Failed to convert value of type java.util.HashMap to String error when I'm trying to retrieve data from firebase to viewpager2

caspernim 0
Viewed 33

For my application, I added a ViewPager2 to show the recommended containing image, name, and country. But when I try to retrieve data from firebase this error shows. I tried tweaking the code but I think I'm only making it worse because the error is replaced by No setter/field for a class error. I have been stuck with the same error for a few days now and still can't solve it. I badly need help.

Below is my code for MainActivity

database = FirebaseDatabase.getInstance().getReference();
        DatabaseReference myRef = database.child("Packages");
        recommendList = new ArrayList<Recommendation>();
        adapter = new RecommendAdapter(this, recommendList);
        recommendViewPager.setAdapter(adapter);
        setupRecommendViewPager();



        myRef.addValueEventListener(new ValueEventListener() {
            List<Recommendation> recommendList = new ArrayList<>();
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {

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

                    Recommendation recommendation = dataSnapshot.getValue(Recommendation.class);
                    //String recommendation = dataSnapshot.getValue(String.class);

                    recommendList.add(recommendation);
                }
                adapter.notifyDataSetChanged();

            }

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

            }
        });

And this is my Recommendation.class

public class Recommendation {

    public String package_attractions;
    public String package_availability;
    public String package_country;
    public String package_description;
    public String package_name;
    public String package_photos;
    public Double package_price;
    public Double package_rating;
    public String package_region;
    public String package_video;

    public Recommendation(){}

    public Recommendation(String package_attractions, String package_availability, String package_country, String package_description, String package_name, String package_photos, Double package_price, Double package_rating, String package_region, String package_video) {
        this.package_attractions = package_attractions;
        this.package_availability = package_availability;
        this.package_country = package_country;
        this.package_description = package_description;
        this.package_name = package_name;
        this.package_photos = package_photos;
        this.package_price = package_price;
        this.package_rating = package_rating;
        this.package_region = package_region;
        this.package_video = package_video;
    }

    
    public String getPackage_attractions() {
        return package_attractions;
    }

    public void setPackage_attractions(String package_attractions) {
        this.package_attractions = package_attractions;
    }

    public String getPackage_availability() {
        return package_availability;
    }

    public void setPackage_availability(String package_availability) {
        this.package_availability = package_availability;
    }
.........

And this is my firebase data

P.S I'm only retrieving photo, name, and country

firebase-realtime-database java google-cloud-platform firebase android
1 Answers

You're getting the following error:

Failed to convert value of type java.util.HashMap to String

Because you're trying to convert an object (map) that exists in your database into a string, and this is not possible in Java. Why is this happening? It's because your package_photos field inside the database is an object:

enter image description here

See, you can dig deeper to get data, which basically means that this field it's not a String but an object (map), since each node in the Realtime Database is composed of key-value pairs.

When you're using the following line of code:

Recommendation recommendation = dataSnapshot.getValue(Recommendation.class);

It means that you're trying to map each node under "Packages" into an object of type Recommendation. This means that each field in the database should have the exact same type as in your class, which isn't happening. Your package_photos field in the database is a map, while in the class is a string, hence the error.

To solve this, you should change the type of your package_photos field inside the class to be either an object or a map. Since I cannot see the content of your package_photos node, I can only assume that you have a key that is named "url" and a value that is represented by the actual value of the URL, "https://...".

So it most likely it looks similar to this:

Packages
 |
 --- BG0PH108
      |
      --- package_photos
            |
            --- url: "https://..."

So in this case, you need to create a class with at a minimum declaration, that looks like this:

public class PackagePhotos {
    public String url;
}

Or if you want to use encapsulation:

public class PackagePhotos {
    private String url;

    public PackagePhotos() {}

    public PackagePhotos(String url) {
        this.url = url;
    }

    public getUrl() {
        return url;
    }
}

And inside the Recommendation class, the field should be changed to:

public class Recommendation {
    //...    
    public PackagePhotos package_photos;

    public Recommendation() {}

    //                           
    public Recommendation(..., PackagePhotos package_photos, ...) {
        //...
        this.package_photos = package_photos;
        //...
    }

    
    //...
}

Be aware that package_video filed should follow the same rules.

If you don't want to use a class, then you should simply set the type of the field to Map<String, Object>.

Alex Mamo0
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