如何在我的列表中的simple_list_item_multiple_choice中设置checked =“checked”项，如果我想要总是检查2个元素？

    private ListView LVmain;

    private ArrayList<String> tasks = new ArrayList<String>();
    private ArrayAdapter<String> adapter;

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
 adapter = new ArrayAdapter(this, android.R.layout.simple_list_item_multiple_choice, tasks);
tasks.add("first");
tasks.add("second");
tasks.add("thirst");
tasks.add("fourth");
adapter.notifyDataSetChanged();
    private ListView LVmain;

    private Array