无法从ViewPager

Question

我的目标是在用户点击按钮时从ViewPager中删除片段。 填充ViewPager工作正常，但是当我尝试删除它时，我收到一个指示空引用的错误。我合并了Remove Fragment Page from ViewPager in Android

在我要删除的片段中，我有：

Button delete = (Button) getActivity().findViewById(R.id.dont_show_button_1);
    delete.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            db.deletePerson(count); // SQLiteDatabase, works fine
            displayActivity.removeCurrentFragment(count-1);

        }
    });

DisplayActivity如下：

public class DisplayActivity extends FragmentActivity {

ViewPager viewPager;
PagerAdapter pagerAdapter;
String TAG = "DisplayActivity";

@Override
protected void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.db_layout);

    viewPager = (ViewPager) findViewById(R.id.pager);

    pagerAdapter = new PagerAdapter(getSupportFragmentManager());
    viewPager.setAdapter(pagerAdapter);
}

public void removeCurrentFragment(int position){
    pagerAdapter.fragmentArrayList.remove(position);
    pagerAdapter.notifyChangeInPosition(1);
    pagerAdapter.notifyDataSetChanged();
    Log.e(TAG, "in removeCurrentFragment");
}

}

PagerAdapter

public class PagerAdapter extends FragmentPagerAdapter {

long baseId = 0;
public static List<Fragment> fragmentArrayList = new ArrayList<Fragment>();

public PagerAdapter(FragmentManager fm){
    super(fm);
    fragmentArrayList.add(new FragmentOne());
    fragmentArrayList.add(new FragmentTwo());
    fragmentArrayList.add(new FragmentThree());
}
@Override
public Fragment getItem(int position) {
    return fragmentArrayList.get(position);
}

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

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

@Override
public long getItemId(int position) {
    // give an ID different from position when position has been changed
    return baseId + position;
}

/**
 * Notify that the position of a fragment has been changed.
 * Create a new ID for each position to force recreation of the fragment
 * @param n number of items which have been changed
 */
public void notifyChangeInPosition(int n) {
    // shift the ID returned by getItemId outside the range of all previous fragments
    baseId += getCount() + n;
}

}

这是错误：

java.lang.NullPointerException: Attempt to invoke virtual method 'void .DisplayActivity.removeCurrentFragment(int)' on a null object reference

从片段

触发

编辑：

public class FragmentOne extends Fragment {

DatabaseHelper db;
WebView mWebView;
DisplayActivity displayActivity;
int count = 1;

这是我从displayActivity获取引用的方式，这是获取引用的错误方法吗？

Answer 1

if (count > 0) {
    displayActivity.removeCurrentFragment(count - 1);
}