Retrofit 完成下载我的数据并更新 HashMap 后，MutableLiveData 没有 return HashMap 对象

Question

所以，我最近学习了 Retrofit，并试图创建一个使用 API 来下载 Pokemon 详细信息的应用程序。这是 MainActivity.java class 和 MainActivityViewModel.java class 的代码。还有其他 classes，但它们主要是模型 classes，所以我没有提到它们：

MainActivity.java

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.ViewModelProvider;

import android.os.Bundle;
import android.widget.Toast;

import com.arpansircar.java.pokemonapplication.R;
import com.arpansircar.java.pokemonapplication.viewmodel.MainActivityViewModel;

public class MainActivity extends AppCompatActivity {

    private MainActivityViewModel mainActivityViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        mainActivityViewModel = new ViewModelProvider(this).get(MainActivityViewModel.class);
    }

    @Override
    protected void onResume() {
        super.onResume();
        observeRetrofitFailures();

        mainActivityViewModel.downloadMainPokemonData();
        mainActivityViewModel.returnMainDownloadedData().observe(this, resultsPokemonServiceModels ->
                mainActivityViewModel.downloadSelectedPokemonData(resultsPokemonServiceModels));

        mainActivityViewModel.returnDownloadedPokemonData().observe(this, map -> {

        });
    }

    private void observeRetrofitFailures() {
        mainActivityViewModel.returnMainServiceErrorLiveData().observe(this, s ->
                Toast.makeText(MainActivity.this, s, Toast.LENGTH_SHORT).show());

        mainActivityViewModel.returnSelectedPokemonServiceErrorLiveData().observe(this, s ->
                Toast.makeText(this, s, Toast.LENGTH_SHORT).show());
    }
}

MainActivityViewModel.java

import androidx.lifecycle.LiveData;
import androidx.lifecycle.MutableLiveData;
import androidx.lifecycle.ViewModel;

import com.arpansircar.java.pokemonapplication.model.GetPokemonId;
import com.arpansircar.java.pokemonapplication.model.MainPokemonServiceModel;
import com.arpansircar.java.pokemonapplication.model.ResultsPokemonServiceModel;
import com.arpansircar.java.pokemonapplication.model.SelectedPokemonModel;
import com.arpansircar.java.pokemonapplication.retrofit.MainPokemonRetrofitInstance;
import com.arpansircar.java.pokemonapplication.retrofit.PokemonServiceInterface;

import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Objects;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.internal.EverythingIsNonNull;

public class MainActivityViewModel extends ViewModel {

    private MainPokemonServiceModel mainPokemonServiceModel;
    private final Map<String, String> pokemonHashMap = new HashMap<>();
    private final PokemonServiceInterface mainPokemonServiceInterface = MainPokemonRetrofitInstance.getInstance();

    private final MutableLiveData<String> mainServiceErrorLiveData = new MutableLiveData<>();
    private final MutableLiveData<String> selectedPokemonServiceErrorLiveData = new MutableLiveData<>();
    private final MutableLiveData<Map<String, String>> downloadMainPokemonData = new MutableLiveData<>();
    private final MutableLiveData<List<ResultsPokemonServiceModel>> resultsPokemonServiceModelListLiveData = new MutableLiveData<>();

    public void downloadMainPokemonData() {
        Call<MainPokemonServiceModel> mainPokemonServiceModelCall = mainPokemonServiceInterface.getResultsDataFromService();
        mainPokemonServiceModelCall.enqueue(new Callback<MainPokemonServiceModel>() {

            @Override
            @EverythingIsNonNull
            public void onResponse(Call<MainPokemonServiceModel> call, Response<MainPokemonServiceModel> response) {
                if (!response.isSuccessful()) {
                    mainServiceErrorLiveData.postValue(String.valueOf(response.code()));
                    return;
                }

                mainPokemonServiceModel = response.body();
                resultsPokemonServiceModelListLiveData.postValue(Objects.requireNonNull(mainPokemonServiceModel).resultsPokemonServiceModel);
            }

            @Override
            @EverythingIsNonNull
            public void onFailure(Call<MainPokemonServiceModel> call, Throwable t) {
                mainServiceErrorLiveData.postValue(t.getMessage());
            }
        });
    }

    public void downloadSelectedPokemonData(List<ResultsPokemonServiceModel> resultsPokemonServiceModelList) {
        for (ResultsPokemonServiceModel resultsPokemonServiceModel : resultsPokemonServiceModelList) {
            String pokemonId = GetPokemonId.getId(resultsPokemonServiceModel.url);
            Call<SelectedPokemonModel> selectedPokemonModelCall = MainPokemonRetrofitInstance.getInstance().getSelectedPokemonSprite(pokemonId);

            selectedPokemonModelCall.enqueue(new Callback<SelectedPokemonModel>() {
                @Override
                @EverythingIsNonNull
                public void onResponse(Call<SelectedPokemonModel> call, Response<SelectedPokemonModel> response) {
                    if (!response.isSuccessful()) {
                        selectedPokemonServiceErrorLiveData.postValue(String.valueOf(response.code()));
                        return;
                    }

                    SelectedPokemonModel selectedPokemonModel = response.body();
                    String pokemonName = Objects.requireNonNull(selectedPokemonModel).pokemonName;
                    String pokemonSpriteUrl = selectedPokemonModel.pokemonSpriteModel.spriteUrl;
                    pokemonHashMap.put(pokemonName, pokemonSpriteUrl);
                }

                @Override
                @EverythingIsNonNull
                public void onFailure(Call<SelectedPokemonModel> call, Throwable t) {
                    selectedPokemonServiceErrorLiveData.postValue(t.getMessage());
                }
            });
        }

        downloadMainPokemonData.postValue(pokemonHashMap);
    }

    public LiveData<Map<String, String>> returnDownloadedPokemonData() {
        return downloadMainPokemonData;
    }

    public LiveData<List<ResultsPokemonServiceModel>> returnMainDownloadedData() {
        return resultsPokemonServiceModelListLiveData;
    }

    public LiveData<String> returnMainServiceErrorLiveData() {
        return mainServiceErrorLiveData;
    }

    public LiveData<String> returnSelectedPokemonServiceErrorLiveData() {
        return selectedPokemonServiceErrorLiveData;
    }

}

我的主要问题在 downloadMainPokemonData.postValue(pokemonHashMap); 行。下载完成后，MutableLiveData 对象（出于某种原因）不会收到关于此的通知，即 HashMap 不会 return 返回 MainActivity。

我进行了一些日志检查，发现该方法确实被触发了。然而，系统甚至在下载完成之前就退出该方法。下载确实完成了，是的。但是由于某些原因，它不会 return 将下载的 HashMap 返回到 MainActivity。我认为这可能是因为 Retrofit 提供的入队方法是异步的，并且在后台线程中完成所有任务。

有人可以提供任何关于我如何解决这个问题的提示吗？谢谢！

Answer 1

selectedPokemonModelCall.enqueue 是异步请求。 downloadMainPokemonData.postValue(pokemonHashMap) 在处理 Response<SelectedPokemonModel> 数据之前调用

Retrofit 完成下载我的数据并更新 HashMap 后，MutableLiveData 没有 return HashMap 对象

MutableLiveData doesn't return HashMap object after Retrofit finishes downloading my data and updating the HashMap

java

android

retrofit

android-livedata