Attempt to invoke virtual method 'void android.widget.ListView.setAdapter -

i trying make list view contains pictures , text within fragment on viewpager tabs, can swipe left or right bring fragment.

i'm relatively new android may doing wrong. can build project fine when emulator runs crashes (log displayed @ bottom of page).

i created separate application , able create list view, when try combine within fragment so, doesn't work. here following code

mainactivity.java

import java.util.arraylist; import java.util.list; import java.util.locale;  import android.app.listfragment; import android.content.intent; import android.support.v7.app.actionbaractivity; import android.support.v7.app.actionbar; import android.support.v4.app.fragment; import android.support.v4.app.fragmentmanager; import android.support.v4.app.fragmenttransaction; import android.support.v4.app.fragmentpageradapter; import android.os.bundle; import android.support.v4.view.viewpager; import android.view.gravity; import android.view.layoutinflater; import android.view.menu; import android.view.menuitem; import android.view.view; import android.view.viewgroup; import android.widget.adapterview; import android.widget.arrayadapter; import android.widget.imageview; import android.widget.listview; import android.widget.textview; import android.widget.toast;   public class mainactivity extends actionbaractivity implements actionbar.tablistener {      /**      * {@link android.support.v4.view.pageradapter} provide      * fragments each of sections. use      * {@link fragmentpageradapter} derivative, keep every      * loaded fragment in memory. if becomes memory intensive,      * may best switch      * {@link android.support.v4.app.fragmentstatepageradapter}.      */     sectionspageradapter msectionspageradapter;      /**      * {@link viewpager} host section contents.      */     viewpager mviewpager;    private list<posts> myposts = new arraylist<posts>();     @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);         // set action bar.         final actionbar actionbar = getsupportactionbar();         actionbar.setnavigationmode(actionbar.navigation_mode_tabs);          // create adapter return fragment each of 3         // primary sections of activity.         msectionspageradapter = new sectionspageradapter(getsupportfragmentmanager());          // set viewpager sections adapter.         mviewpager = (viewpager) findviewbyid(r.id.pager);         mviewpager.setadapter(msectionspageradapter);          // when swiping between different sections, select corresponding         // tab. can use actionbar.tab#select() if have         // reference tab.         mviewpager.setonpagechangelistener(new viewpager.simpleonpagechangelistener() {             @override             public void onpageselected(int position) {                 actionbar.setselectednavigationitem(position);             }         });          // each of sections in app, add tab action bar.         (int = 0; < msectionspageradapter.getcount(); i++) {             // create tab text corresponding page title defined             // adapter. specify activity object, implements             // tablistener interface, callback (listener) when             // tab selected.             actionbar.addtab(                     actionbar.newtab()                             .settext(msectionspageradapter.getpagetitle(i))                             .settablistener(this));          }           intent intent = new intent(mainactivity.this, notmainactivity.class);         startactivity(intent);         finish();     }      @override     public boolean oncreateoptionsmenu(menu menu) {         // inflate menu; adds items action bar if present.         getmenuinflater().inflate(r.menu.menu_main, menu);         return true;     }      @override     public boolean onoptionsitemselected(menuitem item) {         // handle action bar item clicks here. action bar         // automatically handle clicks on home/up button, long         // specify parent activity in androidmanifest.xml.         int id = item.getitemid();          //noinspection simplifiableifstatement         if (id == r.id.action_settings) {             return true;         }          return super.onoptionsitemselected(item);     }      @override     public void ontabselected(actionbar.tab tab, fragmenttransaction fragmenttransaction) {         // when given tab selected, switch corresponding page in         // viewpager.         mviewpager.setcurrentitem(tab.getposition());     }      @override     public void ontabunselected(actionbar.tab tab, fragmenttransaction fragmenttransaction) {     }      @override     public void ontabreselected(actionbar.tab tab, fragmenttransaction fragmenttransaction) {     }     /**      * {@link fragmentpageradapter} returns fragment corresponding      * 1 of sections/tabs/pages.      */     public class sectionspageradapter extends fragmentpageradapter {          public sectionspageradapter(fragmentmanager fm) {             super(fm);         }          @override         public fragment getitem(int position) {             // getitem called instantiate fragment given page.             // return placeholderfragment (defined static inner class below).             switch (position){                 case 0:                     return new thewallfragment();                 case 1:                     return new peekfragment();                 case 2:                     return new camerafragment();                 default:                     break;              }              return placeholderfragment.newinstance(position + 1);         }             @override         public int getcount() {             // show 3 total pages.             return 3;         }          @override         public charsequence getpagetitle(int position) {             locale l = locale.getdefault();             switch (position) {                 case 0:                     return getstring(r.string.title_section1).touppercase(l);                 case 1:                     return getstring(r.string.title_section2).touppercase(l);                 case 2:                     return getstring(r.string.title_section3).touppercase(l);             }             return null;         }     }      /**      * placeholder fragment containing simple view.      */     public static class placeholderfragment extends fragment {         /**          * fragment argument representing section number          * fragment.          */         private static final string arg_section_number = "section_number";          /**          * returns new instance of fragment given section          * number.          */         public static placeholderfragment newinstance(int sectionnumber) {             placeholderfragment fragment = new placeholderfragment();             bundle args = new bundle();             args.putint(arg_section_number, sectionnumber);             fragment.setarguments(args);             return fragment;         }          public placeholderfragment() {         }          @override         public view oncreateview(layoutinflater inflater, viewgroup container,                                  bundle savedinstancestate) {             view rootview = inflater.inflate(r.layout.wall_layout, container, false);              return rootview;         }     }  } 

notmainactivity.java

public class notmainactivity extends fragmentactivity {      private list<posts> myposts = new arraylist<posts>();      @override     protected void oncreate(bundle savedinstancestate) {         super.oncreate(savedinstancestate);         setcontentview(r.layout.activity_main);         populatepostlist();         populatelistview();         registerclickcallback();         system.out.print("main activity started");        }       private void populatepostlist()     {         myposts.add(new posts("ottawa, ontario", "787", "picture of dog!", r.drawable.dog));         myposts.add(new posts("ottawa, ontario", "787", "picture of dog!", r.drawable.dog));         myposts.add(new posts("ottawa, ontario", "787", "picture of dog!", r.drawable.dog));         myposts.add(new posts("ottawa, ontario", "787", "picture of dog!", r.drawable.dog));         myposts.add(new posts("ottawa, ontario", "787", "picture of dog!", r.drawable.dog));         myposts.add(new posts("ottawa, ontario", "787", "picture of dog!", r.drawable.dog));         myposts.add(new posts("ottawa, ontario", "787", "picture of dog!", r.drawable.dog));         myposts.add(new posts("ottawa, ontario", "787", "picture of dog!", r.drawable.dog));        }      private void populatelistview() {         arrayadapter<posts> adapter = new mylistadapter();         listview list = (listview) findviewbyid(android.r.id.list);         list.setadapter(adapter);          }       //handles clicks on list items     private void registerclickcallback(){         listview list = (listview) findviewbyid(android.r.id.list);         list.setonitemclicklistener(new adapterview.onitemclicklistener() {             @override             public void onitemclick(adapterview<?> parent, view view, int position, long id) {                 posts clickedpost = myposts.get(position);                 string message = "you clicked" + position                         +"location of post is" + clickedpost.getpostlocation();                 toast.maketext(notmainactivity.this, message, toast.length_long).show();             }         });     }       private class mylistadapter extends arrayadapter<posts> {         public mylistadapter() {             super(notmainactivity.this, r.layout.item_view, myposts);         }           @override         public view getview(int position, view convertview, viewgroup parent) {             // make sure have view work {may have given null}             view itemview = convertview;             if (itemview != null) {                 itemview = getlayoutinflater().inflate(r.layout.item_view, parent, false);             }             // find post work with.             posts currentpost = myposts.get(position);               //fill view             imageview imageview = (imageview)itemview.findviewbyid(r.id.item_postimage);             imageview.setimageresource(currentpost.geticonid());              //fill in title              textview titletext = (textview) itemview.findviewbyid(r.id.item_posttext);             titletext.settext(currentpost.getposttitle());              //set vote number             textview votetext = (textview) itemview.findviewbyid(r.id.item_postvotetext);             votetext.settext(currentpost.getpostvote());                return itemview;         }      }  } 

posts.java

public class posts {     private string postlocation;     private string postvote;     private string posttitle;     private int iconid;      public posts(string postlocation, string postvote, string posttitle, int iconid) {         this.postlocation = postlocation;         this.postvote = postvote;         this.posttitle = posttitle;         this.iconid = iconid;     }            public string getpostlocation() {         return postlocation;     }      public string getpostvote() {         return postvote;     }      public string getposttitle() {         return posttitle;     }     public int geticonid() {         return iconid;     } 

thewallfragment.java

public class thewallfragment extends android.support.v4.app.listfragment {     list<posts> myposts = new arraylist<posts>();     private string[] strlistview;     private listview mylistview;     private int number;     public view oncreateview(layoutinflater inflater, viewgroup container,                              bundle savedinstancestate) {         view rootview = inflater.inflate(r.layout.wall_layout, container, false);         return rootview;     }   } 

activity_main.xml

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

androidmanifest.xml

<?xml version="1.0" encoding="utf-8"?> <manifest xmlns:android="http://schemas.android.com/apk/res/android"     package="com.gnumbu.errolgreen.testing" >      <application         android:allowbackup="true"         android:icon="@mipmap/ic_launcher"         android:label="@string/app_name"         android:theme="@style/apptheme" >         <activity             android:name=".mainactivity"             android:label="@string/app_name" >             <intent-filter>                 <action android:name="android.intent.action.main" />                  <category android:name="android.intent.category.launcher" />             </intent-filter>         </activity> <activity     android:name=".notmainactivity">     </activity>     </application>  </manifest> 

item_view.xml

    <?xml version="1.0" encoding="utf-8"?> <relativelayout xmlns:android="http://schemas.android.com/apk/res/android"     android:layout_width="match_parent" android:layout_height="match_parent">      <imageview         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:id="@+id/item_postimage"         android:src="@drawable/dog"         android:maxwidth="80dp"         android:minheight="80dp"         android:adjustviewbounds="true"         android:layout_marginleft="14dp"         android:layout_marginstart="14dp"         android:layout_alignparenttop="true"         android:layout_torightof="@+id/item_upvotearrow"         android:layout_toendof="@+id/item_upvotearrow"         android:layout_alignbottom="@+id/item_downvotearrow" />      <textview         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="this dog! dog amazing, give lick!"         android:id="@+id/item_posttext"         android:paddingstart="5dp"         android:layout_above="@+id/item_downvotearrow"         android:layout_torightof="@+id/item_postimage"         android:layout_toendof="@+id/item_postimage" />      <imageview         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:id="@+id/item_upvotearrow"         android:src="@drawable/upvotearrow"         android:maxheight="24dp"         android:maxwidth="24dp"         android:adjustviewbounds="true"         android:layout_alignparenttop="true"         android:layout_alignleft="@+id/item_downvotearrow"         android:layout_alignstart="@+id/item_downvotearrow"         android:clickable="true" />      <imageview         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:id="@+id/item_downvotearrow"         android:src="@drawable/downvotearrow"         android:maxwidth="24dp"         android:maxheight="24dp"         android:adjustviewbounds="true"         android:layout_marginleft="9dp"         android:layout_marginstart="9dp"         android:layout_below="@+id/item_postvotetext"         android:layout_alignparentleft="true"         android:layout_alignparentstart="true"         android:longclickable="false"         android:clickable="true" />      <textview         android:layout_height="wrap_content"         android:text="22"         android:id="@+id/item_postvotetext"         android:maxheight="20dp"         android:focusableintouchmode="false"         android:visibility="visible"         android:singleline="true"         android:gravity="center"         android:enabled="true"         android:layout_below="@+id/item_upvotearrow"         android:layout_alignleft="@+id/item_upvotearrow"         android:layout_alignstart="@+id/item_upvotearrow"         android:nestedscrollingenabled="false"         android:layout_width="wrap_content"         android:layout_tostartof="@+id/item_postimage" />  </relativelayout> 

wall_layout.xml

<?xml version="1.0" encoding="utf-8"?> <linearlayout xmlns:android="http://schemas.android.com/apk/res/android"     android:orientation="vertical" android:layout_width="match_parent"     android:layout_height="match_parent">      <textview         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:text="new text"         android:id="@+id/textview"         android:layout_gravity="center_horizontal" />      <listview         android:id="@android:id/list"         android:layout_width="wrap_content"         android:layout_height="wrap_content"             /> </linearlayout> 

