更换碎片后，回收站视图丢失了

问题描述

我有一个活动，将一个包含回收者视图的片段替换为一个包含所选Viewholder项目详细信息的片段。当按下“后退”按钮时，包含“回收者”视图的片段将被还原，但是“回收者”视图项将不再显示。但是，视图会在设备旋转时恢复。所有模型数据都存储在sqlite数据库中，并且适配器列表在其片段恢复后会更新。

CrimeListFragment.Java

public class CrimeListFragment extends Fragment {

    private Callbacks callbacks;

    public interface Callbacks {
        public void onItemSelected(UUID id);
    }

    @Override
    public void onAttach(@NonNull Context context) {
        super.onAttach(context);
        callbacks = (Callbacks) context;
    }

    @Override
    public void onDetach() {
        super.onDetach();
        callbacks = null;
    }

    private RecyclerView crimeListRecycler;
    private Crimelistadapter adapter;

    @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setHasOptionsMenu(true);
    }

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater,@Nullable ViewGroup container,@Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_crime_list,container,false);

        crimeListRecycler = view.findViewById(R.id.crime_list);
        crimeListRecycler.setLayoutManager(new linearlayoutmanager(getActivity()));

        updateUI();

        return view;
    }

    @Override
    public void onResume() {
        super.onResume();
        updateUI();
    }

    @Override
    public void onCreateOptionsMenu(@NonNull Menu menu,@NonNull MenuInflater inflater) {
        super.onCreateOptionsMenu(menu,inflater);
        inflater.inflate(R.menu.fragment_crime_list,menu);

        MenuItem showSubtitle = menu.findItem(R.id.show_subtitle);

    }

    @Override
    public boolean onoptionsItemSelected(@NonNull MenuItem item) {
        switch (item.getItemId()) {
            case R.id.new_crime:
                Crime crime = new Crime();
                CrimeLab.get(getActivity()).addCrime(crime);
                /*Intent intent = CrimeActivity.createIntent(getActivity(),crime.getId());
                startActivity(intent);*/
                callbacks.onItemSelected(crime.getId());
                return true;
            default:
                return onoptionsItemSelected(item);
        }
    }

    private void updateUI() {
        List<Crime> crimes = CrimeLab.get(getActivity()).getCrimes();
        if (adapter == null) {
            adapter = new Crimelistadapter(crimes);
            crimeListRecycler.setAdapter(adapter);
        } else {
            adapter.setCrimesList(crimes);
            adapter.notifyDataSetChanged();
        }
    }

    public class Crimelistadapter extends RecyclerView.Adapter<Crimelistadapter.CrimeHolder> {

        private List<Crime> crimeList;

        public Crimelistadapter(List<Crime> crimes) {
            crimeList = crimes;
        }

        @NonNull
        @Override
        public CrimeHolder onCreateViewHolder(@NonNull ViewGroup parent,int viewType) {
            View view = LayoutInflater.from(getActivity()).inflate(R.layout.list_item_crime,parent,false);

            return new CrimeHolder(view);
        }

        @Override
        public void onBindViewHolder(@NonNull CrimeHolder holder,int position) {
            Crime crime = crimeList.get(position);
            holder.bind(crime);
        }

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

        public void setCrimesList(List<Crime> crimes) {
            crimeList = crimes;
        }

        public class CrimeHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

            private Crime crime;

            private TextView crimeTitleTextView;
            private TextView crimeDateTextView;

            public CrimeHolder(@NonNull View itemView) {
                super(itemView);
                crimeTitleTextView = itemView.findViewById(R.id.crime_title);
                crimeDateTextView = itemView.findViewById(R.id.crime_date);
                itemView.setonClickListener(this);
            }

            public void bind(Crime crime) {
                this.crime = crime;
                crimeTitleTextView.setText(crime.getTitle());
                crimeDateTextView.setText(crime.getDate().toString());
            }

            @Override
            public void onClick(View v) {
                callbacks.onItemSelected(crime.getId());
                /*Intent intent = CrimeActivity.createIntent(getActivity(),crime.getId());
                startActivity(intent);*/
            }
        }
    }
}

Masteractivity

public class Masteractivity extends AppCompatActivity implements CrimeListFragment.Callbacks {


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

        FragmentManager fm = getSupportFragmentManager();
        Fragment fragment = fm.findFragmentById(R.id.fragment_container);

        if (fragment == null) {
            fragment = new CrimeListFragment();
            fm.beginTransaction()
                    .add(R.id.fragment_container,fragment)
                    .commit();
        }
    }

    @Override
    public void onItemSelected(UUID id) {
        Fragment fragment = CrimeFragment.newInstance(id);
        FragmentManager fm = getSupportFragmentManager();
        fm.beginTransaction()
                .replace(R.id.fragment_container,fragment)
                .addToBackStack(null)
                .commit();
    }
}

解决方法

请分享您的代码。在recyclerview片段顶部替换/添加片段时需要检查的东西。