java - 火力地堡用户界面 3.0.0 : Retrieve data to recycle view

Question

谁能帮我从节点“foods”中检索数据并将其放入RecyclerView。这些是我一直在处理的文件，但结果是一个空列表。我在 Internet 上查看了教程，但其中大部分使用的是旧版本的 Firebase。最近，Firebase UI 更新，数据绑定(bind)过程更改为新的 FirebaseRecyclerAdapter 结构

这是我的数据库结构:

"foods" : {
"AntipastoSalad" : {
  "duration" : "30",
  "img" : "https://firebasestorage.googleapis.com/v0/b/mealplanner-ec8ca.appspot.com/o/res%2Fsalad.jpg?alt=media&token=257d4392-8a1f-4fb7-84b5-b63abb4643f4",
  "name" : "Antipasto salad",
  "type" : "Salad"
},

这是我的 Activity :

    private RecyclerView mRecycleView;
    private Query query;
    private FirebaseRecyclerOptions<Meal> options;
    private DatabaseReference mDatabase;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_food_list_row);

        mDatabase = FirebaseDatabase.getInstance().getReference().child("foods");

        //Recycle View
        mRecycleView = (RecyclerView) findViewById(R.id.meal_items);
        mRecycleView.setHasFixedSize(true);
        mRecycleView.setLayoutManager(new LinearLayoutManager(this));
    }


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

        query = FirebaseDatabase.getInstance().getReferenceFromUrl("https://mealplanner-ec8ca.firebaseio.com/foods/AntipastoSalad");

        options = new FirebaseRecyclerOptions.Builder<Meal>()
                .setQuery(query, Meal.class)
                .build();

        FirebaseRecyclerAdapter<Meal, FoodListRowActivity.MealRowHolder> firebaseRecyclerAdapter = new FirebaseRecyclerAdapter<Meal, FoodListRowActivity.MealRowHolder>(
                options) {
            @Override
            public FoodListRowActivity.MealRowHolder onCreateViewHolder(ViewGroup parent, int viewType) {
                View v = LayoutInflater.from(parent.getContext()).inflate(R.layout.food_row, parent, false);
                return new FoodListRowActivity.MealRowHolder(v);
            }

            @Override
            protected void onBindViewHolder(FoodListRowActivity.MealRowHolder holder, int position, Meal current) {
                holder.setTitle(current.getName());
                String duration = current.getDuration() + "min";
                holder.setDuration(duration);
            }
        };

        //Populate Item into Adapter
        mRecycleView.setAdapter(firebaseRecyclerAdapter);

        mRecycleView.addOnItemTouchListener(new RecycleViewItemClickListener(this, mRecycleView, new RecycleViewItemClickListener.OnItemClickListener() {
            @Override
            public void onItemClick(View view, int position) {
                Intent viewMeal = new Intent(FoodListRowActivity.this, CookingInstructionActivity.class);
                startActivity(viewMeal);
            }

            @Override
            public void onLongItemClick(View view, int position) {
                //TODO: DELETE
            }
        }));
    }

    public static class MealRowHolder extends RecyclerView.ViewHolder {

        View mView;

        public MealRowHolder(View itemView) {
            super(itemView);
            mView = itemView;

        }

        public void setTitle(String title) {
            TextView foodTitle = (TextView) mView.findViewById(R.id.list_item_foodList_name);
            foodTitle.setText(title);
        }


        public void setDuration(String title) {
            TextView foodDuration = (TextView) mView.findViewById(R.id.list_item_foodList_calories);
            foodDuration.setText(title);
        }
    }
}

和类结构:

public class Meal{

private String img;
private String duration;
private String name;
private String instruction;

public Meal(){

}

public Meal (String img, String duration, String name, String instruction){
    this.img = img;
    this.name = name;
    this.duration = duration;
    this.instruction = instruction;
}

public void update(String duration, String name, String instruction)
{
    this.name = name;
    this.duration = duration;
    this.instruction = instruction;
}
public String getName(){
    return name;
}

public String getDuration() {
    return duration;
}

public String getInstruction() {
    return instruction;
}

public String getImg(){return img;}

Answer 1

setQuery() 方法中指定的query 应该是对要在RecyclerView 中显示的列表的根目录的引用，所以像这样:

query = FirebaseDatabase.getInstance().getReference().child("foods");

您还需要在适配器上调用 startListening() 以指示它开始从数据库中检索数据。

来自FirebaseRecyclerAdapter lifecycle documentation :

The FirebaseRecyclerAdapter uses an event listener to monitor changes to the Firebase query. To begin listening for data, call the startListening() method. You may want to call this in your onStart() method. Make sure you have finished any authentication necessary to read the data before calling startListening() or your query will fail.

@Override protected void onStart() {
    super.onStart();
    adapter.startListening();
}

Similarly, the stopListening() call removes the event listener and all data in the adapter. Call this method when the containing Activity or Fragment stops:

@Override protected void onStop() {
    super.onStop();
    adapter.stopListening();
 }