Question

我正在创建一个在回收者视图中显示视频的应用程序，我已经可以将这些视频存储在Database Firestore中，但是在运行我的应用程序时出现此错误：

java.lang.NullPointerException: Attempt to invoke interface method 'int java.util.List.size()' on a null object reference
    at com.example.carlos.trendy.FeedRecyclerAdapter.getItemCount(FeedRecyclerAdapter.java:35)

我的代码：

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

public List<Feed>feedList;

public FeedRecyclerAdapter(List<Feed> feedList){
    this.feedList = feedList;
}

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

    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.feed_row, parent, false);
    return new ViewHolder(view);
}

@Override
public void onBindViewHolder(ViewHolder holder, int position) {

    String desc_data = feedList.get(position).getDesc();
    holder.setDesc(desc_data);
}

@Override
public int getItemCount() {
    return feedList.size();///ERROR
}

public  class ViewHolder extends RecyclerView.ViewHolder{

    private TextView desc;
    private View mView;

    public ViewHolder(View itemView) {
        super(itemView);
        mView=itemView;
    }
    public void setDesc(String descText){
        desc = mView.findViewById(R.id.post_desc);
        desc.setText(descText);
    }
}
}

FeedActivity：

public class FeedActivity extends AppCompatActivity {

private Context mContext = FeedActivity.this;
private static final int ACTIVITY_NUM = 0;
private FirebaseFirestore firebaseFirestore;


private RecyclerView mFeedList;
private List<Feed> feedList;
private FeedRecyclerAdapter feedRecyclerAdapter;

public void videoPicker(View view){
    Intent intent = new Intent(FeedActivity.this, postActivity.class);
    intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
    startActivity(intent);

}

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

    mFeedList = this.findViewById(R.id.feed_list);
    feedRecyclerAdapter = new FeedRecyclerAdapter(feedList);
    mFeedList.setLayoutManager(new LinearLayoutManager(this));
    mFeedList.setAdapter(feedRecyclerAdapter);

    feedList = new ArrayList<>();


    firebaseFirestore = FirebaseFirestore.getInstance();
    firebaseFirestore.collection("Posts").addSnapshotListener(new EventListener<QuerySnapshot>() {
        @Override
        public void onEvent(QuerySnapshot documentSnapshots, FirebaseFirestoreException e) {
            for (DocumentChange documentChange: documentSnapshots.getDocumentChanges()){
                if (documentChange.getType() == DocumentChange.Type.ADDED){
                    Feed feed = documentChange.getDocument().toObject(Feed.class);
                    feedList.add(feed);
                    feedRecyclerAdapter.notifyDataSetChanged();
                }
            }
        }
    });



    setupBottomNavigationView();


}

private void setupBottomNavigationView() {
    BottomNavigationView bottomNavigationView = findViewById(R.id.bottomNavViewBar);
    BottomNavigationViewHelper.enableNavigation(mContext, bottomNavigationView);
    Menu menu = bottomNavigationView.getMenu();
    MenuItem menuItem = menu.getItem(ACTIVITY_NUM);
    menuItem.setChecked(true);
}

@Override
protected void onStart() {
    super.onStart();


}

public static class FeedViewHolder extends RecyclerView.ViewHolder {
    View mView;

    public FeedViewHolder(View itemView) {
        super(itemView);
        itemView = mView;
    }
    public void setDesc(String desc){
        TextView post_desc = mView.findViewById(R.id.post_desc);
        post_desc.setText(desc);
    }
}

}

有人可以帮助我吗？

Answer 1

您在此处初始化适配器：
feedRecyclerAdapter = new FeedRecyclerAdapter(feedList);
但feedList为空。
您必须对其进行初始化
移动所有这些行：

feedRecyclerAdapter = new FeedRecyclerAdapter(feedList);
mFeedList.setLayoutManager(new LinearLayoutManager(this));
mFeedList.setAdapter(feedRecyclerAdapter);

在此行之后：

feedList = new ArrayList<>();

错误：尝试在空对象引用上调用接口方法'int java.util.List.size（）'

1 个答案: