NullPointerException when insertData() called in android [duplicate] - sqlite

Question

This question already has answers here:
What is a NullPointerException, and how do I fix it?
(12 answers)
Closed 4 years ago.
I am currently working on android stenography project,
but at registration time the error was occur
"java.lang.NullPointerException: Attempt to invoke virtual method 'boolean com.example.devd.stangnograpyonimage.DBHelper.insertData(java.lang.String, java.lang.String, java.lang.String, java.lang.String)' on a null object reference"
DataBaseHelper.java
public static final String DATABASE_NAME = "STAGNODB";
public static final String TABLE_NAME = "Satgno_Table";
//public static final String COLUUMN_ID = "ID";
public static final String COLUUMN_USERNAME = "UserName";
public static final String COLUUMN_PASSWORD = "Password";
public static final String COLUUMN_NAME = "Name";
public static final String COLUUMN_EMAIL = "Email";
public DBHelper(Context context) {
super(context, DATABASE_NAME, null, 1);
}
#Override
public void onCreate(SQLiteDatabase db) {
try {
db.execSQL("CREATE TABLE " + TABLE_NAME + "(" + COLUUMN_USERNAME + " VARCHAR(50),"
+ COLUUMN_PASSWORD + " VARCHAR(50),"
+ COLUUMN_NAME + " VARCHAR(50),"
+ COLUUMN_EMAIL + " VARCHAR(50));", null);
}catch (Exception e){
Log.e("SQL Table Creation ", "Table Not Created");
}
}
#Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("DROP TABLE IF EXISTS " + TABLE_NAME);
}
public boolean insertData(String userName, String password, String name, String email){
SQLiteDatabase mydb = this.getWritableDatabase();
ContentValues cv = new ContentValues();
cv.put(COLUUMN_USERNAME, userName);
cv.put(COLUUMN_PASSWORD, password);
cv.put(COLUUMN_NAME, name);
cv.put(COLUUMN_EMAIL, email);
long result = mydb.insert(TABLE_NAME, null, cv);
if(result == -1){
return false;
}
else {
return true;
}
}
MainActivity.java
public class MainActivity extends AppCompatActivity {
DBHelper myDB;
EditText etUserName, etPassword, etName, etEmail;
Button btnRegister, btnLogin;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
etUserName = (EditText) findViewById(R.id.etUserName);
etPassword = (EditText) findViewById(R.id.etPassword);
etName = (EditText) findViewById(R.id.etName);
etEmail = (EditText) findViewById(R.id.etEmail);
btnRegister = (Button) findViewById(R.id.btnRegister);
btnLogin = (Button) findViewById(R.id.btnLogin);
register();
}
public void register() {
btnRegister.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
boolean isInserted = myDB.insertData(etUserName.getText().toString(), etPassword.getText().toString(), etName.getText().toString(), etEmail.getText().toString());
if(isInserted==true){
Toast.makeText(MainActivity.this,"Data Inserted", Toast.LENGTH_LONG).show();
}
else {
Toast.makeText(MainActivity.this,"Data not Inserted", Toast.LENGTH_LONG).show();
}
}
});
}
}

Answer 1

In your activity class, you have not initialized the variable DBHelper myDB. Thus when your activity calls
myDB.insertData(etUserName.getText().toString(), ...
You get a NullPointerException because myDB is null. To fix this, create the object in the onCreate method of your activity
myDB = new DBHelper(this);

Answer 2

You are declaring but not instantiating myDB so it is null.
i.e.
DBHelper myDB;
Just declares myDB so it is null at this point as nothing has been assigned to the variable.
You need to add something like :-
myDB = new DBHelper(this);
In the onCreate method of the MainActivity.
e.g. :-
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
etUserName = (EditText) findViewById(R.id.etUserName);
etPassword = (EditText) findViewById(R.id.etPassword);
etName = (EditText) findViewById(R.id.etName);
etEmail = (EditText) findViewById(R.id.etEmail);
btnRegister = (Button) findViewById(R.id.btnRegister);
btnLogin = (Button) findViewById(R.id.btnLogin);
myDB = new DBHelper(this); //<<<< ADDED
register();
}