Firebase UI 3.0.0：檢索數據以回收視圖

Question

誰能幫助我從“食物”節點中檢索數據並將其放入RecyclerView 。 這些是我一直在處理的文件，但事實證明它是一個空列表。 我已經查看了Internet上的教程，但是其中大多數都是使用較舊版本的Firebase的。 最近，Firebase UI已更新，並且數據綁定過程已更改為其新的FirebaseRecyclerAdapter結構

這是我的數據庫結構：

"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"
},

這是我的活動：

    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);
        }
    }
}

和類結構：

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應該是要在RecyclerView顯示的列表根目錄的引用，如下所示：

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

您還需要在適配器上調用startListening()來指示適配器開始從數據庫中檢索數據。

從FirebaseRecyclerAdapter生命周期文檔中 ：

FirebaseRecyclerAdapter使用事件偵聽器監視對Firebase查詢的更改。 要開始偵聽數據，請調用startListening()方法。 您可能要在onStart()方法中調用它。 在調用startListening()之前，請確保已完成讀取數據所需的所有身份驗證，否則查詢將失敗。

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

同樣， stopListening()調用將刪除事件偵聽器和適配器中的所有數據。 當包含的Activity或Fragment停止時調用此方法：

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

Answer 2

這是我使用Firebase UI在recyclerview中檢索數據的方式：

 private FirebaseRecyclerAdapter<TaskPOJO, TaskViewHolder> adapter;
 private void loadTasks() {


        database = FirebaseDatabase.getInstance();
        tasks = database.getReference("Tasks");
        adapter = new FirebaseRecyclerAdapter<TaskPOJO, TaskViewHolder>(TaskPOJO.class, R.layout.task_item, TaskViewHolder.class, tasks) {
            @Override
            protected void populateViewHolder(TaskViewHolder viewHolder, final TaskPOJO model, int position) {


                Log.wtf("valueTEst", "populateViewHolder: "+model.toString() );
                Log.wtf("TEstScript1", "populateViewHolder: "+model.getTitle() );
                viewHolder.title.setText(model.getTitle());
                viewHolder.desc.setText(model.getDescripttion()+"\n");
                viewHolder.remaining.setText(model.getRemaining()+"/"+model.getPoint());
                viewHolder.points.setText("Points "+model.getRemaining());
                Glide.with(viewHolder.title.getContext())
                        .load(model.getImage())
                        .into(viewHolder.image);


                viewHolder.setClickListener(new ItemClickListener() {
                    @Override
                    public void onClick(View view, int position, boolean isLongClick) {
                        Toast.makeText(getActivity(), "" /*+ model.getTitle()*/, Toast.LENGTH_SHORT).show();

                        Intent TaskPOJODetail = new Intent(getActivity(), Main.class);
                        TaskPOJODetail.putExtra("value","detail");
                        TaskPOJODetail.putExtra("taskId",adapter.getRef(position).getKey());
                        startActivity(TaskPOJODetail);
                    }
                });
            }
        };
        progressBar.setVisibility(View.GONE);
        recyclerViewTasks.setAdapter(adapter);
    }

這是我的firebase結構：

希望這會幫助你。

Answer 3

請重寫FirebaseRecyclerAdapter getItemCount()方法。

@Override
    public int getItemCount() {
        return 1;
    }

參考。