背景關系：我有一個User看起來像這樣的類：
public class User {
private String firstname;
private String lastname;
private GeoPoint location;
/* Constructor and getters */
...
}
和兩個Fragments，其中我將使用 aRecyclerView和 a在第一個片段GoogleMap中顯示用戶姓名的串列，在第二個片段中顯示用戶設備位置的標記。我正在使用ViewModel這兩個片段之間的共享來提供所需的資料。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;
}
}
在我的存盤庫類中，
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);
}
});
}
}
我有一個名為的方法getUsers()，它將從 firestore 資料庫中實際獲取用戶。我還創建了一個看起來像這樣的介面回呼
public interface OnFetchDataCallback {
void onFetchData(List<User> users);
}
以便稍后我可以訪問我的兩個片段中獲取的用戶。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();
}
}
在為 my構造配接器并通過呼叫并將其作為配接器的建構式引數傳遞給它所需的資料之前，我呼叫fetchUsers()并訪問了回呼內部的 of 并將其設定為 my List。現在，我的問題是在我的第二個片段中，usersviewModelusersRecyclerViewviewModel.getUsers()
@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()
)
);
}
}
});
}
}
我再次呼叫fetchUsers()內部onMapReady()，以便我可以在其回呼內部訪問用戶并使用它們在地圖中創建標記。本質上，我嘗試呼叫fetchUsers()兩次，但我認為有一種更有效的方法可以做到這一點，但我不知道如何處理這個問題。請幫幫我，對不起我的英語不好。
uj5u.com熱心網友回復：
您可以在 ViewModel 中使用實時資料：請參見下面給出的代碼：
@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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