我遇到的问题是解析器分配空值但是当检查对象字段时（feed变量）它不是null。代码如下。任何帮助表示赞赏。
导致错误的行是：xpp.setInput（new StringReader（mwordItem.getFeed（）））;
package com.example.wffd;
import android.os.Bundle;
import android.os.AsyncTask;
import android.app.Activity;
import android.view.View;
import android.widget.Button;
import android.widget.TextView;
import android.view.Menu;
import java.io.BufferedInputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.BufferedReader;
import java.io.InputStreamReader;
import java.io.StringReader;
import java.net.URL;
import java.net.HttpURLConnection;
import org.xmlpull.v1.XmlPullParser;
import org.xmlpull.v1.XmlPullParserException;
import org.xmlpull.v1.XmlPullParserFactory;
public class WffdhomeActivity extends Activity {
Button updateButton;
TextView wdTextView, cwTextView;
WordItem myWordItem ;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_wffdhome);
updateButton = (Button)findViewById(R.id.button1);
wdTextView = (TextView)findViewById(R.id.textView2);
cwTextView = (TextView)findViewById(R.id.textView3);
myWordItem= new WordItem();
updateButton.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
try {
URL url = new URL("http://www.dictionary.reference.com/wordoftheday/wotd.rss");
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
new FeedGrab(myWordItem).execute(urlConnection);
update_screen(myWordItem);
cwTextView.setText(myWordItem.getWord());
wdTextView.setText(myWordItem.getDefinition());
} catch (XmlPullParserException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
}
private class FeedGrab extends AsyncTask<HttpURLConnection,Void,Boolean>{
WordItem aWordItem;
public FeedGrab( WordItem mWordItem){
this.aWordItem=mWordItem;
}
protected Boolean doInBackground(HttpURLConnection... urls) {
try {
InputStream in = new BufferedInputStream(urls[0].getInputStream());
aWordItem.setFeed(readStream(in));
}
catch(IOException e)
{
e.printStackTrace();
}
finally {
urls[0].disconnect();
}
return true;
}
private String readStream(InputStream is) throws IOException {
StringBuilder sb = new StringBuilder();
BufferedReader r = new BufferedReader(new InputStreamReader(is),1000);
for (String line = r.readLine(); line != null; line =r.readLine()){
sb.append(line);
}
is.close();
return sb.toString();
}
}
public void update_screen( WordItem mwordItem)throws XmlPullParserException, IOException
{
XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
factory.setNamespaceAware(true);
XmlPullParser xpp = factory.newPullParser();
xpp.setInput( new StringReader ( mwordItem.getFeed()) );
int eventType = xpp.getEventType();
String tag_id="item";
boolean in_item = false,in_description = false;
String tag_def="description";
while (eventType != XmlPullParser.END_DOCUMENT) {
if((eventType == XmlPullParser.START_TAG) )
{
if(tag_id.equalsIgnoreCase(xpp.getName()))
{
in_item = true;
}else if(tag_def.equalsIgnoreCase(xpp.getName()))
{
in_description= true;
}
} else if(eventType == XmlPullParser.END_TAG) {
System.out.println("End tag "+xpp.getName());
} else if((eventType == XmlPullParser.TEXT ) &&(in_description & in_item)) {
mwordItem.processString(xpp.getText());
in_description=false;
in_item = false;
}
eventType = xpp.next();
}
System.out.println("End document");
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.wffdhome, menu);
return true;
}
}
WordItemClass：
package com.example.wffd;
public class WordItem {
private String word;
private String definition;
private String feed;
public String getFeed() {
return feed;
}
public void setFeed(String feed) {
this.feed = feed;
}
public String getWord() {
return word;
}
public void setWord(String word) {
this.word = word;
}
public String getDefinition() {
return definition;
}
public void setDefinition(String definition) {
this.definition = definition;
}
public void processString(String text){
String[] phrase = text.split(":");
this.setWord(phrase[0]);
this.setDefinition(phrase[1]);
}
}
编辑：不确定这是否是堆栈跟踪..但是在这里：
Thread [<1> main] (Suspended (exception NullPointerException))
<VM does not provide monitor information>
WffdhomeActivity.update_screen(WordItem) line: 110
WffdhomeActivity$1.onClick(View) line: 51
Button(View).performClick() line: 4204
View$PerformClick.run() line: 17355
Handler.handleCallback(Message) line: 725
ViewRootImpl$ViewRootHandler(Handler).dispatchMessage(Message) line: 92
Looper.loop() line: 137
ActivityThread.main(String[]) line: 5041
Method.invokeNative(Object, Object[], Class, Class[], Class, int, boolean) line: not available [native method]
Method.invoke(Object, Object...) line: 511
ZygoteInit$MethodAndArgsCaller.run() line: 793
ZygoteInit.main(String[]) line: 560
**更新：使用调试器mwordItem.getfeed（）返回null但feed字符串包含数据。不知道这里发生了什么
**更新@andy256：我认为使用aWordItem作为对myWordItem的引用并修改feed变量我已经解决了这个问题显然这不是我所做的。如何从异步线程传递值？我尝试通过onpostexecute传递值但没有成功。
protected void onPostExecute（WordItem result）{
this.aWordItem=result;
return;
}
答案 0 :(得分：1)
堆栈跟踪显示
WffdhomeActivity.update_screen（WordItem）行：110
WffdhomeActivity $ 1.onClick（查看）行：51
第110行的内容是null：
xpp.setInput( new StringReader ( mwordItem.getFeed()) );
由于似乎设置了xpp，请查看mwordItem。它来自第51行的调用，其中myWordItem被传递。在发布的代码中，永远不会设置myWordItem。
因此，根据您发布的代码：myWordItem为null。