Problem by refreshing listView: UnsupportedOperationException

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, e. g., "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);
    // he开发者_如何学编程re, 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.

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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.

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clear TST all time you update your listview