即使设置了 getitemcount 和布局管理器，RecyclerView 也不显示任何项目

Question

我尝试了这里提到的大多数解决方案，但都遇到了类似的问题，但 none 似乎对我有用......现在我观察到的是代码能够从 firebase 获取数据并且它能够设置数据，但是 getitemcount 方法没有更新它仍然显示为零，即使我已经将它设置为项目列表大小关于我做错了什么的任何帮助都会有所帮助

Activity class

package com.example.sololeveling;

import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import android.os.Bundle;
import android.widget.Toast;

import com.example.sololeveling.DAO.CasinoCouponsDao;
import com.example.sololeveling.DAO.CasinoHistoryDao;
import com.example.sololeveling.DAO.CouponDao;
import com.example.sololeveling.DAO.UserDAO;
import com.example.sololeveling.Entity.CasinoHistory;
import com.example.sololeveling.adapter.CasinoHistoryAdapter;
import com.google.firebase.database.DataSnapshot;
import com.google.firebase.database.DatabaseError;
import com.google.firebase.database.ValueEventListener;

import java.util.ArrayList;

public class HistoryActivity extends AppCompatActivity {

    CasinoHistoryDao casinoHistoryDao;
    RecyclerView casinoHistoryView;
    CasinoHistoryAdapter casinoHistoryAdapter;

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

        initializeLevelObjects();
        loadRollHistory();


        casinoHistoryView.setAdapter(casinoHistoryAdapter);
        casinoHistoryView.setLayoutManager(new LinearLayoutManager(this));
    }

    private void loadRollHistory()
    {
        casinoHistoryDao.get().addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                ArrayList<CasinoHistory> casinoHistoryArrayList = new ArrayList<>();
                for(DataSnapshot dataSnapshot : snapshot.getChildren())
                {
                    CasinoHistory casinoHistory = dataSnapshot.getValue(CasinoHistory.class);
                    casinoHistory.setKey(dataSnapshot.getKey());
                    casinoHistoryArrayList.add(casinoHistory);
                }
                casinoHistoryAdapter.setCasinoHistoryArrayList(casinoHistoryArrayList);
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {
                Toast.makeText(HistoryActivity.this, "Fail to get data.", Toast.LENGTH_SHORT).show();
            }
        });
    }

    private void initializeLevelObjects()
    {
        casinoHistoryDao = new CasinoHistoryDao();
        casinoHistoryView = findViewById(R.id.historyrollview);
        casinoHistoryAdapter = new CasinoHistoryAdapter(this);
    }
}

Adapter class

package com.example.sololeveling.adapter;

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.example.sololeveling.Entity.CasinoHistory;
import com.example.sololeveling.R;
import com.example.sololeveling.ViewHolder.CasinoHistoryViewHolder;

import java.util.ArrayList;

public class CasinoHistoryAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder>
{
    private Context context;
    ArrayList<CasinoHistory> casinoHistoryArrayList = new ArrayList<>();

    public CasinoHistoryAdapter(Context context) {
        this.context = context;
    }

    public void setCasinoHistoryArrayList(ArrayList<CasinoHistory> casinoHistories)
    {
        this.casinoHistoryArrayList = casinoHistories;
    }

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        View view = LayoutInflater.from(context).inflate(R.layout.casino_history_list, parent, false);
        return new CasinoHistoryViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull RecyclerView.ViewHolder holder, int position) {
        CasinoHistoryViewHolder casinoHistoryViewHolder = (CasinoHistoryViewHolder) holder;
        CasinoHistory casinoHistory = casinoHistoryArrayList.get(position);
        casinoHistoryViewHolder.historyView.setText("you got " + casinoHistory.getCoupon() + " at " + casinoHistory.getDate());
    }

    @Override
    public int getItemCount()
    {
        return casinoHistoryArrayList.size();
    }
}

ViewHolder class

package com.example.sololeveling.ViewHolder;

import android.util.Log;
import android.view.View;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.example.sololeveling.R;

public class CasinoHistoryViewHolder extends RecyclerView.ViewHolder implements View.OnClickListener
{
    public TextView historyView;

    public CasinoHistoryViewHolder(@NonNull View itemView) {
        super(itemView);
        historyView = itemView.findViewById(R.id.historyview);
        Log.d("CasinoHistoryViewHolder","inside");
    }

    @Override
    public void onClick(View view) {

    }
}

main activity xml

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".HistoryActivity">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/historyrollview"
        android:layout_width="412dp"
        android:layout_height="729dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintHorizontal_bias="0.0"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

item list xml

<?xml version="1.0" encoding="utf-8"?>
<com.google.android.material.card.MaterialCardView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:layout_width="match_parent"
    android:layout_height="75dp"
    android:clickable="true"
    android:focusable="true"
    app:cardUseCompatPadding="true">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        android:padding="10dp">

        <TextView
            android:id="@+id/historyview"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:text="daily task"
            android:textAppearance="@style/TextAppearance.AppCompat.Large" />
    </LinearLayout>

</com.google.android.material.card.MaterialCardView>

Answer 1

更改数据后调用 notifyDataSetChanged() 方法。此 android 函数通知附加的观察者基础数据已更改，任何反映数据集的视图都应自行刷新。

public void setCasinoHistoryArrayList(ArrayList<CasinoHistory> casinoHistories)
{
    this.casinoHistoryArrayList = casinoHistories;
    notifyDataSetChanged();
}

即使设置了 getitemcount 和布局管理器，RecyclerView 也不显示任何项目

RecyclerView not displaying any items even after getitemcount is set and layoutmanager is set

java

android

android-layout

android-studio