需要从 FirebaseDatabase 检索数据到 Fragment答案

【问题标题】：Need retrieve data from FirebaseDatabase to Fragment需要从 FirebaseDatabase 检索数据到 Fragment
【发布时间】：2017-02-21 07:57:47
【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。我希望从 FireBase 接收数据并使用 RecyclerView 显示它。

在我的代码下方。该应用程序在启动过程中不会掉落。没有任何错误。我想我应该使用一些方法来达到我的目的，但我是 Firebase 的新手。

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);
        }

    }
}

【问题讨论】：

标签： android android-fragments firebase firebase-realtime-database

【解决方案1】：

如果我是你，我不会覆盖 onActivityCreated()，你可以在 onCreateView() 中创建并返回 RecyclerView。您确定您在 Firebase 中有数据吗？您可以像这样覆盖 parseSnapshot() 并可能设置一个断点以确保某些内容正在返回，如果确实如此，那么您可能需要检查您的 RecyclerView 自定义布局。

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);
        }

    }
}

【讨论】：