passing string from an activity to a fragment

Question

Hi ive been going through questions and found a solution to pass a string from an activity (not the fragment activity) to a fragment. i want to pass a document ID on click from RestaurantsList.class to Mainsfragment.class, inside my onclick.

The error message i get is the following:

Attempt to invoke virtual method 'android.content.Intent android.app.Activity.getIntent()' on a null object reference

here is my code for the activity:

package com.example.hostapp;

import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.widget.RelativeLayout;

import com.example.hostapp.Adapters.RestaurantAdapter;
import com.example.hostapp.Adapters.categoryCardAdapter;
import com.example.hostapp.MenuFragments.MainsFragment;
import com.example.hostapp.Models.Restaurant;
import com.example.hostapp.Models.categoryCard;
import com.firebase.ui.firestore.FirestoreRecyclerOptions;
import com.google.firebase.firestore.CollectionReference;
import com.google.firebase.firestore.DocumentSnapshot;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.Query;

public class RestaurantList extends AppCompatActivity {

    private FirebaseFirestore db = FirebaseFirestore.getInstance();
    private CollectionReference restaurantref = db.collection("restaurants");
    private RestaurantAdapter adapter;

    String categoryid = "";

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


        setUpRecyclerView();
    }

    private void setUpRecyclerView() {


        //Get intent
        if (getIntent() != null)
            categoryid = getIntent().getStringExtra("categoryid");
        if (!categoryid.isEmpty() && categoryid != null) {
            Query query = restaurantref.whereEqualTo("categoryid", categoryid).orderBy("name");

            final FirestoreRecyclerOptions<Restaurant> options = new FirestoreRecyclerOptions.Builder<Restaurant>().setQuery(query, Restaurant.class).build();

            adapter = new RestaurantAdapter(options);

            RecyclerView recyclerView = findViewById(R.id.restaurant_recycler);
            recyclerView.setHasFixedSize(true);
            recyclerView.setLayoutManager(new LinearLayoutManager(this));
            recyclerView.setAdapter(adapter);

            adapter.setOnItemClickListerner(new RestaurantAdapter.OnItemClickListener() {
                @Override
                public void onItemClick(DocumentSnapshot documentSnapshot, int position) {
                    Restaurant restaurant = documentSnapshot.toObject(Restaurant.class);
                    Intent foodlist = new Intent(RestaurantList.this, Foodlist.class);


                    Bundle bundle = new Bundle();
                    bundle.putString("restaurantid", documentSnapshot.getId());
                    MainsFragment m4 = new MainsFragment();
                    m4.setArguments(bundle);


                    //foodlist.putExtra("restaurantid", documentSnapshot.getId());
                    startActivity(foodlist);


                }
            });
        }
    }


    @Override
    protected void onStart() {
        super.onStart();
        adapter.startListening();
    }

    @Override
    protected void onStop() {
        super.onStop();
        adapter.stopListening();
    }
}

here is my code for the fragment:

package com.example.hostapp.MenuFragments;

import android.os.Bundle;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.example.hostapp.Adapters.FoodAdapter;
import com.example.hostapp.Models.FoodModel;
import com.example.hostapp.R;
import com.example.hostapp.RestaurantList;
import com.firebase.ui.firestore.FirestoreRecyclerOptions;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.Query;


public class MainsFragment extends Fragment {


    private FirebaseFirestore db = FirebaseFirestore.getInstance();
    private FoodAdapter adapter;


    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_mains, container, false);

        String restaurantNumber = getArguments().getString("restaurantid");
        Query menuref = db.collectionGroup("Foods").whereEqualTo("menuid", restaurantNumber);

        FirestoreRecyclerOptions<FoodModel> options = new FirestoreRecyclerOptions.Builder<FoodModel>().
                setQuery(menuref, FoodModel.class)
                .build();

        adapter = new FoodAdapter(options);

        RecyclerView recyclerView = view.findViewById(R.id.recycler_mains);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(this.getActivity()));
        recyclerView.setAdapter(adapter);


        return view;
    }

    private void setUpRecyclerView() {


    }

    @Override
    public void onStart() {
        super.onStart();
        adapter.startListening();
    }

    @Override
    public void onStop() {
        super.onStop();
        adapter.stopListening();
    }
}

Answer 1

I had the same experience like this. Here is how I handled it:

1, Pass your data from RestaurantList activity to your foodlist activity via intent.putExtra();

Intent foodlist = new Intent(RestaurantList.this, Foodlist.class);
foodlist.putExtra("restaurantid", documentSnapshot.getId());
startActivity(foodlist);

2, Get the value by getIntent() from Foodlist activity;

String id = getIntent().getStringExtra("restaurantid");

3, Pass your data to the Adapter where you are initializing the adapter. (sth like this :)

YourAdapter adapter = new YourAdapter(getSupportFragmentManager(), tabLayout.getTabCount(),id);

4, Get the data in constractor of adapter (you have to create a global variable and fill it in constructor) and create a bundle in getItem() method and pass the data to it and set arguments to the fragment (like below code)

public class YourAdapter extends FragmentStatePagerAdapter {
    int mNumOfTabs;
    String id;
    public AdapterPagerShift(FragmentManager fm, int NumOfTabs, String id) {
        super(fm);
        this.mNumOfTabs = NumOfTabs;
        this.id = id;
    }

    @Override
    public Fragment getItem(int position) {

        Bundle bundle = new Bundle();
        bundle.putString("restaurantid", documentSnapshot.getId());
        switch (position) {
            case 0:
                MainsFragment main = new MainsFragment();
                main.setArguments(bundle);
                return main;
            case 1:
                //...
            case 2:
               //...
            default:
                return null;
        }
    }

    @Override
    public int getCount() {
        return mNumOfTabs;
    }
}

5, Get the data by using below code in your MainsFragment class :

@Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        String id = getArguments().getString("restaurantid");

}

Hope it helps!