android - NullPointerException when initializing NavigationDrawer -

i'm trying use navagation drawer in application , keep running nullpointerexceptions , don't understand why. current code based largely off of this developer link is:

public class mainactivity extends activity { private string[] mpages; private drawerlayout mdrawerlayout; private listview mdrawerlist; private actionbardrawertoggle mdrawertoggle; private charsequence mdrawertitle; private charsequence mtitle;  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);      mpages = getresources().getstringarray(r.array.page_titles);     mdrawerlayout = (drawerlayout) findviewbyid(r.id.drawer_layout);     mdrawerlist = (listview) findviewbyid(r.id.left_drawer);     mdrawerlist.setadapter(new arrayadapter<string>(this,             r.layout.drawer_list_item, mpages));      mtitle = mdrawertitle = gettitle();     mdrawerlayout = (drawerlayout) findviewbyid(r.id.drawer_layout);     mdrawertoggle = new actionbardrawertoggle(this,      mdrawerlayout,     r.drawable.ic_drawer,      r.string.drawer_open,      r.string.drawer_close      ) {           public void ondrawerclosed(view view) {             getactionbar().settitle(mtitle);         }           public void ondraweropened(view drawerview) {             getactionbar().settitle(mdrawertitle);         }     };       mdrawerlayout.setdrawerlistener(mdrawertoggle);      getactionbar().setdisplayhomeasupenabled(true);     getactionbar().sethomebuttonenabled(true); }  @override protected void onpostcreate(bundle savedinstancestate) {     super.onpostcreate(savedinstancestate);     // sync toggle state after onrestoreinstancestate has occurred.     mdrawertoggle.syncstate(); }  @override public void onconfigurationchanged(configuration newconfig) {     super.onconfigurationchanged(newconfig);     mdrawertoggle.onconfigurationchanged(newconfig); }  @override public boolean onoptionsitemselected(menuitem item) {      if (mdrawertoggle.onoptionsitemselected(item)) {         return true;     }      return super.onoptionsitemselected(item); }  @override public boolean oncreateoptionsmenu(menu menu) {     getmenuinflater().inflate(r.menu.main, menu);     return true; }  } 

and drawer_layout.xml:

<android.support.v4.widget.drawerlayout xmlns:android="http://schemas.android.com/apk/res/android" android:id="@+id/drawer_layout" android:layout_width="match_parent" android:layout_height="match_parent"> <!-- main content view --> <framelayout     android:id="@+id/content_frame"     android:layout_width="match_parent"     android:layout_height="match_parent" /> <!-- navigation drawer --> <listview android:id="@+id/left_drawer"     android:layout_width="240dp"     android:layout_height="match_parent"     android:layout_gravity="start"     android:choicemode="singlechoice"     android:divider="@android:color/transparent"     android:dividerheight="0dp"     android:background="#111"/> 

my stacktrace:

08-12 15:55:54.524: e/androidruntime(1409): fatal exception: main 08-12 15:55:54.524: e/androidruntime(1409): java.lang.runtimeexception:     unable start activity     componentinfo{com.test.android.nav/com.test.android.nav.mainactivity}:     java.lang.nullpointerexception 08-12 15:55:54.524: e/androidruntime(1409):     @     android.app.activitythread.performlaunchactivity(activitythread.java:2059) 08-12 15:55:54.524: e/androidruntime(1409):     @ android.app.activitythread.handlelaunchactivity(activitythread.java:2084) 08-12 15:55:54.524: e/androidruntime(1409):     @ android.app.activitythread.access$600(activitythread.java:130) 08-12 15:55:54.524: e/androidruntime(1409):     @ android.app.activitythread$h.handlemessage(activitythread.java:1195) 08-12 15:55:54.524: e/androidruntime(1409):     @ android.os.handler.dispatchmessage(handler.java:99) 08-12 15:55:54.524: e/androidruntime(1409):     @ android.os.looper.loop(looper.java:137) 08-12 15:55:54.524: e/androidruntime(1409):     @ android.app.activitythread.main(activitythread.java:4745) 08-12 15:55:54.524: e/androidruntime(1409):     @ java.lang.reflect.method.invokenative(native method) 08-12 15:55:54.524: e/androidruntime(1409):     @ java.lang.reflect.method.invoke(method.java:511) 08-12 15:55:54.524: e/androidruntime(1409):     @ com.android.internal.os.zygoteinit$methodandargscaller.run(zygoteinit.java:786) 08-12 15:55:54.524: e/androidruntime(1409):     @ com.android.internal.os.zygoteinit.main(zygoteinit.java:553) 08-12 15:55:54.524: e/androidruntime(1409):     @ dalvik.system.nativestart.main(native method) 08-12 15:55:54.524: e/androidruntime(1409): caused by: java.lang.nullpointerexception 08-12 15:55:54.524: e/androidruntime(1409):     @ com.test.android.nav.mainactivity.oncreate(mainactivity.java:30) 08-12 15:55:54.524: e/androidruntime(1409):     @ android.app.activity.performcreate(activity.java:5008) 08-12 15:55:54.524: e/androidruntime(1409):     @ android.app.instrumentation.callactivityoncreate(instrumentation.java:1079) 08-12 15:55:54.524: e/androidruntime(1409):     @ android.app.activitythread.performlaunchactivity(activitythread.java:2023) 08-12 15:55:54.524: e/androidruntime(1409):     ... 11 more 

line 30 : mdrawerlist.setadapter(new arrayadapter<string>(this, r.layout.drawer_list_item, mpages)); , have xml file in res folder.

now, before put in line, getting nullpointerexception on line: mdrawerlayout.setdrawerlistener(mdrawertoggle);

any appreciated!

i see 2 potential reasons nullpointerexception:

the first 1 line:

mpages = getresources().getstringarray(r.array.page_titles); 

does not return valid array mpages. suppose you not have string array called "page_titles" in resources folder.

if posted code absolutely correct, 1 other reason line:

setcontentview(r.layout.activity_main); 

since according code, layoutfile of navigationdrawer drawer_layout.xml. should this:

setcontentview(r.layout.drawer_layout); 

in opinion, resource id of drawerlayout , name of .xml file both being "drawer_layout" misleading, recommend change that.

furthermore, don't see reason why calling line:

 mdrawerlayout = (drawerlayout) findviewbyid(r.id.drawer_layout); 

twice in oncreate() method.