[英]Efficient way to fetch FireStore data into two fragments with a shared ViewModel
上下文:我有一個User
class,如下所示:
public class User {
private String firstname;
private String lastname;
private GeoPoint location;
/* Constructor and getters */
...
}
和兩個Fragment
,其中我將使用RecyclerView
在第一個片段中顯示用戶名列表,在第二個片段中使用GoogleMap
顯示用戶設備位置的標記。 我在這兩個片段之間使用共享的ViewModel
來提供所需的數據。 ViewModel
看起來像這樣:
@HiltViewModel
public class UsersViewModel extends ViewModel {
private List<User> users;
private UserRepository repository;
@Inject
public UsersViewModel(UserRepository repository) {
this.repository = repository;
}
public void fetchUsers(OnFetchDataCallback callback) {
repository.getUsers(callback);
}
public void setUsers(List<User> users) {
this.users = users;
}
public List<User> getUsers() {
return users;
}
}
在我的存儲庫 class 中,
public class UserRepository {
private final FirebaseFirestore db;
@Inject
public UserRepository(FirebaseFirestore db) {
this.db = db;
}
public List<User> getUsers(OnFetchDataCallback callback) {
db.collection("users")
.addSnapshotListener(new EventListener<QuerySnapshot>() {
@Override
public void onEvent(@Nullable QuerySnapshot val,
@FirebaseFirestoreException e) {
List<User> users = new ArrayList<>();
for (QueryDocumentSnapshot document : val) {
users.add(document.toObject(User.class);
}
callback.onFetchData(users);
}
});
}
}
我有一個名為getUsers()
的方法,它將從 firestore 數據庫中實際獲取用戶。 我還創建了一個接口回調,看起來像這樣
public interface OnFetchDataCallback {
void onFetchData(List<User> users);
}
這樣以后我就可以在我的兩個片段中訪問獲取的用戶。 在我的第一個片段中,
@AndroidEntryPoint
public class DisplayUsersFragment extends Fragment {
private FragmentDisplayUsersBinding binding;
private UsersViewModel viewModel;
private UsersAdapter adapter;
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
viewModel = new ViewModelProvider(this).get(UsersViewModel.class);
}
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater,
@Nullable ViewGroup container,
@Nullable Bundle savedInstanceState) {
binding = FragmentDisplayUsersBinding.inflate(inflater, container, false);
binding.usersRecyclerView.setLayoutManager(
new LinearLayoutManager(getContext()));
viewModel.fetchUsers(new OnFetchDataCallback() {
@Override
public void onFetchData(List<User> users) {
viewModel.setUsers(users);
adapter = new UsersAdapter(viewModel.getUsers());
binding.usersRecyclerView.setAdapter(adapter);
}
});
return binding.getRoot();
}
}
我調用了fetchUsers()
並訪問了回調中的users
List
,並將其設置為我的viewModel
的users
,然后為我的RecyclerView
構建了一個適配器,並通過調用viewModel.getUsers()
並將其作為適配器的構造函數參數。 現在,我的問題是,在我的第二個片段中,
@AndroidEntryPoint
public class UsersMapFragment extends Fragment implements OnMapReadyCallback {
private FragmentUsersMapBinding binding;
private UsersViewModel viewModel;
@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
viewModel = new ViewModelProvider(this).get(UsersViewModel.class);
}
@Nullable
@Override
public View onCreateView(@NonNull LayoutInflater inflater,
@Nullable ViewGroup container,
@Nullable Bundle savedInstanceState) {
binding = FragmentUsersMapBinding.inflate(inflater, container, false);
return binding.getRoot();
}
@Override
public void onViewCreated(@NonNull View view,
@Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
SupportMapFragment mapFragment = SupportMapFragment.newInstance();
getChildFragmentManager().beginTransaction()
.add(R.id.users_map_fragment_container, mapFragment)
.commit()
mapFragment.getMapAsync(this);
}
@Override
public void onMapReady(@NonNull GoogleMap googleMap) {
viewModel.fetchUsers(new OnFetchDataCallback() {
@Override
public void onFetchData(List<User> users) {
viewModel.setUsers(users);
for (User user : viewModel.getUsers()) {
googleMap.addMarker(new MarkerOptions()
.position(new LatLng(
user.getLocation().getLatitude(),
user.getLocation().getLongitude())
)
.title(user.getFirstname() + " "
user.getLastname()
)
);
}
}
});
}
}
我在 onMapReady() 中再次調用了fetchUsers()
onMapReady()
以便我可以在其回調中訪問用戶並使用它們在 map 中創建標記。本質上,我嘗試調用fetchUsers()
兩次,但我認為有一個更有效的方法方法來做到這一點,但我不知道如何處理這個。 請幫助我,對不起我的英語不好。
您可以在 ViewModel 中使用實時數據:請參閱下面給出的代碼:
@HiltViewModel
public class UsersViewModel extends ViewModel {
private List<User> users;
MutableLiveData<List<User>> usersLiveData = new MutableLiveData();
private UserRepository repository;
@Inject
public UsersViewModel(UserRepository repository) {
this.repository = repository;
}
public void fetchUsers() {
repository.getUsers(new OnFetchDataCallback() {
@Override
public void onFetchData(List<User> users) {
usersLiveData.setValue(users);
// you can observe this data after calling fetch users from your activity
setUsers(users);
});
}
public void setUsers(List<User> users) {
this.users = users;
}
public List<User> getUsers() {
return users;
}
}
在活動中:
mViewModel.fetchUsers();
在這兩個片段中:
viewModel.usersLiveData.observe(this,{ list->
// user your list here in both fragments
// rather than fetch users on both fragments
});
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