RecyclerView-Adapter getItemCount löst NullPointerException aus

Question

In meinem Projekt hole ich Daten von einem Server und zeige sie in einer Recyclerview an. Nachdem ich Daten zu einer Liste hinzugefügt und sie in getItemCount() aufgerufen habe, bekomme ich null und es wird eine Ausnahme ausgelöst.

public class AppointmentResponse { 
    private static final String TAG = "Appointment Response"; 
    @SerializedName("data") 
    @Expose 
    private List<AppntRespData> data = null; 
    @SerializedName("error_code") 
    @Expose 
    private String errorCode; 
    @SerializedName("message") 
    @Expose 
    private String message; 
    @SerializedName("status") 
    @Expose 
    private String status; 

    public List<AppntRespData> getData() { 
     return data; 
    } 

    public AppointmentResponse() { 
    } 

    public AppointmentResponse(List<AppntRespData> data, String errorCode, String message, String status) { 
     this.data = data; 
     this.errorCode = errorCode; 
     this.message = message; 
     this.status = status; 
    } 

    public void setData(List<AppntRespData> data) { 
     this.data = data; 
    } 

    public String getErrorCode() { 
     return errorCode; 
    } 

    public void setErrorCode(String errorCode) { 
     this.errorCode = errorCode; 
    } 

    public String getMessage() { 
     return message; 
    } 

    public void setMessage(String message) { 
     this.message = message; 
    } 

    public String getStatus() { 
     return status; 
    } 

    public void setStatus(String status) { 
     this.status = status; 
    } 

    @Override 
    public String toString() { 
     return "AppointmentResponse{" + 
      "data=" + data + 
      ", errorCode='" + errorCode + '\'' + 
      ", message='" + message + '\'' + 
      ", status='" + status + '\'' + 
      '}'; 
    } 

    @Override 
    public boolean equals(Object o) { 
     if (this == o) return true; 
     if (o == null || getClass() != o.getClass()) return false; 

     AppointmentResponse that = (AppointmentResponse) o; 

     if (data != null ? !data.equals(that.data) : that.data != null) return false; 
     if (errorCode != null ? !errorCode.equals(that.errorCode) : that.errorCode != null) 
      return false; 
     if (message != null ? !message.equals(that.message) : that.message != null) return false; 
    return status != null ? status.equals(that.status) : that.status == null; 

    } 

    @Override 
    public int hashCode() { 
     int result = data != null ? data.hashCode() : 0; 
     result = 31 * result + (errorCode != null ? errorCode.hashCode() : 0); 
     result = 31 * result + (message != null ? message.hashCode() : 0); 
     result = 31 * result + (status != null ? status.hashCode() : 0); 
     return result; 
    } 

public static class AppntRespData 
{ 
    @SerializedName("with_whom") 
    @Expose 
    private String withWhom; 
    @SerializedName("service_type") 
    @Expose 
    private String serviceType; 
    @SerializedName("appointment_time") 
    @Expose 
    private String appointmentTime; 
    @SerializedName("appointment_status") 
    @Expose 
    private String appointmentStatus; 
    @SerializedName("appointment_id") 
    @Expose 
    private String appointmentId; 
    @SerializedName("appointment_date") 
    @Expose 
    private String appointmentDate; 

    public AppntRespData() { 
    } 

    public AppntRespData(String withWhom, String serviceType, String appointmentTime, String appointmentStatus, String appointmentId, String appointmentDate) { 
     this.withWhom = withWhom; 
     this.serviceType = serviceType; 
     this.appointmentTime = appointmentTime; 
     this.appointmentStatus = appointmentStatus; 
     this.appointmentId = appointmentId; 
     this.appointmentDate = appointmentDate; 
    } 

    public String getWithWhom() { 
     return withWhom; 
    } 

    public void setWithWhom(String withWhom) { 
     this.withWhom = withWhom; 
    } 

    public String getServiceType() { 
     return serviceType; 
    } 

    public void setServiceType(String serviceType) { 
     this.serviceType = serviceType; 
    } 

    public String getAppointmentTime() { 
     return appointmentTime; 
    } 

    public void setAppointmentTime(String appointmentTime) { 
     this.appointmentTime = appointmentTime; 
    } 

    public String getAppointmentStatus() { 
     return appointmentStatus; 
    } 

    public void setAppointmentStatus(String appointmentStatus) { 
     this.appointmentStatus = appointmentStatus; 
    } 

    public String getAppointmentId() { 
     return appointmentId; 
    } 

    public void setAppointmentId(String appointmentId) { 
     this.appointmentId = appointmentId; 
    } 

    public String getAppointmentDate() { 
     return appointmentDate; 
    } 

    public void setAppointmentDate(String appointmentDate) { 
     this.appointmentDate = appointmentDate; 
    } 

    @Override 
    public String toString() { 
     return "AppntRespData{" + 
       "withWhom='" + withWhom + '\'' + 
       ", serviceType='" + serviceType + '\'' + 
       ", appointmentTime='" + appointmentTime + '\'' + 
       ", appointmentStatus='" + appointmentStatus + '\'' + 
       ", appointmentId='" + appointmentId + '\'' + 
       ", appointmentDate='" + appointmentDate + '\'' + 
       '}'; 
    } 

    @Override 
    public boolean equals(Object o) { 
     if (this == o) return true; 
     if (o == null || getClass() != o.getClass()) return false; 

     AppntRespData that = (AppntRespData) o; 

     if (withWhom != null ? !withWhom.equals(that.withWhom) : that.withWhom != null) 
      return false; 
     if (serviceType != null ? !serviceType.equals(that.serviceType) : that.serviceType != null) 
      return false; 
     if (appointmentTime != null ? !appointmentTime.equals(that.appointmentTime) : that.appointmentTime != null) 
      return false; 
     if (appointmentStatus != null ? !appointmentStatus.equals(that.appointmentStatus) : that.appointmentStatus != null) 
      return false; 
     if (appointmentId != null ? !appointmentId.equals(that.appointmentId) : that.appointmentId != null) 
      return false; 
     return appointmentDate != null ? appointmentDate.equals(that.appointmentDate) : that.appointmentDate == null; 

    } 

    @Override 
    public int hashCode() { 
     int result = withWhom != null ? withWhom.hashCode() : 0; 
     result = 31 * result + (serviceType != null ? serviceType.hashCode() : 0); 
     result = 31 * result + (appointmentTime != null ? appointmentTime.hashCode() : 0); 
     result = 31 * result + (appointmentStatus != null ? appointmentStatus.hashCode() : 0); 
     result = 31 * result + (appointmentId != null ? appointmentId.hashCode() : 0); 
     result = 31 * result + (appointmentDate != null ? appointmentDate.hashCode() : 0); 
     return result; 
    } 
} 
} 

Meine JSON-Daten holen Methode

ApiInterface service = RestClient.getApiInterface(); 

    final Call<AppointmentResponse> AppResp = service.postAppointListData(appntRequest); 

    AppResp.enqueue(new Callback<AppointmentResponse>() { 
     @Override 
     public void onResponse(@NonNull Call<AppointmentResponse> call, @NonNull Response<AppointmentResponse> response) { 

      try { 
       if (response.body().getErrorCode().equals("0")) { 

        AppointmentResponse.AppntRespData mAppData = new AppointmentResponse.AppntRespData(); 


        for (int i=0;i<response.body().getData().size();i++) { 


         mAppData.setWithWhom(response.body().getData().get(i).getWithWhom()); 
         mAppData.setAppointmentDate(response.body().getData().get(i).getAppointmentDate()); 
         mAppData.setAppointmentId(response.body().getData().get(i).getAppointmentId()); 
         mAppData.setAppointmentStatus(response.body().getData().get(i).getAppointmentStatus()); 
         mAppData.setAppointmentTime(response.body().getData().get(i).getAppointmentTime()); 
         mAppData.setServiceType(response.body().getData().get(i).getServiceType()); 

       //public ArrayList<AppointmentResponse.AppntRespData> appointmentlist; 

         appointmentlist.add(mAppData); 


        } 


        Log.d(TAG, "onResponse: appointList--"+appointmentlist); 



       } 

       else { 
        Toast.makeText(getContext(), response.body().getMessage(), Toast.LENGTH_SHORT).show();; 
       } 
      }catch (Exception e) 
      { 
       e.getMessage(); 
      } 
     } 

     @Override 
     public void onFailure(@NonNull Call<AppointmentResponse> call, @NonNull Throwable t) { 

      t.getMessage(); 

     } 
    }); 

