求救，关于spinner无法使设置默认值

[a304693255]

以下是源码，各位大牛拯救下小弟
private void add_list() {
sp = (Spinner) findViewById(R.id.duty_spinner);
List<String> mCountries = positionNames;


ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_spinner_item, mCountries);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
sp.setAdapter(adapter);
sp.setSelection(2, true);



sp.setOnItemSelectedListener(new OnItemSelectedListener() {

@Override
public void onItemSelected(AdapterView<?> adapterView, View view,
int position, long id) {

// str = (String) sp.getSelectedItem();
// Spinner spinner = (Spinner) adapterView;
// String data = (String) spinner.getItemAtPosition(position);
}

@Override
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub

}
});

}