多项选择题。如何将3个随机答案添加到数组并显示4个不同的选项而不重复？

Question

我正在尝试学习如何构建一个简单的mcq图片测验应用程序。我有此代码用作模板。显示一张图片，用户必须选择4个选项/答案之一。问题是4个选项不是应有的4个不同答案。甚至似乎您玩的越多，答案就越少。有人可以帮助我了解问题是什么吗？

//picks a random number for the answer
    correctAnswer = 0 + (int)(Math.random() * ((3 - 0) + 1));

    //create an array of answers from file names
    ArrayList<String> answers = new ArrayList<String>();
    List<Integer> categoryList = new ArrayList<Integer>();

    for (int subArrayFlag = 0; subArrayFlag < imagesShuffled.size();subArrayFlag++){
        if(imagesShuffled.get(currentQuestion).getName().substring(0,1)
                .equalsIgnoreCase(imagesShuffled.get(subArrayFlag).getName().substring(0,1))){
            categoryList.add(subArrayFlag);

        }
    }

    //get 3 random answers and add it to the array

    for (int i = 0 ; i < 4 ;i++ ){

        if (i == correctAnswer){
            answers.add(imagesShuffled.get(currentQuestion).getName());
        }else {

            do {
                randomFileIndex = (int) (Math.random() * ((categoryList.size() - 1) + 1));
            } while ( categoryList.get(randomFileIndex) == currentQuestion && categoryList.size() > 0 );

            answers.add(imagesShuffled.get(categoryList.get(randomFileIndex)).getName());
        }

    }



    try
    {
        // get input stream
        InputStream ims = getAssets().open(imagesShuffled.get(currentQuestion).getPath());
        // load image as Drawable
        Drawable d = Drawable.createFromStream(ims, null);
        // set image to ImageView
        mainIV.setImageDrawable(d);
    }
    catch(IOException ex)
    {
        return;
    }



    btn1.setText(answers.get(0).substring(2));
    btn2.setText(answers.get(1).substring(2));
    btn3.setText(answers.get(2).substring(2));
    btn4.setText(answers.get(3).substring(2));





    btn1.setBackgroundDrawable(d);
    btn2.setBackgroundDrawable(d);
    btn3.setBackgroundDrawable(d);
    btn4.setBackgroundDrawable(d);



}