需要从FirebaseDatabase中将数据检索到Fragment [英] Need retrieve data from FirebaseDatabase to Fragment

问题描述

我正在开发简单的项目。 CategoryFragment是MainActivity中第一个添加的片段。我期望从FireBase接收数据并使用RecyclerView显示。

在我的代码下面。该应用程序不会在启动过程中下降。没有任何错误。
我想我应该使用一些方法来达到我的目的，但是我是Firebase的新手。

  public class CategoryFragment扩展Fragment {
 
 public DatabaseReference mRootDB; 
 private RecyclerView mRecyclerView; 
 public FirebaseRecyclerAdapter< Category，CategoryViewHolder>适配器; 
 
 
 @Override 
 public void onActivityCreated（@Nullable Bundle savedInstanceState）{
 super.onActivityCreated（savedInstanceState）; 
 mRootDB = FirebaseDatabase.getInstance（）。getReference（）。child（categories）; 
 adapter = new FirebaseRecyclerAdapter< Category，CategoryViewHolder>（
 Category.class，
 R.layout.model_category，
 CategoryViewHolder.class，
 mRootDB）
 {
 @Override 
 protected void populateViewHolder（CategoryViewHolder viewHolder，Category model，int position）{
 viewHolder.setCategory（model.getName（））; 
} 
}; 
 mRecyclerView.setAdapter（adapter）; 
 
 $ b $ @ $可
 @Override 
 public查看onCreateView（LayoutInflater inflater，ViewGroup容器，Bundle savedInstanceState）{
查看rootView = inflater.inflate R.layout.frag_category，container，false）; 
 
 mRecyclerView =（RecyclerView）rootView.findViewById（R.id.category_RV）; 
 
 return rootView; 
 
 
 $ b $ public static class CategoryViewHolder extends RecyclerView.ViewHolder {
 
 View mView; 
 TextView category_CV; 
 
 public CategoryViewHolder（View itemView）{
 super（itemView）; 
 mView = itemView; 
 category_CV =（TextView）mView.findViewById（R.id.category_CV）; 
 
 
 public void setCategory（String data）{
 category_CV.setText（data）; 
 
 
 
 
 $ b 
解决方案
如果我是你，我不会重写onActivityCreated（），你可以在onCreateView（）中创建并返回RecyclerView。您确定您拥有Firebase中的数据吗？你可以像这样覆盖parseSnapshot（），也许会放一个断点来确保返回的东西，如果是这样，那么你可能要检查你的RecyclerView自定义布局。
 
 
  public class CategoryFragment extends Fragment {
 
 public DatabaseReference mRootDB; 
 private RecyclerView mRecyclerView; 
 public FirebaseRecyclerAdapter< Category，CategoryViewHolder>适配器; 
 
 
 $ b @Nullable 
 @Override 
 public查看onCreateView（LayoutInflater inflater，ViewGroup容器，Bundle savedInstanceState）{
查看rootView = inflater .inflate（R.layout.frag_category，container，false）; 
 
 mRecyclerView =（RecyclerView）rootView.findViewById（R.id.category_RV）; 
 mRootDB = FirebaseDatabase.getInstance（）。getReference（）。child（categories）; 
 adapter = new FirebaseRecyclerAdapter< Category，CategoryViewHolder>（
 Category.class，
 R.layout.model_category，
 CategoryViewHolder.class，
 mRootDB）
 {
 @Override 
 protected Category parseSnapshot（DataSnapshot snapshot）{
 Category category = super.parseSnapshot（snapshot）; 
 if（category！= null）{
 category.setId（snapshot.getKey（））; 
} 
返回类别; 
 
 $ b @Override 
保护无效populateViewHolder（CategoryViewHolder viewHolder，类别模型，int位置）{
 viewHolder.setCategory（model.getName（））; 
} 
}; 
 
 mRecyclerView.setAdapter（adapter）; 
 
 return rootView; 
 
 
 $ b $ public static class CategoryViewHolder extends RecyclerView.ViewHolder {
 
 View mView; 
 TextView category_CV; 
 
 public CategoryViewHolder（View itemView）{
 super（itemView）; 
 mView = itemView; 
 category_CV =（TextView）mView.findViewById（R.id.category_CV）; 
 
 
 public void setCategory（String data）{
 category_CV.setText（data）; 
} 
 
} 
} 
  
 
I'm developing simple project. CategoryFragment is the first added fragment in MainActivity. I expect receive data from FireBase and display it with RecyclerView. 

Below my code. The app doesn't fall during launching. There is no any error. 
I guess I should use some method for my purpose, but I'm new in Firebase.
public class CategoryFragment extends Fragment {

    public DatabaseReference mRootDB;
    private RecyclerView mRecyclerView;
    public FirebaseRecyclerAdapter<Category, CategoryViewHolder> adapter;


    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        mRootDB = FirebaseDatabase.getInstance().getReference().child("categories");
        adapter = new FirebaseRecyclerAdapter <Category, CategoryViewHolder>(
                Category.class,
                R.layout.model_category,
                CategoryViewHolder.class,
                mRootDB)
        {
            @Override
            protected void populateViewHolder(CategoryViewHolder viewHolder, Category model, int position) {
                viewHolder.setCategory(model.getName());
            }
        };
        mRecyclerView.setAdapter(adapter);
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.frag_category, container, false);

        mRecyclerView = (RecyclerView) rootView.findViewById(R.id.category_RV);

        return rootView;
    }


    public static class CategoryViewHolder extends RecyclerView.ViewHolder {

        View mView;
        TextView category_CV;

        public CategoryViewHolder(View itemView) {
            super(itemView);
            mView = itemView;
            category_CV = (TextView) mView.findViewById(R.id.category_CV);
        }

        public void setCategory(String data){
            category_CV.setText(data);
        }

    }
}

解决方案
I would not override onActivityCreated() if I were you, you can create and return the RecyclerView in the onCreateView(). Are you sure you have data in Firebase? You can override parseSnapshot() like this and maybe put a break point to make sure that something is coming back, and if it does then you may want to check your RecyclerView custom layout.
public class CategoryFragment extends Fragment {

    public DatabaseReference mRootDB;
    private RecyclerView mRecyclerView;
    public FirebaseRecyclerAdapter<Category, CategoryViewHolder> adapter;



    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.frag_category, container, false);       

        mRecyclerView = (RecyclerView) rootView.findViewById(R.id.category_RV);
        mRootDB = FirebaseDatabase.getInstance().getReference().child("categories");
        adapter = new FirebaseRecyclerAdapter <Category, CategoryViewHolder>(
                Category.class,
                R.layout.model_category,
                CategoryViewHolder.class,
                mRootDB)
        {
            @Override
            protected Category parseSnapshot(DataSnapshot snapshot) {
                Category category = super.parseSnapshot(snapshot);
                if (category != null){
                    category.setId(snapshot.getKey());
                }
                return category;
            }

            @Override
            protected void populateViewHolder(CategoryViewHolder viewHolder, Category model, int position) {
                viewHolder.setCategory(model.getName());
            }
        };

        mRecyclerView.setAdapter(adapter);

        return rootView;
    }


    public static class CategoryViewHolder extends RecyclerView.ViewHolder {

        View mView;
        TextView category_CV;

        public CategoryViewHolder(View itemView) {
            super(itemView);
            mView = itemView;
            category_CV = (TextView) mView.findViewById(R.id.category_CV);
        }

        public void setCategory(String data){
            category_CV.setText(data);
        }

    }
}


                        
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