分页库不会向我的PagedListAdapter发送任何数据

Question

我有一个Android待办事项列表应用程序,使用Room访问SQLite数据库.然后我想在导航抽屉中列出可用列表.所以我使用了Paging Library.现在RecyclerView是空的,我不知道为什么.顺便说一句:我的名单都没有.我是初学者,所以我坚持官方教程.我已经发现,他们错了,ViewModel需要一个空的构造函数.现在的情况如下:设置适配器的方法成功调用(8),ViewModel创建(7)Adapter创建(1),setList()方法调用(9),但没有Holder创建(4),没有onCreateViewHolder或被onBindViewHolder调用(2,3),没有DiffCalback调用任何方法(5,6),只显示一个空的Recycler视图.该PagedList<SQLList>包含正确的信息,但没有信息被传递给适配器.有谁知道为什么？//对不起我的英语不好.

适配器类:

//this is my Adapter. SQLList is my object (Equivalent to the User object in 
the tutorial)
public class ListsAdapter extends PagedListAdapter<SQLList,ListsAdapter.Holder> {
private Context context;

public ListsAdapter(Context context) {
//1
    super(DIFF_CALLBACK);
    this.context = context;
}

@Override
public Holder onCreateViewHolder(ViewGroup parent, int viewType) {
    //2
    LayoutInflater inflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View view = inflater.inflate(R.layout.list_item,null);
    return new Holder(view);
}

@Override
public void onBindViewHolder(Holder holder, int position) {
    //3
    SQLList item = getItem(position);
    if (item == null){
        holder.clear();
    }else {
        holder.bindTo(item);
    }
}




public static class Holder extends RecyclerView.ViewHolder {
    public TextView textView;
    public int id;
    public TextView idView;

    public Holder(View itemView) {
        //4
        super(itemView);
        textView = itemView.findViewById(R.id.textView);
        idView = itemView.findViewById(R.id.idTextView);
    }

    public void bindTo(SQLList list) {
        textView.setText(list.getName());
        id = list.getId();
        idView.setText(Integer.toString(list.getId()));
    }

    public void clear() {
        textView.setText("");
        id = 0;
        idView.setText("0");
    }
}

private static final DiffCallback<SQLList> DIFF_CALLBACK = new DiffCallback<SQLList>() {
    @Override
    public boolean areItemsTheSame(@NonNull SQLList oldItem, @NonNull SQLList newItem) {
        //5
        return oldItem.getId() == newItem.getId();
    }

    @Override
    public boolean areContentsTheSame(@NonNull SQLList oldItem, @NonNull SQLList newItem) {
        //6
        return oldItem.getName().equals(newItem.getName());
    }
};
}

查看型号:

public static class ListViewModel extends ViewModel {
    public final LiveData<PagedList<SQLList>> listsList;
    public ListViewModel(){
        //7
        listsList = new LivePagedListBuilder<>(DMO.getDao().loadListFactory(),20).build();
    }
}

片段的一部分RecyclerView放在:

 ...
 //8
 ListViewModel listViewModel = ViewModelProviders.of(this).get(ListViewModel.class);
    adapter = new ListsAdapter(context);
    listViewModel.listsList.observe(this, new Observer<PagedList<SQLList>>() {
        @Override
        public void onChanged(@Nullable PagedList<SQLList> sqlLists) {
          //9  
          adapter.setList(sqlLists);
        }
    });
    recyclerView.setAdapter(adapter);
...

Answer 1

发现问题:我忘了设置布局管理器!

Answer 2

我有同样的问题，但我不小心添加了-

RecyclerView.setHasFixedSize(true);

删除后，它起作用了。