從另一個片段回傳后如何防止片段重繪recyclerview/保存recyclerview位置

在這部分中，我嘗試在我的應用程式中添加一項功能并解決一個問題，我想保存 recyclerview 位置，因此當單擊并導航到詳細資訊片段并單擊回傳時，這應該回到相同的位置，這里的問題是我點擊回傳我看到專案重疊，大約有 8 個專案，它從下一個串列位置開始，當我尋找這個問題的解決方案時，我找到了這個答案然后我決定單獨添加 recyclerview 的依賴項implementation "androidx.recyclerview:recyclerview:1.2.1"來使用這個功能

adapter.setStateRestorationPolicy(RecyclerView.Adapter.StateRestorationPolicy.PREVENT_WHEN_EMPTY);

但它不起作用，下一個GIF描述問題

recyclerview位置問題

以及具有此功能的應用程式示例

目標

首頁片段

@AndroidEntryPoint
public class HomeFragment extends Fragment {

    private FragmentHomeBinding binding;
    private PostViewModel postViewModel;
    public static final String TAG = "HomeFragment";
    private PostAdapter adapter;
    private List<Item> itemArrayList;
    private GridLayoutManager titleLayoutManager, gridLayoutManager;
    WrapContentLinearLayoutManager layoutManager;

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

        binding.homeRecyclerView.addOnItemTouchListener(new RecyclerItemClickListener(requireContext(),
                binding.homeRecyclerView, new RecyclerItemClickListener.OnItemClickListener() {
            @Override
            public void onItemClick(View view, int position) {

                Item item = itemArrayList.get(position);

                if (Objects.requireNonNull
                        (Navigation.findNavController(requireView())
                                .getCurrentDestination()).getId() == R.id.nav_home) {
                    Navigation.findNavController(requireView())
                            .navigate(HomeFragmentDirections.actionNavHomeToDetailsFragment(item));
                }
            }

            @Override
            public void onLongItemClick(View view, int position) {

            }
        }));
    }


    public View onCreateView(@NonNull LayoutInflater inflater,
                             @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {


        binding = FragmentHomeBinding.inflate(inflater, container, false);
        setHasOptionsMenu(true);

        postViewModel = new ViewModelProvider(this).get(PostViewModel.class);
        postViewModel.finalURL.setValue(Constants.getBaseUrl()   "?key="   Constants.getKEY());
        itemArrayList = new ArrayList<>();
        adapter = new PostAdapter(getContext(), itemArrayList, this, postViewModel);

        layoutManager = new WrapContentLinearLayoutManager(requireContext(),
                LinearLayoutManager.VERTICAL, false);
        titleLayoutManager = new GridLayoutManager(getContext(), 2);
        gridLayoutManager = new GridLayoutManager(getContext(), 3);


//        binding.homeRecyclerView.setAdapter(adapter);
        binding.shimmerLayout.setVisibility(View.VISIBLE);
        binding.homeRecyclerView.setVisibility(View.INVISIBLE);

        adapter.setStateRestorationPolicy(RecyclerView.Adapter.StateRestorationPolicy.PREVENT_WHEN_EMPTY);


        postViewModel.recyclerViewLayoutMT.observe(getViewLifecycleOwner(), layout -> {
            Log.w(TAG, "getSavedLayout: called");
            switch (layout) {
                case "cardLayout":
                    binding.loadMoreBtn.setVisibility(View.VISIBLE);
                    binding.homeRecyclerView.setLayoutManager(layoutManager);
                    binding.homeRecyclerView.setAdapter(adapter);
                    adapter.setViewType(0);

                    break;
                case "cardMagazineLayout":
                    binding.loadMoreBtn.setVisibility(View.VISIBLE);
                    binding.homeRecyclerView.setLayoutManager(layoutManager);
                    binding.homeRecyclerView.setAdapter(adapter);
                    adapter.setViewType(1);
                    break;
                case "titleLayout":
                    binding.loadMoreBtn.setVisibility(View.GONE);
                    binding.homeRecyclerView.setLayoutManager(titleLayoutManager);
                    binding.homeRecyclerView.setAdapter(adapter);
                    adapter.setViewType(2);
                    break;
                case "gridLayout":
                    binding.loadMoreBtn.setVisibility(View.GONE);
                    binding.homeRecyclerView.setLayoutManager(gridLayoutManager);
                    binding.homeRecyclerView.setAdapter(adapter);
                    adapter.setViewType(3);
            }
        });


        if (Utils.hasNetworkAccess(requireContext())) {

            postViewModel.getPosts();

            postViewModel.postListMutableLiveData.observe(getViewLifecycleOwner(), postList -> {
                itemArrayList.addAll(postList.getItems());
                binding.shimmerLayout.stopShimmer();
                binding.shimmerLayout.setVisibility(View.GONE);
                binding.homeRecyclerView.setVisibility(View.VISIBLE);
                adapter.notifyDataSetChanged();

                Log.e(TAG, "ItemsArrayList :"   itemArrayList.get(0).getTitle());

            });


        } else {

            binding.shimmerLayout.setVisibility(View.VISIBLE);
//            binding.shimmerLayout.startShimmer();


            if (postViewModel.getAllItemsFromDataBase == null) {

                noInternetConnectionLayout();

            } else {
//                Log.e(TAG, "RoomDB Items size :"   itemsDatabase.itemDAO().getAlItems());

                binding.shimmerLayout.stopShimmer();
                binding.shimmerLayout.setVisibility(View.GONE);
                binding.emptyView.setVisibility(View.GONE);
                binding.homeRecyclerView.setVisibility(View.VISIBLE);
                postViewModel.getAllItemsFromDataBase.observe(getViewLifecycleOwner(), items -> {
                    if (items.isEmpty()) {
                        noInternetConnectionLayout();
                    } else {
                        binding.loadMoreBtn.setVisibility(View.GONE);
                        itemArrayList.addAll(items);
                        adapter.notifyDataSetChanged();
                    }
                });

            }
        }

        postViewModel.errorCode.observe(getViewLifecycleOwner(), errorCode -> {
            if (errorCode == 400) {
                Snackbar.make(requireView(), R.string.lastPost, Snackbar.LENGTH_LONG).show();
            } else {
                binding.homeRecyclerView.setVisibility(View.INVISIBLE);
                binding.emptyView.setVisibility(View.VISIBLE);
            }
        });

        binding.loadMoreBtn.setOnClickListener(view -> {
            AlertDialog dialog = Utils.setProgressDialog(requireContext());

            postViewModel.isLoading.observe(getViewLifecycleOwner(), isLoading -> {
                if (isLoading) {
                    dialog.show();
                } else {
                    dialog.dismiss();
                }
            });

            if (Utils.hasNetworkAccess(requireContext())) {
                postViewModel.getPosts();
//                Log.w(TAG, "loadMoreBtn: "   dialog.isShowing());
            } else {
                postViewModel.isLoading.postValue(true);
                postViewModel.getAllItemsFromDataBase.getValue();
                postViewModel.isLoading.postValue(false);
            }

        });

        return binding.getRoot();

    }

    private void noInternetConnectionLayout() {
        binding.shimmerLayout.stopShimmer();
        binding.shimmerLayout.setVisibility(View.GONE);
        binding.homeRecyclerView.setVisibility(View.GONE);
        binding.emptyView.setVisibility(View.VISIBLE);
    }

    @Override
    public void onDestroyView() {
        super.onDestroyView();
        itemArrayList.clear();
        binding = null;
    }


    @Override
    public void onCreateOptionsMenu(@NonNull Menu menu, @NonNull MenuInflater inflater) {

        inflater.inflate(R.menu.main, menu);
        super.onCreateOptionsMenu(menu, inflater);

        SearchManager searchManager = (SearchManager) requireContext().getSystemService(Context.SEARCH_SERVICE);
        SearchView searchView = (SearchView) menu.findItem(R.id.app_bar_search).getActionView();
        searchView.setSearchableInfo(searchManager.getSearchableInfo(requireActivity().getComponentName()));
        searchView.setQueryHint(getResources().getString(R.string.searchForPosts));

        searchView.setOnQueryTextListener(new SearchView.OnQueryTextListener() {
            @Override
            public boolean onQueryTextSubmit(String keyword) {
                if (keyword.isEmpty()) {
                    Snackbar.make(requireView(), "please enter keyword to search", Snackbar.LENGTH_SHORT).show();
                }
                if (Utils.hasNetworkAccess(requireContext())) {
                    itemArrayList.clear();
                    postViewModel.getItemsBySearch(keyword);
                    adapter.notifyDataSetChanged();
                } else {
                    postViewModel.getItemsBySearchInDB(keyword);
                    postViewModel.getItemsBySearchMT.observe(getViewLifecycleOwner(), items ->
                            {
                                Log.d(TAG, "onQueryTextSubmit database called");
                                itemArrayList.clear();
                                itemArrayList.addAll(items);
                                adapter.notifyDataSetChanged();
                            }
                    );
                }
                return false;
            }

            @Override
            public boolean onQueryTextChange(String newText) {
                return false;
            }
        });


        searchView.setOnCloseListener(() -> {

            if (Utils.hasNetworkAccess(requireContext())) {
                Log.d(TAG, "setOnCloseListener: called");
                itemArrayList.clear();
                binding.emptyView.setVisibility(View.GONE);
                binding.homeRecyclerView.setVisibility(View.VISIBLE);
                postViewModel.getPosts();
                adapter.notifyDataSetChanged();
            } else {
                Log.d(TAG, "setOnCloseListener: called");
                binding.emptyView.setVisibility(View.GONE);
                binding.homeRecyclerView.setVisibility(View.VISIBLE);
                postViewModel.getAllItemsFromDataBase.observe(getViewLifecycleOwner(), items ->
                        {
                            itemArrayList.addAll(items);
                            adapter.notifyDataSetChanged();
                        }
                );
            }
            return false;
        });


        postViewModel.searchError.observe(getViewLifecycleOwner(), searchError -> {
            if (searchError) {
                Toast.makeText(requireContext(),
                        "There's no posts with this keyword", Toast.LENGTH_LONG).show();
            }
        });


    }

    @Override
    public boolean onOptionsItemSelected(@NonNull MenuItem item) {

        if (item.getItemId() == R.id.change_layout) {
            changeAndSaveLayout();
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

視圖模型

@HiltViewModel
public class PostViewModel extends ViewModel {

    public static final String TAG = "PostViewModel";


    private final com.blogspot.abtallaldigital.data.Repository repository;
    public final MutableLiveData<PostList> postListMutableLiveData = new MutableLiveData<>();
    public final MutableLiveData<String> finalURL = new MutableLiveData<>();
    public final MutableLiveData<String> token = new MutableLiveData<>();
    public final MutableLiveData<String> label = new MutableLiveData<>();
    public final MutableLiveData<Integer> errorCode = new MutableLiveData<>();
    public final MutableLiveData<Boolean> searchError = new MutableLiveData<>();
    public final LiveData<List<Item>> getAllItemsFromDataBase;
    public final MutableLiveData<List<Item>>
            getItemsBySearchMT = new MutableLiveData<>();
    public final MutableLiveData<Boolean> isLoading = new MutableLiveData<>();
    public final MutableLiveData<String> recyclerViewLayoutMT = new MutableLiveData<>();
    private final Utils.DataStoreRepository dataStoreRepository;
    public final MutableLiveData<Integer> currentDestination = new MutableLiveData<>();


//    public MutableLiveData<Boolean> ifAnythingWrongHappened = new MutableLiveData<>();

    @Inject
    public PostViewModel(Repository repository, Utils.DataStoreRepository dataStoreRepository) {
        this.repository = repository;
        getAllItemsFromDataBase = repository.localDataSource.getAllItems();
        this.dataStoreRepository = dataStoreRepository;
        dataStoreRepository.readLayoutFlow
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new FlowableSubscriber<String>() {
                    @Override
                    public void onSubscribe(@NonNull Subscription s) {
                        s.request(Long.MAX_VALUE);
                    }

                    @Override
                    public void onNext(String layout) {
                        if (layout != null) {
                            recyclerViewLayoutMT.setValue(layout);
                        }
                    }

                    @Override
                    public void onError(Throwable t) {
                        Log.e(TAG, "onError: "   t.getMessage());
                        Log.e(TAG, "onError: "   t.getCause());
                    }

                    @Override
                    public void onComplete() {

                    }
                });

        dataStoreRepository.readCurrentDestination
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .firstOrError().subscribeWith(new SingleObserver<Integer>() {
            @Override
            public void onSubscribe(@NonNull Disposable d) {

            }

            @Override
            public void onSuccess(@NonNull Integer destination) {
                currentDestination.setValue(destination);
            }

            @Override
            public void onError(@NonNull Throwable e) {
                Log.e(TAG, "onError: "   e.getMessage());
            }
        });

