Retrofit 和 Simple 的问题 - 尝试为 Android 制作 RSS 阅读器

Question

我正在尝试使用 Retrofit 下载 XML 数据并使用 Simple 对其进行解析，然后将其加载到 ListView 中。

遗憾的是，下载的数据不会出现在屏幕上。谁能告诉我问题出在哪里？

这是我的模型：

@Root(name = "item")
public class Article {
    @Element(name = "title")
    private String title;
    @Element(name = "author")
    private String author;
    @Element(name = "description")
    private String description;

接口代码：

public interface Service {
    @GET("/rss/news")
    public void getArticle(Callback<List<Article>> callback);
}

片段代码：

public class ArticlePreviewFragment extends Fragment {

    protected ArticlePreviewAdapter adapter;
    protected List<Article> previewList;
    private ListView listView;

    public ArticlePreviewFragment() {}

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        previewList = new ArrayList<>();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_article_preview, container, false);
        listView = (ListView) view.findViewById(R.id.previewList);
        return view;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
        adapter = new ArticlePreviewAdapter(getActivity(), previewList);
        listView.setAdapter(adapter);

        RestAdapter restAdapter = new RestAdapter.Builder()
                .setLogLevel(RestAdapter.LogLevel.FULL)
                .setEndpoint("http://muse.mu")
                .setConverter(new SimpleXMLConverter())
                .build();

        Service service = restAdapter.create(Service.class);

        Callback<List<Article>> callback = new Callback<List<Article>>() {
            @Override
            public void success(List<Article> articles, Response response) {
                adapter.clear();
                adapter.addAll(articles);
                adapter.notifyDataSetChanged();
            }

            @Override
            public void failure(RetrofitError error)
        };
        service.getArticle(callback);
    }
}

我正在使用此处找到的转换器 - 我已将其复制到我的项目中 retrofit/converter/SimpleXMLConverter.java

最后，适配器的代码：

public class ArticlePreviewAdapter extends ArrayAdapter<Article> {
    List<Article> articlePreviewItems;
    public ArticlePreviewAdapter(Activity activity, List<Article> articlePreviewItems) {
        super(activity, R.layout.item_article_preview, articlePreviewItems);
        this.articlePreviewItems = articlePreviewItems;
    }

    private static class ViewHolder {
        TextView articlePreviewTitle;
        TextView articlePreviewAuthor;
        TextView articlePreviewDescription;
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        ViewHolder viewHolder;
        Article articlePreviewItem = getItem(position);

        if (convertView == null) {
            viewHolder = new ViewHolder();
            LayoutInflater inflater = LayoutInflater.from(getContext());
            convertView = inflater.inflate(R.layout.item_article_preview, parent, false);
            viewHolder.articlePreviewTitle = (TextView) convertView.findViewById(R.id.articleTitle);
            viewHolder.articlePreviewAuthor = (TextView) convertView.findViewById(R.id.articleAuthor);
            viewHolder.articlePreviewDescription = (TextView) convertView.findViewById(R.id.articleDescription);
            convertView.setTag(viewHolder);
        } else {
            viewHolder = (ViewHolder) convertView.getTag();
        }

        viewHolder.articlePreviewTitle.setText(articlePreviewItem.getTitle());
        viewHolder.articlePreviewAuthor.setText(articlePreviewItem.getAuthor());
        viewHolder.articlePreviewDescription.setText(articlePreviewItem.getDescription());

        return convertView;
    }
}

编辑：我添加了 error.printStackTrace();在失败方法中并在 logcat 中找到：

rss.reader W/System.err﹕ retrofit.RetrofitError: java.lang.ClassCastException: libcore.reflect.ParameterizedTypeImpl cannot be cast to java.lang.Class
rss.reader W/System.err﹕ at retrofit.RestAdapter$RestHandler.invokeRequest(RestAdapter.java:378)
rss.reader W/System.err﹕ at retrofit.RestAdapter$RestHandler.access0(RestAdapter.java:220)
rss.reader W/System.err﹕ at retrofit.RestAdapter$RestHandler.obtainResponse(RestAdapter.java:278)
rss.reader W/System.err﹕ at retrofit.CallbackRunnable.run(CallbackRunnable.java:42)
rss.reader W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
rss.reader W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
rss.reader W/System.err﹕ at retrofit.Platform$Android.run(Platform.java:142)
rss.reader W/System.err﹕ at java.lang.Thread.run(Thread.java:818)
rss.reader W/System.err﹕ Caused by: retrofit.converter.ConversionException: java.lang.ClassCastException: libcore.reflect.ParameterizedTypeImpl cannot be cast to java.lang.Class
rss.reader W/System.err﹕ at rss.reader.SimpleXMLConverter.fromBody(SimpleXMLConverter.java:39)
rss.reader W/System.err﹕ at retrofit.RestAdapter$RestHandler.invokeRequest(RestAdapter.java:362)
rss.reader W/System.err﹕ ... 7 more
rss.reader W/System.err﹕ Caused by: java.lang.ClassCastException: libcore.reflect.ParameterizedTypeImpl cannot be cast to java.lang.Class
rss.reader W/System.err﹕ at rss.reader.SimpleXMLConverter.fromBody(SimpleXMLConverter.java:37)
rss.reader W/System.err﹕ ... 8 more
rss.reader W/System.err﹕ retrofit.RetrofitError: java.lang.ClassCastException: libcore.reflect.ParameterizedTypeImpl cannot be cast to java.lang.Class
rss.reader W/System.err﹕ at retrofit.RestAdapter$RestHandler.invokeRequest(RestAdapter.java:378)
rss.reader W/System.err﹕ at retrofit.RestAdapter$RestHandler.access0(RestAdapter.java:220)
rss.reader W/System.err﹕ at retrofit.RestAdapter$RestHandler.obtainResponse(RestAdapter.java:278)
rss.reader W/System.err﹕ at retrofit.CallbackRunnable.run(CallbackRunnable.java:42)
rss.reader W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
rss.reader W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
rss.reader W/System.err﹕ at retrofit.Platform$Android.run(Platform.java:142)
rss.reader W/System.err﹕ at java.lang.Thread.run(Thread.java:818)
rss.reader W/System.err﹕ Caused by: retrofit.converter.ConversionException: java.lang.ClassCastException: libcore.reflect.ParameterizedTypeImpl cannot be cast to java.lang.Class
rss.reader W/System.err﹕ at rss.reader.SimpleXMLConverter.fromBody(SimpleXMLConverter.java:39)
rss.reader W/System.err﹕ at retrofit.RestAdapter$RestHandler.invokeRequest(RestAdapter.java:362)
rss.reader W/System.err﹕ ... 7 more
rss.reader W/System.err﹕ Caused by: java.lang.ClassCastException: libcore.reflect.ParameterizedTypeImpl cannot be cast to java.lang.Class
rss.reader W/System.err﹕ at rss.reader.SimpleXMLConverter.fromBody(SimpleXMLConverter.java:37)
rss.reader W/System.err﹕ ... 8 more

Answer 1

这是一个 Retrofit 错误。请提交关于项目的 GitHub 问题。

作为目前的解决方法，不要使用泛型类型作为顶级类型。

public final class ArticleList extends ArrayList<Article> {
}

public interface Service {
  @GET("/rss/news")
  public void getArticle(Callback<ArticleList> callback);
}

Answer 2

Jake Wharton 的回答最终使我找到了如下所示的最终解决方案。问题的根源确实在于回调的类型。写错了。

有些人可能会觉得这有帮助顺便说一句； Convert XML or JSON to Java Pojo Classes - Online.

默认情况下，Simple 将元素视为必填字段，并且在定义根元素时是严格的。这个在官网的教程里有提到

RSS.java

@Root(name = "rss", strict = false)
public class RSS {
    @Element
    private Channel channel;
    @Attribute
    private String version;

    public Channel getChannel() {
        return channel;
    }
}

Channel.java

@Root(name = "channel", strict = false)
public class Channel {
    @ElementList(name = "item", inline = true)
    List<Article> articleList;
    @Element
    private String title;
    @Element
    private String link;
    @Element
    private String description;

Article.java

@Root(name = "item", strict = false)
public class Article {
    @Element
    private String title;
    @Element
    private String description;
    @Element
    private String link;
    @Element(required = false)
    private String author;
    @Element(required = false)
    private String pubDate;

Answer 3

我觉得应该在RetroFit网站上明确指出：类型变量禁止在响应类型中使用。

来源：Issue #807 GitHub。

Retrofit 和 Simple 的问题 - 尝试为 Android 制作 RSS 阅读器

Issue with Retrofit and Simple - attempt at making a RSS Reader for Android

java

android

retrofit

simple-framework

rss-reader