Xây dựng view model cho item - Tài liệu lập trình android

package com.vantinviet.adayroionline.viewmodel.item;

import com.vantinviet.adayroionline.Config;
import com.vantinviet.adayroionline.repository.item.ItemRepository;
import com.vantinviet.adayroionline.utils.AbsentLiveData;
import com.vantinviet.adayroionline.viewmodel.common.PSViewModel;
import com.vantinviet.adayroionline.viewobject.Item;
import com.vantinviet.adayroionline.viewobject.common.Resource;

import java.util.List;

import javax.inject.Inject;

import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.Transformations;

public class ItemViewModel extends PSViewModel {
    private final LiveData<Resource<List<Item>>> itemsData;
    private MutableLiveData<TmpDataHolder> itemsObj = new MutableLiveData<>();

    private final LiveData<Resource<Boolean>> nextPageItemsData;
    private MutableLiveData<TmpDataHolder> nextPageItemsObj = new MutableLiveData<>();

    private final LiveData<Resource<Item>> itemByIdData;
    private MutableLiveData<ItemByIdTmpDataHolder> itemByIdObj = new MutableLiveData<>();

    public String shopName, shopId;

    @Inject
    ItemViewModel(ItemRepository repository) {

        itemsData = Transformations.switchMap(itemsObj, obj -> {

            if (obj == null) {
                return AbsentLiveData.create();
            }

            return repository.getItemList(obj.limit, obj.offset);

        });

        nextPageItemsData = Transformations.switchMap(nextPageItemsObj, obj -> {

            if (obj == null) {
                return AbsentLiveData.create();
            }

            return repository.getNextPageItemList(Config.API_KEY, obj.limit, obj.offset);

        });

        itemByIdData = Transformations.switchMap(itemByIdObj, obj -> {

            if (obj == null) {
                return AbsentLiveData.create();
            }

            return repository.getItemById(obj.id);

        });

    }

    public void setItemsObj(String limit, String offset) {
        TmpDataHolder tmpDataHolder = new TmpDataHolder(limit, offset);

        this.itemsObj.setValue(tmpDataHolder);
    }

    public LiveData<Resource<List<Item>>> getItemsData() {
        return itemsData;
    }

    public void setNextPageItemsObj(String limit, String offset) {
        TmpDataHolder tmpDataHolder = new TmpDataHolder(limit, offset);

        this.nextPageItemsObj.setValue(tmpDataHolder);
    }

    public LiveData<Resource<Boolean>> getNextPageItemsData() {
        return nextPageItemsData;
    }

    public void setItemByIdObj(String id) {
        ItemByIdTmpDataHolder itemByIdTmpDataHolder = new ItemByIdTmpDataHolder(id);

        this.itemByIdObj.setValue(itemByIdTmpDataHolder);
    }

    public LiveData<Resource<Item>> getItemByIdData() {
        return itemByIdData;
    }


    class TmpDataHolder {

        String  limit, offset;

        public TmpDataHolder(String limit, String offset) {
            this.limit = limit;
            this.offset = offset;
        }
    }

    class ItemByIdTmpDataHolder {

        String id;

        private ItemByIdTmpDataHolder(String id) {
            this.id = id;
        }
    }
}