NullPointerException异常Android中的RSS应用 [英] NullPointerException in Android RSS app
本文介绍了NullPointerException异常Android中的RSS应用的处理方法，对大家解决问题具有一定的参考价值，需要的朋友们下面随着小编来一起学习吧！
问题描述
我想建立一个Android RSS阅读器应用程序，但我不断收到一个空指针异常。我是新来的Java，如果它的饲料网址不返回任何数据或数据不被妥善保存也说不清。
I'm trying to build an android RSS reader app but I keep getting a Null pointer exception. I'm new to java and can't tell if its the feed url not returning any data or the data not being stored properly.
我logcat的内容如下：
my logcat reads:
08-08 18:44:25.840: E/Trace(621): error opening trace file: No such file or directory (2)
08-08 18:44:25.910: W/ActivityThread(621): Application com.app.fullmetalmanga is waiting for the debugger on port 8100...
08-08 18:44:25.930: I/System.out(621): Sending WAIT chunk
08-08 18:44:25.951: I/dalvikvm(621): Debugger is active08-08 18:44:26.140: I/System.out(621): Debugger has connected
08-08 18:44:27.710: I/System.out(621): debugger has settled (1382)
08-08 18:44:29.291: D/gralloc_goldfish(621): Emulator without GPU emulation detected.
08-08 18:44:48.060: W/System.err(621): java.lang.NullPointerException
08-08 18:44:48.760: W/System.err(621): at java.util.Calendar.setTime(Calendar.java:1324)
08-08 18:44:48.810: W/System.err(621): at java.text.SimpleDateFormat.formatImpl(SimpleDateFormat.java:536)
08-08 18:44:49.050: W/System.err(621): at java.text.SimpleDateFormat.format(SimpleDateFormat.java:821)
08-08 18:44:49.150: W/System.err(621): at java.text.DateFormat.format(DateFormat.java:376)
08-08 18:44:49.490: W/System.err(621): at com.app.fullmetalmanga.RssItem.getDate(RssItem.java:48)
08-08 18:44:49.810: W/System.err(621): at com.app.fullmetalmanga.MainActivity$RSSHandler.endElement(MainActivity.java:146)
08-08 18:44:50.090: W/System.err(621): at org.apache.harmony.xml.ExpatParser.endElement(ExpatParser.java:156)
08-08 18:44:50.250: W/System.err(621): at org.apache.harmony.xml.ExpatParser.appendBytes(Native Method)
08-08 18:44:50.410: W/System.err(621): at org.apache.harmony.xml.ExpatParser.parseFragment(ExpatParser.java:513)
08-08 18:44:50.610: W/System.err(621): at org.apache.harmony.xml.ExpatParser.parseDocument(ExpatParser.java:474)
08-08 18:44:50.791: W/System.err(621): at org.apache.harmony.xml.ExpatReader.parse(ExpatReader.java:321)
08-08 18:44:50.990: W/System.err(621): at org.apache.harmony.xml.ExpatReader.parse(ExpatReader.java:279)
08-08 18:44:51.800: W/System.err(621): at com.app.fullmetalmanga.MainActivity$SAXHelper.parseContent(MainActivity.java:112)
08-08 18:44:51.870: W/System.err(621): at com.app.fullmetalmanga.MainActivity$loadingTask.doInBackground(MainActivity.java:74)
08-08 18:44:52.350: W/System.err(621): at com.app.fullmetalmanga.MainActivity$loadingTask.doInBackground(MainActivity.java:1)
08-08 18:44:52.700: W/System.err(621): at android.os.AsyncTask$2.call(AsyncTask.java:287)
08-08 18:44:53.070: W/System.err(621): at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:305)
08-08 18:44:53.190: W/System.err(621): at java.util.concurrent.FutureTask.run(FutureTask.java:137)
08-08 18:44:53.370: W/System.err(621): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
08-08 18:44:53.561: W/System.err(621): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1076)
08-08 18:44:53.980: W/System.err(621): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:569)
08-08 18:44:54.051: W/System.err(621): at java.lang.Thread.run(Thread.java:856)
和我的主要活动：
public class MainActivity extends Activity {
/** Called when the activity is first created. */
ListView lv1;
ProgressDialog ShowProgress;
public ArrayList<RssItem> RssItemList = new ArrayList<RssItem>();
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
lv1 = (ListView) findViewById(R.id.listView1);
ShowProgress = ProgressDialog.show(MainActivity.this, "",
"Loading. Please wait...", true);
new loadingTask().execute("http://fandom.com/rss/news/manga");
lv1.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
Intent intent = new Intent(Intent.ACTION_VIEW).setData(Uri