error log

 java.lang.nullpointerexception: attempt invoke virtual method 'void android.widget.listview.setadapter(android.widget.listadapter)' on null object reference             @ android.app.activitythread.performlaunchactivity(activitythread.java:2298)             @ android.app.activitythread.handlelaunchactivity(activitythread.java:2360)             @ android.app.activitythread.access$800(activitythread.java:144)             @ android.app.activitythread$h.handlemessage(activitythread.java:1278)             @ android.os.handler.dispatchmessage(handler.java:102)             @ android.os.looper.loop(looper.java:135)             @ android.app.activitythread.main(activitythread.java:5223)             @ java.lang.reflect.method.invoke(native method)             @ java.lang.reflect.method.invoke(method.java:372)             @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:899)             @ com.android.internal.os.zygoteinit.main(zygoteinit.java:694)      caused by: java.lang.nullpointerexception: attempt invoke virtual method 'void android.widget.listview.setadapter(android.widget.listadapter)' on null object reference             @ com.gnumbu.errolgreen.testing.notmainactivity.populatelistview(notmainactivity.java:70)             @ com.gnumbu.errolgreen.testing.notmainactivity.oncreate(notmainactivity.java:43)             @ android.app.activity.performcreate(activity.java:5937)             @ android.app.instrumentation.callactivityoncreate(instrumentation.java:1105)             @ android.app.activitythread.performlaunchactivity(activitythread.java:2251)             at android.app.activitythread.handlelaunchactivity(activitythread.java:2360)             at android.app.activitythread.access$800(activitythread.java:144)             at android.app.activitythread$h.handlemessage(activitythread.java:1278)             at android.os.handler.dispatchmessage(handler.java:102)             at android.os.looper.loop(looper.java:135)             at android.app.activitythread.main(activitythread.java:5223)             at java.lang.reflect.method.invoke(native method)             at java.lang.reflect.method.invoke(method.java:372)             at com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:899)             at com.android.internal.os.zygoteinit.main(zygoteinit.java:694) 

new error

 process: com.gnumbu.errolgreen.testing, pid: 5304     java.lang.nullpointerexception: attempt invoke virtual method 'int android.view.view.getimportantforaccessibility()' on null object reference             @ android.widget.abslistview.obtainview(abslistview.java:2360)             @ android.widget.listview.measureheightofchildren(listview.java:1270)             @ android.widget.listview.onmeasure(listview.java:1182)             @ android.view.view.measure(view.java:17430)             @ android.view.viewgroup.measurechildwithmargins(viewgroup.java:5463)             @ android.widget.linearlayout.measurechildbeforelayout(linearlayout.java:1436)             @ android.widget.linearlayout.measurevertical(linearlayout.java:722)             @ android.widget.linearlayout.onmeasure(linearlayout.java:613)             @ android.view.view.measure(view.java:17430)             @ android.view.viewgroup.measurechildwithmargins(viewgroup.java:5463)             @ android.widget.framelayout.onmeasure(framelayout.java:430)             @ android.view.view.measure(view.java:17430)             @ android.view.viewgroup.measurechildwithmargins(viewgroup.java:5463)             @ android.widget.linearlayout.measurechildbeforelayout(linearlayout.java:1436)             @ android.widget.linearlayout.measurevertical(linearlayout.java:722)             @ android.widget.linearlayout.onmeasure(linearlayout.java:613)             @ android.view.view.measure(view.java:17430)             @ android.view.viewgroup.measurechildwithmargins(viewgroup.java:5463)             @ android.widget.framelayout.onmeasure(framelayout.java:430)             @ com.android.internal.policy.impl.phonewindow$decorview.onmeasure(phonewindow.java:2560)             @ android.view.view.measure(view.java:17430)             @ android.view.viewrootimpl.performmeasure(viewrootimpl.java:2001)             @ android.view.viewrootimpl.measurehierarchy(viewrootimpl.java:1166)             @ android.view.viewrootimpl.performtraversals(viewrootimpl.java:1372)             @ android.view.viewrootimpl.dotraversal(viewrootimpl.java:1054)             @ android.view.viewrootimpl$traversalrunnable.run(viewrootimpl.java:5779)             @ android.view.choreographer$callbackrecord.run(choreographer.java:767)             @ android.view.choreographer.docallbacks(choreographer.java:580)             @ android.view.choreographer.doframe(choreographer.java:550)             @ android.view.choreographer$framedisplayeventreceiver.run(choreographer.java:753)             @ android.os.handler.handlecallback(handler.java:739)             @ android.os.handler.dispatchmessage(handler.java:95)             @ android.os.looper.loop(looper.java:135)             @ android.app.activitythread.main(activitythread.java:5221)             @ java.lang.reflect.method.invoke(native method)             @ java.lang.reflect.method.invoke(method.java:372)             @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:899)             @ com.android.internal.os.zygoteinit.main(zygoteinit.java:694) 

notmainactivity calls setcontentview r.layout.activity_main parameter contains viewpager , not listview. since don't have listview declare in layout, findviewbyid(android.r.id.list) returns null, , when try access (calling setadapter) nullpointerexception thrown.

in myadapter, change from

if (itemview != null) {       itemview = getlayoutinflater().inflate(r.layout.item_view, parent, false); } 

to

if (itemview == null) {       itemview = getlayoutinflater().inflate(r.layout.item_view, parent, false); }