Question

I’ve been trying to set up a UI Thread and Handler for a SAX parser. This is my parser without a UI Thread and Handler implemented:

public class AndroidXMLReader extends ListActivity {

    private XMLFeed myXMLFeed = null;


    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
            try {
                URL xmlUrl = new URL("http://feeds.bbci.co.uk/news/uk/rss.xml");
                SAXParserFactory mySAXParserFactory = SAXParserFactory.newInstance();
                SAXParser mySAXParser = mySAXParserFactory.newSAXParser();
                XMLReader myXMLReader = mySAXParser.getXMLReader();
                XMLHandler myXMLHandler = new XMLHandler();
                myXMLReader.setContentHandler(myXMLHandler);
                InputSource myInputSource = new InputSource(xmlUrl.openStream());
                myXMLReader.parse(myInputSource);

                myXMLFeed = myXMLHandler.getFeed();

            }

        catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
        catch (ParserConfigurationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
        catch (SAXException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
        catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        if (myXMLFeed!=null)
        {
            ArrayAdapter<XMLItem> adapter =
             new ArrayAdapter<XMLItem>(this,
               android.R.layout.simple_list_item_1,myXMLFeed.getList());
            setListAdapter(adapter);
        }
        }
    }

Then here I went and tried to add the UI Thread & Handler. Edit 1 – this is the amended code as per HellBoy’s reply:

   public class AndroidXMLReader extends ListActivity {

    private static final int THREAD_FINISHED = 0;
    private XMLFeed myXMLFeed = null;
    private ProgressDialog progressDialog;
    private Button refreshFeed;
    Handler handler = new Handler();

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        initControls();
    }

    public void initControls(){


          refreshFeed = (Button) findViewById(R.id.refresh);

          refreshFeed.setOnClickListener(new Button.OnClickListener(){
              @Override
              public void onClick(View v){
                  progressDialog = ProgressDialog.show(AndroidXMLReader.this, "",
                            "Please wait for few seconds...", true);
                  processThread();          
              }
          });
    }
    protected void processThread() {
        Thread t = new Thread()
        {
            public void run(){
                 getNews();
                 //UI();
                 // Sends message to the handler so it updates the UI
                 handler.sendMessage(Message.obtain(mHandler, THREAD_FINISHED));

                 ; }
        };
        t.start();
    }

    private Handler mHandler = new Handler() {
        @Override
            public void handleMessage(Message msg) {
                super.handleMessage(msg);

                switch (msg.what) {
                case THREAD_FINISHED:

                           progressDialog.dismiss();
                           break;    
                    };

            };
    };

    private void getNews(){
        try {
            URL xmlUrl = new URL("http://feeds.bbci.co.uk/news/uk/rss.xml");
            SAXParserFactory mySAXParserFactory = SAXParserFactory.newInstance();
            SAXParser mySAXParser = mySAXParserFactory.newSAXParser();
            XMLReader myXMLReader = mySAXParser.getXMLReader();
            XMLHandler myXMLHandler = new XMLHandler();
            myXMLReader.setContentHandler(myXMLHandler);
            InputSource myInputSource = new InputSource(xmlUrl.openStream());
            myXMLReader.parse(myInputSource);

            myXMLFeed = myXMLHandler.getFeed();

        }

        catch (MalformedURLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
        catch (ParserConfigurationException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
        catch (SAXException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } 
        catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }

        if (myXMLFeed!=null){
            ArrayAdapter<XMLItem> adapter =
                 new ArrayAdapter<XMLItem>(this,
                   android.R.layout.simple_list_item_1,myXMLFeed.getList());
                setListAdapter(adapter);
        }

    }
}

At the moment it hangs at the progress dialog and I can’t figure out why … Any help would be appreciated.

Edit 1 – The error message that I get now is:

Only the original thread that created a view hierarchy can touch its
views.

    10-04 21:39:27.570: ERROR/AndroidRuntime(17454):     at com.android.testfeed3.AndroidXMLReader.getNews(AndroidXMLReader.java:121)
10-04 21:39:27.570: ERROR/AndroidRuntime(17454):     at com.android.testfeed3.AndroidXMLReader.access$2(AndroidXMLReader.java:85)
10-04 21:39:27.570: ERROR/AndroidRuntime(17454):     at com.android.testfeed3.AndroidXMLReader$3.run(AndroidXMLReader.java:60)
10-04 21:39:27.645: WARN/ActivityManager(2703):   Force finishing activity com.android.testfeed3/.AndroidXMLReader
10-04 21:39:33.495: ERROR/WindowManager(17454): Activity com.android.testfeed3.AndroidXMLReader has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@40527a20 that was originally added here
10-04 21:39:33.495: ERROR/WindowManager(17454): android.view.WindowLeaked: Activity com.android.testfeed3.AndroidXMLReader has leaked window com.android.internal.policy.impl.PhoneWindow$DecorView@40527a20 that was originally added here
10-04 21:39:33.495: ERROR/WindowManager(17454):     at com.android.testfeed3.AndroidXMLReader$2.onClick(AndroidXMLReader.java:50)

Any help would be appreciated.

Answer 1

In order to make changes to the UI the commands must come from thread that created it, i.e. the main (or UI) thread.

At a quick glance, this line:

if (myXMLFeed!=null)
{
   ArrayAdapter<XMLItem> adapter =
    new ArrayAdapter<XMLItem>(this,
      android.R.layout.simple_list_item_1,myXMLFeed.getList());
   setListAdapter(adapter);
}

needs to be put in a separate Handler and that Handler called from your new thread.