I am following one tutorial from youtube for making a clone of tinder. I am getting the following error. What can be the possible solution? The code of main activity doesn't show any error in the android studio but on running it shows an error.
This is the error it is showing on testing the app on android device .
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String java.lang.Object.toString()' on a null object reference
at com.techjd.hubu.MainActivity$6.onChildAdded(MainActivity.java:201)
at com.google.firebase.database.core.ChildEventRegistration.fireEvent(com.google.firebase:firebase-database@@19.2.0:79)
at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@19.2.0:63)
at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@19.2.0:55)
at android.os.Handler.handleCallback(Handler.java:815)
at android.os.Handler.dispatchMessage(Handler.java:104)
at android.os.Looper.loop(Looper.java:207)
at android.app.ActivityThread.main(ActivityThread.java:5740)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:905)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:766)
This is the main activity.
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;
import com.google.firebase.database.ChildEventListener;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.google.firebase.database.ValueEventListener;
import com.lorentzos.flingswipe.SwipeFlingAdapterView;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends AppCompatActivity {
private cards cards_data[];
private ArrayAdapter arrayAdapter;
private int i;
private FirebaseAuth mAuth;
private String currentUId;
private DatabaseReference usersDb;
ListView listView;
List<cards> rowItems;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
usersDb = FirebaseDatabase.getInstance().getReference().child("Users");
mAuth = FirebaseAuth.getInstance();
currentUId = mAuth.getCurrentUser().getUid();
checkUserSex();
rowItems = new ArrayList<cards>();
arrayAdapter = new arrayAdapter(this, R.layout.item, rowItems );
SwipeFlingAdapterView flingContainer = (SwipeFlingAdapterView) findViewById(R.id.frame);
flingContainer.setAdapter(arrayAdapter);
flingContainer.setFlingListener(new SwipeFlingAdapterView.onFlingListener() {
@Override
public void removeFirstObjectInAdapter() {
// this is the simplest way to delete an object from the Adapter (/AdapterView)
Log.d("LIST", "removed object!");
rowItems.remove(0);
arrayAdapter.notifyDataSetChanged();
}
@Override
public void onLeftCardExit(Object dataObject) {
cards obj = (cards) dataObject;
String userId = obj.getUserId();
usersDb.child(oppositeUserSex).child(userId).child("connections").child("nope").child(currentUId).setValue(true);
Toast.makeText(MainActivity.this, "Left", Toast.LENGTH_SHORT).show();
}
@Override
public void onRightCardExit(Object dataObject) {
cards obj = (cards) dataObject;
String userId = obj.getUserId();
usersDb.child(oppositeUserSex).child(userId).child("connections").child("yes").child(currentUId).setValue(true);
isConnectionMatch(userId);
Toast.makeText(MainActivity.this, "Right", Toast.LENGTH_SHORT).show();
}
@Override
public void onAdapterAboutToEmpty(int itemsInAdapter) {
}
@Override
public void onScroll(float scrollProgressPercent) {
}
});
// Optionally add an OnItemClickListener
flingContainer.setOnItemClickListener(new SwipeFlingAdapterView.OnItemClickListener() {
@Override
public void onItemClicked(int itemPosition, Object dataObject) {
Toast.makeText(MainActivity.this, "Item Clicked", Toast.LENGTH_SHORT).show();
}
});
}
private void isConnectionMatch(String userId) {
DatabaseReference currentUserConnectionsDB = usersDb.child(userSex).child(currentUId).child("connections").child("yes").child(userId);
currentUserConnectionsDB.addListenerForSingleValueEvent(new ValueEventListener() {
@Override
public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
if (dataSnapshot.exists()) {
Toast.makeText(MainActivity.this, "new Connection", Toast.LENGTH_LONG).show();
usersDb.child(oppositeUserSex).child(dataSnapshot.getKey()).child("connections").child("matches").child(currentUId).setValue(true);
usersDb.child(userSex).child(currentUId).child("connections").child("matches").child(dataSnapshot.getKey()).setValue(true);
}
}
@Override
public void onCancelled(@NonNull DatabaseError databaseError) {
}
});
}
private String userSex;
private String oppositeUserSex;
public void checkUserSex(){
final FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
DatabaseReference maleDb = FirebaseDatabase.getInstance().getReference().child("Users").child("Male");
maleDb.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
if (dataSnapshot.getKey().equals(user.getUid())){
userSex = "Male";
oppositeUserSex = "Female";
getOppositeSexUsers();
}
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
DatabaseReference femaleDb = FirebaseDatabase.getInstance().getReference().child("Users").child("Female");
femaleDb.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
if (dataSnapshot.getKey().equals(user.getUid())){
userSex = "Female";
oppositeUserSex = "Male";
getOppositeSexUsers();
}
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
public void getOppositeSexUsers(){
DatabaseReference oppositeSexDb = FirebaseDatabase.getInstance().getReference().child("Users").child(oppositeUserSex);
oppositeSexDb.addChildEventListener(new ChildEventListener() {
@Override
public void onChildAdded(DataSnapshot dataSnapshot, String s) {
if (dataSnapshot.exists() && !dataSnapshot.child("connections").child("nope").hasChild(currentUId) && !dataSnapshot.child("connections").child("yes").hasChild(currentUId)){
String profileImageUrl = "default";
Object profileImageUrlData = dataSnapshot.child("profileImageUrl").getValue();
if (profileImageUrlData != null && !profileImageUrlData.equals("default")){
profileImageUrl = profileImageUrlData.toString();
}
cards item = new cards(dataSnapshot.getKey(), dataSnapshot.child("name").getValue().toString(), profileImageUrl);
rowItems.add(item);
arrayAdapter.notifyDataSetChanged();
}
}
@Override
public void onChildChanged(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onChildRemoved(DataSnapshot dataSnapshot) {
}
@Override
public void onChildMoved(DataSnapshot dataSnapshot, String s) {
}
@Override
public void onCancelled(DatabaseError databaseError) {
}
});
}
public void logoutUser(View view) {
mAuth.signOut();
Intent intent = new Intent(MainActivity.this, ChooseLoginRegistrationActivity.class);
startActivity(intent);
finish();
return;
}
public void goToSettings(View view) {
Intent intent = new Intent(MainActivity.this, SettingsActivity.class);
intent.putExtra("userSex",userSex);
startActivity(intent);
return;
}
}
Line 201 is cards item = new cards(dataSnapshot.getKey(), dataSnapshot.child("name").getValue().toString(), profileImageUrl);
