Question

我不知道是什么原因造成的，但是没有图像显示任何图像。请帮助我纠正该问题。

我的适配器类：

public class Images_Adapter extends RecyclerView.Adapter<Images_Adapter.ViewHolder> {

    private List<Images_Item> items;
    private int itemLayout;

    public Images_Adapter(List<Images_Item> items, int itemLayout) {
        this.items = items;
        this.itemLayout = itemLayout;
    }

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

    @Override
    public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
        Images_Item item = items.get(position);

        Glide.with(holder.image.getContext())
                .load(item.getImageURL())
                .into(holder.image);
    }

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

    static class ViewHolder extends RecyclerView.ViewHolder {
        ImageView image;

        ViewHolder(View itemView) {
            super(itemView);
            image = itemView.findViewById(R.id.ImageItem);
        }
    }
}

我的Images_Item类：

class Images_Item {

    private String imageURL;

    String getImageURL() {
        return imageURL;
    }

    Images_Item(String string) {
    }
}

我的活动班级：

public class Events_and_Participations extends AppCompatActivity {

    StorageReference reference;
    RecyclerView recyclerView;
    Images_Adapter adapter;
    FirebaseAuth auth;
    Button button;
    FirebaseUser user;
    List<Images_Item> items = new ArrayList<>();

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

        user = FirebaseAuth.getInstance().getCurrentUser();

        reference = FirebaseStorage.getInstance().getReference("images");


        if (user != null){
            reference.listAll()
                    .addOnSuccessListener(listResult -> {
                        for (StorageReference item : listResult.getItems()) {
                            item.getDownloadUrl().addOnCompleteListener(task -> {
                                items.add(new Images_Item(task.getResult().toString()));
                            });
                        }
                    })
                    .addOnFailureListener(e -> Toast.makeText(Events_and_Participations.this, e.getMessage(), Toast.LENGTH_SHORT).show());
        }



        adapter = new Images_Adapter(items, R.layout.item_events_image);
        recyclerView = findViewById(R.id.events_photos);
        recyclerView.setAdapter(adapter);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setItemAnimator(new DefaultItemAnimator());
    }
}

即使没有任何错误，它也只是显示一个空白屏幕。我正确地获得了链接，但不会显示图像。没有显示Log Cat，也没有显示图像。

Answer 1

ImageUrl从未初始化，因此它始终为null。

class Images_Item {

private String imageURL;

String getImageURL() {
    return imageURL;
}

Images_Item(String string) {
   this.imageURL = string;
}

}

Answer 2

您可以处理的几个问题：

首先，您没有在onCreateViewHolder中添加有效的布局路径，该路径应包括R.layout.xx，将xx替换为项目布局名称。

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

第二，您的Firebase物品需要花费一些时间，直到它们在后台线程中被接收，因此您需要在接收物品时执行adapter.notifiyDataSetChanged()之类的操作，或者设置适配器

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

    user = FirebaseAuth.getInstance().getCurrentUser();

    reference = FirebaseStorage.getInstance().getReference("images");

    recyclerView = findViewById(R.id.events_photos);
    recyclerView.setHasFixedSize(true);
    recyclerView.setLayoutManager(new LinearLayoutManager(this));
    recyclerView.setItemAnimator(new DefaultItemAnimator());

    if (user != null){
        reference.listAll()
                .addOnSuccessListener(listResult -> {
                    for (StorageReference item : listResult.getItems()) {
                        item.getDownloadUrl().addOnCompleteListener(task -> {
                            items.add(new Images_Item(task.getResult().toString()));
                        });
                    }

                    adapter = new Images_Adapter(items, R.layout.item_events_image);
                    recyclerView.setAdapter(adapter);

                })
                .addOnFailureListener(e -> Toast.makeText(Events_and_Participations.this, e.getMessage(), Toast.LENGTH_SHORT).show());


    }

}

最后，您没有在带有图像URL的construcotr中设置imageURL属性，因此在构造函数中进行设置。

class Images_Item {

    private String imageURL;

    String getImageURL() {
        return imageURL;
    }

    Images_Item(String string) {
        imageURL = string; //<<<<<<<<<<<<< here is the change
    }
}

Answer 3

您没有设置imageUrl：

class Images_Item {

private String imageURL;

String getImageURL() {
    return imageURL;
}

Images_Item(String string) {
   this.imageURL = string;
}

回收器视图显示为空而不是显示图像？

3 个答案: