Cuando se utiliza la biblioteca de paginación, mostrando observador tamaño de la lista como cero

matriz:

Estoy tratando de utilizar la biblioteca de paginación con las nuevas versiones. Estoy usando volea a buscar a mis datos de la red. Siempre que voy a buscar los datos de la red, los datos es exagerado, pero cuando la llamada se dirige al observador el tamaño de la lista mostrada no es cero. No estoy seguro de lo que estoy haciendo mal.

Soy nuevo en android así que no sé mucho acerca de paginación. Ya hace días que no estoy tratando, pero todavía no ha podido averiguarlo.

Mi Gradle es el siguiente

apply plugin: 'com.android.application'

android {
compileSdkVersion 27
defaultConfig {
    applicationId "com.example.athansys.mypagingapplication"
    minSdkVersion 22
    targetSdkVersion 27
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}
}

dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
implementation 'com.android.support:appcompat-v7:27.1.1'
implementation 'com.android.support:support-v4:27.1.1'
implementation 'com.android.support:cardview-v7:27.1.1'
implementation 'com.android.support:recyclerview-v7:27.1.1'
implementation 'com.android.volley:volley:1.1.0'
implementation 'com.google.code.gson:gson:2.8.1'
implementation 'com.android.support:design:27.1.1'
implementation 'com.android.support.constraint:constraint-layout:1.1.2'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'

implementation "android.arch.paging:runtime:1.0.1"
implementation "android.arch.lifecycle:runtime:1.1.1"
implementation "android.arch.lifecycle:extensions:1.1.1"
annotationProcessor "android.arch.lifecycle:compiler:1.1.1"

}

Mis MainActivity se ve así:

package com.example.athansys.mypagingapplication;

import android.arch.lifecycle.Observer;
import android.arch.lifecycle.ViewModelProviders;
import android.arch.paging.PagedList;
import android.support.annotation.Nullable;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.View;

public class MainActivity extends AppCompatActivity {

private MyPatientAdapter mPatientAdapter;
private RecyclerView mRecyclerView;

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

    FilterModel viewModel = ViewModelProviders.of(this).get(FilterModel.class);
    viewModel.getData(this).observe(this, new Observer<PagedList<FilterPatientList>>() {
        @Override
        public void onChanged(@Nullable PagedList<FilterPatientList> results) {
            mPatientAdapter.submitList(results);
            //mPatientAdapter.setList(results);
            mPatientAdapter.notifyDataSetChanged();
            mRecyclerView.setAdapter(mPatientAdapter);
        }
    });
}

private void setAdapter() {

    mRecyclerView = findViewById(R.id.my_patient_recycler_view);
    RecyclerView.LayoutManager layoutManager = new LinearLayoutManager(this);
    mPatientAdapter = new MyPatientAdapter();
    mRecyclerView.setLayoutManager(layoutManager);
    mRecyclerView.setAdapter(mPatientAdapter);

}
}

filterModel clase es la siguiente:

package com.example.athansys.mypagingapplication;


import android.arch.lifecycle.LiveData;
import android.arch.lifecycle.ViewModel;
import android.arch.paging.LivePagedListBuilder;
import android.arch.paging.PagedList;
import android.content.Context;
import android.util.Log;

public class FilterModel extends ViewModel {
private LiveData<PagedList<FilterPatientList>> listLiveData;

LiveData<PagedList<FilterPatientList>> getData(Context context) {
    if (listLiveData == null) {

        PagedList.Config pagedListConfig =
                (new PagedList.Config.Builder()).setEnablePlaceholders(false)
                        .setPrefetchDistance(5)
                        .setPageSize(1).build();

        listLiveData = new LivePagedListBuilder<>
                (new MyPatientPagedListProvider(context)
                        .getAll()
                        , pagedListConfig).
                build();

