带有 CardView 和 Firebase 的片段中的 RecyclerView

Question

我正在尝试在带有 CardView 和 Firebase 的片段中使用 RecyclerView （数据库有所有图像、名称和数量要传入卡），但我有一个问题：

我的片段中没有显示任何内容，我的 RecyclerView 不起作用，我的卡也没有显示。 我的片段是空的，我在日志中没有错误。

这是片段的 Java：

package com.example.progettocontab.assistenza;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.LinearLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import com.example.progettocontab.R;

import com.example.progettocontab.app.Articolo;
import com.example.progettocontab.app.ArticoloAdapter;
import com.firebase.ui.database.FirebaseRecyclerOptions;
import com.google.firebase.database.FirebaseDatabase;

public class FragmentAssistenza extends Fragment {

    RecyclerView recyclerView;
    ArticoloAdapter adapter;

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_assistenza, container, false);

        recyclerView = (RecyclerView) view.findViewById(R.id.recview);
        recyclerView.setLayoutManager(new LinearLayoutManager(getActivity().getApplicationContext()));

        FirebaseRecyclerOptions<Articolo> options =
                new FirebaseRecyclerOptions.Builder<Articolo>()
                        .setQuery(FirebaseDatabase.getInstance().getReference().child("Articoli"), Articolo.class)
                        .build();

        adapter = new ArticoloAdapter(options);
        recyclerView.setAdapter(adapter);

        return view;
    }

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

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

这是片段的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=".assistenza.FragmentAssistenza">

    <androidx.recyclerview.widget.RecyclerView
        android:id="@+id/recview"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginStart="1dp"
        android:layout_marginLeft="1dp"
        android:layout_marginTop="1dp"
        android:layout_marginEnd="1dp"
        android:layout_marginRight="1dp"
        android:layout_marginBottom="1dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintEnd_toEndOf="parent"
        app:layout_constraintStart_toStartOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>

这是适配器（带有 ViewHolder 类）：

package com.example.progettocontab.app;

import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;

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

import com.bumptech.glide.Glide;
import com.example.progettocontab.R;
import com.firebase.ui.database.FirebaseRecyclerAdapter;
import com.firebase.ui.database.FirebaseRecyclerOptions;


public class ArticoloAdapter extends FirebaseRecyclerAdapter<Articolo, ArticoloAdapter.ViewHolder> {

    public ArticoloAdapter(@NonNull FirebaseRecyclerOptions<Articolo> options) {
        super(options);
    }

    @Override
    protected void onBindViewHolder(@NonNull ViewHolder holder, final int position, @NonNull Articolo model) {
        holder.nome.setText(model.getNome());
        holder.quantita.setText(model.getQuantita());
        Glide.with(holder.img.getContext()).load(model.getImg()).into(holder.img);

        holder.itemView.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                Toast.makeText(v.getContext(), model.getNome(), Toast.LENGTH_SHORT).show();
            }
        });
    }

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

    class ViewHolder extends RecyclerView.ViewHolder {

        ImageView img;
        TextView nome;
        TextView quantita;

        public ViewHolder(@NonNull View itemView) {
            super(itemView);
            img = (ImageView) itemView.findViewById(R.id.img);
            nome = (TextView) itemView.findViewById(R.id.nameText);
            quantita = (TextView) itemView.findViewById(R.id.amountText);
        }

    }

}

这是Articolo的Java：

package com.example.progettocontab.app;

public class Articolo {

    private String nome;
    private String descrizione;
    private String quantita;
    private String img;
    private int ID;

    public Articolo(String nome, String descrizione, String quantita, String img, int ID) {
        this.nome = nome;
        this.descrizione = descrizione;
        this.quantita = quantita;
        this.img = img;
        this.ID = ID;
    }

    public String getNome() {
        return nome;
    }

    public void setNome(String nome) {
        this.nome = nome;
    }

    public String getDescrizione() {
        return descrizione;
    }

    public void setDescrizione(String descrizione) {
        this.descrizione = descrizione;
    }

    public String getQuantita() {
        return quantita;
    }

    public void setQuantita(String quantita) {
        this.quantita = quantita;
    }

    public String getImg() {
        return img;
    }

    public void setImg(String img) {
        this.img = img;
    }

    public int getID() {
        return ID;
    }

    public void setID(int ID) {
        this.ID = ID;
    }
}

这是 CardView 的 XML：

<?xml version="1.0" encoding="utf-8"?>
<androidx.cardview.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    app:cardCornerRadius="5dp"
    android:elevation="5dp"
    app:cardUseCompatPadding="true">

    <RelativeLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:padding="15dp">

        <androidx.appcompat.widget.AppCompatImageView
            android:layout_width="80dp"
            android:layout_height="80dp"
            android:src="@mipmap/ic_launcher"
            android:layout_centerVertical="true"
            android:id="@+id/img"
            />

        <TextView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/nameText"
            android:text="This is Demo Name"
            android:textStyle="bold"
            android:textSize="25sp"
            android:textColor="#000"
            android:layout_toRightOf="@id/img"
            android:layout_marginLeft="10dp"/>

        <TextView
            android:id="@+id/amountText"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/nameText"
            android:layout_marginLeft="6dp"
            android:layout_marginTop="12dp"
            android:layout_toRightOf="@id/img"
            android:text="This is Course Name"
            android:textColor="#000"
            android:textSize="25sp" />


    </RelativeLayout>

</androidx.cardview.widget.CardView>

Answer 1

我认为您可能会收到该错误，因为您在模块的 gradle 中implementation 'com.google.firebase:firebase-messaging' ，但您尚未在清单中注册该服务。 因此，要么从您的 gradle 中删除该行（如果您不需要 firebase 的消息传递功能），或者将服务添加到您的清单中，如下所示：

<service
    android:name=".java.MyFirebaseMessagingService"
    android:exported="false">
    <intent-filter>
        <action android:name="com.google.firebase.MESSAGING_EVENT" />
    </intent-filter>
</service>

Answer 2

开始startListening后尝试移动recyclerView.setAdapter(adapter)

因此，将其从onViewCreated()中删除，并将其添加到onStart()

@Override
public void onStart() {
    super.onStart();
    adapter.startListening();
    recyclerView.setAdapter(adapter);
}

Answer 3

尝试将 recyclerview 转移到 onViewCreated ，因为此时片段的视图会被填充，您可以访问 recyclerview 并对其进行膨胀。

@Override
public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
   View view = inflater.inflate(R.layout.fragment_assistenza, container, false);
   return view;
}

@Override
public void onViewCreated() {
   recyclerView = (RecyclerView) view.findViewById(R.id.recview);
   recyclerView.setLayoutManager(new LinearLayoutManager(getActivity().getApplicationContext()));

   FirebaseRecyclerOptions<Articolo> options =
                new FirebaseRecyclerOptions.Builder<Articolo>()
                        .setQuery(FirebaseDatabase.getInstance().getReference().child("Articoli"), Articolo.class)
                        .build();

   adapter = new ArticoloAdapter(options);
   recyclerView.setAdapter(adapter);
}