Android RecyclerView 无法正常处理来自改造请求的数据

Question

我在 RecyclerView 中有一个带有 CardViews 的屏幕。从 ArrayList 中检索每张卡片的数据。一旦我手动将数据添加到 ArrayList，一切正常。但是，当 API 使用改造添加数据时，仅当手动将至少一个元素添加到 ArrayList 时才会显示卡片。另外，如果我切换到另一个菜单，然后返回卡片列表，则只会显示手动添加的卡片。

List with cards

Only manually added card is visible

Full code

public class CurrencyRates extends Fragment {
ArrayList<CurrencyModel> currencyModelArrayList;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    // Inflate the layout for this fragment
    View view = inflater.inflate(R.layout.fragment_currency_rates, container, false);
    currencyModelArrayList = new ArrayList<>();
    getRates("EUR", "USD");
    getRates("USD", "AUD");
    getRates("EUR", "GBP");
    getRates("EUR", "CNY");
    currencyModelArrayList.add(new CurrencyModel("EUR", "CZK", 24.8821));
    RecyclerView currencyRV;
    currencyRV = view.findViewById(R.id.RVCurrency);

    CurrencyAdapter currencyAdapter = new CurrencyAdapter(getActivity().getBaseContext(), currencyModelArrayList);

    //cardview two columns
    RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(getActivity().getBaseContext(), 2);
    currencyRV.setLayoutManager(mLayoutManager);

    currencyRV.setAdapter(currencyAdapter);

    return view;
}

public void getRates(String baseCurrency, String exchangeCurrency) {

    RetrofitInterface retrofitInterface = RetrofitClient.getRetrofitInstance().create(RetrofitInterface.class);
    Call<JsonObject> call = retrofitInterface.getData(baseCurrency, exchangeCurrency);

    call.enqueue(new Callback<JsonObject>() {

        @Override
        public void onResponse(Call<JsonObject> call, Response<JsonObject> response) {
            JsonObject res = response.body();
            JsonPrimitive rate = res.getAsJsonObject().getAsJsonPrimitive("conversion_rate");
            currencyModelArrayList.add(new CurrencyModel(baseCurrency, exchangeCurrency, Double.parseDouble(rate.toString())));

        }

        public void onFailure(Call<JsonObject> call, Throwable t) {
        }

    });
}}

适配器类：

public class CurrencyAdapter extends RecyclerView.Adapter<CurrencyAdapter.ViewHolder> {
private Context context;
private ArrayList<CurrencyModel> currencyModelArrayList;

public CurrencyAdapter(Context context, ArrayList<CurrencyModel> currencyModelArrayList) {
    this.context = context;
    this.currencyModelArrayList = currencyModelArrayList;
}

@NonNull
@Override
public CurrencyAdapter.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
    View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.card_item, parent, false);
    return new ViewHolder(view);
}

@Override
public void onBindViewHolder(@NonNull CurrencyAdapter.ViewHolder holder, int position) {
    CurrencyModel model = currencyModelArrayList.get(position);
    holder.baseCurrencyTV.setText(model.getBaseCurrency());
    holder.exchangeCurrencyTV.setText("/ " + model.getExchangeCurrency());
    holder.rateTV.setText(String.valueOf(model.getRate()));
}

@Override
public int getItemCount() {
    return currencyModelArrayList.size();
}

public class ViewHolder extends RecyclerView.ViewHolder {
    private TextView baseCurrencyTV, exchangeCurrencyTV, rateTV;

    public ViewHolder(@NonNull View itemView) {
        super(itemView);
        baseCurrencyTV = itemView.findViewById(R.id.TVBaseCurrency);
        exchangeCurrencyTV = itemView.findViewById(R.id.TVExchangeCurrency);
        rateTV = itemView.findViewById(R.id.TVRate);
    }
}}

主活动：

public class MainActivity extends AppCompatActivity {


@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    //Navigation
    BottomNavigationView bottomNavigationView = findViewById(R.id.bottomNavigationView);
    AppBarConfiguration appBarConfiguration = new AppBarConfiguration.Builder(R.id.currencyRates, R.id.converter).build();
    NavController navController = Navigation.findNavController(this, R.id.fragment);
    NavigationUI.setupActionBarWithNavController(this, navController, appBarConfiguration);
    NavigationUI.setupWithNavController(bottomNavigationView, navController);
}}

改造：

    public class RetrofitClient {
    private static Retrofit retrofit;
    private static RetrofitClient instance;
    public static RetrofitInterface myRetrofitInterface;

    public static Retrofit getRetrofitInstance() {
        if (retrofit == null) {
            retrofit = new Retrofit.Builder()
                    .baseUrl(RetrofitInterface.BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();
        }
        return retrofit;
    }

}
    public interface RetrofitInterface {

    String BASE_URL = "https://v6.exchangerate-api.com/";

    @GET("v6/API_KEY/pair/{baseCurrency}/{exchangeCurrency}")
    Call<JsonObject> getData(@Path("baseCurrency") String baseCurrency,
                                @Path("exchangeCurrency") String exchangeCurrency);
}

Answer 1

当您将项目添加到列表中时，您应该通知适配器

public void getRates(String baseCurrency, String         exchangeCurrency) {

 RetrofitInterface retrofitInterface =   RetrofitClient.getRetrofitInstance().create(RetrofitInterface.class);
Call<JsonObject> call = retrofitInterface.getData(baseCurrency, exchangeCurrency);

call.enqueue(new Callback<JsonObject>() {

    @Override
    public void onResponse(Call<JsonObject> call, Response<JsonObject> response) {
        JsonObject res = response.body();
        JsonPrimitive rate = res.getAsJsonObject().getAsJsonPrimitive("conversion_rate");
        currencyModelArrayList.add(new CurrencyModel(baseCurrency, exchangeCurrency, Double.parseDouble(rate.toString())));           
        CurrencyAdapter.notifyDataSetChanged();// add this line
    }      
  });

}}