listView.setOnItemClickListener(new OnItemClickListener() {

    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        Object o = prestListView.getItemAtPosition(position);
        prestationEco str = (prestationEco)o; //As you are using Default String Adapter
        Toast.makeText(getBaseContext(),str.getTitle(),Toast.LENGTH_SHORT).show();
    }
});