How to set up tabs with view pager in android? -

i have followed following instructions in order sliding tabs view pager.

here oncreate method:

mviewpager.setadapter(new navigationpageradapter(getsupportfragmentmanager())); mtablayout.setupwithviewpager(mviewpager); 

here navigation pager adapter:

public static class navigationpageradapter extends fragmentpageradapter {     private static final int num_items = 3;      public navigationpageradapter(fragmentmanager fragmentmanager) {         super(fragmentmanager);     }      // returns total number of pages     @override     public int getcount() {         return num_items;     }      // returns fragment display page     @override     public fragment getitem(int position) {         switch (position) {             case 0: // fragment # 0 - show firstfragment                 return new feedfragment();             default:                 return null;         }     }      // returns page title top indicator     @override     public charsequence getpagetitle(int position) {         return "page " + position;     } } 

here content_main.xml activity layout:

<android.support.design.widget.tablayout     android:id="@+id/navigation_sliding_tabs"     android:layout_width="match_parent"     android:layout_height="wrap_content"     app:tabmode="scrollable"/>  <android.support.v4.view.viewpager     android:id="@+id/navigation_pager"     android:layout_width="match_parent"     android:layout_height="0px"     android:layout_weight="1"/> 

this error when running code:

java.lang.nullpointerexception: attempt write field 'android.support.v4.app.fragmentmanagerimpl android.support.v4.app.fragment.mfragmentmanager' on null object reference 

i not sure if error lies in pager adapter seems fragment manager causing trouble.

try in adapter

feedfragment feedfragment; public navigationpageradapter(fragmentmanager fragmentmanager) {     super(fragmentmanager);     feedfragment=new feedfragment(); }  // returns total number of pages @override public int getcount() {     return num_items; }  // returns fragment display page @override public fragment getitem(int position) { fragment fragment;     switch (position) {         case 0: // fragment # 0 - show firstfragment             fragment=feedfragment;             break;          return fragment;      } }  // returns page title top indicator @override public charsequence getpagetitle(int position) {     return "page " + position; } }