Android LiveData: Transformation :对原始列表进行过滤，展示过滤后的数据

public class ItemViewModel extends ViewModel {
    private final LiveData<List<Item>> allItems;
    private final LiveData<List<Item>> approvedItems;

    public ItemViewModel(ItemRepository repository) {
        allItems = repository.getAllItems();
        approvedItems = Transformations.map(allItems, items -> {
            List<Item> filteredItems = new ArrayList<>();
            for (Item item : items) {
                if (item.isApproved()) {
                    filteredItems.add(item);
                }
            }
            return filteredItems;
        });
    }

    public LiveData<List<Item>> getApprovedItems() {
        return approvedItems;
    }
}

public class ItemActivity extends AppCompatActivity {
    private ItemViewModel viewModel;

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

        viewModel = new ViewModelProvider(this).get(ItemViewModel.class);

        viewModel.getApprovedItems().observe(this, items -> {
            // 更新 UI，展示过滤后的项目列表
        });
    }
}