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java - 无法实现 RecycleAdapter 到自定义 ArrayList 以获取数据库上的随机查询结果

问题描述

我有一个数据库Firestore并RecycleView从中放入数据。我发送了一些查询Firestore，它会根据我的请求得到结果。但是，如果我想从应要求发给我的集合中获取 3 个随机结果。也就是说，例如，我得到 20 个结果，并且每次发送请求时只想获取 3 个结果。并且每次都必须从这 20 个结果中随机抽取 3 个结果？

我被帮助实现了在代码中选择 3 个随机结果的机制，但我不明白如何将它连接到我的adapter.

    public class Myactivity extends AppCompatActivity {

    public RecyclerView mResultList;
    public FirebaseFirestore mFirestore;
    public com.google.firebase.firestore.Query query;
    public FirestoreRecyclerAdapter<Places, PlaceViewHolder> firestoreRecyclerAdapter;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_recycle_activity);
        mResultList = findViewById(R.id.list_result);

        Boolean l_check1 = getIntent().getExtras().getBoolean("1");
        Boolean l_check2 = getIntent().getExtras().getBoolean("2");
        Boolean l_check3 = getIntent().getExtras().getBoolean("3");
        mFirestore = FirebaseFirestore.getInstance();  
        if (l_check1) {
            query = mFirestore.collection("Places").whereEqualTo("colour", "1").limit(20);
            query.get().addOnCompleteListener(new OnCompleteListener<QuerySnapshot>() {
            @Override
            public void onComplete(@NonNull Task<QuerySnapshot> task) {
                if (task.isSuccessful()) {
                    List<Places> placesList = new ArrayList<>();
                    for (DocumentSnapshot document : task.getResult()) {
                        Places place = document.toObject(Places.class);
                        placesList.add(place);
                    }
                    int placeCount = placesList.size();
                    int randomNumber = new Random().nextInt(placeCount);

                    List<Places> randomPlaceList = new ArrayList<>();
                    for (int i=1; i<=3; i++) {
                        randomPlaceList.add(placesList.get(randomNumber));
                    }
                }
            }
        });
        } else if (l_check2) {
            query = mFirestore.collection("Places").whereEqualTo("colour", "2").limit(3);
        } else if (l_check3) {
            query = mFirestore.collection("Places").whereEqualTo("colour", "3").limit(3);
        }
        mResultList.setLayoutManager(new LinearLayoutManager(this));
        FirestoreRecyclerOptions<Places> options = new FirestoreRecyclerOptions.Builder<Places>()
                .setQuery(query, Places.class)
                .build();
        firestoreRecyclerAdapter = new FirestoreRecyclerAdapter<Places, PlaceViewHolder>(options) {
            @Override
            protected void onBindViewHolder(PlaceViewHolder holder, int position, Places model) {

                holder.setDetails(getApplicationContext(), model.getName(), model.getImage());
            }

            @Override
            public PlaceViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
                View view = LayoutInflater.from(parent.getContext())
                        .inflate(R.layout.list_layout, parent, false);
                return new PlaceViewHolder(view);
            }

        };
        mResultList.setAdapter(firestoreRecyclerAdapter);
    }
    @Override
    protected void onStart() {
        super.onStart();
        firestoreRecyclerAdapter.startListening();
    }
    class PlaceViewHolder extends RecyclerView.ViewHolder {

        View mView;

        public PlaceViewHolder(View itemView) {
            super(itemView);

            mView = itemView;
        }

        public void setDetails(Context context, String placeName, String placeImage) {

            final TextView place_Name = mView.findViewById(R.id.text_image_id);
            ImageView place_Image = mView.findViewById(R.id.image_id);

            place_Name.setText(placeName);
            Glide.with(context).load(placeImage).into(place_Image);

            place_Name.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Intent intent = new Intent(getApplicationContext(), Card_activity.class);
                    intent.putExtra("qwerty", place_Name.getText());
                    startActivity(intent);
                }
            });
        }
    }
    @Override
    protected void onStop() {
        super.onStop();
        if (firestoreRecyclerAdapter != null) {
            firestoreRecyclerAdapter.stopListening();
        }
    }
}

我的地方.class：

public class Places {
private String image, name;
public Places() { }

public Places(String image, String name) {
    this.image = image;
    this.name = name; 
}
public String getImage() { return image; }
public String getName() { return name; }   
}

标签： javaandroidarraylistandroid-recyclerview

解决方案

首先，您生成的逻辑randomPlaceList是不正确的，因为您只是使用生成一个随机数new Random().nextInt(placeCount)，然后继续使用它三次将条目添加到您的列表中。

你应该更新你的逻辑如下，

...
final int placeCount = placesList.size();
final Random randomGenerator = new Random();
List<Places> randomPlaceList = new ArrayList<>();
for (int i = 0; i<=3; i++) {
    randomPlaceList.add(placesList.get(randomGenerator.nextInt(placeCount)));
}
...

请参阅此线程以查看从以下位置RecyclerView获取结果后如何填充Firebase： 如何使用 Firebase 填充 RecyclerView 适配器

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