How to preload an Activity?

问题:

I searched everywhere for this but no one appears to have an answer.

My simple question is:

Is there a way to preload an activity? I need this because I use a tab,and a tab has multiple activities. One of my activities is a rss reader,and it loads pretty hard(about 2-3 seconds).

All I found on the web is a joke.Everyone has an opinion,but no one can point you to a sample code. Waiting for an answer,thanks!

This is the code that loads the feed:

At onCreate: // go get our feed!         feed = getFeed(RSSFEEDOFCHOICE);          // display UI         UpdateDisplay();          countdown();   And the functions:  private RSSFeed getFeed(String urlToRssFeed)     {         try         {             // setup the url            URL url = new URL(urlToRssFeed);             // create the factory            SAXParserFactory factory = SAXParserFactory.newInstance();            // create a parser            SAXParser parser = factory.newSAXParser();             // create the reader (scanner)            XMLReader xmlreader = parser.getXMLReader();            // instantiate our handler            RSSHandler theRssHandler = new RSSHandler();            // assign our handler            xmlreader.setContentHandler(theRssHandler);            // get our data via the url class            InputSource is = new InputSource(url.openStream());            // perform the synchronous parse                       xmlreader.parse(is);            // get the results - should be a fully populated RSSFeed instance, or null on error             return theRssHandler.getFeed();         }         catch (Exception ee)         {             // if we have a problem, simply return null             return null;         }     }   private void UpdateDisplay()     {         TextView feedtitle = (TextView) findViewById(R.id.feedtitle);         TextView feedpubdate = (TextView) findViewById(R.id.feedpubdate);         ListView itemlist = (ListView) findViewById(R.id.itemlist);           if (feed == null)         {             feedtitle.setText("No RSS Feed Available");         return;         }          feedtitle.setText(feed.getTitle());         feedpubdate.setText(feed.getPubDate());          ArrayAdapter<RSSItem> adapter = new ArrayAdapter<RSSItem>(this,android.R.layout.simple_list_item_1,feed.getAllItems());          itemlist.setAdapter(adapter);          itemlist.setOnItemClickListener(this);          itemlist.setSelection(0);          } 

回答1:

You have to use Asyc Task http://developer.android.com/reference/android/os/AsyncTask.html in the OnCreate function of the activity . And remember you have to create a interface(here I used EVRequestCallback) by which you need to update the UI of Activity after completion of rss loading. Below is the sample code of Async task for RSS feed.

public class RetrieveRssAsync {           public RetrieveRssAsync(Context ct,EVRequestCallback gt)         {          }            public static abstract class EVRequestCallback {                 public abstract void requestDidFail(ArrayList<EventItem> ei);                 public abstract void requestDidLoad(ArrayList<EventItem> ei);           }           public static class RetrieveEventFeeds extends AsyncTask<Void, Void, ArrayList<EventItem>>         {               Context mContext;               private EVRequestCallback mCallback;             public RetrieveEventFeeds(Context ct,EVRequestCallback gt)             {                 mContext= ct;                 mCallback=gt;             }             private ProgressDialog progress = null;              @Override             protected ArrayList<EventItem> doInBackground(Void... params) {                  return retrieveRSSFeed("--URL of RSS here--",this.mContext);               }              @Override             protected void onCancelled() {                 super.onCancelled();             }              @Override             protected void onPreExecute() {                 progress = ProgressDialog.show(                         mContext, null, "Loading ...",true,true);                  super.onPreExecute();             }              @Override             protected void onPostExecute(ArrayList<EventItem> result) {             //setListAdapter();                 mCallback.requestDidLoad(result);                 progress.dismiss();                 //Toast.makeText(this.mContext, "current done", Toast.LENGTH_SHORT).show();                 super.onPostExecute(result);             }              @Override             protected void onProgressUpdate(Void... values) {                 super.onProgressUpdate(values);             }         }       } 

回答2:

The blog "Styling Android" provides detail examples to show how to do background tasks. FYI.

Links:

http://blog.stylingandroid.com/archives/833
Styling Android - http://blog.stylingandroid.com/

文章来源: How to preload an Activity?