爲什麼片段中的RecyclerView沒有顯示來自Firebase後端的任何數據？

Question

我正嘗試在用戶登錄後使用RecyclerView在儀表板中顯示來自Firebase數據庫的帖子。我不知道出了什麼問題。 RecyclerView沒有被填充。它甚至沒有顯示一個單一的項目。我在谷歌搜索了很多，但沒有解決方案似乎工作。

Post.java：

public class Post { 

    private String bloodGroup; 
    private String postDescription; 
    private String postTitle; 
    private String timestamp; 
    private String userId; 

    public Post(){ 

    } 

    public Post(String postTitle, String bloodGroup, String postDescription, String userId, String timestamp) { 
     this.postTitle = postTitle; 
     this.bloodGroup = bloodGroup; 
     this.postDescription = postDescription; 
     this.userId = userId; 
     this.timestamp = timestamp; 
    } 



    public String getPostTitle() { 
     return postTitle; 
    } 

    public void setPostTitle(String postTitle) { 
     this.postTitle = postTitle; 
    } 

    public String getBloodGroup() { 
     return bloodGroup; 
    } 

    public void setBloodGroup(String bloodGroup) { 
     this.bloodGroup = bloodGroup; 
    } 

    public String getPostDescription() { 
     return postDescription; 
    } 

    public void setPostDescription(String postDescription) { 
     this.postDescription = postDescription; 
    } 

    public String getUserId() { 
     return userId; 
    } 

    public void setUserId(String userId) { 
     this.userId = userId; 
    } 

    public String getTimestamp() { 
     return timestamp; 
    } 

    public void setTimestamp(String timestamp) { 
     this.timestamp = timestamp; 
    } 
} 

DashboardFragment.java：

public class DashboardFragment extends Fragment { 

    private static final String TAG = "Dashboard_Fragment"; 
    private RecyclerView postsListRcview; 

    View postsListView; 

    DatabaseReference firebaseDbUsers, firebaseDbPosts; 

    FirebaseRecyclerAdapter<Post, PostViewHolder> postsRecyclerAdapter; 

    LinearLayoutManager linearLayoutManager; 

    public DashboardFragment() { 
     // Required empty public constructor 
    } 

    @Override 
    public void onCreate(@Nullable Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 


    } 

    @Override 
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
          Bundle savedInstanceState) { 
     // Inflate the layout for this fragment 
     postsListView = inflater.inflate(R.layout.fragment_dashboard, container, false); 
     postsListView.setTag(TAG); 

     initVariables(); 

     return postsListView; 
    } 

    @Override 
    public void onSaveInstanceState(Bundle outState) { 
     super.onSaveInstanceState(outState); 
    } 

    private void printMessage(String msg){ 
     Toast.makeText(getContext(), msg, Toast.LENGTH_SHORT).show(); 
    } 

    private void initVariables(){ 

     postsListRcview = (RecyclerView) postsListView.findViewById(R.id.posts_list_rcview); 
     postsListRcview.setHasFixedSize(true); 

     linearLayoutManager = new LinearLayoutManager(getActivity()); 
     linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL); 
     postsListRcview.setLayoutManager(linearLayoutManager); 
     postsRecyclerAdapter = null; 
     postsListRcview.setAdapter(postsRecyclerAdapter); 

     firebaseDbUsers = FirebaseDatabase.getInstance().getReference().child("User"); 
     firebaseDbPosts = FirebaseDatabase.getInstance().getReference().child("Post"); 

    } 

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

     postsRecyclerAdapter = new FirebaseRecyclerAdapter<Post, PostViewHolder>(

       Post.class, 
       R.layout.posts_rcview_item, 
       PostViewHolder.class, 
       firebaseDbPosts 

     ) { 
      @Override 
      protected void populateViewHolder(PostViewHolder viewHolder, Post model, int position) { 

       viewHolder.setTitle(model.getPostTitle()); 
       printMessage("Hello"); 

      } 
     }; 

     postsRecyclerAdapter.notifyDataSetChanged(); 
     postsListRcview.setAdapter(postsRecyclerAdapter); 
    } 

    public static class PostViewHolder extends RecyclerView.ViewHolder{ 

     View mView; 
     TextView postTitleTv; 
     TextView requesterNameTv; 
     ImageView requesterPropic; 
     TextView timestampTv; 

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

      mView = itemView; 
     } 

     public void setTitle(String title){ 

      postTitleTv = (TextView) mView.findViewById(R.id.post_title_tv); 
      postTitleTv.setText(title); 
     } 

     public void setRequesterName(String name){ 
      requesterNameTv = (TextView) mView.findViewById(R.id.requester_name_tv); 
      requesterNameTv.setText(name); 
     } 

     public void setRequesterPropic(Context context, String path){ 
      requesterPropic = (ImageView) mView.findViewById(R.id.requester_propic_imgview); 
      Picasso.with(context).load(path).into(requesterPropic); 
     } 

     public void setTimestamp(String timestamp){ 
      timestampTv = (TextView) mView.findViewById(R.id.timestamp_tv); 
      timestampTv.setText(timestamp); 
     } 
    } 
} 

火力地堡數據庫：

請幫幫我。提前致謝。

Answer 1

問題已解決。問題出在Post類。 Post.java中成員變量「timestamp」的類型是String，但在Firebase中，數據類型很長。所以這是檢索數據的問題。我只是將「timestamp」變量的數據類型從String更改爲long。另一個問題是RecyclerView在一秒鐘後消失。我剛剛在DashboardFragment.java中評論了以下代碼：postsListRcview.setHasFixedSize(true);。就這樣。謝謝。