Passing variable to paging library class

问题

I am creating an app with Android Paging Library. I'm using retrofit with it. Retrofit code is in ItemDataSource and there i can't pass variable to it. I have some variable coming with intent. How can i set my variable in Retrofit Post method.

ItemDataSource

public class ItemDataSource extends PageKeyedDataSource<Integer, Item> {
//we will start from the first page which is 1
private static final int PAGE_NUMBER = 1;
//this will be called once to load the initial data
String table
ItemDataSource(String table){
this.table = table;
}
@Override
public void loadInitial(@NonNull LoadInitialParams<Integer> params, @NonNull 
final LoadInitialCallback<Integer, Item> callback) {

   RetrofitClient.getInstance()
      // I want to pass table variable here.
            .getApi().getAnswers("table","","","",PAGE_NUMBER,"")
            .enqueue(new Callback<StackApiResponse>() {
                @Override
                public void onResponse(Call<StackApiResponse> call, 
                    Response<StackApiResponse> response) {
                    if (response.body() != null) {
                        callback.onResult(response.body().images, null, 
                 PAGE_NUMBER + 1);
                    }
                }

                @Override
                public void onFailure(Call<StackApiResponse> call, 
  Throwable 
                   t) {

                }
            });
               }
            }

Main Activity

    public class Detail extends AppCompatActivity {
    ArrayList<Item> items;
    Api api;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_detail);
      // I'm getting intent here.
        final     RecyclerView recyclerView = 
        findViewById(R.id.recyclerview);
         recyclerView.setLayoutManager(new LinearLayoutManager(this));
        recyclerView.setHasFixedSize(true);
        ItemViewModel itemViewModel = 
       ViewModelProviders.of(this).get(ItemViewModel.class);

        //creating the Adapter

        //observing the itemPagedList from view model
        itemViewModel.itemPagedList.observe(this, new 
       Observer<PagedList<Item>>() {
            @Override
            public void onChanged(@Nullable PagedList<Item> items) {

                //in case of any changes
                //submitting the items to adapter
                adapter.submitList(items);
            }
        });

        //setting the adapter
        recyclerView.setAdapter(adapter);

    }
 }

Item View Model

public class ItemViewModel extends ViewModel {

//creating livedata for PagedList  and PagedKeyedDataSource
LiveData<PagedList<Item>> itemPagedList;
LiveData<PageKeyedDataSource<Integer, Item>> liveDataSource;

//constructor
public ItemViewModel() {
    //getting our data source factory
    ItemDataSourceFactory itemDataSourceFactory = new 
 ItemDataSourceFactory();

    //getting the live data source from data source factory
    liveDataSource = itemDataSourceFactory.getItemLiveDataSource();

    //Getting PagedList config
    PagedList.Config pagedListConfig =
            (new PagedList.Config.Builder())
                    .setEnablePlaceholders(false)
                    .setPageSize(10).build();

    //Building the paged list
    itemPagedList = (new LivePagedListBuilder(itemDataSourceFactory, 
 pagedListConfig))
            .build();
 }

}

BTW i'm following this https://www.simplifiedcoding.net/android-paging-library-tutorial/

回答1:

for doing this, you have to create a constructor in ItemDataSource class which you did, a new object of that class is created in ItemDataSourceFactory so you have to create a constructor there to get the value and pass it to ItemDataSource. and you have to pass the value to ItemDataSourceFactory from your viewModel. this is how it should look (based on the link that you posted)

public class ItemViewModel extends ViewModel {
 LiveData<PagedList<Item>> itemPagedList;
LiveData<PageKeyedDataSource<Integer, Item>> liveDataSource;

public ItemViewModel(String table) {
    ItemDataSourceFactory itemDataSourceFactory = new ItemDataSourceFactory(table);
     liveDataSource = itemDataSourceFactory.getItemLiveDataSource();
     PagedList.Config pagedListConfig =
            (new PagedList.Config.Builder())
                    .setEnablePlaceholders(false)
                    .setPageSize(ItemDataSource.PAGE_SIZE).build();
     itemPagedList = (new LivePagedListBuilder(itemDataSourceFactory,pagedListConfig))
            .build();
}}

then in your activity/fragment you should pass the value like this:

ItemViewModel itemViewModel = ViewModelProviders.of(this, new ViewModelProvider.Factory() {
        @NonNull
        @Override
        public <T extends ViewModel> T create(@NonNull Class<T> modelClass) {
            return (T)new ItemViewModel ("your table name");
        }
    }).get(ItemViewModel.class);

来源：https://stackoverflow.com/questions/52694980/passing-variable-to-paging-library-class

标签

android

retrofit

android-paging