title: When using Paging Library, observer showing list size as zero
body: <p>I am trying to use paging library with newer versions. I am using volley to fetch my data from network. Whenever I fetch data from network, the data is fetched but when the call goes to observer the list size shown there is zero. I am unsure what I am doing wrong.</p>
  
  <p>I am new to android so don't know much about paging. Its been days since I m trying but still unable to figure it out.</p>
  
  <p>My gradle is as follows</p>
  
  <pre><code>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"
  </code></pre>
  
  <p>}</p>
  
  <p>My MainActivity looks like:</p>
  
  <pre><code>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&lt;PagedList&lt;FilterPatientList&gt;&gt;() {
          @Override
          public void onChanged(@Nullable PagedList&lt;FilterPatientList&gt; 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);
  
  }
  }
  </code></pre>
  
  <p>FilterModel class is as follows:</p>
  
  <pre><code>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&lt;PagedList&lt;FilterPatientList&gt;&gt; listLiveData;
  
  LiveData&lt;PagedList&lt;FilterPatientList&gt;&gt; getData(Context context) {
      if (listLiveData == null) {
  
          PagedList.Config pagedListConfig =
                  (new PagedList.Config.Builder()).setEnablePlaceholders(false)
                          .setPrefetchDistance(5)
                          .setPageSize(1).build();
  
          listLiveData = new LivePagedListBuilder&lt;&gt;
                  (new MyPatientPagedListProvider(context)
                          .getAll()
                          , pagedListConfig).
                  build();
  
      }
      return listLiveData;
  }
  }
  </code></pre>
  
  <p>MyProvider class is:</p>
  
  <pre><code>    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&lt;FilterPatientList&gt; convertToItems(List&lt;FilterPatientList&gt; result, int size) {
          return result;
      }
  };
  
  public LivePagedListProvider&lt;Integer, FilterPatientList&gt; getAll() {
      return new LivePagedListProvider&lt;Integer, FilterPatientList&gt;() {
          @Override
          protected DataSource&lt;Integer, FilterPatientList&gt; createDataSource() {
              return dataClass;
          }
      };
  }
  }
  </code></pre>
  
  <p>MyDataSource is as follows:</p>
  
  <pre><code>    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&lt;FilterPatientList&gt; {
  
  private Context mContext;
  private List&lt;FilterPatientList&gt; patientList;
  
  @Override
  public int countItems() {
      return 10;
  }
  
  @Override
  public List&lt;FilterPatientList&gt; loadRange(int startPosition, int count) {
      String url = "My URl";
      return postStringRequestForMyPatient(url);
  }
  
  public List&lt;FilterPatientList&gt; postStringRequestForMyPatient(String url) {
      StringRequest stringRequest = new StringRequest(Request.Method.GET, url, new Response.Listener&lt;String&gt;() {
          @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&lt;&gt;();
  
                  mPatientList.addAll(mPatientsForDoctor.getPatientList());
  
              } catch (JSONException e) {
                  e.printStackTrace();
              }
  
          }
      }, new Response.ErrorListener() {
          @Override
          public void onErrorResponse(VolleyError error) {
  
          }
      }) {
  
          @Override
          protected Map&lt;String, String&gt; getParams() throws AuthFailureError {
              return super.getParams();
          }
  
          @Override
          public String getBodyContentType() {
              return super.getBodyContentType();
          }
  
          @Override
          public Map&lt;String, String&gt; getHeaders() throws AuthFailureError {
              return new HashMap&lt;&gt;();
          }
      };
      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&lt;FilterPatientList&gt; convertToItems(List&lt;FilterPatientList&gt; result, int size);
  }
  </code></pre>
  
  <p>My Adapter class</p>
  
  <pre><code>    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&lt;FilterPatientList, MyPatientAdapter.PatientViewHolder&gt; {
  
  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);
      }
  }
  }
  </code></pre>
  
  <p>My POJO(MODEL CLASSES ARE AS FOLLOWS)</p>
  
  <p>FilterPatientList class:</p>
  
  <pre><code>    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&lt;FilterPatientList&gt; CREATOR = new Creator&lt;FilterPatientList&gt;() {
      @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&lt;FilterPatientList&gt; DIFF_CALLBACK = new DiffUtil.ItemCallback&lt;FilterPatientList&gt;() {
      @Override
      public boolean areItemsTheSame(FilterPatientList oldItem, FilterPatientList newItem) {
          return false;
      }
  
      @Override
      public boolean areContentsTheSame(FilterPatientList oldItem, FilterPatientList newItem) {
          return false;
      }
  };
  }
  </code></pre>
  
  <p>PATIENT CLASS:</p>
  
  <pre><code>   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&lt;Patient&gt; CREATOR = new Creator&lt;Patient&gt;() {
      @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);
  }
  }
  </code></pre>
  
  <p>When I receive data from network in Data source class(MyPatientData) the call automatically goes to observer in main activity. There the list size shown is zero whereas the list when fetched from network had a size of 10 items.</p>
  
  <p>Can you please help me out. I am really stuck for days with no clue what to do next.
  Thanks a lot in advance. :)</p>