如何从Firebase中的列表中检索数据？

Question

我在firebase上保存了一个包含坐标（LatLng）的列表。我正在尝试使用此代码检索它们，并使用它们添加折线：

ThePath1 = new ArrayList<Double>();
ThePath2 = new ArrayList<Double>();
ThePath = new ArrayList<LatLng>();
databasePaths = FirebaseDatabase.getInstance().getReference("Paths").child("Ola");
databasePaths.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(@NonNull DataSnapshot dataSnapshot) {


        for (DataSnapshot items: dataSnapshot.getChildren())
        {


            double infos = items.child("latitude").getValue(double.class);
            double info = items.child("longitude").getValue(double.class);
            ThePath1.add(infos);
            ThePath2.add(info);
        }

        for (int i = 0; i < ThePath1.size(); i++){
            latt = ThePath1.get(i);
            longg = ThePath2.get(i);
            latLng1 = new LatLng(latt, longg);
            ThePath.add(latLng1);
        }
   }

public void onMapReady(GoogleMap googleMap) {
    mMap = googleMap;
 options = new PolylineOptions().width(5).color(Color.BLUE).geodesic(true);
for  (int i = 0; i  <  ThePath.size(); i++)  {
        LatLng  point  = (LatLng) ThePath.get(i);
        options.add(point);
    }
    line = mMap.addPolyline(options);

问题在于ArrayList“ ThePath”似乎为空，因为地图上没有折线出现。如何从Firebase获取纬度和经度？我在这里发布Paths.class和Ola.class。请帮助我，我被困住了。

在这里我发布Paths.class：

import java.util.List;


public class Paths {
String id;
String name;
String city;
String nomos;
String perifereia;
List<Ola> ola;


public Paths(){

}



public Paths(String id, String name, String city, String nomos, String perifereia, List<Ola> ola) {
    this.id = id;
    this.name = name;
    this.city = city;
    this.nomos = nomos;
    this.perifereia = perifereia;
    this.ola = ola;

}

public String getId() {
    return id;
}

public String getName() {
    return name;
}

public String getCity() {
    return city;
}

public String getNomos() {
    return nomos;
}

public String getPerifereia() {
    return perifereia;
}

public List<Ola> getOla() {
    return ola;
}


}

还有Ola.class：

public class Ola {

public double latitude;
public double longitude;


public Ola() {}

public Ola(double latitude, double longitude) {
    this.latitude = latitude;
    this.longitude = longitude;
}

public double getLatitude() {
    return latitude;
}

public void setLatitude(double latitude) {
    this.latitude = latitude;
}

public double getLongitude() {
    return longitude;
}

public void setLongitude(double longitude) {
    this.longitude = longitude;
}
}