Question

我不确定为什么RecyclerView不在UI上显示任何图像或数据。

这是我的Firebase数据库表的结构图

CategoryFragment.java

这是我使用FirebaseRecyclerAdapter配置RecyclerView的片段。在这里，我认为该错误在哪里，但我找不到它。

Breedte : ‎1920 pixels
Hoogte  : ‎1080 pixels
Grootte : 388 kB
Name    : sunset.jpg
Width   : 
Height  : 
Size    : 388

CategoryItem

import android.os.Bundle;
import android.support.annotation.NonNull;
import android.support.v4.app.Fragment;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;

import com.example.abdullah.livewallpapers.Interface.ItemClickListener;
import com.example.abdullah.livewallpapers.Model.CategoryItem;
import com.example.abdullah.livewallpapers.R;
import com.example.abdullah.livewallpapers.Viewholder.CategoryViewholder;
import com.firebase.ui.database.FirebaseRecyclerAdapter;
import com.firebase.ui.database.FirebaseRecyclerOptions;
import com.google.firebase.database.DatabaseReference;
import com.google.firebase.database.FirebaseDatabase;
import com.squareup.picasso.Callback;
import com.squareup.picasso.NetworkPolicy;
import com.squareup.picasso.Picasso;
import java.util.List;

/**
  * A simple {@link Fragment} subclass.
*/
public class CategoryFragment extends Fragment {

private static final String STR_CATEGORY_BACKGROUND = "CategoryBackground";
DatabaseReference categoryBackground;
FirebaseDatabase database;

FirebaseRecyclerOptions<CategoryItem> options;
FirebaseRecyclerAdapter<CategoryItem,CategoryViewholder> adapter;

RecyclerView recyclerView;

private static CategoryFragment INSTANCE = null;

public CategoryFragment() {

    database = FirebaseDatabase.getInstance();
    categoryBackground = database.getReference(STR_CATEGORY_BACKGROUND);

    options = new FirebaseRecyclerOptions.Builder<CategoryItem>()
            .setQuery(categoryBackground,CategoryItem.class)
            .build();

    adapter = new FirebaseRecyclerAdapter<CategoryItem, CategoryViewholder>(options) {
        @Override
        protected void onBindViewHolder(@NonNull final CategoryViewholder holder, int position, @NonNull final CategoryItem model) {


            Picasso.with(getActivity())
                    .load(model.getImageLink())
                    .networkPolicy(NetworkPolicy.OFFLINE)
                    .into(holder.backgroud_image, new Callback(){
                        @Override
                        public void onSuccess() {

                        }

                        @Override
                        public void onError() {

                            Picasso.with(getActivity())
                                    .load(model.getImageLink())
                                    .error(R.drawable.ic_terrain_black_24dp)
                                    .into(holder.backgroud_image, new Callback() {
                                        @Override
                                        public void onSuccess() {

                                        }

                                        @Override
                                        public void onError() {

                                            Log.i("category_error","error comes");
                                        }
                                    });
                        }
                    } );

            holder.category_name.setText(model.getName());

            holder.setItemClickListener(new ItemClickListener() {
                @Override
                public void onClick(View view, int postion) {

                }
            });
        }

        @NonNull
        @Override
        public CategoryViewholder onCreateViewHolder(@NonNull ViewGroup viewGroup, int i) {

            View itemView = LayoutInflater.from(viewGroup.getContext())
                    .inflate(R.layout.layout_category_item,viewGroup,false);

            return new CategoryViewholder(itemView);
        }
    };
}

private void setCategory() {
    adapter.startListening();
    recyclerView.setAdapter(adapter);
}

@Override
public void onStart() {
    super.onStart();
    if (adapter!=null)
    adapter.startListening();
}

@Override
public void onStop() {

    super.onStop();
    if (adapter!=null)
        adapter.stopListening();
}

@Override
public void onResume() {
    super.onResume();
    if (adapter!=null)
        adapter.startListening();
}

public static CategoryFragment getInstance() {

    if (INSTANCE == null)
        INSTANCE = new CategoryFragment();
    return INSTANCE;
}


@Override
public View onCreateView(@NonNull LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_category, container, false);
    recyclerView = (RecyclerView)view.findViewById(R.id.category_recyclerview);
    recyclerView.setHasFixedSize(true);
    GridLayoutManager gridLayoutManager = new GridLayoutManager(getActivity(),2);
    recyclerView.setLayoutManager(gridLayoutManager);
    setCategory();

    return view;
}

}

来自Logcat的错误

这些是logcat中出现的错误。

public class CategoryItem {
    public String Name;
    public String ImageLink;
    public CategoryItem() {
    }

    public CategoryItem(String name, String imageLink) {
        Name = name;
        ImageLink = imageLink;
    }

    public String getName() {
        return Name;
    }

    public void setName(String name) {
        Name = name;
    }

    public String getImageLink() {
        return ImageLink;
    }

    public void setImageLink(String imageLink) {
        ImageLink = imageLink;
    }
}

Answer 1

您的POJO通过公开公开一个属性和一个具有相同名称的getter来混淆Firebase SDK：imageLink

public class CategoryItem {
    public String ImageLink;

    // ...

    public String getImageLink() {
        return ImageLink;
    }

    // ...    
}

它不知道使用哪个，因为它们具有相同的名称。相反，您应该做的是将该字段设为私有，并将访问者设置为公共，这样就不会有两个具有相同名称的公共事物：

public class CategoryItem {
    private String Name;
    private String ImageLink;
    // ...
}

这是创建POJO类型对象的标准方法。

我的带有FirebaseRecyclerAdapter的RecyclerView没有在屏幕上显示任何内容

1 个答案: