Android Updating ListView

Question

I have looked at Android - how to update ListView item that is currently displayed and http://commonsware.com/Android/excerpt.pdf and the Android documentation but I still don't understand.

My problem:
Using a handler, I am trying to update a Stock data multi-column listview which I have populated from a webservice which retrieves data from a MySQL database. To update the listview, I am calling a servlet which returns an XML that I loop through using DOM.

I cannot find a working way to apply the new data (from the XML) into the Listview, though only the third column (Trade Column) has to be updated. Also when I try to cast a View from a ListView row, I get a NullPointerException and can't figure out why.

The code I have done so far is below.

java Code:

private void updateUI() throws Exception
{        
    Date dt = new Date();                 
    int hours = dt.getHours();
    int minutes = dt.getMinutes();                 
    int seconds = dt.getSeconds();                 
    String curTime = hours + ":" + minutes + ":"+ seconds;

    refreshHandler.sleep(60000);

    ListView listview = (ListView) findViewById(R.id.listview); 

    DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
    DocumentBuilder db = dbf.newDocumentBuilder();
    Document doc = db.parse("http://10.0.0.29:8080/CI3500/FTSEXML");

    //Filter and store ALL 'update' XML elements into node array
    NodeList nodeList = doc.getElementsByTagName("update");
    View v = null;
    TextView t = null;

    Adapter adapter = listview.getAdapter();

    for (int i = 0; i < adapter.getCount(); i++) 
    {
        v = listview.getChildAt(i);
        t = (TextView)v.findViewById(R.id.item2);

        String companyCode = t.getText().toString(); //Column 1

        for(int j = 0; j < nodeList.getLength(); j++) 
        {
            if(companyCode == nodeList.item(j).getFirstChild().getNodeValue())
            {
                //TODO Update Listview Code
            }
        }
    }       

    txtStatus.setText(String.valueOf("Last Update: " + curTime));
}

The listview mapping is as follows:

// create the grid item mapping
String[] columns = new String[] {"col_1", "col_2", "col_3" };
int[] rows = new int[] { R.id.CodeColumn, R.id.NameColumn, R.id.TradeColumn };

Answer 1

You should implement you own ListView Adapter that will provide data to the list view. Calling notifyDataSetChanged() from adapter will force list view to fetch data from the adapter. Updating list view views directly looks strange.

Answer 2

You can call invalidate to let the listview redraw.