.parse(RssItemList.get(position).getTitle()));
startActivity(intent);
}
});
}
class loadingTask extends AsyncTask<String, Void, String> {
protected String doInBackground(String... urls) {
SAXHelper sh = null;
try {
sh = new SAXHelper(urls[0]);
} catch (MalformedURLException e) {
e.printStackTrace();
}
sh.parseContent("");
return "";
}
protected void onPostExecute(String s) {
lv1.setAdapter(new EfficientAdapter(MainActivity.this, RssItemList));
ShowProgress.dismiss();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.activity_main, menu);
return true;
}
class SAXHelper {
public HashMap<String, String> userList = new HashMap<String, String>();
private URL url2;
public SAXHelper(String url1) throws MalformedURLException {
this.url2 = new URL(url1);
}
public RSSHandler parseContent(String parseContent) {
RSSHandler df = new RSSHandler();
try {
SAXParserFactory spf = SAXParserFactory.newInstance();
SAXParser sp = spf.newSAXParser();
XMLReader xr = sp.getXMLReader();
xr.setContentHandler(df);
xr.parse(new InputSource(url2.openStream()));
} catch (Exception e) {
e.printStackTrace();
}
return df;
}
}
class RSSHandler extends DefaultHandler {
private RssItem currentPost = new RssItem();
StringBuffer chars = new StringBuffer();
@Override
public void startElement(String uri, String localName, String qName,
Attributes atts) {
chars = new StringBuffer();
if (localName.equalsIgnoreCase("item")) {
}
}
@Override
public void endElement(String uri, String localName, String qName)
throws SAXException {
if (localName.equalsIgnoreCase("title")
&& currentPost.getTitle() == null) {
currentPost.setTitle(chars.toString());
}
if (localName.equalsIgnoreCase("pubDate")
&& currentPost.getDate() == null) {
currentPost.setDate(chars.toString());
}
/*if (localName.equalsIgnoreCase("thumbnail")
&& currentPost.getThumbnail() == null) {
currentPost.setThumbnail(chars.toString());
} */
if (localName.equalsIgnoreCase("link")
&& currentPost.getLink() == null) {
currentPost.setLink(chars.toString());
}
if (localName.equalsIgnoreCase("item")) {
RssItemList.add(currentPost);
currentPost = new RssItem();
}
}
@Override
public void characters(char ch[], int start, int length) {
chars.append(new String(ch, start, length));
}
}
}
我的RSSItem类：
My RssItem Class:
public class RssItem {
static SimpleDateFormat FORMATTER =
new SimpleDateFormat("EEE, dd MMM yyyy HH:mm:ss Z");
private String title;
private URL link;
private String description;
private Date date;
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title.trim();
}
// getters and setters omitted for brevity
public URL getLink() {
return link;
}
public void setLink(String link) {
try {
this.link = new URL(link);
} catch (MalformedURLException e) {
throw new RuntimeException(e);
}
}
public String getDescription() {
return description;
}
public void setDescription(String description) {
this.description = description.trim();
}
public String getDate() {
return FORMATTER.format(this.date);
}
public void setDate(String date) {
// pad the date if necessary
while (!date.endsWith("00")){
date += "0";
}
try {
this.date = FORMATTER.parse(date.trim());
} catch (ParseException e) {
throw new RuntimeException(e);
}
}
}
我的code，采用的这个的例子。只改变URL，并用自己改装邮报的文件。 （改名的RSSItem）
My code was made using this example. Changing only the URL and using my own modified "Post" file. (Renamed RssItem)
推荐答案
看来，日期中的RSSItem在空，当你把它传递给你的SimpleDateFormat引发异常
It appears that date in RssItem in null, when you pass it to your SimpleDateFormat the exception is thrown:
public String getDate() {
return FORMATTER.format(this.date); // FORMATTER cannot format a null value
}
您需要定义一个默认的日期或处理这种礼貌的其他方式：
You need to define a default date or other polite method of handling this:
public String getDate() {
if(this.date == null)
return "";
return FORMATTER.format(this.date);
}
这篇关于NullPointerException异常Android中的RSS应用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
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