ListAdapter如何知道何时分离?

如何 firstAdapter 知道它何时与listView的实际适配器分离(因为 secondAdapter 替换它)?

final ListAdapter firstAdapter = new SimpleAdapter(
    this,
    new ArrayList<Map<String, Object>>(),
    android.R.layout.simple_list_item_1,
    new String[] {"AAA"},
    new int[] {android.R.id.text1}
);
final ListAdapter secondAdapter = new SimpleAdapter(
    this,
    new ArrayList<Map<String, Object>>(),
    android.R.layout.simple_list_item_1,
    new String[] {"AAA"},
    new int[] {android.R.id.text1}
);

setListAdapter(firstAdapter);

(new Timer()).schedule(new TimerTask() {
  @Override
  public void run() {
    Runnable r = new Runnable() {
      @Override
      public void run() {
        setListAdapter(secondAdapter);
      }
    };
    new Handler(Looper.getMainLooper()).post(r);
  }
}, 1000);