空对象引用上的 RecyclerView

Question

所以我试图将图像从 firebase 显示到 recyclerview，但它给了我一个错误。错误说 E/nitecompetitiv: [qarth_debug:] get PatchStore::createDisableExceptionQarthFile 方法失败。 E/AndroidRuntime: 致命异常: main 进程：com.example.fortnitecompetitive，PID：15205 java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法 'void androidx.recyclerview.widget.RecyclerView.setAdapter(androidx.recyclerview.widget.RecyclerView$Adapter)' 在 com.example.fortnitecompetitive.NewsActivity$1.onDataChange(NewsActivity.java:66) 在 com.google.firebase.database.core.ValueEventRegistration.fireEvent(ValueEventRegistration.java:75) 在 com.google.firebase.database.core.view.DataEvent.fire(DataEvent.java:63) 在 com.google.firebase.database.core.view.EventRaiser$1.run(EventRaiser.java:55) 在 android.os.Handler.handleCallback(Handler.java:907) 在 android.os.Handler.dispatchMessage(Handler.java:105) 在 android.os.Looper.loop(Looper.java:216) 在 android.app.ActivityThread.main(ActivityThread.java:7625) 在 java.lang.reflect.Method.invoke（本机方法） 在 com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:524) 在 com.android.internal.os.ZygoteInit.main(ZygoteInit.java:987)。 非常感谢您的帮助。

public class NewsActivity extends AppCompatActivity {
FirebaseDatabase mDatabase;
DatabaseReference mRef;
FirebaseStorage mStorage;
RecyclerView recyclerView;
List<Post> postList;
private RecyclerView mRecyclerView;
private ImageAdapter mAdapter;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_news);
        
        getSupportActionBar().setDisplayOptions(ActionBar.DISPLAY_SHOW_CUSTOM);
        getSupportActionBar().setCustomView(R.layout.action_bar);

        mDatabase = FirebaseDatabase.getInstance();
        mRef = FirebaseDatabase.getInstance().getReference("Posts");
        mStorage = FirebaseStorage.getInstance();
        recyclerView = findViewById(R.id.recycler_news);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));

        postList = new ArrayList<>();

        mRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                for (DataSnapshot postSnapshot : snapshot.getChildren()){
                    Post post = postSnapshot.getValue(Post.class);
                    postList.add(post);
                }
                mAdapter = new ImageAdapter(NewsActivity.this, postList);

                mRecyclerView.setAdapter(mAdapter);
            }

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



    }
}

适配器

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.squareup.picasso.Picasso;

import java.util.List;

public class ImageAdapter extends RecyclerView.Adapter<ImageAdapter.ImageViewHolder> {
    private Context mContext;
    private List<Post> mUploads;

    public ImageAdapter(Context context, List<Post> uploads){
        mContext = context;
        mUploads = uploads;
    }

    @NonNull
    @Override
    public ImageViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View v = LayoutInflater.from(mContext).inflate(R.layout.news_row,parent,false);
        return  new ImageViewHolder(v);
    }

    @Override
    public void onBindViewHolder(@NonNull ImageAdapter.ImageViewHolder holder, int position) {
        Post post = mUploads.get(position);
        holder.textViewName.setText(post.getmTitle());
        Picasso.get().load(post.getmImage()).fit().centerCrop().into(holder.imageView);
    }

    @Override
    public int getItemCount() {
        return mUploads.size();
    }

    public class ImageViewHolder extends  RecyclerView.ViewHolder{
        public TextView textViewName;
        public ImageView imageView;

        public ImageViewHolder (View itemView) {
            super (itemView);

            textViewName = itemView.findViewById(R.id.newsTitle);
            imageView = itemView.findViewById(R.id.newsImage);

        }

    }
}

帖子类

public class Post {

    public String mTitle;
    public String mImage;

    public Post(){

    }
    public Post(String mTitle, String mImage){
        this.mTitle = mTitle;
        this.mImage = mImage;
    }

    public String getmImage(){
        return mImage;

    }
    public String getmTitle() {
        return mTitle;
    }
}

Answer 1

您的活动中有两个回收站视图实例。

    RecyclerView recyclerView;
    private RecyclerView mRecyclerView;//remove this line and set adapter for above recyclerView instance

    recyclerView.setAdapter(mAdapter);