如何在Android Studio中从Firebase实时数据库子节点调用图片列表到RecyclerView？

1. 定义实体类 #

先创建一个和数据库节点匹配的实体类，用来封装图片URL数据：

public class ImageItem {
    private String imageUrl;

    // Firebase序列化必须有空构造函数
    public ImageItem() {}

    public ImageItem(String imageUrl) {
        this.imageUrl = imageUrl;
    }

    public String getImageUrl() {
        return imageUrl;
    }

    public void setImageUrl(String imageUrl) {
        this.imageUrl = imageUrl;
    }
}

2. 编写RecyclerView适配器 #

实现适配器负责数据绑定和图片加载，推荐用Glide处理网络图片：

public class ImageAdapter extends RecyclerView.Adapter<ImageAdapter.ImageViewHolder> {
    private List<ImageItem> imageList;
    private Context context;

    public ImageAdapter(Context context, List<ImageItem> imageList) {
        this.context = context;
        this.imageList = imageList;
    }

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

    @Override
    public void onBindViewHolder(@NonNull ImageViewHolder holder, int position) {
        ImageItem item = imageList.get(position);
        // 用Glide加载图片
        Glide.with(context)
             .load(item.getImageUrl())
             .into(holder.imageView);
    }

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

    public static class ImageViewHolder extends RecyclerView.ViewHolder {
        ImageView imageView;

        public ImageViewHolder(@NonNull View itemView) {
            super(itemView);
            imageView = itemView.findViewById(R.id.iv_image);
        }
    }
}

对应的item布局item_image.xml：

<ImageView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/iv_image"
    android:layout_width="match_parent"
    android:layout_height="200dp"
    android:scaleType="centerCrop"/>

3. 从Firebase读取数据并绑定到RecyclerView #

在Activity/Fragment中初始化RecyclerView，监听数据库节点变化获取数据：

public class MainActivity extends AppCompatActivity {
    private RecyclerView recyclerView;
    private ImageAdapter adapter;
    private List<ImageItem> imageList;
    private DatabaseReference dbRef;

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

        // 初始化RecyclerView
        recyclerView = findViewById(R.id.recyclerView);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        imageList = new ArrayList<>();
        adapter = new ImageAdapter(this, imageList);
        recyclerView.setAdapter(adapter);

        // 替换成你的数据库节点路径，比如"images"
        dbRef = FirebaseDatabase.getInstance().getReference("images");

        // 监听数据变化
        dbRef.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot snapshot) {
                imageList.clear();
                for (DataSnapshot childSnapshot : snapshot.getChildren()) {
                    ImageItem imageItem = childSnapshot.getValue(ImageItem.class);
                    if (imageItem != null) {
                        imageList.add(imageItem);
                    }
                }
                adapter.notifyDataSetChanged();
            }

            @Override
            public void onCancelled(@NonNull DatabaseError error) {
                Toast.makeText(MainActivity.this, "读取失败：" + error.getMessage(), Toast.LENGTH_SHORT).show();
            }
        });
    }
}

4. 必要配置 #

• 在项目build.gradle中添加依赖：

// Firebase实时数据库
implementation 'com.google.firebase:firebase-database:20.3.0'
// Glide图片加载
implementation 'com.github.bumptech.glide:glide:4.16.0'
annotationProcessor 'com.github.bumptech.glide:compiler:4.16.0'

• 开发阶段可临时设置Firebase数据库读写规则为公开（上线后需修改为安全规则）：

{
  "rules": {
    ".read": true,
    ".write": true
  }
}

内容的提问来源于stack exchange，提问作者John Idama