Android ViewPager keeps crashing with NullPointerException on orientation change -

i trying add viewpager android app one-time setup screen user. problem facing app keeps crashing when orientation of screen changed amidst setup process.

if app opened in either portrait or landscape mode , used without orientation change, works fine. if orientation changed during runtime, using method setcurrentitem(int position) on viewpager crashes app.

here's fragment class -

package com.cosine.arc;   import android.content.context; import android.graphics.typeface; import android.os.bundle; import android.support.v4.app.fragment; import android.support.v4.view.viewpager; import android.view.layoutinflater; import android.view.view; import android.view.viewgroup; import android.widget.button; import android.widget.textview;  /**  * simple {@link fragment} subclass.  */ public class welcomefragment extends fragment {  private int mposition; private context mcontext; private viewpager mpager;  private final int[] welcomefragments = {r.layout.fragment_welcome1};  public welcomefragment() {     // required empty public constructor }  public welcomefragment(context context, viewpager viewpager, int position) {      this.mposition = position;     this.mcontext = context;     this.mpager = viewpager;  }  @override public view oncreateview(final layoutinflater inflater, final viewgroup container, bundle savedinstancestate) {      view view = null;      try {         switch (mposition) {              case 0:                 view = inflater.inflate(r.layout.fragment_welcome1, container, false);                  typeface robotolight = typeface.createfromasset(getactivity().getassets(), "fonts/roboto-light.ttf");                 textview welcometxt1x2 = (textview) view.findviewbyid(r.id.welcome_text_1_2);                  button startbutton = (button) view.findviewbyid(r.id.welcome_btn_1_1);                   startbutton.setonclicklistener(new view.onclicklistener() {                     @override                     public void onclick(view view) {                         mpager.setcurrentitem(1);                     }                 });                 welcometxt1x2.settypeface(robotolight);         }     } catch (nullpointerexception e) {         e.printstacktrace();     }      return view; }  } 

and here's fragmentactivity class fragmentstatepageradapter class within -

package com.cosine.arc;  import android.os.bundle; import android.support.v4.app.fragment; import android.support.v4.app.fragmentactivity; import android.support.v4.app.fragmentmanager; import android.support.v4.app.fragmentstatepageradapter; import android.support.v4.view.pageradapter;  public class introactivity extends fragmentactivity {  private static int num_pages = 3;  private nonswipeableviewpager mpager; private pageradapter mpageradapter;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_intro);      mpager = (nonswipeableviewpager) findviewbyid(r.id.intro_pager);     mpageradapter = new introslideradapter(getsupportfragmentmanager());     mpager.setadapter(mpageradapter);  }  @override public void onbackpressed() {     if (mpager.getcurrentitem()==0) {         super.onbackpressed();     }     else {         mpager.setcurrentitem(mpager.getcurrentitem()-1);     } }  public int getcurrentitem() {     return mpager.getcurrentitem(); }  public nonswipeableviewpager getpagerupdate() {      return mpager; }  private class introslideradapter extends fragmentstatepageradapter {      public introslideradapter(fragmentmanager fm) {         super(fm);     }      @override     public fragment getitem(int position) {         return new welcomefragment(getbasecontext(), mpager, position);     }      @override     public int getcount() {         return num_pages;     }  } } 

and here error log -

04-07 15:25:13.774 12186-12186/com.cosine.arc e/androidruntime: fatal exception: main    process: com.cosine.arc, pid: 12186 java.lang.nullpointerexception: attempt invoke virtual method 'void android.support.v4.view.viewpager.setcurrentitem(int)' on null object reference    @ com.cosine.arc.welcomefragment$1.onclick(welcomefragment.java:58)    @ android.view.view.performclick(view.java:5612)    @ android.view.view$performclick.run(view.java:22288)    @ android.os.handler.handlecallback(handler.java:751)    @ android.os.handler.dispatchmessage(handler.java:95)    @ android.os.looper.loop(looper.java:154)    @ android.app.activitythread.main(activitythread.java:6123)    @ java.lang.reflect.method.invoke(native method)    @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:867)    @ com.android.internal.os.zygoteinit.main(zygoteinit.java:757) 

fragment_welcome1.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"     tools:context="com.cosine.arc.welcomefragment">  <relativelayout     android:layout_width="match_parent"     android:layout_height="match_parent"     android:background="@color/colorprimary">      <textview         android:id="@+id/welcome_text_1_1"         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:text="@string/welcome_to_"         android:textcolor="@android:color/white"         android:textsize="36sp"         android:padding="16dp"         android:layout_margintop="16dp"         android:gravity="center"/>      <imageview         android:id="@+id/welcome_img_1_1"         android:layout_width="150dp"         android:layout_height="150dp"         android:src="@drawable/ic_logo"         android:layout_below="@id/welcome_text_1_1"         android:layout_centerhorizontal="true"/>      <textview         android:id="@+id/welcome_text_1_2"         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:layout_below="@id/welcome_img_1_1"         android:text="@string/lets_get_things_started_"         android:textsize="42sp"         android:textcolor="@android:color/white"         android:padding="16dp"         android:layout_margintop="32dp"/>      <button         android:id="@+id/welcome_btn_1_1"         android:layout_width="match_parent"         android:layout_height="wrap_content"         android:layout_alignparentbottom="true"         android:background="@android:color/white"         android:text="start"         android:textcolor="@android:color/black"         android:layout_margin="16dp"         android:layout_alignparentright="true"         android:drawableright="@mipmap/ic_arrow_right_light"/>  </relativelayout> 

please note have 2 different layout files fragment_welcome1.xml , fragment_welcome1.xml-land.

on orientation change, have save instance of fragment if want retain references. have @ answer, hope helps you. in nutshell, think need save instance of fragment in container activity's onsaveinstancestate(), , recreate saved fragment when orientation changes.

please note making config changes in manifest not recommended way save instance of fragment. making config changes lead memory leaks.