java - indexOf 不断返回-1。超级卡住

Question

我已经正确初始化了所有变量，但它一直返回-1。

private void RandomCard(int spreadname, int spreadposition) {
    try {
        SecureRandom rand = SecureRandom.getInstanceStrong();
        Collections.shuffle(list_unusedCards, rand);

        Random ranNum = new Random();
        int numUnusedCards = list_unusedCards.size();
        int pickedCard = ranNum.nextInt(numUnusedCards);

        str_cardName = list_unusedCards.get(pickedCard).GetName();
        str_cardDesc = list_unusedCards.get(pickedCard).GetDescription();
        str_imageName = list_unusedCards.get(pickedCard).GetImageName();

        String str_spreadPos = Integer.toString(spreadposition);

        cl_chosenCards = new CardList(str_cardName, str_cardDesc, str_deckChosen, str_imageName, str_spreadPos);
        list_chosenCards.add(cl_chosenCards);

        String btnPos = list_chosenCards.get(0).GetButtonPosition(); //GetButtonPosition returns value of str_spreadPos
        int int_index = list_chosenCards.indexOf(str_spreadPos);

        tv_test0.setText(str_cardName);
        tv_test1.setText(str_cardDesc);

        //tv_test2.setText("spread pos: " + str_spreadPos);             //WORKS
        //tv_test2.setText("button pos: " + btnPos);                    //WORKS
        //tv_test2.setText("index: " + int_index);                      //DOESN'T WORK, RETURNS -1

对于我注释掉的最后 3 行代码，我一直在测试这些变量是否被正确分配以及它们是否存在于列表中。它们不为空，它们返回正确的值。但由于某种原因，第三个一直返回-1。