Attempt to invoke virtual method 'boolean java.lang.String.isEmpty()' on a null object reference

Question

Please Help... Whenever I am trying to go to foodDetailActivity..it is throwing page back to the signup-signin activity?? When i debug the fooddetail activity..it is showing below mentioned logcat..

public class FoodList extends AppCompatActivity {

    RecyclerView recyclerView;
    RecyclerView.LayoutManager layoutManager;

    FirebaseDatabase database;
    DatabaseReference foodList;
    String categoryId="";

    FirebaseRecyclerAdapter<Food,FoodViewHolder> adapter;

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

        database=FirebaseDatabase.getInstance();
        foodList=database.getReference("Foods");

        recyclerView=findViewById(R.id.recycler_food);
        recyclerView.setHasFixedSize(true);
        layoutManager=new LinearLayoutManager(this);
        recyclerView.setLayoutManager(layoutManager);

        if(getIntent() !=null)
            categoryId=getIntent().getStringExtra(CategoryId);
        if(!categoryId.isEmpty() && categoryId !=null)
        {
            loadListFood(categoryId);
        }
    }

    private void loadListFood(String categoryId) {
        adapter=new FirebaseRecyclerAdapter<Food, FoodViewHolder>(Food.class,R.layout.food_item,FoodViewHolder.class,
                foodList.orderByChild("MenuId").equalTo(categoryId)) {
            @Override
            protected void populateViewHolder(FoodViewHolder viewHolder, Food model, int position) {

                viewHolder.food_name.setText(model.getName());
                Picasso.with(getBaseContext()).load(model.getImage())
                        .into(viewHolder.food_image);

                final Food local=model;
                viewHolder.setItemClickListener(new ItemClickListener() {
                    @Override
                    public void onClick(View view, int position, boolean isLongClick) {
                        Intent foodDetail=new Intent(FoodList.this,FoodDetail.class);
                      foodDetail.putExtra(FoodId,adapter.getRef(position).getKey());
                        startActivity(foodDetail);
                    }
                });
            }
        };
        Log.d("TAG",""+adapter.getItemCount());
        recyclerView.setAdapter(adapter);
    }
}

It is my FoodDetail activity...

public class FoodDetail extends AppCompatActivity {

    TextView food_name,food_price,food_description;
    ImageView food_image;
    CollapsingToolbarLayout collapsingToolbarLayout;
    FloatingActionButton btnCart;
    ElegantNumberButton numberButton;

    String foodId="";

    FirebaseDatabase database;
    DatabaseReference foods;
    Food currentFood;

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

        database = FirebaseDatabase.getInstance();
        foods = database.getReference("Foods");

        numberButton = findViewById(R.id.number_button);
        btnCart = findViewById(R.id.btnCart);
        btnCart.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                new Database(getBaseContext()).addToCart(new Order(
                        foodId,
                        currentFood.getName(),
                        numberButton.getNumber(),
                        currentFood.getPrice(),
                        currentFood.getDiscount()
                ));

                Toast.makeText(FoodDetail.this, "Added to Cart", Toast.LENGTH_SHORT).show();
            }
        });

        food_description = findViewById(R.id.food_description);
        food_name = findViewById(R.id.food_name);
        food_price = findViewById(R.id.food_price);
        food_image = findViewById(R.id.img_food);

        collapsingToolbarLayout = findViewById(R.id.collapsing);

        collapsingToolbarLayout.setExpandedTitleTextAppearance(R.style.ExpandedAppbar);
        collapsingToolbarLayout.setCollapsedTitleTextAppearance(R.style.CollapsedAppbar);

        if (getIntent() != null)
            foodId = getIntent().getStringExtra(FoodId);

        if(!foodId.isEmpty())
            getDetailFood(foodId);

    }

    private void getDetailFood(String foodId) {

        foods.child(foodId).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                currentFood=dataSnapshot.getValue(Food.class);

                //set image

                Picasso.with(getBaseContext()).load(currentFood.getImage()).into(food_image);
                collapsingToolbarLayout.setTitle(currentFood.getName());

                food_price.setText(currentFood.getPrice());
                food_name.setText(currentFood.getName());

                food_description.setText(currentFood.getDescription());
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }
}

It is showing error in "if(!foodId.isEmpty())"??

and it is showing below mentioned logcat..

02-14 11:49:21.238 6803-6803/com.example.rajatraturi.myrestaur E/AndroidRuntime: FATAL EXCEPTION: main Process: com.example.rajatraturi.myrestaur, PID: 6803 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.rajatraturi.myrestaur/com.example.rajatraturi.myrestaur.FoodDetail}: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.isEmpty()' on a null object reference at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2423) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2483) at android.app.ActivityThread.access$900(ActivityThread.java:153) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5441) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628) Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean java.lang.String.isEmpty()' on a null object reference at com.example.rajatraturi.myrestaur.FoodDetail.onCreate(FoodDetail.java:81) at android.app.Activity.performCreate(Activity.java:6303) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1108) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2376) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2483) at android.app.ActivityThread.access$900(ActivityThread.java:153) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1349) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:148) at android.app.ActivityThread.main(ActivityThread.java:5441) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:738) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:628) 02-14 11:49:21.292 6803-6803/com.example.rajatraturi.myrestaur I/Process: Sending signal. PID: 6803 SIG: 9

help me to solve this..i am not getting what is wrong??

Possible duplicate of [What is a NullPointerException, and how do I fix it?](https://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — ADM, Feb 14 '18 at 06:35

score 10 · Answer 1 · answered Feb 14 '18 at 08:28

10

The error log is saying the code is trying to execute isEmpty() method on a NULL object. I see you have 2 places calling isEmpty(). Before the not empty check, check the object for not null first. Something like this:

public class FoodList extends AppCompatActivity {
    .....

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        .....

        // check for not null first
        if (categoryId !=null && !categoryId.isEmpty())
        {
            loadListFood(categoryId);
        }
    }

}


public class FoodDetail extends AppCompatActivity {
    ....

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        .....

        // check for not null first
        if (foodId != null && !foodId.isEmpty())
            getDetailFood(foodId);

    }

Good luck!

answered Feb 14 '18 at 08:28

Shuwn Yuan Tee

5,578
6
28
42

Thanks for your help!! It solved my debugging problem.. now the fooddetail activity is working only when i put this activity in launcher but when im trying to go with the flow of app..it is keep throwing page back to the signin-signup activity after the foodlist activity....and there is no logcat at all? means no error... why this is happening? Again thanks... – Rajat Raturi Feb 14 '18 at 11:41
Couldn't tell from your provided code as there is no `signup-signin activity`. I would suggest you to add some debugging log to check the flow of your activities. Glad that I helped with your `NullPointerException` problem, why don't mark it as answer then :) – Shuwn Yuan Tee Feb 19 '18 at 05:20

score 0 · Answer 2 · answered Feb 14 '18 at 06:45

0

I can't see the "FoodId" in your code,and you should make sure "FoodId" is the same as another activity.

answered Feb 14 '18 at 06:45

TangXianQiang

136
5

now, nullpointerexception solved...but it is keep throwing page back to the sign-signup activity after the foodlist activity? and there are no errors in the logcat...Is there any problem in the Intent? – Rajat Raturi Feb 14 '18 at 11:45

Attempt to invoke virtual method 'boolean java.lang.String.isEmpty()' on a null object reference

2 Answers2