Android：notifydatasetchanged后页面标题不会更改

Question

我正在使用带有Pager适配器的viewpager并在适配器中传递一个arraylist。 arraylist在开始时的大小为“0”但是一旦填充，我就调用了viewpager.notifydatasetchanged（）。在调用notifydatasetchanged之后，没有调用方法 CharSequence getPageTitle（int position）并且标题不是动态更新。

我的适配器代码：

public class MyViewPagerAdapter extends PagerAdapter {
    private ArrayList<String> arrayList;
    private Activity activity;

    public ViewPagerAdapter(Activity activity, ArrayList<String> arrayList) {
        this.activity = activity;
        this.arrayList = arrayList;
    }

    @Override
    public int getItemPosition(Object object) {
        return POSITION_NONE;
    }

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

    @Override
    public boolean isViewFromObject(@NonNull View view, Object o) {
        return o == view;
    }

    @NonNull
    @Override
    public Object instantiateItem(@NonNull ViewGroup container, int position) {
        // Inflate a new layout from our resources
        View view = activity.getLayoutInflater().inflate(R.layout.pager_item,
                container, false);
        // Add the newly created View to the ViewPager
        container.addView(view);

        // Retrieve a TextView from the inflated View, and update it's text
        TextView tvWeatherDescription = view.findViewById(R.id.tv);

        // Return the View
        return view;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return arrayList.get(position);
    }

    @Override
    public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
        container.removeView((View) object);
    }

}

我的活动代码：

@Override
    protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.activity_main);
         ArrayList<String> arrayList = new ArrayList<String>
         ViewPager viewpager = findviewbyId(R.id.viewpager);
         MyViewPagerAdapter adapter = new MyViewPagerAdapter(MainActivity.this, arraylist); 
         viewpager.setAdapter(adapter);

         SlidingTabLayout slidingTabLayout = findViewById(R.id.sliding_tabs);
         slidingTabLayout.setViewPager(viewpager);
    }

一旦arraylist的大小改变了，我就这样称呼它：

arraylist.add("Item1")
adapter.notifydatasetchanged();

但标题值没有改变。有没有办法在notifydatasetchanged之后调用方法CharSequence getPageTitle（int position）？