Activity to fragment Communication in Android

Question

I am using fragment for the first time. I am trying to get List of videos from youtube present in my fragment. I am retrieving a youtube url from firebase and extract playlist id from it. This playlist id is passed as a parameter to fragment which would then list out all the videos present in the playist. i am successfully able to retrieve the playlist id in the fragment, but it changes to null in the url. Any help is appreciable.thanks in advance. CollegeGallery.java

    public CollegeImageGrid imagegrid;
    private static final String TAG = "CollegeGallery";
    public GridView grid_image, grid_video;
    public DatabaseReference ref;
    private String collegeid;
    private TextView moreimages, morevideos;
    private String playlistid;

    public void setPlayid(String playlistid) {
        this.playlistid = playlistid;
    }

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

        ref = FirebaseDatabase.getInstance().getReference("collegedata");
        //this will get the data from previous intent
        collegeid = getIntent().getStringExtra("gallery");
        grid_image = findViewById(R.id.grid_image);
//        grid_video = findViewById(R.id.grid_video); //for grid view of videos

        moreimages = findViewById(R.id.more_images);
        morevideos = findViewById(R.id.more_videos);

        //a list of string will  be passed to  imagegrid object
        ref.child(String.valueOf(collegeid)).addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
               //object of College class to get getImageurls() which has the list of urls
                College clg = dataSnapshot.getValue(College.class);
                //setting the list to imagegrid, passing url from this activity to imageview.
                imagegrid = new CollegeImageGrid(CollegeGallery.this,clg.getImageurls());
                //setting adapter to grid with the list of urls
                grid_image.setAdapter(imagegrid); //check error, getCount is null, crashes application.
                //extracting playlist id
                String playid = getYoutubeVideoId(clg.getVideourls());
                //fragment code
                YoutubeVideoList yt = new YoutubeVideoList();
                FragmentTransaction tr = getSupportFragmentManager().beginTransaction();
                tr.replace(R.id.youtube_frag, YoutubeVideoList.newInstance(playid)).commit();
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {
                Toast.makeText(CollegeGallery.this, "No images", Toast.LENGTH_SHORT).show();
            }
        });

        moreimages.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Intent image_in = new Intent(CollegeGallery.this,AllCollegeImages.class);
                image_in.putExtra("image",collegeid);
                startActivity(image_in);
            }
        });

        //will take to activity with only playlist video list fragment
        morevideos.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                startActivity(new Intent(CollegeGallery.this, CompleteVideoList.class));
            }
        });

    }

    //function to extract playlist id
    public static String getYoutubeVideoId(String youtubeUrl) {
        String video_id = "";
        if (youtubeUrl != null && youtubeUrl.trim().length() > 0 && youtubeUrl.startsWith("http")) {

            String expression = "^.*?(?:list)=(.*?)(?:&|$)";

            CharSequence input = youtubeUrl;
            Pattern pattern = Pattern.compile(expression, Pattern.CASE_INSENSITIVE);
            Matcher matcher = pattern.matcher(input);
            if (matcher.matches()) {
                String groupIndex1 = matcher.group(1);
                video_id = groupIndex1;
            }
        }
        return video_id;
    }

}

YoutubeVideoList.java(Fragment)

    private static String ARG_Param1;
    private static String id;
    List<YoutubeVideoModel> vids;
    Button btn;
    YoutubeAdapter adapter;
    RecyclerView recyclerView;
    RecyclerView.LayoutManager manager;
    String mparam1;

    public YoutubeVideoList() {
    }

    //retrieving playlist id from the previous activity
    public static YoutubeVideoList newInstance(String id) {
        YoutubeVideoList yt = new YoutubeVideoList();
        Bundle args = new Bundle();
        args.putString(ARG_Param1, id);
        yt.setArguments(args);
        return yt;
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mparam1 = getArguments().getString(ARG_Param1);
        }

    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_youtube_video_list, container, false);
    }

