Java – Problems with Retrofit and Simple – Try making an RSS reader for Android

Problems with Retrofit and Simple – Try making an RSS reader for Android… here is a solution to the problem.

Problems with Retrofit and Simple – Try making an RSS reader for Android

I’m trying to use Retrofit to download XML data and parse it with Simple and load it into a ListView.

Unfortunately, the downloaded data does not appear on the screen. Can anyone tell me what the problem is?

Here is my model:

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

Interface code:

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

fragment code:

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);
    }
}

I’m using the converter found here – I’ve copied it into my project retrofit/converter/SimpleXMLConverter.java

Finally, the code for the adapter:

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;
    }
}

Edit:
I added error.printStackTrace(); In the failed method, find in logcat:

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.access$100(RestAdapter.java:220)
rss.reader W/System.err﹕ at retrofit. RestAdapter$RestHandler$2.obtainResponse(RestAdapter.java:278)
rss.reader W/System.err﹕ at retrofit. CallbackRunnable.run(CallbackRunnable.java:42)
rss.reader W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
rss.reader W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
rss.reader W/System.err﹕ at retrofit. Platform$Android$2$1.run(Platform.java:142)
rss.reader W/System.err﹕ at java.lang.Thread.run(Thread.java:818)
rss.reader W/System.err﹕ Caused by: retrofit.converter.ConversionException: java.lang.ClassCastException: libcore.reflect.ParameterizedTypeImpl cannot be cast to java.lang.Class
rss.reader W/System.err﹕ at rss.reader.SimpleXMLConverter.fromBody(SimpleXMLConverter.java:39)
rss.reader W/System.err﹕ at retrofit. RestAdapter$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.access$100(RestAdapter.java:220)
rss.reader W/System.err﹕ at retrofit. RestAdapter$RestHandler$2.obtainResponse(RestAdapter.java:278)
rss.reader W/System.err﹕ at retrofit. CallbackRunnable.run(CallbackRunnable.java:42)
rss.reader W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1112)
rss.reader W/System.err﹕ at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:587)
rss.reader W/System.err﹕ at retrofit. Platform$Android$2$1.run(Platform.java:142)
rss.reader W/System.err﹕ at java.lang.Thread.run(Thread.java:818)
rss.reader W/System.err﹕ Caused by: retrofit.converter.ConversionException: java.lang.ClassCastException: libcore.reflect.ParameterizedTypeImpl cannot be cast to java.lang.Class
rss.reader W/System.err﹕ at rss.reader.SimpleXMLConverter.fromBody(SimpleXMLConverter.java:39)
rss.reader W/System.err﹕ at retrofit. RestAdapter$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

Solution

This is a Retrofit bug. Please submit a GitHub issue about the project.

As a workaround for now, do not use generic types as top-level types.

public final class ArticleList extends ArrayList<Article> {
}

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

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