为什么我的 RecyclerView 不显示任何内容？

Question

I have a big issue. My RecyclerView doesnt work and I don´t know how to solve my problem. In my Logcat it seems that the Fragment doesn't call onResponse and only call the ErrorResponse .
I tried everything but nothing helped at all.
Don't know which part is wrong and why it doesnt work.

My Home Fragment:

public class Home_Fragment extends Fragment {
private String URL= "http://localhost/pages/index.php";
private RecyclerAdapter recyclerAdapter;
private RecyclerView recyclerView;
private ArrayList<Data> listdata;
private static final String TAG = "Home_Fragment";


private GridLayoutManager gridLayoutManager;

// TODO: Rename parameter arguments, choose names that match
// the fragment initialization parameters, e.g. ARG_ITEM_NUMBER
public Home_Fragment() {
    // Required empty public constructor
}
private void AmbilData() {
    JsonArrayRequest aarRequest = new JsonArrayRequest(URL,
            new Response.Listener<JSONArray>() {
        @Override
        public void onResponse(JSONArray response) {
            if (response.length()>0){
                for (int i =0 ; i<response.length();i++){
                    try {
                        JSONObject data = response.getJSONObject(i);
                        Data item = new Data();
                        item.setEventname(data.getString("Eventname"));
                        item.setEventhost(data.getString("Eventclub"));
                        item.setEventclub(data.getString("Eventhost"));
                        item.setGenre(data.getString("Genre"));
                        item.setDate(data.getString("Date"));
                        item.setAdress(data.getString("Adress"));
                        item.setTime(data.getString("Time"));
                        item.setPrice(data.getString("Price"));


                    } catch (JSONException e) {
                    }
                }
                recyclerAdapter.addData(listdata);
            }
        }
        },
            new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
                                }
                            }){

                    };
                    Volley.newRequestQueue(getActivity()).add(aarRequest);
                }

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    Log.d(TAG, "onCreateView: createview");

    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_home_, container, false);

    AmbilData();
    recyclerView = view.findViewById(R.id.recyclerview);
    recyclerView.setHasFixedSize(true);
    gridLayoutManager = new GridLayoutManager(getActivity(), 2);
    gridLayoutManager.setOrientation(GridLayoutManager.VERTICAL);
    recyclerView.setLayoutManager(gridLayoutManager);
    listdata = new ArrayList<Data>();
    recyclerAdapter = new RecyclerAdapter(getActivity(),listdata);
    recyclerView.setAdapter(recyclerAdapter);
    recyclerAdapter.notifyDataSetChanged();
    Log.d(TAG, "onCreateView: viewreturned");

    return view;
}
}

My RecyclerAdapter

public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.ViewHolder> {
    private ArrayList<Data> listdata;
    private Activity activity;
    private Context context;
    private static final String TAG = "Recycler";

public RecyclerAdapter(Activity activity, ArrayList<Data> listdata) {
    this.listdata = listdata;
    this.activity = activity;
}

@Override
public RecyclerAdapter.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
    Log.d(TAG, "onCreateViewHolder: create Holder");
    View v = LayoutInflater.from(parent.getContext())
            .inflate(R.layout.event_cardview, parent, false);
    ViewHolder vh = new ViewHolder(v);
    return vh;
}

@Override
public void onBindViewHolder(ViewHolder holder, int position) {
    Log.d(TAG, "onBindViewHolder: Create holder Items");
    //holder.mImage.setImageResource(listdata.get(position).getThubnail());
    holder.eventname.setText(listdata.get(position).getEventname());
    holder.eventclub.setText(listdata.get(position).getEventclub());
    holder.eventhost.setText(listdata.get(position).getEventhost());
    holder.genre.setText(listdata.get(position).getGenre());
    holder.date.setText(listdata.get(position).getDate());
    holder.adress.setText(listdata.get(position).getAdress());
    holder.time.setText(listdata.get(position).getTime());
    holder.price.setText(listdata.get(position).getPrice());


