RecyclerView不顯示收到的數據

Question

我從Firebase（在線數據存儲）獲取數據，但以某種方式在我的適配器類中，數據集爲[]。然而，當我使用同一個類通過20個隨機事物時，它完美地工作。這是代碼。

片段類：

@Override 
public void onCreate(Bundle savedInstanceState) { 
    super.onCreate(savedInstanceState); 
    myFirebaseRef = new Firebase("http..."); 
    initListItems(); 
} 



@Override 
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
         Bundle savedInstanceState) { 
    View rootView = inflater.inflate(R.layout.fragment_products, container, false); 
    // Inflate the layout for this fragment 
    mRecyclerView = (RecyclerView) rootView.findViewById(R.id.list); 
    mRecyclerView.setLayoutManager(new LinearLayoutManager(getActivity().getApplicationContext())); 

    mAdapter = new MyAdapter(mDataset); 
    mRecyclerView.setAdapter(mAdapter); 


    return rootView; 

} 
// Get the data from Firebase and set it to List 
private void initListItems() { 

    // Attach an listener to read the data at our posts reference 
    myFirebaseRef.addValueEventListener(new ValueEventListener() { 
     @Override 
     public void onDataChange(DataSnapshot snapshot) { 
      System.out.println("There are " + snapshot.getChildrenCount() + "children"); 

      for (DataSnapshot postSnapshot : snapshot.getChildren()) { 

       title = postSnapshot.child("name").getValue().toString(); 
       description = postSnapshot.child("description").getValue().toString(); 
       location = postSnapshot.child("location").getValue().toString(); 
       //This displays the information so it is properly reading data in 
       System.out.println("title: " + title + 
         "description" + description + "location" + location); 

       mDataset.add(new ListItem(title, description, location, 0.00, 0.00)); 


      } 

     } 
    }); 
    // If i remove the above code and just put this, the recycleview displays this information 
    for (int i = 0; i<20; i++) { 
     String name ="This is element #" + i; 
     mDataset.add(new ListItem(name, "description", "location", 0.00, 0.00)); 
    } 
} 

適配器類別：

public class MyAdapter extends RecyclerView.Adapter<MyAdapter.ViewHolder> { 
    private static final String TAG = "MyAdapter"; 
    private List<ListItem> mDataSet; 
    /** 
    * Provide a reference to the type of views that you are using (custom ViewHolder) 
    */ 
    public static class ViewHolder extends RecyclerView.ViewHolder { 
     private final TextView textView; 
     private final ImageView imageView; 
     private final TextView textViewLocation; 

     public ViewHolder(View v) { 
      super(v); 
      // Define click listener for the ViewHolder's View. 
      v.setOnClickListener(new View.OnClickListener() { 
       ... 
      }); 
      textView = (TextView) v.findViewById(R.id.startupName); 
      textViewLocation = (TextView) v.findViewById((R.id.startupLocation)); 
      imageView = (ImageView) v.findViewById(R.id.startupImage); 
     } 

     public TextView getTextView() { 
      return textView; 
     } 
     public TextView getTextViewLocation() { 
      return textViewLocation; 
     } 
     public ImageView getImageView() { 
      return imageView; 
     } 

    } 



// When I try to send the data received from Firebase, it prints out [ ] but if i use the random data I created, it works    
public MyAdapter(List<ListItem> dataSet) { 
     System.out.println("THE DATASET IS " + dataSet); 
     mDataSet = dataSet; 
    } 

    // Create new views (invoked by the layout manager) 
    @Override 
    public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) { 
     // Create a new view. 
     View v = LayoutInflater.from(viewGroup.getContext()) 
       .inflate(R.layout.row_item, viewGroup, false); 

     return new ViewHolder(v); 
    } 

    // Replace the contents of a view (invoked by the layout manager) 
    @Override 
    public void onBindViewHolder(ViewHolder viewHolder, final int position) { 
     Log.d(TAG, "Element " + position + " set."); 

     // Get element from your dataset at this position and replace the contents of the view with that element 
     ... 

    } 

    // Return the size of your dataset (invoked by the layout manager) 
    @Override 
    public int getItemCount() { 
     return mDataSet == null ? 0 : mDataSet.size(); 
    } 
} 

有沒有人有一個想法，爲什麼發生這種情況，爲什麼從火力地堡我的數據沒有出現？

感謝

Answer 1

在onCreate你去異步獲取數據 - 這可能需要一些時間。在此期間，程序流程會一直移動，並且您在onCreateView中設置了回收站，但是在收到數據迴應之前會發生這種情況，因此mDataset仍然沒有值。在得到結果並將其放入mDataset之後的一段時間內，但我沒有看到通知RecyclerView有關更改的地方。

因此，您必須推遲設置RecyclerView，直到您獲得結果或通知RecyclerView有關數據集更新後纔會得到它。