Android :: Unable To Get Correct Selected Items

I am to display the list and store the selected items in an array. But I am not able to get the correct items that were selected. Here whenever the user clicks an item, the array is getting updated, irrespective if the user is clicking the item to select it or deselect it. Could some one please help me solve this. I could actually perform an iteration to remove the odd numbered items in the array but I feel that would become an overload on the phone. Is there something for efficient. Please advise.

public class MainActivity extends ListActivity { TextView selection; String[] items={"sodium", "O2", "C02", "HCL", "NaCl", "H2So4", "O3", "Ag"}; String names[] = new String[10]; static int i=0; int posarray[] = new int[10]; @Override public void onCreate(Bundle icicle) { super.onCreate(icicle); setContentView(R.layout.main); setListAdapter(new ArrayAdapter<String>(this, android.R.layout.simple_list_item_multiple_choice, items)); .........