我正在创建一个带有片段和可转换视图标签的应用... 我有xml解析器片段，它在后台的asynctask中工作。 问题是，当我打开另一个片段而不是xml解析器片段时，它会启动asynctask并显示progressbar对话框，让用户等待任务完成！我怎么做它只会在我去那个xmlparser片段时启动异步任务？有人可以帮忙吗？
我的代码：
public class CircularsFragment extends Fragment {
// All static variables
public static final String URL = "https://dl.dropboxusercontent.com/7978967896/something.xml";
// XML node keys
static final String KEY_ITEM = "item"; // parent node
static final String KEY_ID = "id";
static final String KEY_NAME = "name";
static final String KEY_COST = "cost";
static final String KEY_DESC = "description";
ProgressDialog dialog;
// flag for Internet connection status
Boolean isInternetPresent = false;
// Connection detector class
ConnectionDetector cd;
private static class GetStuffFromUrlTask extends AsyncTask<String, Void, String> {
@Override
protected String doInBackground(String... params) {
String url = params[0];
String xml = "";
try {
// defaultHttpClient
DefaultHttpClient httpClient = new DefaultHttpClient();
HttpPost httpPost = new HttpPost(url);
HttpResponse httpResponse = httpClient.execute(httpPost);
HttpEntity httpEntity = httpResponse.getEntity();
xml = EntityUtils.toString(httpEntity);
} catch (UnsupportedEncodingException e) {
e.printStackTrace();
} catch (ClientProtocolException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return xml;
}
public final String getElementValue( Node elem ) {
Node child;
if( elem != null){
if (elem.hasChildNodes()){
for( child = elem.getFirstChild(); child != null; child = child.getNextSibling() ){
if( child.getNodeType() == Node.TEXT_NODE ){
return child.getNodeValue();
}
}
}
}
return "";
}
/**
* Getting node value
* @param Element node
* @param key string
* */
public String getValue(Element item, String str) {
NodeList n = item.getElementsByTagName(str);
return this.getElementValue(n.item(0));
}
}
private static class ParseStuffIGotFromSomeWhereTask extends AsyncTask<String, Void, Document> {
@Override
protected Document doInBackground(String... params) {
String stringToParse = params[0];
Document document = new XMLParser().getDomElement(stringToParse);
return document;
}
}
private static class XMLParser {
public Document getDomElement(String xml){
Document doc = null;
DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
try {
DocumentBuilder db = dbf.newDocumentBuilder();
InputSource is = new InputSource();
is.setCharacterStream(new StringReader(xml));
doc = db.parse(is);
} catch (ParserConfigurationException e) {
Log.e("Error: ", e.getMessage());
return null;
} catch (SAXException e) {
Log.e("Error: ", e.getMessage());
return null;
} catch (IOException e) {
Log.e("Error: ", e.getMessage());
return null;
}
return doc;
}
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,Bundle savedInstanceState) {
final View rootView = inflater.inflate(R.layout.fragment_games, container, false);
setRetainInstance(true);
//check internet
cd = new ConnectionDetector(getActivity().getApplicationContext());
isInternetPresent = cd.isConnectingToInternet();
//This is the task we use to parse the XML we got back from the getStuffFromUrlTask
//do only if internet is present
if (isInternetPresent) {
final ParseStuffIGotFromSomeWhereTask parseTask = new ParseStuffIGotFromSomeWhereTask() {
@Override
protected void onPreExecute(){
}
@Override
public void onPostExecute(Document document) {
// here you can access the document that is the result of our parse operation
// progressDialog.dismiss();
//document.getElementsByTagName(XYZ)...
ArrayList<HashMap<String, String>> menuItems = new ArrayList<HashMap<String, String>>();
NodeList nl = document.getElementsByTagName(KEY_ITEM);
// looping through all item nodes <item>
for (int i = 0; i < nl.getLength(); i++) {
// creating new HashMap
HashMap<String, String> map = new HashMap<String, String>();
Element e = (Element) nl.item(i);
GetStuffFromUrlTask parser1 = new GetStuffFromUrlTask();
// adding each child node to HashMap key => value
map.put(KEY_ID, parser1.getValue(e, KEY_ID));
map.put(KEY_NAME, parser1.getValue(e, KEY_NAME));
map.put(KEY_COST, "Rs." + parser1.getValue(e, KEY_COST));
map.put(KEY_DESC, parser1.getValue(e, KEY_DESC));
// adding HashList to ArrayList
menuItems.add(map);
}
// Adding menuItems to ListView
ListAdapter adapter = new SimpleAdapter(getActivity(), menuItems,R.layout.list_item,
new String[] { KEY_NAME, KEY_DESC, KEY_COST }, new int[] {
R.id.name, R.id.desciption, R.id.cost });
final ListView lview = (ListView) rootView.findViewById(R.id.lview);
lview.setAdapter(adapter);
// selecting single ListView item
//ListView lv = getListView();
lview.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// getting values from selected ListItem
String name = ((TextView) view.findViewById(R.id.name)).getText().toString();
String cost = ((TextView) view.findViewById(R.id.cost)).getText().toString();
String description = ((TextView) view.findViewById(R.id.desciption)).getText().toString();
// Starting new intent
Intent in = new Intent(getActivity().getApplicationContext(), SingleMenuItemActivity.class);
in.putExtra(KEY_NAME, name);
in.putExtra(KEY_COST, cost);
in.putExtra(KEY_DESC, description);
startActivity(in);
}
});
}
};
//This is the task we use to get stuff from the URL
GetStuffFromUrlTask getStuffFromUrlTask = new GetStuffFromUrlTask() {
protected void onPreExecute(){
dialog=ProgressDialog.show(getActivity(), "", "Loading...Please wait!");
}
@Override
public void onPostExecute(String result) {
//The task has completed, the string result contains the XML data we got from the URL
parseTask.execute(result); //Now we start the task to parse the xml
dialog.dismiss();
}
};
getStuffFromUrlTask.execute(URL);
}
else{
Toast.makeText(
getActivity().getApplicationContext(),
"No INTERNET! Circulars can't be loaded.",
Toast.LENGTH_LONG).show();
}
return rootView;
}
}