Question

我是Android Studio的新手，因此我尝试使用其Adapter和ViewHolder制作一个RecyclerView，Adapter类需要一个列表来制作列表中的每个项目，该列表应从FireBase的数据库中填充。 FireBase参考检索所需的数据并将其添加到列表中，但是列表始终保持为空，为什么？

这是代码：

MainActivity：

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;

public class MainActivity extends AppCompatActivity {

private RecyclerView rView;
private RecyclerView.LayoutManager layout;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        rView = findViewById(R.id.rView);
        layout = new LinearLayoutManager(this);
        rView.setLayoutManager(layout);
        rView.setHasFixedSize(true);
        ProjectAdapter reAdapter = new ProjectAdapter();
        rView.setAdapter(reAdapter);
    }
}

适配器：

import android.net.Uri;
import android.support.annotation.NonNull;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import com.google.firebase.firestore.DocumentSnapshot;
import com.google.firebase.firestore.EventListener;
import com.google.firebase.firestore.FirebaseFirestore;
import com.google.firebase.firestore.FirebaseFirestoreException;
import com.google.firebase.firestore.QuerySnapshot;
import com.google.firebase.storage.FirebaseStorage;
import com.google.firebase.storage.StorageReference;
import java.util.ArrayList;
import java.util.List;

public class ProjectAdapter extends RecyclerView.Adapter<ProjectAdapter.ProjectViewHolder> {

    private List<Project> proList;
    private FirebaseFirestore firestore;
    private FirebaseStorage storage;
    private StorageReference storageRef;
    private Project p;

    public ProjectAdapter(){
        firestore = FirebaseFirestore.getInstance();
        storage = FirebaseStorage.getInstance();
        storageRef = FirebaseStorage.getInstance().getReference();
        proList = new ArrayList<>();
        firestore.collection("Projects").addSnapshotListener(new EventListener<QuerySnapshot>() {
        @Override
        public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {

            if(e == null){
                for(DocumentSnapshot doc : documentSnapshots){
                    Log.d("MainActivity", "onComplete: " + doc.getString("proName"));
                    p = new Project();
                    p.setProName(doc.getString("proName"));
                    p.setProDes(doc.getString("proDescription"));
                    p.setProPic(doc.getString("picture"));
                    System.out.println(p.getProName());
                    proList.add(p);
                }
            }
        }
    });
}

public static class ProjectViewHolder extends RecyclerView.ViewHolder {

    public TextView proName;
    public ImageView proPic;
    public TextView proBreif;

    public ProjectViewHolder(@NonNull View itemView) {
        super(itemView);
        proName = itemView.findViewById(R.id.proName);
        proBreif = itemView.findViewById(R.id.DesctextView);
        proPic = itemView.findViewById(R.id.proPic);
    }
}

    @NonNull
    @Override
    public ProjectViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
        View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.activity_item, viewGroup, false);
        return  new ProjectViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull ProjectViewHolder projectViewHolder, int i) {
        projectViewHolder.proName.setText(proList.get(i).getProName());
        projectViewHolder.proBreif.setText(proList.get(i).getProDes());
    [projectViewHolder.proPic.setImageURI(Uri.parse(proList.get(i).getProPic()));][1]
    }


    @Override
    public int getItemCount() {
        System.out.println(proList.size()); // the output always 0, it got called before retrieving form the database.
        return proList.size();
    }

    @Override
    public int getItemViewType(final int position) {
        return R.layout.activity_item;
    }
}

输出为：

名称是从数据库中检索的数据。

Answer 1

我建议您使用Firestore的内置适配器之一-Firestore Recycler Adapter。 https://github.com/firebase/FirebaseUI-Android/tree/master/firestore

它是专门为此目的而构建的，并且易于实现。

为什么在填充适配器之前使用适配器中的列表？

1 个答案: