Android 每次滑动片段时更改drawable，并在语音结束时将文本图标更改为语音

我正在实现一个字典。有一个活动（WordMeaningActivity）显示一个单词的意思。它由片段和viewPager（滑动视图）组成。使用fragmentStatePagerAdapter填充片段。 每个片段中都有一个扬声器按钮，用于实现文本到语音的转换。当tts关闭时，按钮图标为扬声器，否则当它说话时图标变为静音。我提供的图像链接-

我有两个问题- 1） 当我滑动并更改片段时（当tts说话时），它停止说话，但当我滑动回该片段时，图标不会更改（保持静音），应该是扬声器。暂停，停止工作。我使用hashmap保留了以前的位置和片段本身，在方法onPageSelected中，我访问了片段并更改了图标，但在几次滑动（左和右）后，它抛出NullPointerException

2） 当tts完成它的演讲时，它不会改变图标。SetOnPatternanceProgressListener中的OnOne未更改图标。 这是密码-

@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_word_meaning);

    initViews();

    Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    setTitle(title);

    getSupportActionBar().setDisplayHomeAsUpEnabled(true);
    mSectionsPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager());
    mViewPager = (ViewPager) findViewById(R.id.container);
    mViewPager.setAdapter(mSectionsPagerAdapter);

    mViewPager.setPageTransformer(true, new ViewPager.PageTransformer() {
        @Override
        public void transformPage(View page, float position) {
            if (position < -1) {
                // [-00,-1): the page is way off-screen to the left.
                 right = true;


            } else if (position <= 1) {
                // [-1,1]: the page is "centered"
            } else {
                // (1,+00]: the page is way off-screen to the right.
                left = true;
            }
        }
    });

    mViewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
        @Override
        public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
            posOffset = positionOffset;
        }

        @Override
        public void onPageSelected(int position) {
            String word = list.get(position);
            insertToRecent(word);

            PlaceholderFragment frag;

                if (right) {
                    frag = fragMap.get(position - 1);
                    frag.btnspeak.setBackgroundResource(R.drawable.speaker);
                    right = false;
                } else if (left) {
                    frag = fragMap.get(position + 1);
                    frag.btnspeak.setBackgroundResource(R.drawable.speaker);
                    left = false;
                }

        @Override
        public void onPageScrollStateChanged(int state) {
        }
    });
    mViewPager.setCurrentItem(position);
}

提前感谢您的帮助

    public static class PlaceholderFragment extends Fragment{

    TextView txtMeaning,txtHeading;
    String word,meaning;
    boolean on,speaker;
    Button btnspeak,btnfav,btnshare;
    static TextToSpeech tts;
    int prevFragPos;

    public PlaceholderFragment() {
    }

    public  PlaceholderFragment newInstance(String w,String m, boolean bool) {

        PlaceholderFragment fragment = new PlaceholderFragment();
        Bundle args = new Bundle();
        args.putString("word", w);
        args.putString("meaning",m);
        args.putBoolean("fabState",bool);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        word=getArguments().getString("word");
        on=getArguments().getBoolean("fabState");
        meaning=getArguments().getString("meaning");

        View rootView = inflater.inflate(R.layout.fragment_word_meaning, container, false);

        txtMeaning = (TextView) rootView.findViewById(R.id.txtMeaning);
        txtHeading = (TextView)rootView.findViewById(R.id.textHeading);
        btnspeak = (Button) rootView.findViewById(R.id.speaker);
        btnfav = (Button)rootView.findViewById(R.id.fav);
        btnshare = (Button)rootView.findViewById(R.id.share);

        txtHeading.setText(word);
        txtMeaning.setText(meaning);

        btnspeak.setBackgroundResource(R.drawable.speaker);

        speaker=false;

        Bundle bun = this.getArguments();
        prevFragPos = bun.getInt("fragPos") - 1;
        posSend = bun.getBoolean("bool");

        final HashMap<String, String> map = new HashMap<String, String>();
        map.put(TextToSpeech.Engine.KEY_PARAM_UTTERANCE_ID,"messageID");


        tts=new TextToSpeech(getActivity(), new TextToSpeech.OnInitListener() {
            @Override
            public void onInit(int status) {
                if(status!=TextToSpeech.ERROR){
                    tts.setLanguage(Locale.ENGLISH);
                }
            }
        });

        if(on){
            btnfav.setBackgroundResource(R.drawable.star_on);
        }
        else{
            btnfav.setBackgroundResource(R.drawable.star_border);
        }

        btnspeak.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                if (speaker == false) {
                    speaker = true;
                    btnspeak.setBackgroundResource(R.drawable.mute);
                    tts.speak(meaning, TextToSpeech.QUEUE_FLUSH, map);
                } else {
                    speaker = false;
                    btnspeak.setBackgroundResource(R.drawable.speaker);
                    tts.stop();
                }
            }
        });

        tts.setOnUtteranceProgressListener(new UtteranceProgressListener() {
            @Override
            public void onStart(String utteranceId) {
            }

            @Override
            public void onDone(String utteranceId) {
                btnspeak.setBackgroundResource(R.drawable.speaker); //not working
            }

            @Override
            public void onError(String utteranceId) {
            }
        });



        btnfav.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (onClickFavourites(v, on, word)) {
                    btnfav.setBackgroundResource(R.drawable.star_on);
                    on = true;
                } else {
                    btnfav.setBackgroundResource(R.drawable.star_border);
                    on = false;
                }
            }
        });

        btnshare.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                Intent waIntent = new Intent(Intent.ACTION_SEND);
                waIntent.setType("text/plain");
                waIntent.putExtra(Intent.EXTRA_TEXT, word + " - \n" + meaning);
                startActivity(Intent.createChooser(waIntent, "Share with"));


            }
        });

        return rootView;
    }

    @Override
    public void onDestroyView() {
        if(tts!=null){
            tts.stop();
            tts.shutdown();
        }
        super.onDestroyView();

    }

    @Override
    public void onDestroy() {
        super.onDestroy();
    }

}

public class SectionsPagerAdapter extends FragmentStatePagerAdapter {



    public SectionsPagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        String word=list.get(position);
        String m=getMeaning(word);
        boolean on=checkIfFav(word);

        PlaceholderFragment fragment = new PlaceholderFragment().newInstance(word, m, on);

        fragMap.put(position, fragment);

        return fragment;
    }

    @Override
    public int getCount() {
        return list.size();
    }
}