Problem by refreshing listView: UnsupportedOperationException

Question

why I am not able to refresh/reload my ListView? I' ve written an app, which read out html-websites, saves the information in a String-Array an present it in my ListView. But every time I close and re-open the app the new content append to the existing content. In the first run I get, eg, "1 2 3 4" and in the second run "1 2 3 4 1 2 3 4" and then " 1 2 3 4 1 2 3 4 1 2 3 4" and so on. I google a lot and find the methods to clear an ArrayAdapter (aa) and refill it with new data -> aa.clear() / aa.setModifyDataChanged() / aa.remove(String Object) / aa.add(String) but every time i call one Method my app does a force close and LogCat shows the exception: java.lang.UnsupportedOperationException. Why? This really grind my gears. The whole saturday afternoon I try to fix it -without success... Maybe somebody could help me!?

Here is my code-snippet

public class viewband extends ListActivity {

private static final int AKTUALISIEREN = 0;

private static ArrayList<String> al = new ArrayList<String>();
static String[] TST;
static ArrayAdapter<String> ad;

public boolean onOptionsItemSelected(MenuItem item)
{
    switch (item.getItemId())
    {
    case AKTUALISIEREN:
    getIt();
        //here a ad.close does a force close 
        setListAdapter(ad);
        ListView lv = getListView();
        lv.setTextFilterEnabled(true);  
        return true;
    default:
        return super.onOptionsItemSelected(item);
    }

}

public void onCreate(Bundle savedInstanceState) {  

    super.onCreate(savedInstanceState);
    getIt();
    ad = new ArrayAdapter<String>(this, R.layout.list_item, TST);
    setListAdapter(ad);
    // here, when I try ad.clear() my app does a force close
    ListView lv = getListView();
    lv.setTextFilterEnabled(true);   
}

public static void getIt ()
{
    // Here I get the source-code of the html-site and parse my content
    // All necessary Information I write in my String Array TST, declared above in a static way        
}

I hope, somebody could help me... Many thanks and a nice sunday.

Answer 1

You need to back your ArrayAdapter by an ArrayList or List rather than a fixed-size array - the size of a fixed-size array cannot change nor can it be cleared (without re-creating it, which defaults the whole purpose)

So set the content of your adapter to be al rather than TST (on a side note you really need to name your variables with sensible names). Then call al.clear() , al.add(String) , to modify the dataset backing the adapter. Once the dataset has been changed call ad.notifyDataSetChanged - this will then cause the list adapter and list to update the display.

Also your adapter should not be static (nor should TST or al probably) -- this will lead to memory leaks since the Adapter holds onto a reference to the current Context. NEVER make anything with a context static (drawables, adapters etc). Unless you know why you want something to be static keep it as a normal variable.

Answer 2

始终在更新列表视图时清除TST