}
public void addData(List<Data> data) {
    listdata.addAll(data);
    notifyDataSetChanged();
}
@Override
public int getItemCount() {
    Log.d(TAG, "getItemCount: return size");
    return listdata.size();
}

public static class ViewHolder extends RecyclerView.ViewHolder {
    private CardView cv;
    private TextView eventname,eventclub,eventhost,genre,date,adress,time,price;
    private static final String TAG = "Class";


    public ViewHolder(View v) {
        super(v);
        Log.d(TAG, "ViewHolder: created");
        cv=(CardView)v.findViewById(R.id.eventcardview);
        eventname=(TextView)v.findViewById(R.id.EventName);
        eventclub=(TextView)v.findViewById(R.id.EventClub);
        eventhost=(TextView)v.findViewById(R.id.EventHost);
        genre=(TextView)v.findViewById(R.id.Genre);
        date=(TextView)v.findViewById(R.id.dark);
        adress=(TextView)v.findViewById(R.id.location_adress);
        time=(TextView)v.findViewById(R.id.Time);
        price=(TextView)v.findViewById(R.id.Price);

    }
}

}

My Data

public class Data {
    private String eventname;
    private String eventclub;
    private String eventhost;
    private String genre;
    private String date;
    private String adress;
    private String time;
    private String price;

public String getEventname() {
    return eventname;
}
public void setEventname(String eventname) {
    this.eventname = eventname;
}

public String getEventclub() {
    return eventclub;
}
public void setEventclub(String eventlcub) {
    this.eventclub = eventclub;
}

public String getEventhost() {
    return eventhost;
}
public void setEventhost(String eventhost) {
    this.eventhost = eventhost;
}

public String getGenre() {
    return genre;
}
public void setGenre(String genre) {
    this.genre = genre;
}

public String getDate() {
    return date;
}
public void setDate(String date) {
    this.date = date;
}

public String getAdress() {
    return adress;
}

public void setAdress(String adress) {
    this.adress = adress;
}

public String getTime() {
    return time;
}
public void setTime(String time) {
    this.time = time;
}

public String getPrice() {
    return price;
}
public void setPrice(String price) {
    this.price = price;
}

}

When I open localhost/pages/index.php on my Computer it shows this:

 {"ID":1,"Eventname":"Imagine-Event","Eventclub":"Imagine-Club","Eventhost":"Imagine-Host","Genre":"Techno","Date":"2020-12-31","Time":"22:00-06:00","Adress":"Frankfurt Gutleutstra\u00dfe 126a","Price":15}
{"ID":2,"Eventname":"Hello-Event","Eventclub":"Hello-Club","Eventhost":"Hello-Host","Genre":"Hello","Date":"2021-01-01","Time":"21:00-6:00","Adress":"Frankfurt am Main Sachsenhausengasse 128a","Price":5}
{"ID":3,"Eventname":"Fantasy-Event","Eventclub":"Fantasy-Club","Eventhost":"Fantasy-Host","Genre":"Mainstream","Date":"2021-02-19","Time":"00:00-12:00","Adress":"Langen (Hessen) Sehretstra\u00dfe 33a","Price":5}
{"ID":4,"Eventname":"This Event","Eventclub":"This-Club","Eventhost":"This Host","Genre":"Hip-Hop","Date":"2021-03-03","Time":"20:00-2:00","Adress":"Frankfurt am Main Goethestra\u00dfe","Price":15}

When I start it dont show the Recyclerview what is the problem tried to solve it for 10 hours now.

Answer 1

You are adding empty data to the RecyclerView adapter when you call recyclerAdapter.addData(listdata) in AmbilData() method because you iterate over the JSON list and didn't add items to listdata list of data.

To solve this, use listdata.add(item) within the loop.

private void AmbilData() {
    JsonArrayRequest aarRequest = new JsonArrayRequest(URL,
            new Response.Listener<JSONArray>() {
        @Override
        public void onResponse(JSONArray response) {
            if (response.length()>0){
                for (int i =0 ; i<response.length();i++){
                    try {
                        JSONObject data = response.getJSONObject(i);
                        Data item = new Data();
                        item.setEventname(data.getString("Eventname"));
                        item.setEventhost(data.getString("Eventclub"));
                        item.setEventclub(data.getString("Eventhost"));
                        item.setGenre(data.getString("Genre"));
                        item.setDate(data.getString("Date"));
                        item.setAdress(data.getString("Adress"));
                        item.setTime(data.getString("Time"));
                        item.setPrice(data.getString("Price"));
                        listdata.add(item); // <<<<<< Here is the Change

                    } catch (JSONException e) {
                    }
                }
                recyclerAdapter.addData(listdata);
            }
...

Also as @Gabe Sechan pointed out in comments, you have to check the URL

Answer 2

I solved my problem. I got at the getItemcount method the size null cause my PHP-code was wrong. I didnt throw out the right variables.

My Code: `

?php foreach ($events AS $event):
         $ID=json_encode($events);
         print($ID);
endforeach; ?>

Before I used $event now im using $events as param.

`