RecyclerView 在第二次点击时不显示项目

Question

I have a RecyclerView that I am using to display a list that I obtain from making a request to remote api. The list is shown on the first time that the activity appears but when I go back and come back to activity again, the list doesn't show. How can I solve this? This is the activity that I call the recyclerview.

public class DisplayMessage extends AppCompatActivity {
    RecyclerView recyclerView;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.language_selection);
        recyclerView = (RecyclerView) findViewById(R.id.recylerview);

        LanguageAdapter languageAdapter = new LanguageAdapter(this);
        recyclerView.setAdapter(languageAdapter);

        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
        linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
        recyclerView.setLayoutManager(linearLayoutManager);

    }
}

This is the Adapter class.

public class LanguageAdapter extends RecyclerView.Adapter<LanguageAdapter.MyViewHolder> {

    ArrayList<Language> languageArrayList;

    public LanguageAdapter(Context context) {
        this.languageArrayList = new ArrayList<Language>();
        RequestQueue queue = Volley.newRequestQueue(context);
        String url ="https://api.bounswe2019group9.tk/contents/languages";
        JsonObjectRequest jsonObjectRequest = new JsonObjectRequest(Request.Method.GET, url, null,
                new Response.Listener<JSONObject>() {

                    @Override
                    public void onResponse(JSONObject response) {
                        try {
                            JSONArray data = (JSONArray) response.get("data");
                            for(int i=0; i<data.length();i++){
                                Language lang = new Language((String) data.get(i));
                                languageArrayList.add(lang);
                                Log.i("api", ""+lang.getLanguageName());
                            }
                        } catch (JSONException e) {
                            e.printStackTrace();
                        }

                    }
                }
                , new Response.ErrorListener() {

            @Override
            public void onErrorResponse(VolleyError error) {
                Log.e("language_selection", "Error on request to get language list");

            }
        });
        queue.add(jsonObjectRequest);
    }

    @Override
    public MyViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        LayoutInflater layoutInflater = LayoutInflater.from(parent.getContext());
        View view = layoutInflater.inflate(R.layout.languages, parent, false);
        MyViewHolder holder = new MyViewHolder(view);
        return holder;
    }

    @Override
    public void onBindViewHolder(MyViewHolder holder, int position) {
        holder.languageName.setText(languageArrayList.get(position).getLanguageName());
    }

    @Override
    public int getItemCount() {
        return languageArrayList.size();
    }


    class MyViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

        public TextView languageName;
        public RelativeLayout relativeLayout;

        public MyViewHolder(View itemView) {
            super(itemView);
            this.languageName = (TextView) itemView.findViewById(R.id.language);
            this.relativeLayout = (RelativeLayout) itemView.findViewById(R.id.relativeLayout);
        }

        @Override
        public void onClick(View v) {

        }


    }
}

Answer 1

OnCreate() method gets called only once when activity is created. You have set the adapter with the language list in OnCreate() and that it why it gets set only at the first time. When you reenter on the same screen then OnCreate won't get called again.

You have to set the adapter in the OnResume() method because this method will get called every time when you visit this screen.

Answer 2

In your Activity class, override an onResume method, and inside that also declare the following codes-

   LanguageAdapter languageAdapter = new LanguageAdapter(this);
   recyclerView.setAdapter(languageAdapter);