这是合法交易吗？由于某种原因不起作用

Question

所以似乎myList.add（s）无效。我只是想知道是否有人能告诉我为什么？对此很新 - 我可以不在我的onActivityResult中调用.add吗？谢谢！

@Override
public void onStart() {
    super.onStart();

    // get Object from file
    Object obj = getObjectFromFile(this, myFileName);
    // if obj returns something, check it's type
    if (obj != null && obj instanceof ArrayList) {
        // use the existing List id it exists
        myList = (ArrayList<toDo>) obj; //notice the arraylist is of type student
    } else {
        // create new List if one doesn't exist
        //myList = new ArrayList<String>();
        myList = new ArrayList<toDo>();
    }

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);
    if ((requestCode == 101) && (resultCode == Activity.RESULT_OK)) {
        Bundle myResults = data.getExtras();
        String activity1 = myResults.getString("activity");
        String description1 = myResults.getString("description");
        String date1 = myResults.getString("date");
        String assignment1 = myResults.getString("assignment");
        txtMsg.setText(description1);
        s = new toDo(activity1, description1, date1, assignment1);
        myList.add(s);
        mArrayAdapter.notifyDataSetChanged();

    }
}