如何解决Android ListAdapter.getItemCount() 始终返回 0
如果 TextView
为空,我会尝试显示 RecyclerView
。
但是 getItemCount()
of listadapter
始终返回 0,即使 RecyclerView
显示项目。
Fragment.java
public class ProjectsFragment extends Fragment {
private Repoviewmodel repoviewmodel;
@Override
public View onCreateView(LayoutInflater inflater,ViewGroup container,Bundle savedInstanceState) {
FloatingActionButton floatingActionButton = ((MainActivity) requireActivity()).getFloatingActionButton();
floatingActionButton.setVisibility(View.VISIBLE);
return inflater.inflate(R.layout.fragment_projects,container,false);
}
public void onViewCreated(@NonNull View view,Bundle savedInstanceState) {
super.onViewCreated(view,savedInstanceState);
TextView textview_no_project = view.findViewById(R.id.textview_no_project);
RecyclerView recyclerView = view.findViewById(R.id.recyclerview);
recyclerView.setLayoutManager(new linearlayoutmanager(requireActivity().getApplicationContext()));
final Repolistadapter adapter = new Repolistadapter(new Repolistadapter.RepoDiff());
if (adapter.getItemCount() == 0) {
recyclerView.setVisibility(View.INVISIBLE);
textview_no_project.setVisibility(View.VISIBLE);
}
else {
recyclerView.setVisibility(View.VISIBLE);
textview_no_project.setVisibility(View.INVISIBLE);
}
recyclerView.setAdapter(adapter);
repoviewmodel = new viewmodelProvider(requireActivity()).get(Repoviewmodel.class);
repoviewmodel.getAllRepos().observe(getViewLifecycleOwner(),adapter::submitList);
}
}
Repolistadapter.java
public class Repolistadapter extends listadapter<Repo,RepoViewHolder> {
public Repolistadapter(@NonNull DiffUtil.ItemCallback<Repo> diffCallback) {
super(diffCallback);
}
@NonNull
@Override
public RepoViewHolder onCreateViewHolder(@NonNull ViewGroup viewGroup,int viewType) {
return RepoViewHolder.create(viewGroup);
}
@Override
public void onBindViewHolder(RepoViewHolder holder,int position) {
Repo current = getItem(position);
holder.bind(current.getName());
}
public static class RepoDiff extends DiffUtil.ItemCallback<Repo> {
@Override
public boolean areItemsTheSame(@NonNull Repo oldItem,@NonNull Repo newItem) {
return oldItem == newItem;
}
@Override
public boolean areContentsTheSame(@NonNull Repo oldItem,@NonNull Repo newItem) {
return oldItem.getName().equals(newItem.getName());
}
}
}
任何帮助将不胜感激。
解决方法
数据只会在 adapter::submitList
调用之后设置,即在实时数据观察者调用之后。所以你需要在它之后进行更改。有几种方法可以做到这一点。下面的一种方法是您需要将适配器创建为全局或仅从 RecyclerView 中获取。
public void onLoaded(List<Repo> list){
if (list.size() == 0) {
recyclerView.setVisibility(View.INVISIBLE);
textview_no_project.setVisibility(View.VISIBLE);
}
else {
recyclerView.setVisibility(View.VISIBLE);
textview_no_project.setVisibility(View.INVISIBLE);
adapter.submitList(list);
}
}
将 onLoaded
设置为观察者 lambda。
repoViewModel.getAllRepos().observe(getViewLifecycleOwner(),this::onLoaded);
您还可以使用提交列表变体 submitList(@Nullable List<String> list,@Nullable Runnable commitCallback)
,它将为您提供回调,您可以在 Runnable
中执行相同的操作。在这种情况下,这几乎是一样的。
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