    }
    return listLiveData;
}
}

MyProvider clase es:

    package com.example.athansys.mypagingapplication;

import android.arch.paging.DataSource;
import android.arch.paging.LivePagedListProvider;
import android.content.Context;
import android.util.Log;

import java.util.List;


public class MyPatientPagedListProvider {

Context mBaseContext;

public MyPatientPagedListProvider(Context context) {
    mBaseContext = context;
    dataClass.getContextInstance(context);
}

private static final String TAG = MyPatientPagedListProvider.class.getName();

MyPatientData dataClass = new MyPatientData() {
    @Override
    public List<FilterPatientList> convertToItems(List<FilterPatientList> result, int size) {
        return result;
    }
};

public LivePagedListProvider<Integer, FilterPatientList> getAll() {
    return new LivePagedListProvider<Integer, FilterPatientList>() {
        @Override
        protected DataSource<Integer, FilterPatientList> createDataSource() {
            return dataClass;
        }
    };
}
}

MyDataSource es como sigue:

    package com.example.athansys.mypagingapplication;

import android.arch.paging.TiledDataSource;
import android.content.Context;

import com.android.volley.AuthFailureError;
import com.android.volley.DefaultRetryPolicy;
import com.android.volley.Request;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.toolbox.StringRequest;
import com.android.volley.toolbox.Volley;
import com.google.gson.Gson;

import org.json.JSONException;
import org.json.JSONObject;

import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

public abstract class MyPatientData extends TiledDataSource<FilterPatientList> {

private Context mContext;
private List<FilterPatientList> patientList;

@Override
public int countItems() {
    return 10;
}

@Override
public List<FilterPatientList> loadRange(int startPosition, int count) {
    String url = "My URl";
    return postStringRequestForMyPatient(url);
}

public List<FilterPatientList> postStringRequestForMyPatient(String url) {
    StringRequest stringRequest = new StringRequest(Request.Method.GET, url, new Response.Listener<String>() {
        @Override
        public void onResponse(String response) {
            JSONObject jsonObject = null;
            try {
                jsonObject = new JSONObject(response);
                String data = jsonObject.getString("patientsfordoctor");
                mPatientsForDoctor = new Gson().fromJson(data, PatientsForDoctor.class);
                mPatientList = new ArrayList<>();

                mPatientList.addAll(mPatientsForDoctor.getPatientList());

            } catch (JSONException e) {
                e.printStackTrace();
            }

        }
    }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {

        }
    }) {

        @Override
        protected Map<String, String> getParams() throws AuthFailureError {
            return super.getParams();
        }

        @Override
        public String getBodyContentType() {
            return super.getBodyContentType();
        }

        @Override
        public Map<String, String> getHeaders() throws AuthFailureError {
            return new HashMap<>();
        }
    };
    stringRequest.setRetryPolicy(new DefaultRetryPolicy(DefaultRetryPolicy.DEFAULT_TIMEOUT_MS,
            DefaultRetryPolicy.DEFAULT_MAX_RETRIES,
            DefaultRetryPolicy.DEFAULT_BACKOFF_MULT));
    Volley.newRequestQueue(mContext).add(stringRequest);
}

void getContextInstance(Context context) {
    mContext = context;
}

public abstract List<FilterPatientList> convertToItems(List<FilterPatientList> result, int size);
}

Mi clase de adaptador

    package com.example.athansys.mypagingapplication;
import android.arch.paging.PagedListAdapter;
import android.support.annotation.NonNull;
import android.support.v7.util.DiffUtil;
import android.support.v7.widget.RecyclerView;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class MyPatientAdapter extends PagedListAdapter<FilterPatientList, MyPatientAdapter.PatientViewHolder> {

protected MyPatientAdapter() {
    super(FilterPatientList.DIFF_CALLBACK);
}

@NonNull
@Override
public PatientViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    return null;
}

@Override
public void onBindViewHolder(@NonNull PatientViewHolder holder, int position) {

}


class PatientViewHolder extends RecyclerView.ViewHolder {
    TextView patientName, patientPhoneNumber, genderAge;

