Android Retrofit - Wait For Response Before Executing Other Code?

I'm using Retrofit to return a response from an api. The data from that response is to be supplied to a recyclerview. I get a Null pointer exception on the data object when passing

Solution 1:

Rather do it like this:

zapposApi.getWhatever(newCallback<List<YourPOJO>>() {
            @Overridepublicvoidsuccess(List<YourPOJO> YourPOJO, Response response) {
                setupRecyclerView(YourPOJO);
            }

            @Overridepublicvoidfailure(RetrofitError error) {
                //handle your error
            }
        });

Your api will have an interface that might look like something in the line of :

@GET("/user/current")voidgetCurrentUser(Callback<YourPOJO> response);

This way the actual network call is done in the background and the callback is on the UI thread. You don't have to use async for this!.

Solution 2:

Found the solution to my problem. In my original code I wanted to wait until I recieved an api response before setting up the recyclerView. However, Android doesn't like when you delay setting up the recyclerView for too long so I got this error:

java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.support.v7.widget.RecyclerView$LayoutManager.onAddFocusables(android.support.v7.widget.RecyclerView, java.util.ArrayList, int, int)' on a null object reference

This brought me back to the dilemna where I didn't have the response data to setup the recyclerview yet. So in setupRecyclerView(), I imported recyclerview from the xml and setup the layout manager but removed the code that created the adapter and added it to the recyclerview. Then I put the adapter creation code in the success() method of my Callback implementation. This fixed the problem!

Found my solution here: Why my android activity is crashing with "No adapter attached; skipping layout" but sporadically?

and the code is below.

public class SearchResultsActivity extends BaseActivity {

// UIprivateToolbar toolbar;
    privateSearchView searchbox;
    privateRecyclerView rvResults;

    // Business LogicprivateString searchQuery;

    @OverrideprotectedvoidonCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_search_results);
        searchQuery = getSearchQuery();
        setupToolbar();
        setupRecyclerView();
        searchForProducts(searchQuery);
    }

    privatevoidsetupToolbar() {
        toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("");
    }

    privatevoidsetupRecyclerView() {
        rvResults = (RecyclerView) findViewById(R.id.rvResults);
        rvResults.setHasFixedSize(true);
        rvResults.setLayoutManager(newLinearLayoutManager(activityContext));
    }

    privateStringgetSearchQuery() {
        String query = "";
        Intent intent = getIntent();
        if (Intent.ACTION_SEARCH.equals(intent.getAction())) {
            query = intent.getStringExtra(SearchManager.QUERY);
        }
        return query;
    }

    privatevoidsearchForProducts(String query) {

        RestAdapter retrofit = newRestAdapter.Builder()
                .setEndpoint(Constants.BASE_URL)
                .build();

        ZapposAPI api = retrofit.create(ZapposAPI.class);

        api.searchZappos(query, newCallback<Response>() {
            @Overridepublicvoidsuccess(Response apiResponse, retrofit.client.Response response) {
                ResultAdapter adapter = newResultAdapter(apiResponse.getResults());
                rvResults.setAdapter(adapter);
            }

            @Overridepublicvoidfailure(RetrofitError error) {

            }
        });
    }