Mein Recycler Adapter Klasse

public class AppointRecycleAdapter extends RecyclerView.Adapter<AppointRecycleAdapter.AppointViewHolder> { 
    private Context mContext; 
    private ArrayList<AppointmentResponse.AppntRespData> appointmentlist; 
    private static final String TAG = "AppointRecycleAdapter"; 

    public AppointRecycleAdapter(Context mContext, ArrayList<AppointmentResponse.AppntRespData> appointmentlist) { 
     this.mContext = mContext; 
     this.appointmentlist = appointmentlist; 
    } 

    public class AppointViewHolder extends RecyclerView.ViewHolder { 
     private CardView mCradview; 
     private TextView tvInsWith,tvInsApDate,tvInsApStatus; 

     public AppointViewHolder(View itemView) { 
      super(itemView); 

      mCradview = itemView.findViewById(R.id.cardViewAppnt); 
      tvInsApDate = itemView.findViewById(R.id.InsAppntDate); 
      tvInsApStatus = itemView.findViewById(R.id.InsAppntStatus); 
      tvInsWith = itemView.findViewById(R.id.Inswith); 
     } 
    } 



    @Override 
    public AppointViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { 
     View mView = LayoutInflater.from(parent.getContext()).inflate(R.layout.appointmentcardlayout,parent,false); 
     return new AppointViewHolder(mView); 
    } 

    @Override 
    public void onBindViewHolder(AppointViewHolder holder, int position) { 
     Log.d(TAG, "onBindViewHolder: in"); 
     //final AppointmentResponse.AppntRespData bean = appointmentlist.get(position); 

     holder.tvInsApStatus.setText(appointmentlist.get(position).getAppointmentStatus()); 
     //holder.tvInsWith.setText(appointmentResponseList.get(position).getWithWhom()); 
    //holder.tvInsApDate.setText(bean.getAppointmentDate()); 
    // holder.tvInsApStatus.setText(appointmentResponseList.get(position).getAppointmentStatus()); 

    Log.d(TAG, "onBindViewHolder: appRespList---------"+appointmentlist); 


    holder.mCradview.setOnClickListener(new View.OnClickListener() { 
     @Override 
     public void onClick(View view) { 
      AppCompatActivity activity = (AppCompatActivity) view.getContext(); 
      DetailAppointList detailAppointList = new DetailAppointList(); 

      activity.getSupportFragmentManager().beginTransaction() 
        .replace(R.id.content, detailAppointList).addToBackStack(null).commit(); 
     } 
    }); 

} 

@Override 
public int getItemCount() { 

     Log.d(TAG, "getItemCount: list DATA-----" + appointmentlist.size()); 

     //**Here I'm getting Null Pointer exception** 
     return appointmentlist == null ? 0 : appointmentlist.size(); 


    } 

} 

Answer 1

Änderung im Code der Funktion getItemCount()

@Override 
public int getItemCount() { 
     //your problem is here because you are printing size of list which is null, 
     //so instead of that check the null first, then use the list object 
     if (appointmentlist == null) 
      Log.d(TAG, "null list"); 
     else 
      Log.d(TAG, "getItemCount: list DATA-----" + appointmentlist.size()); 

     //**Here I'm getting Null Pointer exception** 
     return appointmentlist == null ? 0 : appointmentlist.size(); 


    } 

} 

Answer 2

Sie bearbeiten den Fall nicht in Log.d(TAG, "getItemCount: list DATA-----" + appointmentlist.size()); Zeile, wenn die Terminliste leer ist und Sie appointmentlist.size() aufrufen. Deshalb wird es NullPointerException geben

Answer 3

Ich habe Antwort nach Arraylist deklarieren, appointmentlist als statische in das Abrufen von JSON-Methode (Instanzvariablen)

public static ArrayList<AppointmentResponse.AppntRespData> appointmentlist; 

und initialisieren es in OnResponse()

i.e before for(int i=0;i<response.body().getData().size();i++)

public void onResponse(@NonNull Call<AppointmentResponse> call, @NonNull Response<AppointmentResponse> response) { 

      try { 
       if (response.isSuccessful()) { 

        appointmentlist = new ArrayList<AppointmentResponse.AppntRespData>(); 

        for (int i=0;i<response.body().getData().size();i++) { 


         AppointmentResponse.AppntRespData mAppData = new AppointmentResponse.AppntRespData();