    PatientViewHolder(View itemView) {
        super(itemView);
    }
}
}

Mi POJO (clases del modelo son los siguientes)

FilterPatientList clase:

    package com.example.athansys.mypagingapplication;
import android.os.Parcel;
import android.os.Parcelable;
import android.support.v7.util.DiffUtil;

import com.google.gson.annotations.SerializedName;

public class FilterPatientList implements Parcelable {

private long patientId;

private Patient patientDetails;

protected FilterPatientList(Parcel in) {
    patientId = in.readLong();
    patientDetails = in.readParcelable(Patient.class.getClassLoader());
}

public static final Creator<FilterPatientList> CREATOR = new Creator<FilterPatientList>() {
    @Override
    public FilterPatientList createFromParcel(Parcel in) {
        return new FilterPatientList(in);
    }

    @Override
    public FilterPatientList[] newArray(int size) {
        return new FilterPatientList[size];
    }
};

public long getPatientId() {
    return patientId;
}

public void setPatientId(long patientId) {
    this.patientId = patientId;
}

public Patient getPatientDetails() {
    return patientDetails;
}

public void setPatientDetails(Patient patientDetails) {
    this.patientDetails = patientDetails;
}


@Override
public int describeContents() {
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeLong(patientId);
    dest.writeParcelable(patientDetails, flags);
}

public static final DiffUtil.ItemCallback<FilterPatientList> DIFF_CALLBACK = new DiffUtil.ItemCallback<FilterPatientList>() {
    @Override
    public boolean areItemsTheSame(FilterPatientList oldItem, FilterPatientList newItem) {
        return false;
    }

    @Override
    public boolean areContentsTheSame(FilterPatientList oldItem, FilterPatientList newItem) {
        return false;
    }
};
}

CLASE DEL PACIENTE:

   package com.example.athansys.mypagingapplication;
import android.os.Parcel;
import android.os.Parcelable;

import com.google.gson.annotations.SerializedName;

public class Patient implements Parcelable{

private long localPatientId;


private long apptDoctorId;

private long patientId;
private boolean isLocalPatient;

private String firstName;
private String lastName;
private String phoneNumber;
private String email;
private String dob;
private int age;
private int height;
private int weight;
private String patientSex;
private String patientSystemRegistrationDate;
private int bloodGroup;


protected Patient(Parcel in) {
    localPatientId = in.readLong();
    apptDoctorId = in.readLong();
    patientId = in.readLong();
    isLocalPatient = in.readByte() != 0;
    firstName = in.readString();
    lastName = in.readString();
    phoneNumber = in.readString();
    email = in.readString();
    dob = in.readString();
    age = in.readInt();
    height = in.readInt();
    weight = in.readInt();
    patientSex = in.readString();
    patientSystemRegistrationDate = in.readString();
    bloodGroup = in.readInt();
}

public static final Creator<Patient> CREATOR = new Creator<Patient>() {
    @Override
    public Patient createFromParcel(Parcel in) {
        return new Patient(in);
    }

    @Override
    public Patient[] newArray(int size) {
        return new Patient[size];
    }
};

public long getLocalPatientId() {
    return localPatientId;
}

public void setLocalPatientId(long localPatientId) {
    this.localPatientId = localPatientId;
}

public long getApptDoctorId() {
    return apptDoctorId;
}

public void setApptDoctorId(long apptDoctorId) {
    this.apptDoctorId = apptDoctorId;
}

public long getPatientId() {
    return patientId;
}

public void setPatientId(long patientId) {
    this.patientId = patientId;
}

public boolean isLocalPatient() {
    return isLocalPatient;
}

public void setLocalPatient(boolean localPatient) {
    isLocalPatient = localPatient;
}

public String getFirstName() {
    return firstName;
}

public void setFirstName(String firstName) {
    this.firstName = firstName;
}

public String getLastName() {
    return lastName;
}

public void setLastName(String lastName) {
    this.lastName = lastName;
}

public String getPhoneNumber() {
    return phoneNumber;
}

public void setPhoneNumber(String phoneNumber) {
    this.phoneNumber = phoneNumber;
}

