public boolean insertData(String name, String price, String url){
    SQLiteDatabase db = this.getWritableDatabase();
    ContentValues contentValues = new ContentValues();
    contentValues.put(NAME, name);
    contentValues.put(PRICE, price);
    contentValues.put(URL, url);
    long result = db.insert(TABLE_NAME,null,contentValues);
    if(result == -1)
        return false;
    else
        return true;
}


public Cursor viewData(){
    SQLiteDatabase db  = this.getReadableDatabase();
    Cursor res = db.rawQuery("select * from "+TABLE_NAME,null);
    return res;
}

This is the textInput Activity

public class textInput extends AppCompatActivity {
SharedPreferences sharedPreferences;
//    Editor editor;
//    Context _context;
//    int PRIVATE_MODE = 0;
//    private static final String PREF_NAME = "Items";
//    public static final String NAME_LIST = "name";


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_text_input);
    //DatabaseHelper db;

    //return's to main activity on press
    Button addButton = (Button) findViewById(R.id.addButton);
    final EditText name = (EditText) findViewById(R.id.itemName);
    final EditText url = (EditText) findViewById(R.id.itemURL);
    final EditText price = (EditText) findViewById(R.id.itemPrice);
 //   final SharedPreferences sharedPreferences = 
getApplicationContext().getSharedPreferences("items", 0);
    final DatabaseHelper db = new DatabaseHelper(this);
    addButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            //Checks to make sure that all fields are filled out, if yes 
then returns to MainActivity
            if (name.length() != 0 && price.length() != 0 && url.length() 
 !=0){
                boolean isInserted = 
db.insertData(name.getText().toString(),
                        price.getText().toString(),
                        url.getText().toString());
                if(isInserted == true)
                    Toast.makeText(textInput.this, "New Item Added", 
 Toast.LENGTH_SHORT).show();
                else
                    Toast.makeText(textInput.this, "Failed to Add", 
Toast.LENGTH_SHORT).show();
                //The graphic and the return to MainActivity
                Intent returnToMain = new Intent(getApplicationContext(), 
MainActivity.class);
                startActivity(returnToMain);
            }
            else{
                Toast.makeText(textInput.this, "Please fill out all 
fields!", Toast.LENGTH_SHORT).show();
            }

        }
    });

Debug (Error?) Log

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.xmaswishlist, PID: 25470
    java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.xmaswishlist/com.example.xmaswishlist.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:2841)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3032)
        at android.app.ActivityThread.-wrap11(Unknown Source:0)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696)
        at android.os.Handler.dispatchMessage(Handler.java:105)
        at android.os.Looper.loop(Looper.java:164)
        at android.app.ActivityThread.main(ActivityThread.java:6944)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)
     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:163)
        at android.view.ContextThemeWrapper.getTheme(ContextThemeWrapper.java:157)
        at android.content.Context.obtainStyledAttributes(Context.java:655)
        at androidx.appcompat.app.AppCompatDelegateImpl.createSubDecor(AppCompatDelegateImpl.java:692)
        at androidx.appcompat.app.AppCompatDelegateImpl.ensureSubDecor(AppCompatDelegateImpl.java:659)
        at androidx.appcompat.app.AppCompatDelegateImpl.findViewById(AppCompatDelegateImpl.java:479)
        at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:214)
        at com.example.xmaswishlist.MainActivity.<init>(MainActivity.java:36)
        at java.lang.Class.newInstance(Native Method)
        at android.app.Instrumentation.newActivity(Instrumentation.java:1180)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2831)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3032) 
        at android.app.ActivityThread.-wrap11(Unknown Source:0) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1696) 
        at android.os.Handler.dispatchMessage(Handler.java:105) 
        at android.os.Looper.loop(Looper.java:164) 
        at android.app.ActivityThread.main(ActivityThread.java:6944) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:327) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1374)

I have tried to fix this using the following:

It would be great if you can also add the error log. It would be much easier and faster to pin point the issue. — Syed Ahmed Jamil, Dec 01 '19 at 03:12

score 4 · Accepted Answer · answered Dec 01 '19 at 03:27

4

You try to get view before setting the content in setContentView, which cause the exception. Instantiate ListView and DatabaseHelper inside onCreate.

ListView lv;
DatabaseHelper db;

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

    ...

    lv = (ListView) findViewById(R.id.list_view);
    db = new DatabaseHelper(this);
    ...
}

answered Dec 01 '19 at 03:27

Md. Asaduzzaman

14,963
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Thanks for the reply! I just fixed those and the error changed. I'll update the post! – Ty Sellers Dec 01 '19 at 03:33
edit: I'll create a new post for a new error, thanks again! – Ty Sellers Dec 01 '19 at 03:35

score 0 · Answer 2 · answered Dec 01 '19 at 03:28

From the stack trace:

at androidx.appcompat.app.AppCompatActivity.findViewById(AppCompatActivity.java:214) at com.example.xmaswishlist.MainActivity.(MainActivity.java:36)

In the MainActivity class you need to move the assignment on this line ListView lv = (ListView) findViewById(R.id.list_view); into onCreate. So define the variable where it already is, but move the = (ListView)... into onCreate.

findViewById is being invoked when the class is instantiated, and before onCreate is called, thus the internal workings are blowing up because the activity itself is not yet initialized.

You'll also need to initialize the database helper in onCreate.

Database Error: "NullPointerException: Attempt to invoke virtual method getApplicationInfo()... on a null object reference"

2 Answers2

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