java - App Crashes in two pane mode on launching -

actually iam making app displays popular movies ( popular movie app project of udacity course) , have 2 activites main activity , detail activity when tried make app run on tablet crashes , can't display main activity on launching app , dont know missing .... , want know how can specify app should run on different screen sizes tablets..

mainactivity.java

public class mainactivity extends appcompatactivity {  private static final string detailfragment_tag ="dftag" ; @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     setcontentview(r.layout.activity_main);  if (findviewbyid(r.id.movie_detail_container) != null) {     mtwopane = true;     if (savedinstancestate == null) {         getsupportfragmentmanager().begintransaction()                 .replace(r.id.movie_detail_container, new moviedetailfragment(),detailfragment_tag)                 .commit();         log.v(log_tag, "crash ");     } } else {     mtwopane = false; } 

moviedetail.java

 @override  protected void oncreate(bundle savedinstancestate) { super.oncreate(savedinstancestate); setcontentview(r.layout.activity_movie_detail);   if (savedinstancestate == null) {     getsupportfragmentmanager().begintransaction()             .add(r.id.movie_detail_container, new moviedetailfragment())             .commit(); } } 

activity_main.xml

<fragment xmlns:android="http://schemas.android.com/apk/res/android"  xmlns:tools="http://schemas.android.com/tools"  android:id="@+id/fragment_movie"  android:name=".moviesfragment"  tools:context=".moviesfragment"  tools:layout="@android:layout/list_content"  android:layout_width="match_parent"  android:layout_height="match_parent"  /> 

sw600dp\activity_main.xml

<linearlayout xmlns:android="http://schemas.android.com/apk/res/android"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:baselinealigned="false"  android:divider="?android:attr/dividerhorizontal"  android:orientation="horizontal">   <fragment   android:id="@+id/fragment_movie"   android:name=".moviesfragment"   android:layout_width="0dp"   android:layout_height="match_parent"   android:layout_weight="3" />    <framelayout     android:id="@+id/movie_detail_container"     android:layout_width="0dp"     android:layout_height="match_parent"     android:layout_weight="4" /> 

activity_movie_detail.xml

<framelayout xmlns:android="http://schemas.android.com/apk/res/android"  xmlns:tools="http://schemas.android.com/tools"  android:id="@+id/movie_detail_container"  android:layout_width="match_parent"  android:layout_height="match_parent"  tools:context=".moviedetail"  tools:ignore="mergerootframe" /> 

logcat

java.lang.runtimeexception: unable start activity componentinfo{.popularmovies/.popularmovies.mainactivity}:  java.lang.nullpointerexception     @ android.app.activitythread.performlaunchactivity(activitythread.java:2059) 

i think not getting xml resource reference correctly. try add "movie_detail_container" in /mainactivity xml too. , try