Android 回收器返回时查看丢失的数据

我有一个NavigationDrawer活动，在那里我加载了一个包含Recyclerview的片段。回收器视图数据来自Firebase。第一次循环使用的观点是显示良好。但是，当我点击该项目时，转到另一个片段以查看详细信息，然后我点击后退按钮，回收视图显示为空

这是导航活动，这里有一个事务片段

这是EmployeeList片段

public class EmployeeList extends Fragment {

    FirebaseDatabase firebaseDatabase;
    DatabaseReference databaseReference;
    String userID;

    List<Employee_Information> employee_informations;

    @BindView(R.id.employee_list_Recycler_ID)
    RecyclerView employeeListRecyclerID;

    View view;
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        if (view==null){
            view = inflater.inflate(R.layout.employee_list, null);
        }
        ButterKnife.bind(this, view);
        return view;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        firebaseDatabase = FirebaseDatabase.getInstance();
        databaseReference = firebaseDatabase.getReference();
        employee_informations = new ArrayList<>();
//get Current Admin User ID
        userID = getUserID();
//get Employee Information as a list
        employee_informations = getUserData();

        GridLayoutManager gridLayoutManager = new GridLayoutManager(getContext(), 2);

        employeeListRecyclerID.setLayoutManager(gridLayoutManager);

        EmployeeList_Adapter adapterClass_recycler = new EmployeeList_Adapter(getContext(), employee_informations);

        employeeListRecyclerID.setAdapter(adapterClass_recycler);

        adapterClass_recycler.setOnItemClickListener(new EmployeeList_Adapter.ClickListener() {
            @Override
            public void onItemClick(int position, View v) {

                Employee_Information employee_information = new Employee_Information(
                        employee_informations.get(position).getUserID_Employee(),
                        employee_informations.get(position).getUserID_company(),
                        employee_informations.get(position).getEmail_Employee(),
                        employee_informations.get(position).getPassword_Employee(),
                        employee_informations.get(position).getName_Employee(),
                        employee_informations.get(position).getJoin_Date(),
                        employee_informations.get(position).getImageLink(),
                        employee_informations.get(position).getDesignation(),
                        employee_informations.get(position).getPhone()
                );

                Fragment fragment = new Employee_profile_view_by_admin();
                Bundle bundle = new Bundle();

                if (fragment != null) {
                    bundle.putSerializable("employee_information", employee_information);
                    fragment.setArguments(bundle);

                    FragmentTransaction fragmentTransaction = getActivity().getSupportFragmentManager().beginTransaction();
                    fragmentTransaction.replace(R.id.screen_Area_For_Admin, fragment);
                    fragmentTransaction.addToBackStack("");
                    fragmentTransaction.commit();
                }
            }

            @Override
            public void onItemLongClick(int position, View v) {

            }
        });


    }

    //get Employee Information as a list
    private List<Employee_Information> getUserData() {
        databaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for (DataSnapshot snapshot : dataSnapshot.child("Company_Employee").child(userID).getChildren()) {

                    Employee_Information employee_information = snapshot.getValue(Employee_Information.class);
                    employee_informations.add(employee_information);
                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });

        return employee_informations;
    }

    //get Current Admin User ID
    private String getUserID() {

        FirebaseAuth firebaseAuth;
        FirebaseUser firebaseUser;
        firebaseAuth = FirebaseAuth.getInstance();
        firebaseUser = firebaseAuth.getCurrentUser();
        String userID = firebaseUser.getUid();
        return userID;
    }

}

public类EmployeeList扩展片段{
FirebaseDatabase FirebaseDatabase；
数据库参考数据库参考；
字符串用户标识；
列出员工信息；
@BindView（R.id.employee\u list\u Recycler\u id）
RecyclerView employeeListRecyclerID；
视图；
@可空
@凌驾
创建视图时的公共视图（@NonNull LayoutInflater inflater、@Nullable ViewGroup container、@Nullable Bundle savedInstanceState）{
如果（视图==null）{
视图=充气机。充气（R.layout.employee_列表，空）；
}
ButterKnife.bind（这个，视图）；
返回视图；
}
@凌驾
已创建公用void onview（@NonNull视图，@Nullable Bundle savedInstanceState）{
super.onViewCreated（视图，savedInstanceState）；
firebaseDatabase=firebaseDatabase.getInstance（）；
databaseReference=firebaseDatabase.getReference（）；
employee_informations=new ArrayList（）；
//获取当前管理员用户ID
userID=getUserID（）；
//以列表形式获取员工信息
员工信息=getUserData（）；
GridLayoutManager GridLayoutManager=新的GridLayoutManager（getContext（），2）；
employeeListRecyclerID.setLayoutManager（gridLayoutManager）；
EmployeeList_Adapter Adapter Class_recycler=新的EmployeeList_Adapter（getContext（），员工信息）；
employeeListRecyclerID.setAdapter（适配器类回收器）；
adapterClass_recycler.setOnItemClickListener（新员工列表_适配器.ClickListener（））{
@凌驾
公共空间单击（内部位置，视图v）{
员工信息员工信息=新员工信息(
employee_informations.get（position）.getUserID_employee（），
employee_informations.get（position）.getUserID_company（），
员工信息.get（position）.getEmail\u employee（），
employee_informations.get（position）.getPassword_employee（），
employee_informations.get（position）.getName_employee（），
员工信息。获取（职位）。获取加入日期（），
员工信息获取（职位）.getImageLink（），
员工信息获取（职位）.getDesignation（），
员工信息获取（职位）.getPhone（）
);
Fragment Fragment=新员工_profile_view_by_admin（）；
Bundle=新Bundle（）；
if（片段！=null）{
bundle.putSerializable（“员工信息”，员工信息）；
fragment.setArguments（bundle）；
FragmentTransaction FragmentTransaction=getActivity（）.getSupportFragmentManager（）.beginTransaction（）；
fragmentTransaction.replace（R.id.screen\u Area\u用于\u Admin，fragment）；
fragmentTransaction.addToBackStack（“”）；
fragmentTransaction.commit（）；
}
}
@凌驾
长点击（内部位置，视图v）{
}
});
}
//以列表形式获取员工信息
私有列表getUserData（）{
databaseReference.addValueEventListener（新的ValueEventListener（）{
@凌驾
public void onDataChange（@NonNull DataSnapshot DataSnapshot）{
for（DataSnapshot快照：DataSnapshot.child（“公司雇员”）.child（userID.getChildren（））{
Employee\u Information Employee\u Information=snapshot.getValue（Employee\u Information.class）；
员工信息。添加（员工信息）；
}
}
@凌驾
已取消的公共void（@NonNull DatabaseError DatabaseError）{
}
});
返回员工信息；
}
//获取当前管理员用户ID
私有字符串getUserID（）{
FirebaseAuth FirebaseAuth；
FirebaseUser FirebaseUser；
firebaseAuth=firebaseAuth.getInstance（）；
firebaseUser=firebaseAuth.getCurrentUser（）；
字符串userID=firebaseUser.getUid（）；
返回用户标识；
}
}

