Ytjoavzkuwuvt
New Member
I am developing an application for college that connects to a web server and reads data from an \[code\]XML\[/code\] on the server.The appilcation is working but I am currently trying to really break down the code and understand exactly what is happening.My question is that I have an inner class that extends the \[code\]AsyncTask\[/code\] class. Within this inner class I create a new \[code\]URL\[/code\] object and get an \[code\]InputStream\[/code\]. I understand that because I am doing this I can then successfully connect to the web server from the background thread and make whatever requests I like.In the past I always used the \[code\]DefaultHttpClient\[/code\] to execute \[code\]HTTP\[/code\] requests. However in this code I do not create an instance of this class anywhere. Instead I just get an input stream to read in the sequence of bytes.Could someone explain in the code below what is meant by parsing spec and also if somewhere behind the scenes a \[code\]HTTP\[/code\] request is actually being made?\[code\]URL url = new URL("http://feeds.pcworld.com/pcworld/latestnews");\[/code\]Documentation on Android Dev says:\[quote\] Creates a new URL instance by parsing spec.\[/quote\]This is my entire \[code\]MainActivity\[/code\]\[code\]public class MainActivity extends ListActivity {List<Item>items;//Holds item objects containing info relating to element pulled from XML file.Item item; //Instance of Item - contains all data relating to a specific Item.ArticleListAdapter adapter;//Generates the Views and links the data source (ArrayList) to the ListView.@Overrideprotected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); //Set the layout setContentView(R.layout.activity_main); //initialize variables items = new ArrayList<Item>(); //Perform a http request for the file on the background thread. new PostTask().execute(); //Create instance of the adapter and pass the list of items to it. adapter = new ArticleListAdapter(this, items); //Attach adapter to the ListView. setListAdapter(adapter); }private InputStream getInputStream(URL url) { try{ return url.openConnection().getInputStream(); }catch(IOException e){ return null; }}/** * Executed when an Item in the List is clicked. Will display the article being clicked in a browser. */@Overrideprotected void onListItemClick(ListView l, View v, int position, long id) { //Get the link from the item object stored in the array list Uri uri = items.get(position).getLink(); //Create new intent to open browser Intent intent = new Intent(Intent.ACTION_VIEW, uri); startActivity(intent);}@Overridepublic boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.activity_main, menu); return true;}//ASYNC CLASSprivate class PostTask extends AsyncTask<String, Integer, String>{ @Override protected String doInBackground(String... arg0) { try{ //link to data source URL url = new URL("http://feeds.pcworld.com/pcworld/latestnews"); //Set up parser XmlPullParserFactory factory = XmlPullParserFactory.newInstance(); factory.setNamespaceAware(false); XmlPullParser xpp = factory.newPullParser(); //get XML from input stream InputStream in = getInputStream(url); if (in == null) { throw new Exception("Empty inputstream"); } xpp.setInput(in, "UTF_8"); //Keep track of which tag inside of XML boolean insideItem = false; //Loop through the XML file and extract data required int eventType = xpp.getEventType(); while (eventType != XmlPullParser.END_DOCUMENT) { if (eventType == XmlPullParser.START_TAG) { Log.v("ENTER", String.valueOf(xpp.getEventType())); if (xpp.getName().equalsIgnoreCase("item")) { insideItem = true; //Create new item object item = new Item(); } else if (xpp.getName().equalsIgnoreCase("title")) { if (insideItem){ item.setTitle(xpp.nextText()); Log.i("title", item.getTitle()); } } else if (xpp.getName().equalsIgnoreCase("description")) { if (insideItem){ item.setDescription(xpp.nextText()); } } else if (xpp.getName().equalsIgnoreCase("link")) { if (insideItem){ item.setLink(Uri.parse(xpp.nextText())); } } }else if(eventType==XmlPullParser.END_TAG && xpp.getName().equalsIgnoreCase("item")){ //If no longer inside item tag then we know we are finished parsing data relating to one specific item. insideItem=false; //add item to list items.add(item); } eventType = xpp.next(); //move to next element publishProgress(); //update progress on UI thread. } } catch (MalformedURLException e) { e.printStackTrace(); } catch (XmlPullParserException e) { e.printStackTrace(); } catch (IOException e) { e.printStackTrace(); } catch (Exception e) { e.printStackTrace(); } return "COMPLETED"; } /* * Update the List as each item is parsed from the XML file. * @see android.os.AsyncTask#onProgressUpdate(Progress[]) */ @Override protected void onProgressUpdate(Integer... values) { adapter.notifyDataSetChanged(); } /* * Runs on UI thread after doInBackground is finished executing. * @see android.os.AsyncTask#onPostExecute(java.lang.Object) */ public void onPostExecute(String s) { //Toast message to inform user of how many articles have been downloaded. Toast.makeText(getApplicationContext(), s + " Items: " + items.size(), Toast.LENGTH_SHORT).show(); adapter.notifyDataSetChanged(); }}\[/code\]}I am sorry if this question is very basic, but like I said I am trying to learn and that is what this site is all about right? I'd appreciate any feedback or help people have in relation to this topic.Many thanks!