public String getEmail() {
    return email;
}

public void setEmail(String email) {
    this.email = email;
}

public String getDob() {
    return dob;
}

public void setDob(String dob) {
    this.dob = dob;
}

public int getAge() {
    return age;
}

public void setAge(int age) {
    this.age = age;
}

public int getHeight() {
    return height;
}

public void setHeight(int height) {
    this.height = height;
}

public int getWeight() {
    return weight;
}

public void setWeight(int weight) {
    this.weight = weight;
}

public String getPatientSex() {
    return patientSex;
}

public void setPatientSex(String patientSex) {
    this.patientSex = patientSex;
}

public String getPatientSystemRegistrationDate() {
    return patientSystemRegistrationDate;
}

public void setPatientSystemRegistrationDate(String patientSystemRegistrationDate) {
    this.patientSystemRegistrationDate = patientSystemRegistrationDate;
}

public int getBloodGroup() {
    return bloodGroup;
}

public void setBloodGroup(int bloodGroup) {
    this.bloodGroup = bloodGroup;
}

@Override
public int describeContents() {
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeLong(localPatientId);
    dest.writeLong(apptDoctorId);
    dest.writeLong(patientId);
    dest.writeByte((byte) (isLocalPatient ? 1 : 0));
    dest.writeString(firstName);
    dest.writeString(lastName);
    dest.writeString(phoneNumber);
    dest.writeString(email);
    dest.writeString(dob);
    dest.writeInt(age);
    dest.writeInt(height);
    dest.writeInt(weight);
    dest.writeString(patientSex);
    dest.writeString(patientSystemRegistrationDate);
    dest.writeInt(bloodGroup);
}
}

Cuando recibo datos de la red en la clase de origen de datos (MyPatientData) la llamada pasa automáticamente al observador en la actividad principal. Allí, el tamaño de la lista que se muestra es cero, mientras que la lista cuando se obtienen de la red tenían un tamaño de 10 artículos.

¿Puede usted por favor me ayude. Realmente estoy atrapado durante días sin idea de qué hacer a continuación. Muchas gracias por adelantado. :)

Abhishek Kumar:

Aquí está la solución simple de la paginación.

La primera vez que private void jsonRequestList(int pageCount) {se invoca con pageCount=1y junto con el incremento de tiempo 2,3,4 ...

Dentro private void jsonRequestList(int pageCount) {método JSON (SOLICITUD) por primera vez if (!isScrollCalled) {se llama y la próxima vez que elsese llama bloque.

Actividad / Fragmento:

     private boolean loading = false;
     private boolean isScrollCalled;
     int isLastPage = 10;
     int pageCount = 1;

     //Paigination
        recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);

                int lastvisibleitemposition = linearLayoutManager.findLastVisibleItemPosition();

                if (lastvisibleitemposition == adapter.getItemCount() - 1) {

                    if (!loading && pageCount != isLastPage) {
                        loading = true;
                        jsonRequestList(++pageCount);
                        isScrollCalled = Boolean.TRUE;
                    }


                }
            }
        });


 private void jsonRequestList(int pageCount) {
  //Json Request

  if (!isScrollCalled) {
          adapter = new FlowerListAdapter(FlowerListActivity.this, list);
          recyclerView.setAdapter(adapter);
          adapter.notifyDataSetChanged();
               //  Log.e("LIST_SIZE", "" + list.size());
          } else {
          adapter.updateList(list);
          //Log.e("LIST_SIZE", "" + list.size());

        }

       loading = false;
}

Adaptador de reciclaje:

 ArrayList<YourModelClass> list;
 Context context;

 //Pagination
public void updateList(ArrayList<YourModelClass> list) {
    this.list.addAll(list);
    this.notifyDataSetChanged();
}