Question

无法从数据库检索Post键和值。这是我第一次尝试使用FirebaseRecyclerAdapter从Firebase数据库检索数据。但是我不知道问题出在哪里。我也尝试调试，但是编译器不会进入onCreateViewHolder或onBindViewHolder函数。但是我完全遵循FirebaseUI进行实时数据库参考。

NEWSFEEDBANK.JAVA

private FirebaseRecyclerAdapter<NewsFeed, NewsFeedViewHolder> adapter;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_news_feed_bank);
    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    SharedPreferences sharedPreferences = getSharedPreferences("BankData", Context.MODE_PRIVATE);
    username = sharedPreferences.getString("UserName", "UserName");

    recyclerView = (RecyclerView) findViewById(R.id.recycler_View_Bank);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));

    mDatabase = FirebaseDatabase.getInstance().getReference().child("Posts");
    mAuth = FirebaseAuth.getInstance();

    mAuthListener = new FirebaseAuth.AuthStateListener() {
        @Override
        public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
            if (mAuth.getCurrentUser() == null) {
                Intent loginIntent = new Intent(NewsFeedBank.this, Login.class);
                loginIntent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TASK);
                startActivity(loginIntent);
            }
        }
    };

    DisplayPosts();
}

private void DisplayPosts() {

    FirebaseRecyclerOptions<NewsFeed> options = new FirebaseRecyclerOptions.Builder<NewsFeed>().setQuery(mDatabase, NewsFeed.class).build();

    adapter = new FirebaseRecyclerAdapter<NewsFeed, NewsFeedViewHolder>(options) {
        @Override
        protected void onBindViewHolder(@NonNull NewsFeedViewHolder holder, int position, @NonNull NewsFeed model) {

          //  holder.title.setText(model.getTitle());
        //    holder.des.setText(model.getDesc());
            holder.usern.setText(model.getUsername());

        }

        @NonNull
        @Override
        public NewsFeedViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {
            View view = LayoutInflater.from(viewGroup.getContext()).inflate(R.layout.card_items, viewGroup, false);
            NewsFeedViewHolder holder = new NewsFeedViewHolder(view);
            return holder;
        }
    };
    recyclerView.setAdapter(adapter);


}

@Override
protected void onStart() {
    super.onStart();
    adapter.startListening();
}

@Override
protected void onStop() {
    super.onStop();
    adapter.stopListening();
}

public static class NewsFeedViewHolder extends RecyclerView.ViewHolder {
    TextView title, des, usern;
    View mView;

    public NewsFeedViewHolder(@NonNull View itemView) {
        super(itemView);
        usern = (TextView) mView.findViewById(R.id.view_poster_username);
    }

}}

NEWSFEED.JAVA

导入com.google.firebase.storage.StorageReference;

公共类NewsFeed {

private String Title, Description ,UserName;
private StorageReference imageUrl;

public NewsFeed(String UserName, String Title, String Description) {
    this.Title = Title;
    this.Description = Description;
    this.UserName = UserName;
}
public NewsFeed() {
}

public void setUsername(String UserName) {
    this.UserName = UserName;
}
public void setTitle(String Title) {
    this.Title = Title;
}
public void setDesc(String Description) {
    this.Description = Description;
}

public String getTitle() {
    return Title;
}
public String getDesc() {
    return Description;
}
public String getUsername() {
    return UserName;
}}

E / Android运行时：致命异常：主要流程：com.example.admin.firstapp，PID：1151 java.lang.NullPointerException：尝试在null上调用虚拟方法'android.view.View android.view.View.findViewById（int）' 对象参考在com.example.admin.firstapp.NewsFeedBank $ NewsFeedViewHolder。（NewsFeedBank.java:119） at com.example.admin.firstapp.NewsFeedBank $ 3.onCreateViewHolder（NewsFeedBank.java:92）在com.example.admin.firstapp.NewsFeedBank $ 3.onCreateViewHolder（NewsFeedBank.java:78）在android.support.v7.widget.RecyclerView $ Adapter.createViewHolder（RecyclerView.java:6794）在android.support.v7.widget.RecyclerView $ Recycler.tryGetViewHolderForPositionByDeadline（RecyclerView.java:5975）在android.support.v7.widget.RecyclerView $ Recycler.getViewForPosition（RecyclerView.java:5858）在android.support.v7.widget.RecyclerView $ Recycler.getViewForPosition（RecyclerView.java:5854）在android.support.v7.widget.LinearLayoutManager $ LayoutState.next（LinearLayoutManager.java:2230）在android.support.v7.widget.LinearLayoutManager.layoutChunk（LinearLayoutManager.java:1557）在android.support.v7.widget.LinearLayoutManager.fill（LinearLayoutManager.java:1517）在android.support.v7.widget.LinearLayoutManager.onLayoutChildren（LinearLayoutManager.java:612）在android.support.v7.widget.RecyclerView.dispatchLayoutStep2（RecyclerView.java:3924）在android.support.v7.widget.RecyclerView.dispatchLayout（RecyclerView.java:3641）在android.support.v7.widget.RecyclerView.onLayout（RecyclerView.java:4194）在android.view.View.layout（View.java:20672）在android.view.ViewGroup.layout（ViewGroup.java:6194）在android.support.constraint.ConstraintLayout.onLayout（ConstraintLayout.java:1915）在android.view.View.layout（View.java:20672）在android.view.ViewGroup.layout（ViewGroup.java:6194）在android.support.design.widget.CoordinatorLayout.layoutChild（CoordinatorLayout.java:1183）在android.support.design.widget.CoordinatorLayout.onLayoutChild（CoordinatorLayout.java:870）在android.support.design.widget.ViewOffsetBehavior.layoutChild（ViewOffsetBehavior.java:62）在android.support.design.widget.HeaderScrollingViewBehavior.layoutChild（HeaderScrollingViewBehavior.java:146）在android.support.design.widget.ViewOffsetBehavior.onLayoutChild（ViewOffsetBehavior.java:41）在android.support.design.widget.AppBarLayout $ ScrollingViewBehavior.onLayoutChild（AppBarLayout.java:1556）在android.support.design.widget.CoordinatorLayout.onLayout（CoordinatorLayout.java:888）

Firebase数据库结构：

Answer 1

尝试

usern = (TextView) itemView.findViewById(R.id.view_poster_username);

代替

usern = (TextView) mView.findViewById(R.id.view_poster_username);

如果再次遇到错误，请发布您的布局文件

无法使用FirebaseRecyclerViewAdapter从Firebase实时数据库检索数据

1 个答案: