Android viewpager: strange error when adding / removing page

Question

I do not know how to explain this, so I uploaded the video to Youtube. Everything works fine when I add pages. Also, deleting the page is performed if I start at the end of the list and gradually go to the first page, but if I delete somewhere between 0-end and after that I add the page, I get a blank page. A fragment is created, but no.

Is there something wrong with my code? Yes, I saw this question, returning POSITION_NONE not an option, because the application I'm working on downloading content from the Internet and displays it in a listview, so recreating fragments every time a user deletes a page is not very efficient.

 Button click: Result: Add page [Fragment 1] Add page [Fragment 1][Fragment 2] Add page [Fragment 1][Fragment 2][Fragment 3] remove page(position2) [Fragment 1][Fragment 2] remove page(position1) [Fragment 1] Add page [Fragment 1][Fragment 2] remove page(position1) [Fragment 1] remove page(position0) ---No pages--- Add page [Fragment 0] Add page [Fragment 0][Fragment 1] Add page [Fragment 0][Fragment 1][Fragment 2] add page [Fragment 0][Fragment 1][Fragment 2][fragment 3] remove page(position2) [Fragment 0][Fragment 1][Fragment 3] add page [Fragment 0][Fragment 1][Fragment 3][Blank page] remove page(position0) [Fragment 1][Fragment 3][Fragment 3][Blank page] 

MainActivity.class

  public class MainActivity extends FragmentActivity { private static final String TAG = "MainActivity"; private ViewPager mViewpager; private ArrayList<Fragment> fragmentslist; private SectionsPagerAdapter mPagerAdapter; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); fragmentslist = new ArrayList<Fragment>(); mPagerAdapter = new SectionsPagerAdapter(getSupportFragmentManager()); mViewpager = (ViewPager)findViewById(R.id.pager); mViewpager.setAdapter(mPagerAdapter); mViewpager.setOffscreenPageLimit(4); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.main, menu); return true; } @Override public boolean onOptionsItemSelected (MenuItem item){ switch(item.getItemId()){ case R.id.menu_add_page: Bundle bundle = new Bundle(); bundle.putInt("Position", fragmentslist.size()); fragment frag = new fragment(); frag.setArguments(bundle); fragmentslist.add(frag); mPagerAdapter.notifyDataSetChanged(); mViewpager.setCurrentItem(fragmentslist.indexOf(frag)); Log.i(TAG, "Add fragment"); break; case R.id.menu_remove_page: if(fragmentslist.size() > 0){ mPagerAdapter.removeItem(mViewpager.getCurrentItem()); } Log.i(TAG, "Removing page " + mViewpager.getCurrentItem()); break; } return true; } public class SectionsPagerAdapter extends FragmentPagerAdapter { public SectionsPagerAdapter(FragmentManager fm) { super(fm); } @Override public Fragment getItem(int position) { return fragmentslist.get(position); } @Override public int getCount() { return fragmentslist.size(); } @Override public int getItemPosition(Object object){ int index = fragmentslist.indexOf(object); if(index != -1){ Log.i(TAG, "Position: " + index); return index; } else{ Log.i(TAG, "POSITION_NONE"); return POSITION_NONE; } } public void removeItem(int position){ Fragment fragment = (Fragment)fragmentslist.get(position); getSupportFragmentManager().beginTransaction().remove(fragment).commit(); fragmentslist.remove(position); notifyDataSetChanged(); } } public static class fragment extends Fragment{ private String colors[] = {"#FF0000", "#00FF00", "#FFFF00", "#FF6600"}; public View onCreateView(LayoutInflater inflater, ViewGroup root, Bundle savedInstanceState){ View mView = inflater.inflate(R.layout.fragment_layout, null); RelativeLayout layout = (RelativeLayout)mView.findViewById(R.id.relativelayout); TextView text = (TextView)mView.findViewById(R.id.textView1); int position = this.getArguments().getInt("Position"); text.setText("Page: " + position); layout.setBackgroundColor(Color.parseColor(colors[position])); Log.i("fragment", "Page: " + position + " view created"); return mView; } } } 

activity_main.xml:

 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent"> <android.support.v4.view.ViewPager android:id="@+id/pager" android:layout_width="match_parent" android:layout_height="match_parent"> </android.support.v4.view.ViewPager> 

fragment_layout.xml

 <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="fill_parent" android:layout_height="fill_parent" android:id="@+id/relativelayout"> <TextView android:id="@+id/textView1" android:layout_width="wrap_content" android:layout_height="wrap_content" android:layout_centerHorizontal="true" android:layout_centerVertical="true" android:text="Large Text" android:textSize="40sp" /> 

Answer 1

Try mViewpager.setAdapter (null) before adding or removing items from the list. Then install the adapter back into the mPagerAdapter. It seems that ViewPager was not intended to handle insertions or exceptions, except from the end of the list.

I have an example of working code that may be useful to you. See a sample ViewPager .