[FIXED] Fixing the error code: "Can't convert object of type java.lang.String to type"

Issue

I'm creating my first Android app which is a forum app wherein users can post.

I read a lot of the same error, but I can't figure it out to solve my problem. I got the error once I call the method LoadPost(); which fetches the data from Direbase straight to my RecycleView.

Here is my Firebase data structure:

Here's my ViewHolder:

public class MyViewHolder3 extends RecyclerView.ViewHolder {
CircleImageView circleImageView;
TextView user_name, user_power, user_dep, date_posted, user_post_description, upvote_count;
Button upvote_btn, comment_btn;

public MyViewHolder3(@NonNull View itemView) {
    super(itemView);
    circleImageView = itemView.findViewById(R.id.circleImageView);
    user_name = itemView.findViewById(R.id.user_name);
    user_power = itemView.findViewById(R.id.user_power);
    user_dep = itemView.findViewById(R.id.user_dep);
    date_posted = itemView.findViewById(R.id.date_posted);
    user_post_description = itemView.findViewById(R.id.user_post_description);
    upvote_count = itemView.findViewById(R.id.upvote_count);

    upvote_btn = itemView.findViewById(R.id.upvote_btn);
    comment_btn = itemView.findViewById(R.id.comment_btn);

}

Here's my Post class:

public class Post {

private String postdescription, userdep, date, username, userpower, userprofileimage;

public Post() {
}

public String getPostdescription() {
    return postdescription;
}

public void setPostdescription(String postdescription) {
    this.postdescription = postdescription;
}

public String getUserdep() {
    return userdep;
}

public void setUserdep(String userdep) {
    this.userdep = userdep;
}

public String getDate() {
    return date;
}

public void setDate(String date) {
    this.date = date;
}

public String getUsername() {
    return username;
}

public void setUsername(String username) {
    this.username = username;
}

public String getUserpower() {
    return userpower;
}

public void setUserpower(String userpower) {
    this.userpower = userpower;
}

public String getUserprofileimage() {
    return userprofileimage;
}

public void setUserprofileimage(String userprofileimage) {
    this.userprofileimage = userprofileimage;
}

public Post(String postdescription, String userdep, String date, String username, String userpower, String userprofileimage) {
    this.postdescription = postdescription;
    this.userdep = userdep;
    this.date = date;
    this.username = username;
    this.userpower = userpower;
    this.userprofileimage = userprofileimage;
}

Here's my LoadPost() method:

    private void LoadPost() {

    options = new FirebaseRecyclerOptions.Builder<Post>().setQuery(ForumRef,Post.class).build();
    adapter = new FirebaseRecyclerAdapter<Post, MyViewHolder3>(options) {
        @Override
        protected void onBindViewHolder(@NonNull MyViewHolder3 holder, int position, @NonNull Post model) {
        holder.user_post_description.setText(model.getPostdescription());
        holder.user_dep.setText(model.getUserdep());
        holder.date_posted.setText(model.getDate());
        holder.user_name.setText(model.getUsername());
        holder.user_power.setText(model.getUserpower());
        Picasso.get().load(model.getUserprofileimage()).into(holder.circleImageView);
        }

        @NonNull
        @Override
        public MyViewHolder3 onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.all_post_layout2,parent,false);
            return new MyViewHolder3(view);
        }
    };
    adapter.startListening();
    recyclerView.setAdapter(adapter);
}

And here's the error code I got:

com.google.firebase.database.DatabaseException: Can't convert object of type java.lang.String to type com.example.chitchat.Post

Solution

When you're passing the following reference:

ForumRef = FirebaseDatabase.getInstance().getReference.child("Forums").child(PostKey);

To:

.setQuery(ForumRef,Post.class)

It means that the adapter expects to render on the screen Post objects. If you take a closer look at your database schema, under the post key (1st) node, you can find a Post object and two strings, the count and the forumname:

See, IUSH...2Mon, count, and forumname are children that exist under the exact same (1st) node. So when reading the data from the database, the Firebase-UI library tries to map each child under the above reference into an object of type Post, which is actually not possible since the last two children are strings. To solve this, you have to move those two strings to a different location. As soon as inside that node will only exist Post objects, then the error will go away.

Answered By - Alex Mamo
Answer Checked By - Pedro (JavaFixing Volunteer)