    }

    public void saveRecyclerViewLayout(String layout) {
        dataStoreRepository.saveRecyclerViewLayout("recyclerViewLayout", layout);
    }

    public void saveCurrentDestination(int currentDestination) {
        dataStoreRepository
                .saveCurrentDestination("CURRENT_DESTINATION", currentDestination);
    }


    //    @Override
//    protected void onCleared() {
//        super.onCleared();
//        postListMutableLiveData.setValue(null);
//        finalURL.setValue(null);
//        token.setValue(null);
//    }

    public void getPosts() {
        Log.e(TAG, finalURL.getValue());

        isLoading.setValue(true);
        repository.remoteDataSource.getPostList(finalURL.getValue())
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Observer<Response<PostList>>() {
                    @Override
                    public void onSubscribe(@NonNull Disposable d) {

                    }

                    @Override
                    public void onNext(@NonNull Response<PostList> postListResponse) {

                        if (postListResponse.isSuccessful()) {
                            if (postListResponse.body() != null
                                    && postListResponse.body().getNextPageToken() != null) {
                                Log.e(TAG, postListResponse.body().getNextPageToken());
                                token.setValue(postListResponse.body().getNextPageToken());
                                isLoading.setValue(false);
                            }
                            postListMutableLiveData.setValue(postListResponse.body());

                            for (int i = 0; i < postListResponse.body().getItems().size(); i  ) {
                                repository.localDataSource.insertItem(postListResponse.body()
                                        .getItems().get(i))
                                        .subscribeOn(Schedulers.io())
                                        .observeOn(AndroidSchedulers.mainThread())
                                        .subscribe(new CompletableObserver() {
                                            @Override
                                            public void onSubscribe(@NonNull Disposable d) {

                                            }

                                            @Override
                                            public void onComplete() {

                                            }

                                            @Override
                                            public void onError(@NonNull Throwable e) {

                                            }
                                        });
                            }

                            finalURL.setValue(finalURL.getValue()   "&pageToken="   token.getValue());
                        } else {
                            isLoading.setValue(false);
                            errorCode.setValue(postListResponse.code());
                            Log.e(TAG, "onNext: "   postListResponse.code());
                            Log.e(TAG, "onNext: "   postListResponse.errorBody());
                        }
                    }

                    @Override
                    public void onError(@NonNull Throwable e) {
                        isLoading.setValue(false);
                        Log.e(TAG, e.getMessage()   e.getCause());
//                        ifAnythingWrongHappened.setValue(true);
                        if (e instanceof HttpException) {
                            errorCode.setValue(((HttpException) e).code());
                        }
                    }

                    @Override
                    public void onComplete() {

                    }
                });

    }


    public void getPostListByLabel() {

        isLoading.setValue(true);
        Log.e(TAG, finalURL.getValue());

        repository.remoteDataSource.getPostListByLabel(finalURL.getValue())
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Observer<Response<com.blogspot.abtallaldigital.pojo.PostList>>() {
                    @Override
                    public void onSubscribe(@NonNull Disposable d) {

                    }

                    @Override
                    public void onNext(@NonNull Response<com.blogspot.abtallaldigital.pojo.PostList> postListResponse) {
                        if (postListResponse.isSuccessful()) {
                            if (postListResponse.body() != null) {
//                                Log.e(TAG, postListResponse.body().getNextPageToken());
                                token.setValue(postListResponse.body().getNextPageToken());
                            }
                            postListMutableLiveData.setValue(postListResponse.body());
                            isLoading.setValue(false);
                            finalURL.postValue(Constants.getBaseUrlPostsByLabel()
                                      "posts?labels="   label.getValue()   "&pageToken="
                                      token.getValue()
                                      "&key="   Constants.getKEY());
                        } else {
                            isLoading.setValue(false);
                            errorCode.setValue(postListResponse.code());
                            Log.e(TAG, "onNext: "   postListResponse.code());
                            Log.e(TAG, "onNext: "   postListResponse.errorBody());
                        }
                    }

                    @Override
                    public void onError(@NonNull Throwable e) {
                        isLoading.setValue(false);
                        Log.e(TAG, e.getMessage()   e.getCause());
                        if (e instanceof HttpException) {
                            errorCode.setValue(((HttpException) e).code());
                        }
                    }

                    @Override
                    public void onComplete() {

                    }
                });

