Question

我试图使用ROME Feed Reader在Android 4.1上制作新闻阅读器。但是，当我的应用尝试拨打新闻源时，我一直收到错误消息。我一直在忙着实现Asynctask，因为4.1不允许我在主线程上检索rss-feeds。

ERROR/AndroidRuntime(27669): FATAL EXCEPTION: main
        java.lang.RuntimeException: Unable to start activity ComponentInfo{com.google.cloud.backend.android/com.google.cloud.backend.android.FeedActivity}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
        at android.app.ActivityThread.access$700(ActivityThread.java:140)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4921)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
        at dalvik.system.NativeStart.main(Native Method)
        Caused by: java.lang.NullPointerException
        at com.google.cloud.backend.android.FeedListAdapter.getCount(FeedListAdapter.java:32)
        at android.widget.ListView.setAdapter(ListView.java:466)
        at com.google.cloud.backend.android.FeedActivity.createList(FeedActivity.java:34)
        at com.google.cloud.backend.android.FeedActivity.onCreate(FeedActivity.java:17)
        at android.app.Activity.performCreate(Activity.java:5206)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1094)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2074)

这是我的代码（部分）：

public class FeedListAdapter extends BaseAdapter
{
    private SyndFeed feed;
    private Activity context;

    public FeedListAdapter( Activity context )
    {
        this.context = context;
        String feedUrl = context.getIntent().getExtras().getString("Feed");
        new FeedRetrieval().execute(feedUrl);
    }

    public int getCount()
    {
        return feed.getEntries().size();
    }

    ... (shortened)

    private class FeedRetrieval extends AsyncTask<String, Integer, String>
    {
        @Override
        protected String doInBackground(String... params) {
            RssAtomFeedRetriever feedRetriever = new RssAtomFeedRetriever();
            feed = feedRetriever.getMostRecentNews(params[0]);
            return null;
        }
    }

修改：我已将getCount（）更改为：

if (feed != null) {
    return feed.getEntries().size();
}
return 0;

但现在我明白了：

07-28 01:14:34.182: ERROR/AndroidRuntime(29175): FATAL EXCEPTION: AsyncTask #1
07-28 01:14:34.242: ERROR/android.os.Debug(433): !@Dumpstate > dumpstate -k -t -z -d -o /data/log/dumpstate_app_error

Logcat没有显示导致AsyncTask失败的原因。这对我来说更不合理:(

Answer 1

feed变量为null，直到AsyncTask完成执行。如果您在完成之前致电getCount，它会尝试访问feed，当时为null。

返回默认值或提供检查数据是否实际存在的方法。

Answer 2

解决方案：我知道了。该示例托管在我的GitHub上：https://github.com/praetore/AndroidROMEFeedReader

使用ROME feedreader的问题

2 个答案: