Retrofit 对象返回为 null

Question

我已经为 return 一些对象构建了 RetroFitService。在 MainActivity 中，我只需单击一下按钮即可调用该服务。我似乎得到了某种对象，但我不觉得它实际上是从我指定的 REST API 中 return 编辑的。它显示在调试器中，但其属性为空：

bFetch.setOnClickListener(v -> {
 v.startAnimation(AnimationUtils.loadAnimation(this, R.anim.image_click));
 RetrofitService service = ServiceFactory.createRetrofitService(RetrofitService.class, RetrofitService.SERVICE_ENDPOINT);
 service.getPosts()
 .subscribeOn(Schedulers.newThread())
 .observeOn(AndroidSchedulers.mainThread())
 .subscribe(new Subscriber < Post > () {
  @Override
  public final void onCompleted() {
   Log.e("RetrofitService", "Retrofit Request Completed!");
  }

  @Override
  public final void onError(Throwable e) {
   Log.e("RetrofitService", e.getMessage());
  }

  @Override
  public final void onNext(Post post) {
   if (post != null) {
    // TODO: Some object is returned but its properties are null
    Log.e("RetrofitService", "Returned objects: " + post);
    Log.e("RetrofitService", "Object Id: " + post.getObjectId());
    mCardAdapter.addData(post);
   } else {
    Log.e("RetrofitService", "Object returned is null.");
   }

  }

 });

});

}

服务：

public interface RetrofitService {

 String SERVICE_ENDPOINT = "https://parseapi.back4app.com/";

 @Headers({
  "X-Parse-Application-Id: asdf",
  "X-Parse-REST-API-Key: asdf"
 })
 @GET("/classes/Post")
 Observable < Post > getPosts();

 /*curl -X GET \
         -H "X-Parse-Application-Id: asdf" \
         -H "X-Parse-REST-API-Key: asdf" \
 https://parseapi.back4app.com/classes/Post*/

}

卷曲效果很好。我没有收到任何错误。可能出了什么问题？是不是我的 @GET 方法不正确？`

为了完成，这里是 ServiceFactory class:

public class ServiceFactory {

    /**
     * Creates a retrofit service from an arbitrary class (clazz)
     * @param clazz Java interface of the retrofit service
     * @param endPoint REST endpoint url
     * @return retrofit service with defined endpoint
     */
    public static <T> T createRetrofitService(final Class<T> clazz, final String endPoint) {
        final RestAdapter restAdapter = new RestAdapter.Builder()
                .setEndpoint(endPoint)
                .build();
        T service = restAdapter.create(clazz);

        return service;
    }
}

还有我的 build.gradle 因为我知道所有不同的 Retrofit 版本都存在不一致：

dependencies {

    compile fileTree(dir: 'libs', include: ['*.jar'])
    androidTestCompile('com.android.support.test.espresso:espresso-core:2.2.2', {
        exclude group: 'com.android.support', module: 'support-annotations'
    })
    compile 'com.android.support:appcompat-v7:25.3.1'
    compile 'com.android.support.constraint:constraint-layout:1.0.2'
    testCompile 'junit:junit:4.12'

    /* ReactiveX */
    compile 'io.reactivex:rxjava:1.0.17'
    compile 'io.reactivex:rxandroid:0.23.0'

    /* Retrofit */
    compile 'com.squareup.retrofit:retrofit:1.9.0'

    /* OkHttp3 */
    compile 'com.squareup.okhttp3:okhttp:3.8.1'

    /* RecylerView */
    compile 'com.android.support:recyclerview-v7:25.3.1'

    /* CardView */
    compile 'com.android.support:cardview-v7:25.3.1'

    /* Parse */
    compile 'com.parse:parse-android:1.13.0'

}

Post Class:

public class Post implements Serializable {

    private static final String CLASS_NAME = "Post";

    private String objectId;
    private String text;

    public Post(String objectId) {
        this.setObjectId(objectId);
    }

    public static String getClassName() {
        return CLASS_NAME;
    }

    public String getObjectId() {
        return objectId;
    }

    private void setObjectId(String objectId) {
        this.objectId = objectId;
    }

    public String getText() {
        return text;
    }

    public void setText(String text) {
        this.text = text;
    }

卷曲响应：

>     https://parseapi.back4app.com/classes/Post/
  % Total    % Received % Xferd  Average Speed   Time    Time     Time  Current
                                 Dload  Upload   Total   Spent    Left  Speed
100   259  100   259    0     0    360      0 --:--:-- --:--:-- --:--:--   395{"results":[{"objectId":"ktEfgr1pFt","text":"Hello World.","createdAt":"2017-08-14T14:07:52.826Z","updatedAt":"2017-08-14T14:07:52.826Z"},{"objectId":"Mmh8l9gjCk","text":"Hello?","createdAt":"2017-08-14T15:19:01.515Z","updatedAt":"2017-08-14T15:19:03.743Z"}]}

最终更新： 我更改了 RetrofitService 的 onNext() 方法以传递到 CardAdapter，尽管此处未显示并且超过了问题的范围。

@Override
public final void onNext(PostResponse postResponse) {
 if (postResponse != null) {
  // TODO: Some object is returned but its properties are null
  Log.e("RetrofitService", "Objects successfully added to RecyclerView Adapter.");
  Log.e("RetrofitService", "Returned objects: " + postResponse.getResults());
  Log.e("RetrofitService", "Text " + postResponse.getResults().get(0).getText());

  mCardAdapter.addData(postResponse);
  //
 } else {
  Log.e("RetrofitService", "Object returned is null.");
 }

}

Answer 1

尝试在RetrofitService

中使用以下class

@GET("/classes/Post")
Observable <PostResponse> getPosts();

PostResponse 包装器 class

public class PostResponse {
    private List<Post> results;

    public List<Post> getResults() {
        return results;
    }

    public void setResults(List<Post> results) {
        this.results = results;
    }
}

Answer 2

根据您问题的更新，您收到的不是单个对象，而是包含 Post 个对象集合的对象。

所以你需要再加一个class:

public class Results {
   List<Post> results = ArrayList<>()
}

然后将你的API接口方法更新为return Observable<Results>:

Observable <Results> getPosts();

在订阅中，您最终可以使用 results 字段访问 Result 对象，其中包含 Post 个对象的集合。

一个小错误是你的端点基础 URL 有尾部斜杠：

String SERVICE_ENDPOINT = "https://parseapi.back4app.com/";

同时你的 API 方法在路径的开头有斜杠：

 @GET("/classes/Post")
 Observable < Post > getPosts();

据我所知 进行改造时，您应该在端点地址中使用尾部斜线或在 API 方法中使用起始斜线，否则这可能无法正常工作。

这个应该是正确的：

String SERVICE_ENDPOINT = "https://parseapi.back4app.com"; // No slash here
@GET("/classes/Post") // Keep slash here, or vice verse
Observable<Results> getPosts();

只是对您的依赖项部分的一些评论：

您使用 io.reactivex:rxandroid 版本 0.23.0 而最新稳定版是 1.2.1 是否有任何特殊原因？

你不需要 io.reactivex:rxjava:1.0.17 依赖，因为 retrofit 1.9.0 已经依赖 rxjava 1.0.0

Retrofit 对象返回为 null

Retrofit object returned as null

java

android

rx-java

retrofit

rx-android