java - 未从 IGDB 收到 Cover 数据

Question

我花了几周时间努力使用改造从 IGDB API 获取数据。我正在尝试获取游戏封面的 URL，并希望使用 fragment 将其显示在 GridLayout 中。但我收到“尝试在空对象引用上调用虚拟方法”。有人可以看一下我的代码并看看我缺少什么吗？提前致谢!

游戏.java:

import java.util.List;
import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Game {

    @SerializedName("id")
    @Expose
    private Integer id;
    @SerializedName("cover")
    @Expose
    private Cover cover;
    @SerializedName("name")
    @Expose
    private String name;
    @SerializedName("popularity")
    @Expose
    private Double popularity;
    @SerializedName("summary")
    @Expose
    private String summary;
    @SerializedName("genres")
    @Expose
    private List<Genre> genres = null;
    @SerializedName("platforms")
    @Expose
    private List<Platform> platforms = null;
    @SerializedName("rating")
    @Expose
    private Double rating;
    @SerializedName("release_dates")
    @Expose
    private List<ReleaseDate> releaseDates = null;
    @SerializedName("videos")
    @Expose
    private List<Video> videos = null;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public Cover getCover() {
        return cover;
    }

    public void setCover(Cover cover) {
        this.cover = cover;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Double getPopularity() {
        return popularity;
    }

    public void setPopularity(Double popularity) {
        this.popularity = popularity;
    }

    public String getSummary() {
        return summary;
    }

    public void setSummary(String summary) {
        this.summary = summary;
    }

    public List<Genre> getGenres() {
        return genres;
    }

    public void setGenres(List<Genre> genres) {
        this.genres = genres;
    }

    public List<Platform> getPlatforms() {
        return platforms;
    }

    public void setPlatforms(List<Platform> platforms) {
        this.platforms = platforms;
    }

    public Double getRating() {
        return rating;
    }

    public void setRating(Double rating) {
        this.rating = rating;
    }

    public List<ReleaseDate> getReleaseDates() {
        return releaseDates;
    }

    public void setReleaseDates(List<ReleaseDate> releaseDates) {
        this.releaseDates = releaseDates;
    }

    public List<Video> getVideos() {
        return videos;
    }

    public void setVideos(List<Video> videos) {
        this.videos = videos;
    }

}

封面.java:

import com.google.gson.annotations.Expose;
import com.google.gson.annotations.SerializedName;

public class Cover {

    @SerializedName("id")
    @Expose
    private Integer id;
    @SerializedName("url")
    @Expose
    private String url;

    public Integer getId() {
        return id;
    }

    public void setId(Integer id) {
        this.id = id;
    }

    public String getUrl() {
        return url;
    }

    public void setUrl(String url) {
        this.url = url;
    }

}

GameAdapter.java

import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;

import androidx.annotation.NonNull;
import androidx.recyclerview.widget.RecyclerView;

import com.riceplant.capstoneproject.R;
import com.riceplant.capstoneproject.data.Game;
import com.squareup.picasso.Picasso;

import java.util.ArrayList;

public class GameAdapter extends RecyclerView.Adapter<GameAdapter.GameAdapterViewHolder> {

    private ArrayList<Game> mGameData;
    private Context mContext;

    public GameAdapter(Context context, ArrayList<Game> gameData) {
        mContext = context;
        mGameData = gameData;
    }

    public class GameAdapterViewHolder extends RecyclerView.ViewHolder {
        ImageView mGameCover;

        public GameAdapterViewHolder(@NonNull View itemView) {
            super(itemView);
            mGameCover = itemView.findViewById(R.id.game_cover_image);
        }
    }

    @NonNull
    @Override
    public GameAdapterViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        Context context = parent.getContext();
        int layoutIdForListItem = R.layout.game_list_item;
        LayoutInflater layoutInflater = LayoutInflater.from(context);

        View view = layoutInflater.inflate(layoutIdForListItem, parent, false);
        return new GameAdapterViewHolder(view);
    }

    @Override
    public void onBindViewHolder(@NonNull GameAdapterViewHolder holder, int position) {
        String currentGame = mGameData.get(position).getCover().getUrl();
        Picasso.get()
                .load(currentGame)
                .placeholder(R.drawable.image_loading)
                .error(R.drawable.image_not_found)
                .into(holder.mGameCover);
    }
    @Override
    public int getItemCount() {
        if (mGameData == null) {
            return 0;
        }
        return mGameData.size();
    }

}

PopularGamesFragment.java

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;
import androidx.recyclerview.widget.GridLayoutManager;
import androidx.recyclerview.widget.RecyclerView;

import com.riceplant.capstoneproject.R;
import com.riceplant.capstoneproject.adapter.GameAdapter;
import com.riceplant.capstoneproject.data.Game;
import com.riceplant.capstoneproject.network.GameInstance;
import com.riceplant.capstoneproject.network.GetDataService;

import java.util.ArrayList;
import java.util.List;

import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;

public class PopularGamesFragment extends Fragment {
    private RecyclerView mRecyclerView;
    private TextView mErrorTextMessage;

    private GameAdapter mGameAdapter;

    public static final String FIELDS = "fields name, platforms.name, cover.url, rating, release_dates.human, genres.name, summary, popularity, time_to_beat, videos.name, videos.video_id;";

    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_popular_games, container, false);