    @Override
    public  void onViewCreated(View container, Bundle savedInstanceState) {
        super.onViewCreated(container, savedInstanceState);
        recyclerView = container.findViewById(R.id.vidReclycer);
        manager = new LinearLayoutManager(getActivity());
        recyclerView.setLayoutManager(manager);
        recyclerView.setHasFixedSize(false);


         id = mparam1;
        //right here, id has the playlist id
        System.out.println("this is the playlist id------------------->"+id);
        String url = "https://www.googleapis.com/youtube/v3/playlistItems?key=AIzaSyBmISPZAjsrku2_yKLcTW4Y6qq6aqlht-0&playlistId="+id+"&part=snippet&maxResults=36";
        //even url has the value but the list is not shown and id changes to null
        System.out.println(url);
        RequestQueue queue = Volley.newRequestQueue(getContext());

        StringRequest request = new StringRequest(Request.Method.GET, url,
                new Response.Listener<String>() {
                    @Override
                    public void onResponse(String response) {
                        vids = new ArrayList<>();
                        try {
                            JSONObject mainObject = new JSONObject(response);
                            JSONArray itemArray = (JSONArray) mainObject.get("items");
                            for (int i = 0; i < itemArray.length(); i++) {
                                String title = itemArray.getJSONObject(i).getJSONObject("snippet").getString("title");
                                String url = itemArray.getJSONObject(i).getJSONObject("snippet").getJSONObject("thumbnails").getJSONObject("maxres").getString("url");
                                String vidid = itemArray.getJSONObject(i).getJSONObject("snippet").getJSONObject("resourceId").getString("videoId");
                                YoutubeVideoModel vid = new YoutubeVideoModel(title, url, vidid);
                                vids.add(vid);
                            }
                            adapter = new YoutubeAdapter(getContext(), vids);
                            recyclerView.setAdapter(adapter);
                            recyclerView.getAdapter().notifyDataSetChanged();
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }

                    }
                }, new Response.ErrorListener() {
            @Override
            public void onErrorResponse(VolleyError error) {
//                Log.e("Error in request", error.getMessage());
            }
        });
        queue.add(request);
        }
    }
```this is the image of my logcat. It prints id and url as required, but then it changes to null

Answer 1

Got the answer. there was a problem in sharing data between activity and fragment. the value was being set null twice, one before and one after the function call(i dont know why but). then instead of calling newInstance() i used bundle, checked if it is null or not in fragment class and then set the value of id. CollgeGallery.java

            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
               //object of College class to get getImageurls() which has the list of urls
                College clg = dataSnapshot.getValue(College.class);
                String playid = getYoutubeVideoId(clg.getVideourls());
                //setting the list to imagegrid, passing url from this activity to imageview.
                imagegrid = new CollegeImageGrid(CollegeGallery.this,clg.getImageurls());
                //setting adapter to grid with the list of urls
                grid_image.setAdapter(imagegrid); //check error, getCount is null, crashes application.
                //extracting playlist id
//                String playid = getYoutubeVideoId(clg.getVideourls());
                //fragment code
                setPlayid(playid);
                Bundle bun = new Bundle();
                YoutubeVideoList firstfrag = new YoutubeVideoList();
                bun.putString("test", playid);
                firstfrag.setArguments(bun);
                getSupportFragmentManager().beginTransaction().add(R.id.youtube_frag, firstfrag).commit();
//                FragmentTransaction tr = getSupportFragmentManager().beginTransaction();
//                tr.add(R.id.youtube_frag, YoutubeVideoList.newInstance(playid)).commit();
            }```
**YoutubeVideoList.java**

    ```@Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            Bundle args = this.getArguments();
            if(args != null){
                id = args.getString("test");
            }
        }```

Thanks everyone for your help. :)

Answer 2

In your CollegeGallery.java in place of: yt.newInstance(playid) write this YoutubeVideoList.newInstance(playid)

Also remove the static String id from your YoutubeVideoList fragment if it's useless