How to refresh my RecyclerView with another Room-DAO Query

Question

I have a RecyclerView with an AAC in my Fragment. ViewModel --> Repository --> DAO with some custom Queries and a getAllItems.

I want to use a Filter FAB or a Spinner to call getOrderItemList or getWhereItemList queries but i dont know how must i do it.

I have a Repository Filter for my SearchView but is a different thing, now i want to change list order (alphabetical, year...) and create a WhereCondition with a lot of checkbox that i have in a Dialog (example: i check "complete" and "Action" checkbox and creates the String whereCondition = "(status = 'complete' and genre like '%Action%')" ).

How can i call getWhereItemList and getOrderItemList queries from my Fragment to change my RecyclerView content?

ItemDAO:

@Query("SELECT * from item_table ")
 <List<Item>> getItemList();
@Query("SELECT * from item_table ORDER by :order DESC")
 <List<Item>> getOrderItemList(String order);
@Query("SELECT * from item_table WHERE :whereCondition")
 <List<Item>> getWhereItemList(String whereCondition);

My Fragment fills the RecyclerView with getAllItems:

   private ItemViewModel myItemViewModel;

   RecyclerView myRecyclerView = findViewById(R.id.recyclerview);
   final ItemListAdapter myAdapter = new ItemListAdapter(this);
   myRecyclerView.setAdapter(myAdapter);
   myRecyclerView.setLayoutManager(new LinearLayoutManager(this));

   myItemViewModel = ViewModelProviders.of(this).get(ItemViewModel.class);

   myItemViewModel.getAllItems().observe(this, new Observer<List<Item>>() {
       @Override
       public void onChanged(@Nullable final List<Item> items) {
           myAdapter.setItems(items);
       }  

ItemListAdapter:

private List<Item> myItems;

void setItems(List<Item> items){
   myItems = items;
   notifyDataSetChanged();
 }

ItemViewModel:

private ItemRepository myRepository;
private LiveData<List<Item>> myAllItems;

public ItemViewModel (Application application) {
   super(application);
   myRepository = new ItemRepository(application);
   myAllItems = myRepository.getAllItems();
}

LiveData<List<Item>> getAllItems() { return myAllItems; }

Thanks.

Answer 1

The idea is to have two LiveData instances:

• one that keeps track of the current filter type. You may set its initial value.
• one that emits List<Item>. This also should react to the other LiveData change and get new List<Item> if necessary.

You can use Transformations.SwitchMap to implement LiveData2. What it does is it basically returns a LiveData instance that can switch to a different source in response to another LiveData object.

ItemViewModel:

private ItemRepository myRepository;

/**
 * Keep track of the current filter type.
 * In this example the initial value is set to Filter.ALL, which
 * represents the non-filtered list.
 */
private MutableLiveData<Filter> itemFilter = new MutableLiveData<>(Filter.ALL);

/**
 * Emits list of items
 */
private LiveData<List<Item>> myItems = Transformations.switchMap(itemFilter, filter -> {

    // Everytime itemFilter emits a new value, this piece of code
    // will be invoked. You are responsible for returning the
    // LiveData instance according to the filter value.
    switch(filter.type) {
        case ALL:
            return myRepository.getAllItems();
        case ORDER_BY:
            return myRepository.getOrderItemList(filter.query);
        case WHERE:
            return myRepository.getWhereItemList(filter.query);
    }
});


public ItemViewModel (Application application) {
   super(application);
   myRepository = new ItemRepository(application);
}

public LiveData<List<Item>> getItems() { return myItems; }

/**
 * View should call this method in order to switch to different
 * filter.
 */
public void changeFilter(Filter itemFilter) {
    this.itemFilter.setValue(filter);
}

Define this custom filter class:

public class Filter {

    public enum Type {
        ALL,
        ORDER_BY,
        WHERE
    }

    final public Type type;
    final public String query;

    public Filter(Type type, String query) {
        this.type = type;
        this.query = query;
    }
}