        GetDataService service = GameInstance.getGameInstance().create(GetDataService.class);
        Call<ArrayList<Game>> call = service.getAllGames(FIELDS);
        call.enqueue(new Callback<ArrayList<Game>>() {
            @Override
            public void onResponse(Call<ArrayList<Game>> call, Response<ArrayList<Game>> response) {
                mRecyclerView = view.findViewById(R.id.recycler_view);
                generateDataList(response.body());
            }

            @Override
            public void onFailure(Call<ArrayList<Game>> call, Throwable t) {
                mErrorTextMessage = view.findViewById(R.id.popular_games_error_message);
                mErrorTextMessage.setText("Something went wrong. Try again!");
            }
        });

        return view;
    }

    private void generateDataList(ArrayList<Game> gameList) {
        mGameAdapter = new GameAdapter(getActivity(), gameList);

        GridLayoutManager gridLayoutManager = new GridLayoutManager(getActivity(), 2);
        mRecyclerView.setLayoutManager(gridLayoutManager);
        mRecyclerView.setHasFixedSize(true);
        mRecyclerView.setAdapter(mGameAdapter);
    }

}

GameInstance.java

import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

public class GameInstance {

    private static Retrofit retrofit;
    public static final String BASE_URL = "https://api-v3.igdb.com/";

    public static Retrofit getGameInstance() {
        if (retrofit == null) {
            retrofit = new retrofit2.Retrofit.Builder()
                    .baseUrl(BASE_URL)
                    .addConverterFactory(GsonConverterFactory.create())
                    .build();

        }
        return retrofit;
    }
}

获取数据服务

import com.riceplant.capstoneproject.data.Game;

import java.util.ArrayList;

import retrofit2.Call;
import retrofit2.http.Body;
import retrofit2.http.Headers;
import retrofit2.http.POST;

public interface GetDataService {

    @Headers("user-key: 0d22adeb6cf3650dbefe7f8214537075")
    @POST("games")
    Call<ArrayList<Game>> getAllGames(@Body String fields);
}

堆栈跟踪:

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.riceplant.capstoneproject, PID: 9882
    java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String com.riceplant.capstoneproject.data.Cover.getUrl()' on a null object reference
        at com.riceplant.capstoneproject.adapter.GameAdapter.onBindViewHolder(GameAdapter.java:51)
        at com.riceplant.capstoneproject.adapter.GameAdapter.onBindViewHolder(GameAdapter.java:19)
        at androidx.recyclerview.widget.RecyclerView$Adapter.onBindViewHolder(RecyclerView.java:7065)
        at androidx.recyclerview.widget.RecyclerView$Adapter.bindViewHolder(RecyclerView.java:7107)
        at androidx.recyclerview.widget.RecyclerView$Recycler.tryBindViewHolderByDeadline(RecyclerView.java:6012)
        at androidx.recyclerview.widget.RecyclerView$Recycler.tryGetViewHolderForPositionByDeadline(RecyclerView.java:6279)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6118)
        at androidx.recyclerview.widget.RecyclerView$Recycler.getViewForPosition(RecyclerView.java:6114)
        at androidx.recyclerview.widget.LinearLayoutManager$LayoutState.next(LinearLayoutManager.java:2303)
        at androidx.recyclerview.widget.GridLayoutManager.layoutChunk(GridLayoutManager.java:561)
        at androidx.recyclerview.widget.LinearLayoutManager.fill(LinearLayoutManager.java:1587)
        at androidx.recyclerview.widget.LinearLayoutManager.onLayoutChildren(LinearLayoutManager.java:665)
        at androidx.recyclerview.widget.GridLayoutManager.onLayoutChildren(GridLayoutManager.java:170)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep2(RecyclerView.java:4134)
        at androidx.recyclerview.widget.RecyclerView.onMeasure(RecyclerView.java:3540)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
        at android.view.View.measure(View.java:24530)
        at androidx.viewpager.widget.ViewPager.onMeasure(ViewPager.java:1638)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at androidx.appcompat.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:143)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1552)
        at android.widget.LinearLayout.measureVertical(LinearLayout.java:842)
        at android.widget.LinearLayout.onMeasure(LinearLayout.java:721)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6828)
        at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
        at com.android.internal.policy.DecorView.onMeasure(DecorView.java:742)
        at android.view.View.measure(View.java:24530)
        at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:3006)
E/AndroidRuntime:     at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1833)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2122)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1721)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7598)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:966)
        at android.view.Choreographer.doCallbacks(Choreographer.java:790)
        at android.view.Choreographer.doFrame(Choreographer.java:725)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:951)
        at android.os.Handler.handleCallback(Handler.java:883)
        at android.os.Handler.dispatchMessage(Handler.java:100)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7356)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
I/Process: Sending signal. PID: 9882 SIG: 9

Answer 1

您的 API 调用正确。但响应数组中很少有对象不具有所有必需的字段或对象。

例如:响应中的以下对象没有流派和封面。{ “身份证”:91579， "name": "赛车直播", 「人气」:1.0 }

在这种情况下，您的代码将抛出 NullPointerException。

要解决此问题，请更新 GameAdapter 类中 onBindViewHolder 方法的代码。

  @Override
    public void onBindViewHolder(@NonNull GameAdapterViewHolder holder, int position) {
        Cover cover = mGameData.get(position).getCover()
        String currentGame = null 
        if(cover!=null)
           currentGame = cover.getUrl();
        Picasso.get()
                .load(currentGame)
                .placeholder(R.drawable.image_loading)
                .error(R.drawable.image_not_found)
                .into(holder.mGameCover);
    }