The Activity does not update the content of a ViewPager2

Question

I implemented an Android application that must display the content of a list in an Activity, using ViewPager2. See an extract of the code below:

public class MainActivity extends AppCompatActivity {
    ViewPager2 viewPager2;
    DataPageViewAdapter dataPageViewAdapter;
    private Button btnFind;
    private Control ctrl;
    private List<Movie> movies;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        viewPager2 = findViewById(R.id.view_pager_2);
        ctrl = new Control();
        movies = ctrl.loadAllMovies();        
        btnFind = findViewById(R.id.btn_find);
        btnFind.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(!movies.isEmpty()) {
                    dataPageViewAdapter = new DataPageViewAdapter(getApplicationContext(), movies);
                    dataPageViewAdapter.notifyDataSetChanged();
                    viewPager2.setAdapter(dataPageViewAdapter);
                }else{
                    Toast.makeText(this, "No movies loaded yet!", Toast.LENGTH_LONG).show();
                }
            }
        });       
        
    }
}

There is a Movie class with the data stored and a Control class that returns a list of Movies. The application fulfills its purpose, but I have to press the menu action twice so that the information in the Activity is observed. How can I make the content appear at once when pressing the button? Thanks in advance!

score 0 · Answer 1 · answered Aug 01 '22 at 21:11

0

You should set the adapter first and then call notifyDataSetChanged()

@Override
public void onClick(View v) {
    if(!movies.isEmpty()) {
        dataPageViewAdapter = new DataPageViewAdapter(getApplicationContext(), movies);
        viewPager2.setAdapter(dataPageViewAdapter);
        dataPageViewAdapter.notifyDataSetChanged();
    } else {
        Toast.makeText(this, "No movies loaded yet!", Toast.LENGTH_LONG).show();
    }
}

answered Aug 01 '22 at 21:11

Mieczkoni

505
2
8

it keep doing the same thing, two push to show the data on Activity – No Reply Aug 01 '22 at 22:52

score 0 · Answer 2 · answered Aug 01 '22 at 23:32

This is my Adapter and Holder for the ViewPager2

package com.example.test.view;

import android.annotation.SuppressLint;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;
import com.bumptech.glide.Glide;
import java.util.List;
import com.example.test.R;
import com.example.test.models.Configuration.APIVars;
import com.example.test.models.Movies.Movie;

public class DataPageViewAdapter extends RecyclerView.Adapter<ViewHolderA> {
    Context context;
    List<Movie> myMovies;
    LayoutInflater li;

    public DataPageViewAdapter(Context context, List<Movie> movies){
        this.context = context;
        this.myMovies = movies;
        li = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    }

    @NonNull
    @Override
    public ViewHolderA onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View mv = li.inflate(R.layout.movie_view_detail,parent,false);
        return new ViewHolderA(mv);
    }

    @Override
    public void onBindViewHolder(@NonNull ViewHolderA holder, int position) {
        holder.bindData(myMovies.get(position));
    }

    @Override
    public int getItemCount() {
        return myMovies.size();
    }
}
class ViewHolderA extends RecyclerView.ViewHolder{
    private final ImageView movie_poster;
    private final TextView tv_title;
    private final TextView tv_id;
    private final TextView tv_overview;
    private final TextView tv_genre;
    private final TextView tv_release_date;
    private final TextView tv_vote_count;
    private final TextView tv_vote_avg;
    private final View mv;

    /*My ViewHolderA Constructor*/
    public ViewHolderA(@NonNull View itemView) {
        super(itemView);
        mv = itemView;
        movie_poster = mv.findViewById(R.id.movie_poster);
        tv_id = mv.findViewById(R.id.tv_id);
        tv_title = mv.findViewById(R.id.tv_title);
        tv_overview = mv.findViewById(R.id.tv_overview);
        tv_genre = mv.findViewById(R.id.tv_genre);
        tv_release_date = mv.findViewById(R.id.tv_release_date);
        tv_vote_avg = mv.findViewById(R.id.tv_vote_avg);
        tv_vote_count = mv.findViewById(R.id.tv_vote_count);
    }

    /*Set all the movie data to show*/
    @SuppressLint("SetTextI18n")
    public void bindData(Movie mMovie){
        if(mMovie != null) {            
            Glide.with(mv).load(APIVars.BASE_IMG_URL + mMovie.getBackdrop_path()).into(movie_poster);
            tv_title.setText("Title: " + mMovie.getTitle());
            tv_id.setText("ID: " + mMovie.getId());
            tv_overview.setText("Overview: " + mMovie.getOverview());
            tv_genre.setText("Genre: " + mMovie.getGenres());
            tv_release_date.setText("Release Date: " + mMovie.getRelease_date());
            tv_vote_count.setText("Vote Count: " + mMovie.getVote_count());
            tv_vote_avg.setText("Vote AVG: " + mMovie.getVote_average());
        }
    }
}

I don't see anything wrong that could affect performance, but no matter where I put the notifyDataSetChanged function, the result is still that I have to press the button twice for it to display the information.

Hi. Please add the adapter code to the question above because this code addition is valuable for answering the question but can be easily overlooked. If you could provide a full code sample, others could execute, that would further facilitate answering the question. — Peter F, Aug 04 '22 at 14:55

The Activity does not update the content of a ViewPager2

2 Answers2