無法使用FirebaseRecyclerViewAdapter從Firebase實時數據庫檢索數據

Question

無法從數據庫檢索Post鍵和值。這是我第一次嘗試使用FirebaseRecyclerAdapter從Firebase數據庫檢索數據。 但是我不知道問題出在哪里。 我也嘗試調試，但是編譯器不會進入onCreateViewHolder或onBindViewHolder函數。 但是我完全遵循FirebaseUI進行實時數據庫參考。

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

導入com.google.firebase.storage.StorageReference;

公共類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 / AndroidRuntime：致命例外：主進程：com.example.admin.firstapp，PID：1151 java.lang.NullPointerException：嘗試在其上調用虛擬方法'android.view.View android.view.View.findViewById（int）' com.example.admin.firstapp.NewsFeedBank $ NewsFeedViewHolder。（NewsFeedBank.java:119）處com.example.admin.firstapp.NewsFeedBank $ 3.onCreateViewHolder（NewsFeedBank.java:92）處的空對象引用.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.tryGetViewHyeradad（ android.support.v7.widget.RecyclerView $ Recycler.getViewForPosition（RecyclerView.java:5858）位於android.support.v7.widget.RecyclerView $ Recycler.getViewForPosition（RecyclerView.java:5854）位於RecyclerView.java:5975） .support.v7.widget.LinearLayoutManager $ LayoutState.next（LinearLayoutManager.java:2230）在android.support .v7.widget.LinearLayoutManager.layoutChunk（LinearLayoutManager.java:1557）位於android.support.v7.widget.LinearLayoutManager.fill（LinearLayoutManager.java:1517）位於android.support.v7.widget.LinearLayoutManager.onLayoutChildren（LinearLayoutManager.java ：612）位於android.support.v7.widget.RecyclerView.dispatchLayoutStep2（RecyclerView.java:3924）（位於android.support.v7.widget.RecyclerView.dispatchLayout（RecyclerView.java:3641））。 android.view.View.layout（View.java:20672）位於android.view.ViewGroup.layout（ViewGroup.java:6194）位於android.support.constraint.ConstraintLayout.onLayout的RecyclerView.onLayout（RecyclerView.java:4194） （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（位於android.support.design.widget的CoordinatorLayout.java:1183）。位於android.support.design.widget.Vie的CoordinatorLayout.onLayoutChild（CoordinatorLayout.java:870） android.support.design.widget.HeaderScrollingViewBehavior.layoutChild（HeaderScrollingViewBehavior.java:146）上的wOffsetBehavior.layoutChild（ViewOffsetBehavior.java:62）在android.support.design.widget.ViewOffsetBehavior.onLayoutChild（android：java：java。 .support.design.widget.AppBarLayout $ ScrollingViewBehavior.onLayoutChild（AppBarLayout.java:1556）位於android.support.design.widget.CoordinatorLayout.onLayout（CoordinatorLayout.java:888）

Firebase數據庫結構：

Answer 1

嘗試這個

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

代替

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

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