I am trying to check if a user is following another user. If they are then the follow_btn is invisible, if not then it's visible. But I keep getting this error Attempt to invoke virtual method 'void android.widget.ImageView.setVisibility(int)' on a null object reference.

I have called the function is different methods but I keep getting that error. I also check if the button was null in an if statement and I'm being told it's null. I don't know what else to do can someone help me ?

layout_main.xml:

<ImageView
    android:id="@ id/follow_btn"
    android:layout_width="15dp"
    android:layout_height="15dp"
    android:layout_marginTop="25dp"
    android:layout_marginEnd="10dp"
    app:layout_constraintBottom_toBottomOf="@ id/image_profile"
    app:layout_constraintEnd_toEndOf="parent"
    app:layout_constraintStart_toStartOf="@ id/image_profile"
    app:layout_constraintTop_toTopOf="@ id/image_profile"
    app:srcCompat="@drawable/add" />

PostAdapter.Java:

public class PostAdapter extends RecyclerView.Adapter<PostAdapter.ViewHolder> {

public Context mContext;
public List<Post> mPost;

private FirebaseUser firebaseUser;
public static String mGroupId;
public String profileid;
public ImageView follow_btn;

public PostAdapter(Context mContext, List<Post> mPost) {
    this.mContext = mContext;
    this.mPost = mPost;
}

@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int viewType) {

    View view = LayoutInflater.from(mContext).inflate(R.layout.layout_main, viewGroup, false);
    return new ViewHolder(view);
}

@Override
public void onBindViewHolder(@NonNull ViewHolder viewHolder, int i) {

    if (follow_btn != null) {

        checkFollow();
    } else {

        Toast.makeText(mContext, "Null.", Toast.LENGTH_SHORT).show();
    }

}

    public class ViewHolder extends RecyclerView.ViewHolder {

    // creating a variable for exoplayerview.
    public PlayerView post_video;
    // creating a variable for exoplayer
    public SimpleExoPlayer exoPlayer;

    public ImageView image_profile, like, comment, save, follow_btn; //more
    //public ExoVideoView post_video;
    public TextView username, description, comments, dateAdded, likes;
    FirebaseUser firebaseUser;

    public ViewHolder(@NonNull View itemView) {
        super(itemView);

        image_profile = itemView.findViewById(R.id.image_profile);
        post_video = itemView.findViewById(R.id.thumbnail);
        like = itemView.findViewById(R.id.like);
        comment = itemView.findViewById(R.id.comment);
        comments = itemView.findViewById(R.id.comments);
        dateAdded = itemView.findViewById(R.id.date_post_added);
        save = itemView.findViewById(R.id.save);
        username = itemView.findViewById(R.id.username);
        likes = itemView.findViewById(R.id.likes);
        description = itemView.findViewById(R.id.description);
        //more = itemView.findViewById(R.id.more);

        follow_btn = itemView.findViewById(R.id.follow_btn);
        firebaseUser = FirebaseAuth.getInstance().getCurrentUser();
        SharedPreferences prefs = mContext.getSharedPreferences("PREFS", Context.MODE_PRIVATE);
        profileid = prefs.getString("profileid", "none");
    }
}

    private void checkFollow() {

    DatabaseReference reference = FirebaseDatabase.getInstance().getReference()
            .child("Follow").child(firebaseUser.getUid()).child("following");

    reference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

            if (dataSnapshot.child(profileid).exists()) {
                //.setText("following");
                follow_btn.setVisibility(View.INVISIBLE);
            } else {
                //edit_profile.setText("follow");
                follow_btn.setVisibility(View.VISIBLE);
            }
        }

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

        }
    });
}

}

CodePudding user response：

remove your public ImageView follow_btn; from top declaration. (above your constructor).

inside onBindViewHolder you can use childViews with it's ViewHolder.

@Override
public void onBindViewHolder(@NonNull ViewHolder viewHolder, int i) {

    if (viewHolder.follow_btn != null) {

        checkFollow();
    } else {

        Toast.makeText(mContext, "Null.", Toast.LENGTH_SHORT).show();
    }

}

CodePudding user response：

Pass ViewHolder in argument:-

@Override
    public void onBindViewHolder(@NonNull ViewHolder viewHolder, int i) {
        if (follow_btn != null) {
            checkFollow(viewHolder);
        } else {
    
            Toast.makeText(mContext, "Null.", Toast.LENGTH_SHORT).show();
        }
    }



private void checkFollow(ViewHolder viewHolder) {

    DatabaseReference reference = FirebaseDatabase.getInstance().getReference()
            .child("Follow").child(firebaseUser.getUid()).child("following");

    reference.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

            if (dataSnapshot.child(profileid).exists()) {
                //.setText("following");
                viewHolder.follow_btn.setVisibility(View.INVISIBLE);
            } else {
                //edit_profile.setText("follow");
                viewHolder.follow_btn.setVisibility(View.VISIBLE);
            }
        }

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

        }
    });

I hope this will help you..