What is the error which causes the app to stop when retrieving data from Firebase?

Pranav Kumar :

This is an app that uses the Firebase database.

I have added all the data in firebase and now I need to retrieve it and display using listview.

I tried to fetch and show the data in my app from firebase but the app is stopping every time.

Take a look at the screenshot

This is the Country model class

Country.java

public class Country {

private String name;
private String total;
private String newCases;
private String totalDeaths;
private String newDeaths;
private String totalRecovered;
private String activeCases;
private String seriousCases;

public Country() {
}

public Country(String name, String total, String newCases, String totalDeaths, String newDeaths, String totalRecovered, String activeCases, String seriousCases) {
    this.name = name;
    this.total = total;
    this.newCases = newCases;
    this.totalDeaths = totalDeaths;
    this.newDeaths = newDeaths;
    this.totalRecovered = totalRecovered;
    this.activeCases = activeCases;
    this.seriousCases = seriousCases;
}

public String getName() {
    return name;
}

public void setName(String name) {
    this.name = name;
}

public String getTotal() {
    return total;
}

public void setTotal(String total) {
    this.total = total;
}

public String getNewCases() {
    return newCases;
}

public void setNewCases(String newCases) {
    this.newCases = newCases;
}

public String getTotalDeaths() {
    return totalDeaths;
}

public void setTotalDeaths(String totalDeaths) {
    this.totalDeaths = totalDeaths;
}

public String getNewDeaths() {
    return newDeaths;
}

public void setNewDeaths(String newDeaths) {
    this.newDeaths = newDeaths;
}

public String getTotalRecovered() {
    return totalRecovered;
}

public void setTotalRecovered(String totalRecovered) {
    this.totalRecovered = totalRecovered;
}

public String getActiveCases() {
    return activeCases;
}

public void setActiveCases(String activeCases) {
    this.activeCases = activeCases;
}

public String getSeriousCases() {
    return seriousCases;
}

public void setSeriousCases(String seriousCases) {
    this.seriousCases = seriousCases;
}
}

This is the Activity class

Country_List.java

public class Country_List extends AppCompatActivity {

ListView listView;
FirebaseDatabase firebaseDatabase;
DatabaseReference reff;
ArrayList<String> countries;
ArrayAdapter<String> adapter;
Country country;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_country__list);
    listView = (ListView) findViewById(R.id.listView);
    country = new Country();
    firebaseDatabase = FirebaseDatabase.getInstance();
    reff = firebaseDatabase.getReference().child("country");
    countries = new ArrayList<>();
    adapter = new ArrayAdapter<>(Country_List.this, R.layout.country_info, R.id.country_info_list, countries);

    reff.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
            for (DataSnapshot ds: dataSnapshot.getChildren()){
                country = ds.getValue(Country.class);
                countries.add("Country Name:" + country.getName().toString() + "\n" + "Total Cases:" + country.getTotal().toString() + "\n" + "New Cases:" + country.getNewCases().toString() + "\n" + "Total Deaths:" + country.getTotalDeaths().toString() + "\n" + "New Deaths:" + country.getNewCases().toString() + "Total Recovered:" + country.getTotalRecovered().toString() + "Active Cases:" + country.getActiveCases().toString() + "\n" + "Serious Cases:" + country.getSeriousCases().toString());
            }
            listView.setAdapter(adapter);
        }

        @Override
        public void onCancelled(@NonNull DatabaseError databaseError) {

        }
    });
}

StackTrace

com.google.firebase.database.DatabaseException: Failed to convert value of type java.lang.Long to String
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertString(com.google.firebase:firebase-database@@19.2.1:425)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(com.google.firebase:firebase-database@@19.2.1:216)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToType(com.google.firebase:firebase-database@@19.2.1:178)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.access$100(com.google.firebase:firebase-database@@19.2.1:47)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(com.google.firebase:firebase-database@@19.2.1:592)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper$BeanMapper.deserialize(com.google.firebase:firebase-database@@19.2.1:562)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertBean(com.google.firebase:firebase-database@@19.2.1:432)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.deserializeToClass(com.google.firebase:firebase-database@@19.2.1:231)
    at com.google.firebase.database.core.utilities.encoding.CustomClassMapper.convertToCustomClass(com.google.firebase:firebase-database@@19.2.1:79)
    at com.google.firebase.database.DataSnapshot.getValue(com.google.firebase:firebase-database@@19.2.1:203)
    at com.example.covid_19explorer.Country_List$1.onDataChange(Country_List.java:40)
    at com.google.firebase.database.core.ValueEventRegistration.fireEvent(com.google.firebase:firebase-database@@19.2.1:75)
    at com.google.firebase.database.core.view.DataEvent.fire(com.google.firebase:firebase-database@@19.2.1:63)
    at com.google.firebase.database.core.view.EventRaiser$1.run(com.google.firebase:firebase-database@@19.2.1:55)
    at android.os.Handler.handleCallback(Handler.java:789)
    at android.os.Handler.dispatchMessage(Handler.java:98)
    at android.os.Looper.loop(Looper.java:164)
    at android.app.ActivityThread.main(ActivityThread.java:6541)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

Alex Mamo :

To solve this, you please change all the properties in your Country class to be of type long, except the name, which should remain a String. Please also change all the setters and getters. Your class should look like this:

public class Country {
    private String name;
    private long total, newCases, totalDeaths, newDeaths, totalRecovered, activeCases, seriousCases;

    public Country() {}

    public Country(String name, long total, long newCases, long totalDeaths, long newDeaths, long totalRecovered, long activeCases, long seriousCases) {
        this.name = name;
        this.total = total;
        this.newCases = newCases;
        this.totalDeaths = totalDeaths;
        this.newDeaths = newDeaths;
        this.totalRecovered = totalRecovered;
        this.activeCases = activeCases;
        this.seriousCases = seriousCases;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public long getTotal() {
        return total;
    }

    public void setTotal(long total) {
        this.total = total;
    }

    public long getNewCases() {
        return newCases;
    }

    public void setNewCases(long newCases) {
        this.newCases = newCases;
    }

    public long getTotalDeaths() {
        return totalDeaths;
    }

    public void setTotalDeaths(long totalDeaths) {
        this.totalDeaths = totalDeaths;
    }

    public long getNewDeaths() {
        return newDeaths;
    }

    public void setNewDeaths(long newDeaths) {
        this.newDeaths = newDeaths;
    }

    public long getTotalRecovered() {
        return totalRecovered;
    }

    public void setTotalRecovered(long totalRecovered) {
        this.totalRecovered = totalRecovered;
    }

    public long getActiveCases() {
        return activeCases;
    }

    public void setActiveCases(long activeCases) {
        this.activeCases = activeCases;
    }

    public long getSeriousCases() {
        return seriousCases;
    }

    public void setSeriousCases(long seriousCases) {
        this.seriousCases = seriousCases;
    }
}

There is one more thing that you need to do, which is to change the type for the newCases property in the database this time, to be of type long, as it is a String now. That plus sign (+) is not recommended to be added in the database, you should add it programmatically.

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