    }

    public void getItemsBySearch(String keyword) {

        isLoading.setValue(true);
        searchError.setValue(false);

        String url = Constants.getBaseUrl()  
                "search?q="   keyword   "&key="   Constants.getKEY();

        Log.e(TAG, "getItemsBySearch: "   url);

        repository.remoteDataSource.getPostListBySearch(url)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Observer<Response<com.blogspot.abtallaldigital.pojo.PostList>>() {
                    @Override
                    public void onSubscribe(@NonNull Disposable d) {

                    }

                    @Override
                    public void onNext(@NonNull Response<PostList> postListResponse) {

                        if (postListResponse.isSuccessful()) {
                            if (postListResponse.body() != null
                                    && postListResponse.body().getNextPageToken() != null) {
                                Log.e(TAG, postListResponse.body().getNextPageToken());
                                token.setValue(postListResponse.body().getNextPageToken());
                                isLoading.setValue(false);
                            }
                            postListMutableLiveData.setValue(postListResponse.body());
                        } else {
                            isLoading.setValue(false);
                            searchError.setValue(true);
                            Log.e(TAG, "onNext: list is null");
                        }
                    }

                    @Override
                    public void onError(@NonNull Throwable e) {
                        isLoading.setValue(false);
                        Log.e(TAG, e.getMessage()   e.getCause());
//                        ifAnythingWrongHappened.setValue(true);
                        if (e instanceof HttpException) {
                            errorCode.setValue(((HttpException) e).code());
                        }
                    }

                    @Override
                    public void onComplete() {

                    }
                });

    }

    public void getItemsBySearchInDB(String keyword) {
        Log.d(TAG, "getItemsBySearchInDB: called");
        repository.localDataSource.getItemsBySearch(keyword)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new Observer<List<com.blogspot.abtallaldigital.pojo.Item>>() {
                    @Override
                    public void onSubscribe(@NonNull Disposable d) {

                    }

                    @Override
                    public void onNext(@NonNull List<Item> items) {
                        if (items.isEmpty()) {
                            searchError.setValue(true);
                            Log.e(TAG, "onNext: list is empty");
                        } else {
                            getItemsBySearchMT.setValue(items);
                            Log.d(TAG, "onNext: "   items.size());
                        }
                    }

                    @Override
                    public void onError(@NonNull Throwable e) {
                        searchError.setValue(true);
                    }

                    @Override
                    public void onComplete() {

                    }
                });

    }

    public void insertFavorites(FavoritesEntity favoritesEntity) {
        repository.localDataSource.insertFavorites(favoritesEntity)
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new CompletableObserver() {
                    @Override
                    public void onSubscribe(@NonNull Disposable d) {

                    }

                    @Override
                    public void onComplete() {

                    }

                    @Override
                    public void onError(@NonNull Throwable e) {
                        Log.e(TAG, "onError: "   e.getMessage());
                    }
                });
    }

    public LiveData<List<FavoritesEntity>> getAllFavorites() {
        return repository.localDataSource.getAllFavorites();
    }

    public void deleteFavoritePost(FavoritesEntity favoritesEntity) {
        repository.localDataSource.deleteFavorite(favoritesEntity);
    }

    public void deleteAllFavorites() {
        repository.localDataSource.deleteAllFavorites()
                .subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new CompletableObserver() {
                    @Override
                    public void onSubscribe(@NonNull Disposable d) {

                    }

                    @Override
                    public void onComplete() {

                    }

                    @Override
                    public void onError(@NonNull Throwable e) {
                        Log.e(TAG, "onError: "   e.getMessage());
                    }
                });


    }


}

uj5u.com熱心網友回復：

嘗試在onCreate而不是初始化配接器onViewCreated 然后您可以在 recyclerview 中設定配接器onViewCreated。

還可以嘗試使用 LiveData 事件包裝器：https ://stackoverflow.com/a/51762972/9854554

Java 中的 LiveData 事件包裝器：https ://stackoverflow.com/a/56072658

它會阻止 livedata 觀察者在片段恢復時再次獲取資料（當我們再次訂閱 livedata 時）

uj5u.com熱心網友回復：

您在設定回收視圖資料onViewCreated，要求每次，我建議視圖模型更好的生命周期移交，使用LiveData或Stateflow中的視圖模型來證明你的資料的完整性

標籤：爪哇 安卓 android-fragments android-recyclerview 安卓导航

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