它将始终为空，因为作为方法的结果，您可以简单地返回

列表。请检查重复项，了解您为什么会有这种行为，以及如何使用自定义回调解决此问题。它将始终为空，因为您可以简单地返回
列表
，作为方法的结果。请检查重复项以了解为什么会出现这种行为，以及如何使用自定义回调解决此问题。
public class EmployeeList extends Fragment {

    FirebaseDatabase firebaseDatabase;
    DatabaseReference databaseReference;
    String userID;

    List<Employee_Information> employee_informations;

    @BindView(R.id.employee_list_Recycler_ID)
    RecyclerView employeeListRecyclerID;

    View view;
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        if (view==null){
            view = inflater.inflate(R.layout.employee_list, null);
        }
        ButterKnife.bind(this, view);
        return view;
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        firebaseDatabase = FirebaseDatabase.getInstance();
        databaseReference = firebaseDatabase.getReference();
        employee_informations = new ArrayList<>();
//get Current Admin User ID
        userID = getUserID();
//get Employee Information as a list
        employee_informations = getUserData();

        GridLayoutManager gridLayoutManager = new GridLayoutManager(getContext(), 2);

        employeeListRecyclerID.setLayoutManager(gridLayoutManager);

        EmployeeList_Adapter adapterClass_recycler = new EmployeeList_Adapter(getContext(), employee_informations);

        employeeListRecyclerID.setAdapter(adapterClass_recycler);

        adapterClass_recycler.setOnItemClickListener(new EmployeeList_Adapter.ClickListener() {
            @Override
            public void onItemClick(int position, View v) {

                Employee_Information employee_information = new Employee_Information(
                        employee_informations.get(position).getUserID_Employee(),
                        employee_informations.get(position).getUserID_company(),
                        employee_informations.get(position).getEmail_Employee(),
                        employee_informations.get(position).getPassword_Employee(),
                        employee_informations.get(position).getName_Employee(),
                        employee_informations.get(position).getJoin_Date(),
                        employee_informations.get(position).getImageLink(),
                        employee_informations.get(position).getDesignation(),
                        employee_informations.get(position).getPhone()
                );

                Fragment fragment = new Employee_profile_view_by_admin();
                Bundle bundle = new Bundle();

                if (fragment != null) {
                    bundle.putSerializable("employee_information", employee_information);
                    fragment.setArguments(bundle);

                    FragmentTransaction fragmentTransaction = getActivity().getSupportFragmentManager().beginTransaction();
                    fragmentTransaction.replace(R.id.screen_Area_For_Admin, fragment);
                    fragmentTransaction.addToBackStack("");
                    fragmentTransaction.commit();
                }
            }

            @Override
            public void onItemLongClick(int position, View v) {

            }
        });


    }

    //get Employee Information as a list
    private List<Employee_Information> getUserData() {
        databaseReference.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                for (DataSnapshot snapshot : dataSnapshot.child("Company_Employee").child(userID).getChildren()) {

                    Employee_Information employee_information = snapshot.getValue(Employee_Information.class);
                    employee_informations.add(employee_information);
                }
            }

            @Override
            public void onCancelled(@NonNull DatabaseError databaseError) {

            }
        });

        return employee_informations;
    }

    //get Current Admin User ID
    private String getUserID() {

        FirebaseAuth firebaseAuth;
        FirebaseUser firebaseUser;
        firebaseAuth = FirebaseAuth.getInstance();
        firebaseUser = firebaseAuth.getCurrentUser();
        String userID = firebaseUser.getUid();
        return userID;
    }

}