我正在尝试在此类中实现异步任务，但事实是我正在程序中调用getInputStream函数，该函数返回一个值，并且我不确定将其放在何处。在异步任务中应在哪里定义getInputStream？
我收到以下异常
FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity com.sparkplug.xxxx}: java.lang.NullPointerException
以下是我的主要课程：
public class abcreaderextends ListActivity {
ArrayList<HashMap<String, String>> menuItems = new ArrayList<HashMap<String, String>>();
parsing p=new parsing();
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_awsreader);
((PullToRefreshListView) getListView())
.setOnRefreshListener(new OnRefreshListener() {
public void onRefresh() {
// Do work to refresh the list here.
new GetDataTask().execute();
}
});
InputStreamOperation in= new InputStreamOperation();
in.execute();
//p.parse();
for (int i = 0; i < p.headlines.size(); i++) {
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
// adding each child node to HashMap key => value
map.put("title", p.headlines.get(i));
map.put("dcdate", p.lstDate.get(i));
map.put("description", p.description.get(i));
// adding HashList to ArrayList
menuItems.add(map);
}
ListAdapter rssFeedSection = new SimpleAdapter(this, menuItems,
R.layout.list_item, new String[] { "title", "dcdate",
"description" }, new int[] { R.id.name, R.id.date1,
R.id.desc });
setListAdapter(rssFeedSection);
}
class GetDataTask extends AsyncTask<Void, Void, String[]> {
@Override
protected void onPostExecute(String[] result) {
// **menuItems.addFirst("Added after refresh...");
// Call onRefreshComplete when the list has been refreshed.
((PullToRefreshListView) getListView()).onRefreshComplete();
super.onPostExecute(result);
}
@Override
protected String[] doInBackground(Void... params) {
// TODO Auto-generated method stub
return null;
}
}
@Override
protected void onListItemClick(ListView l, View v, int position, long id) {
Uri uri = Uri.parse((String) p.links.get(position));
Intent intent = new Intent(Intent.ACTION_VIEW, uri);
startActivity(intent);
}
}
这是我的解析类：
公共类解析{
列出标题；
列出链接；
清单说明；
列出lstDate;
列出newDate;
//字符串a，b，c，d;
public InputStream getInputStream（URL url）{
尝试{
返回url.openConnection（）。getInputStream（）;
} catch（IOException e）{
返回null;
}
}
public HashMap<String, ArrayList<String>> parse() {
// Initializing instance variables
headlines = new ArrayList<String>();
links = new ArrayList<String>();
description = new ArrayList<String>();
lstDate = new ArrayList<String>();
try {
URL url = new URL(
"http://feeds.feedburner.com/xxxx");
XmlPullParserFactory factory = XmlPullParserFactory.newInstance();
factory.setNamespaceAware(false);
XmlPullParser xpp = factory.newPullParser();
// We will get the XML from an input stream
xpp.setInput(getInputStream(url), "UTF_8");
int i = 0;
boolean insideItem = false;
// Returns the type of current event: START_TAG, END_TAG, etc..
int eventType = xpp.getEventType();
int k = 0;
while (eventType != XmlPullParser.END_DOCUMENT) {
i++;
// Log.i("Tag : ",xpp.getName().toString());
// Log.i("Text : ",xpp.nextText().toString());
if (eventType == XmlPullParser.START_TAG) {
Log.i("Tag : ", xpp.getName().toString());
// Log.i("Text : ",xpp.nextText().toString());
if (xpp.getName().equalsIgnoreCase("item")) {
insideItem = true;
} else if (xpp.getName().equalsIgnoreCase("title")) {
if (insideItem) {
String var = xpp.nextText().toString();
headlines.add(var); // extract the description of
// article
Log.i("Title : ", var);
// Log.i("Count : ",i+"");
}
} else if (xpp.getName().equalsIgnoreCase("description")) {
if (insideItem) {
String desc = xpp.nextText().toString();
description.add(desc); // extract the description of
// article
Log.i("Desc : ", desc);
}
} else if (xpp.getName().equalsIgnoreCase("dc:date")) {
if (insideItem) {
String strDate = xpp.nextText().toString();
System.out.println("rahul"+strDate.substring(0,10));
//lstDate = Arrays.asList(arr[k].substring(0,10));
lstDate.add(strDate.substring(0,10));
System.out.println("lstDate"+lstDate);
k = k+1;
Log.i("Date : ", strDate);
}
} else if (xpp.getName().equalsIgnoreCase("link")) {
if (insideItem)
links.add(xpp.nextText()); // extract the link of
// article
}
} else if (eventType == XmlPullParser.END_TAG
&& xpp.getName().equalsIgnoreCase("item")) {
insideItem = false;
}
eventType = xpp.next(); // move to next element
}// While end
} catch (MalformedURLException e) {
e.printStackTrace();
} catch (XmlPullParserException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
HashMap<String, ArrayList<String>> alllists =
new HashMap<String, ArrayList<String>>();
alllists.put("headlines",(ArrayList<String>) headlines);
alllists.put("links",(ArrayList<String>) links);
alllists.put("description",(ArrayList<String>) description);
alllists.put("lstDate",(ArrayList<String>) lstDate);
return alllists;
}
}
这是我的InputStreamOperation类：
公共类InputStreamOperation扩展了AsyncTask >> {
@Override
protected void onPreExecute() {
// show progress bar here(have not used any progress bar)
}
@Override
protected HashMap<String, ArrayList<String>>
doInBackground(Void... params) {
//call parse() method here
parsing parsingobj=new parsing();
HashMap<String, ArrayList<String>> alllists=parsingobj.parse();
return alllists; //<<< retun final result from here
}
@Override
protected void onPostExecute(HashMap<String, ArrayList<String>> result) {
// update UI here
}
}
最佳答案
您需要在AsyncTask的getInputStream方法内调用doInBackground，方法是：
首先将解析方法的返回类型更改为HashMap<String, String>：
public HashMap<String, ArrayList<String>> parse() {
///your code here...
HashMap<String, ArrayList<String>> alllists =
new HashMap<String, ArrayList<String>>();
alllists.put("headlines",headlines);
alllists.put("links",links);
alllists.put("description",description);
alllists.put("lstDate",lstDate);
return alllists;
}
并创建AsyncTask类为：
private class InputStreamOperation extends
AsyncTask<String, Void, HashMap<String, ArrayList<String>>> {
@Override
protected void onPreExecute() {
// show progress bar here
}
@Override
protected HashMap<String, ArrayList<String>>
doInBackground(String... params) {
//call parse() method here
parsing parsingobj=new parsing();
HashMap<String, ArrayList<String>> alllists=parsingobj.parse();
return alllists; //<<< retun final result from here
}
@Override
protected void onPostExecute(HashMap<String, ArrayList<String>> result) {
// update UI here
}
}
关于android - 异步任务的实现，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/14456347/