Cannot Update nor Delete in SQLite on Android Studio - android-studio

Question

This is the code that I use
dbhelper mydb;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_profile);
final Intent profile = getIntent();
final String user = profile.getExtras().getString("tete");
final EditText username = (EditText) findViewById(R.id.Pusername);
final EditText password = (EditText) findViewById(R.id.Ppassword);
username.setText(user);
username.setInputType(InputType.TYPE_NULL); //Supaya username tidak dapat diganti
Button update = (Button) findViewById(R.id.btupdate);
update.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
String newpassword = password.getText().toString();
String newusername = username.getText().toString();
if (password.getText().toString().trim().length() < 6) {
Toast.makeText(getApplicationContext(), "Password Baru Harus diisi minimal 6 karakter", Toast.LENGTH_SHORT).show();
} else {
mydb.editData(newusername, newpassword);
Toast.makeText(getApplicationContext(), "berhasil!", Toast.LENGTH_SHORT).show();
}
}
});
This is my code for the dbhelper class
public void editData(String username,String password){
SQLiteDatabase db= this.getWritableDatabase();
ContentValues contentValues = new ContentValues();
contentValues.put(COL_1,username);
contentValues.put(COL_2,password);
db.update(TABLE_NAME,contentValues,"USERNAME = ?", new String[]{username});
//String query="UPDATE " + TABLE_NAME + " SET " + COL_2 + " = '" + password + "' Where " + COL_1 + " = '" + username + "'";
//db.execSQL(query);
}
The logcat gave this error
java.lang.NullPointerException: Attempt to invoke virtual method 'void
com.example.charlie.gate.dbhelper.editData(java.lang.String,
java.lang.String)' on a null object reference
I tried to toast the newusername and the newpassword string to test if it were null and the result were both contain the value as intended, but somehow everytime I click the button the app forced close, Please help

Answer 1

You do not initialize mydb correctly so it is null when you try to use it.
Inside onCreate() add this line:
mydb = new dbhelper(this, ...);
usually you pass this and other parameters for this initialization.