dynamically add and remove view to viewpager

After figuring out which ViewPager methods are called by ViewPager and which are for other purposes, I came up with a solution. I present it here since I see a lot of people have struggled with this and I didn't see any other relevant answers.

First, here's my adapter; hopefully comments within the code are sufficient:

public class MainPagerAdapter extends PagerAdapter{  // This holds all the currently displayable views, in order from left to right.  private ArrayList<View> views = new ArrayList<View>();  //-----------------------------------------------------------------------------  // Used by ViewPager.  "Object" represents the page; tell the ViewPager where the  // page should be displayed, from left-to-right.  If the page no longer exists,  // return POSITION_NONE.  @Override  public int getItemPosition (Object object)  {    int index = views.indexOf (object);    if (index == -1)      return POSITION_NONE;    else      return index;  }  //-----------------------------------------------------------------------------  // Used by ViewPager.  Called when ViewPager needs a page to display; it is our job  // to add the page to the container, which is normally the ViewPager itself.  Since  // all our pages are persistent, we simply retrieve it from our "views" ArrayList.  @Override  public Object instantiateItem (ViewGroup container, int position)  {    View v = views.get (position);    container.addView (v);    return v;  }  //-----------------------------------------------------------------------------  // Used by ViewPager.  Called when ViewPager no longer needs a page to display; it  // is our job to remove the page from the container, which is normally the  // ViewPager itself.  Since all our pages are persistent, we do nothing to the  // contents of our "views" ArrayList.  @Override  public void destroyItem (ViewGroup container, int position, Object object)  {    container.removeView (views.get (position));  }  //-----------------------------------------------------------------------------  // Used by ViewPager; can be used by app as well.  // Returns the total number of pages that the ViewPage can display.  This must  // never be 0.  @Override  public int getCount ()  {    return views.size();  }  //-----------------------------------------------------------------------------  // Used by ViewPager.  @Override  public boolean isViewFromObject (View view, Object object)  {    return view == object;  }  //-----------------------------------------------------------------------------  // Add "view" to right end of "views".  // Returns the position of the new view.  // The app should call this to add pages; not used by ViewPager.  public int addView (View v)  {    return addView (v, views.size());  }  //-----------------------------------------------------------------------------  // Add "view" at "position" to "views".  // Returns position of new view.  // The app should call this to add pages; not used by ViewPager.  public int addView (View v, int position)  {    views.add (position, v);    return position;  }  //-----------------------------------------------------------------------------  // Removes "view" from "views".  // Retuns position of removed view.  // The app should call this to remove pages; not used by ViewPager.  public int removeView (ViewPager pager, View v)  {    return removeView (pager, views.indexOf (v));  }  //-----------------------------------------------------------------------------  // Removes the "view" at "position" from "views".  // Retuns position of removed view.  // The app should call this to remove pages; not used by ViewPager.  public int removeView (ViewPager pager, int position)  {    // ViewPager doesn't have a delete method; the closest is to set the adapter    // again.  When doing so, it deletes all its views.  Then we can delete the view    // from from the adapter and finally set the adapter to the pager again.  Note    // that we set the adapter to null before removing the view from "views" - that's    // because while ViewPager deletes all its views, it will call destroyItem which    // will in turn cause a null pointer ref.    pager.setAdapter (null);    views.remove (position);    pager.setAdapter (this);    return position;  }  //-----------------------------------------------------------------------------  // Returns the "view" at "position".  // The app should call this to retrieve a view; not used by ViewPager.  public View getView (int position)  {    return views.get (position);  }  // Other relevant methods:  // finishUpdate - called by the ViewPager - we don't care about what pages the  // pager is displaying so we don't use this method.}

And here's some snips of code showing how to use the adapter.

class MainActivity extends Activity{  private ViewPager pager = null;  private MainPagerAdapter pagerAdapter = null;  //-----------------------------------------------------------------------------  @Override  public void onCreate (Bundle savedInstanceState)  {    super.onCreate(savedInstanceState);    setContentView (R.layout.main_activity);    ... do other initialization, such as create an ActionBar ...    pagerAdapter = new MainPagerAdapter();    pager = (ViewPager) findViewById (R.id.view_pager);    pager.setAdapter (pagerAdapter);    // Create an initial view to display; must be a subclass of FrameLayout.    LayoutInflater inflater = context.getLayoutInflater();    FrameLayout v0 = (FrameLayout) inflater.inflate (R.layout.one_of_my_page_layouts, null);    pagerAdapter.addView (v0, 0);    pagerAdapter.notifyDataSetChanged();  }  //-----------------------------------------------------------------------------  // Here's what the app should do to add a view to the ViewPager.  public void addView (View newPage)  {    int pageIndex = pagerAdapter.addView (newPage);    // You might want to make "newPage" the currently displayed page:    pager.setCurrentItem (pageIndex, true);  }  //-----------------------------------------------------------------------------  // Here's what the app should do to remove a view from the ViewPager.  public void removeView (View defunctPage)  {    int pageIndex = pagerAdapter.removeView (pager, defunctPage);    // You might want to choose what page to display, if the current page was "defunctPage".    if (pageIndex == pagerAdapter.getCount())      pageIndex--;    pager.setCurrentItem (pageIndex);  }  //-----------------------------------------------------------------------------  // Here's what the app should do to get the currently displayed page.  public View getCurrentPage ()  {    return pagerAdapter.getView (pager.getCurrentItem());  }  //-----------------------------------------------------------------------------  // Here's what the app should do to set the currently displayed page.  "pageToShow" must  // currently be in the adapter, or this will crash.  public void setCurrentPage (View pageToShow)  {    pager.setCurrentItem (pagerAdapter.getItemPosition (pageToShow), true);  }}

Finally, you can use the following for your activity_main.xml layout:

<?xml version="1.0" encoding="utf-8"?><android.support.v4.view.ViewPager    xmlns:android="http://schemas.android.com/apk/res/android"    android:id="@+id/view_pager"    android:layout_width="match_parent"    android:layout_height="match_parent" ></android.support.v4.view.ViewPager>

I was looking for simple solution to remove views from viewpager (no fragments) dynamically. So, if you have some info, that your pages belongs to, you can set it to View as tag. Just like that (adapter code):

@Overridepublic Object instantiateItem(ViewGroup collection, int position){    ImageView iv = new ImageView(mContext);    MediaMessage msg = mMessages.get(position);    ...    iv.setTag(media);    return iv;}@Overridepublic int getItemPosition (Object object){    View o = (View) object;    int index = mMessages.indexOf(o.getTag());    if (index == -1)        return POSITION_NONE;    else        return index;}

You just need remove your info from mMessages, and then call notifyDataSetChanged() for your adapter. Bad news there is no animation in this case.

There are quite a few discussions around this topic

• ViewPager PagerAdapter not updating the View
• Update ViewPager dynamically?
• Removing fragments from FragmentStatePagerAdapter

Although we see it often, using POSITION_NONE does not seem to be the way to go as it is very inefficient memory-wise.

Here in this question, we should consider using Alvaro's approach:

... is to setTag() method in instantiateItem() when instantiating a new view. Then instead of using notifyDataSetChanged(), you can use findViewWithTag() to find the view you want to update.

Here is a SO answer with code based on this idea