Firestore 数据未显示在回收站视图中

Question

我正在尝试从 Firestore 在我的回收站视图中添加数据。 我有名称为 (Level+"levelNo.") 的文件 但我的活动没有显示任何内容 代码如下：

主要活动：

public class LevelActivity extends AppCompatActivity {
    // Recycler View object
    RecyclerView recyclerView;

    // Array list for recycler view data source
    public static List<String> levelList = new ArrayList<>();

    // Layout Manager
    RecyclerView.LayoutManager RecyclerViewLayoutManager;

    // adapter class object
    LevelAdapter adapter;

    // Linear Layout Manager
    LinearLayoutManager HorizontalLayout;

    FirebaseFirestore firebaseFirestore;

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

        // initialisation with id's
        recyclerView = (RecyclerView) findViewById(R.id.recyclerview);
        RecyclerViewLayoutManager = new LinearLayoutManager(getApplicationContext());

        // Set LayoutManager on Recycler View
        recyclerView.setLayoutManager(RecyclerViewLayoutManager);

        firebaseFirestore = FirebaseFirestore.getInstance();

        loadLevel();
        // calling constructor of adapter
        // with source list as a parameter
        adapter = new LevelAdapter(levelList);

        // Set Horizontal Layout Manager
        // for Recycler view
        HorizontalLayout = new LinearLayoutManager(LevelActivity.this, LinearLayoutManager.HORIZONTAL, false);
        recyclerView.setLayoutManager(HorizontalLayout);

        // Set adapter on recycler view
        recyclerView.setAdapter(adapter);
    }

    private void loadLevel(){
        levelList.clear();

        firebaseFirestore.collection("QUIZ LEVELS")
                .document("TOTAL_LEVELS").get()
                .addOnCompleteListener(task -> {
                    if (task.isSuccessful()) {
                        DocumentSnapshot doc = task.getResult();
                        if (doc.exists()) {
                            long levelCount = (long) doc.get("count");

                            for (int i = 1; i <= levelCount; i++) {
                                String levelName = doc.getString("LEVEL" + i);
                                levelList.add(levelName);
                            }

                        }else{
                            Toast.makeText(LevelActivity.this, "no level", Toast.LENGTH_SHORT).show();
                        }

                    }else{

                        Toast.makeText(LevelActivity.this, task.getException().getMessage(), Toast.LENGTH_SHORT).show();
                    }
                });
    }

}

电平适配器：

public class LevelAdapter extends RecyclerView.Adapter<LevelAdapter.MyView> {

    // List with String type
    private final List<String> levelList;

    // View Holder class which
    // extends RecyclerView.ViewHolder
    public class MyView extends RecyclerView.ViewHolder {
        // Text View
        TextView textView;

        // parameterised constructor for View Holder class
        // which takes the view as a parameter
        public MyView(View view) {
            super(view);
            // initialise TextView with id
            textView = (TextView) view.findViewById(R.id.textview);
        }
    }

    // Constructor for adapter class
    // which takes a list of String type
    public LevelAdapter(List<String> horizontalList) {
        this.levelList = horizontalList;
    }

    // Override onCreateViewHolder which deals
    // with the inflation of the card layout
    // as an item for the RecyclerView.
    @Override
    public MyView onCreateViewHolder(ViewGroup parent, int viewType) {
        // Inflate item.xml using LayoutInflator
        View itemView
                = LayoutInflater
                .from(parent.getContext())
                .inflate(R.layout.recycler_view_item,
                        parent, false);

        // return itemView
        return new MyView(itemView);
    }

    // Override onBindViewHolder which deals
    // with the setting of different data
    // and methods related to clicks on
    // particular items of the RecyclerView.
    @Override
    public void onBindViewHolder(final MyView holder, final int position) {
        // Set the text of each item of
        // Recycler view with the list items
        holder.textView.setText(levelList.get(position));
    }

    // Override getItemCount which Returns
    // the length of the RecyclerView.
    @Override
    public int getItemCount() {
        return levelList.size();
    }
}

Answer 1

从 firestore/firebase 加载数据需要一些时间，您应该在从文档获得响应后在负载级别调用 set adapter

 RecyclerView recyclerView;

 // Array list for recycler view data source
 public static List<String> levelList = new ArrayList<>();

// Layout Manager
RecyclerView.LayoutManager RecyclerViewLayoutManager;

// adapter class object
LevelAdapter adapter;

// Linear Layout Manager
LinearLayoutManager HorizontalLayout;

FirebaseFirestore firebaseFirestore;

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


// initialisation with id's
recyclerView = (RecyclerView) findViewById(R.id.recyclerview);
RecyclerViewLayoutManager = new 
LinearLayoutManager(getApplicationContext());

// Set LayoutManager on Recycler View
recyclerView.setLayoutManager(RecyclerViewLayoutManager);

firebaseFirestore = FirebaseFirestore.getInstance();

 HorizontalLayout = new LinearLayoutManager(LevelActivity.this, 
LinearLayoutManager.HORIZONTAL, false);
recyclerView.setLayoutManager(HorizontalLayout);

 loadLevel();




 }

private void loadLevel(){
levelList.clear();

     firebaseFirestore.collection("QUIZ LEVELS")
        .document("TOTAL_LEVELS").get()
        .addOnCompleteListener(task -> {
            if (task.isSuccessful()) {
                DocumentSnapshot doc = task.getResult();
                if (doc.exists()) {
                    long levelCount = (long) doc.get("count");

                    for (int i = 1; i <= levelCount; i++) {
                        String levelName = doc.getString("LEVEL" + i);
                        levelList.add(levelName);
                    }
                  //Set Adapter here
                  adapter = new LevelAdapter(levelList);




                 // Set adapter on recycler view
                 recyclerView.setAdapter(adapter);

                }else{
                    Toast.makeText(LevelActivity.this, "no level", 
 Toast.LENGTH_SHORT).show();
                }

            }else{

                Toast.makeText(LevelActivity.this, 
 task.getException().getMessage(), Toast.LENGTH_SHORT).show();
            }
        });
}

Answer 2

数据是从 Firebase 异步加载的，因为从基于云的数据库中获取数据需要一些时间。这意味着最初您的适配器使用空的levelList 呈现回收器视图。

然后当数据从网络返回时，您的addOnCompleteListener 会被调用并将数据添加到levelList。但此时，您需要通过调用 notifyDataSetChanged() 来告诉适配器您更改了数据并且需要重新渲染。

所以在你将所有数据添加到levelList 之后，在你的addOnCompleteListener 调用adapter.notifyDataSetChanged()：

firebaseFirestore.collection("QUIZ LEVELS")
        .document("TOTAL_LEVELS").get()
        .addOnCompleteListener(task -> {
            if (task.isSuccessful()) {
                DocumentSnapshot doc = task.getResult();
                if (doc.exists()) {
                    long levelCount = (long) doc.get("count");

                    for (int i = 1; i <= levelCount; i++) {
                        String levelName = doc.getString("LEVEL" + i);
                        levelList.add(levelName);
                    }

                }else{
                    Toast.makeText(LevelActivity.this, "no level", Toast.LENGTH_SHORT).show();
                }
                adapter.notifyDataSetChanged(); // ?
            }else{

                Toast.makeText(LevelActivity.this, task.getException().getMessage(), Toast.LENGTH_SHORT).show();
            }
        });