title: My app is crashing in landscape mode
body: <p>I don't know what's wrong, whenever I launch my app on an Emulator and I switch to landscape mode, it crashes. But it work fine in portrait mode. Please what can i do to solve this. Thanks in advance! here's my codes...</p>
  
  <p>MainActivity.class</p>
  
  <pre><code>import android.app.FragmentTransaction;
  import android.os.Bundle;
  import android.support.design.widget.FloatingActionButton;
  import android.support.design.widget.Snackbar;
  import android.support.v7.app.AppCompatActivity;
  import android.support.v7.widget.Toolbar;
  import android.view.Menu;
  import android.view.MenuItem;
  import android.view.View;
  
  import com.actgeek.android.myapplication.R;
  
  public class MainActivity extends AppCompatActivity{
  
      @Override
      protected void onCreate(Bundle savedInstanceState) {
          super.onCreate(savedInstanceState);
          setContentView(R.layout.activity_main);
  
          MAFragment mfrag = new MAFragment();
          FragmentTransaction FT = getFragmentManager().beginTransaction();
          FT.replace(R.id.fragment, mfrag);
          FT.commit();
  
          Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
          setSupportActionBar(toolbar);
  
          FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
          fab.setOnClickListener(new View.OnClickListener() {
              @Override
              public void onClick(View view) {
                  Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                          .setAction("Action", null).show();
              }
          });
      }
  
      @Override
      public boolean onCreateOptionsMenu(Menu menu) {
          // Inflate the menu; this adds items to the action bar if it is present.
          getMenuInflater().inflate(R.menu.menu_main, menu);
          return true;
      }
  
      @Override
      public boolean onOptionsItemSelected(MenuItem item) {
          // Handle action bar item clicks here. The action bar will
          // automatically handle clicks on the Home/Up button, so long
          // as you specify a parent activity in AndroidManifest.xml.
          int id = item.getItemId();
  
          //noinspection SimplifiableIfStatement
          if (id == R.id.action_settings) {
              return true;
          }
  
          return super.onOptionsItemSelected(item);
      }
  }
  </code></pre>
  
  <p>This Fragment displays in the activity_main layout</p>
  
  <p>MAFragment.class</p>
  
  <pre><code>public class MAFragment extends ListFragment {
  
      public MAFragment() {
      }
  
  
     @Override
             public void onActivityCreated(Bundle savedInstanceState){
         super.onActivityCreated(savedInstanceState);
  
         String topics[] = Mylists.TOPICS;
  
         MyArrayAdapter adapter = new MyArrayAdapter(getActivity(),
                 topics);
  
          setListAdapter(adapter);
  
         getListView().setOnItemClickListener(new AdapterView.OnItemClickListener() {
             public void onItemClick(AdapterView&lt;?&gt; parent, View view, int
                     position, long id) {
  
                 Intent intent = new Intent(getActivity(), SubTopicsActivity.class);
                 intent.putExtra("index", position);
                 startActivity(intent);
             }
         });
  
  
     }
  }
  </code></pre>
  
  <p>activity_main layout</p>
  
  <pre><code>&lt;?xml version="1.0" encoding="utf-8"?&gt;
  &lt;LinearLayout
      xmlns:android="http://schemas.android.com/apk/res/android"
      xmlns:app="http://schemas.android.com/apk/res-auto"
      xmlns:tools="http://schemas.android.com/tools"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      app:layout_behavior="@string/appbar_scrolling_view_behavior"
      tools:layout="@layout/fragment_main"
      tools:context="com.actgeek.android.studypack.MainActivity"&gt;
  
  
  &lt;fragment android:id="@+id/fragment"
            android:name="com.actgeek.android.studypack.MAFragment"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            app:layout_behavior="@string/appbar_scrolling_view_behavior"/&gt;
  &lt;/LinearLayout&gt;
  </code></pre>
  
  <p>Here's the error i'm getting whenever the app crashes.</p>
  
  <pre><code>12-19 11:08:18.383 28644-28644/com.actgeek.android.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
                                                                                     java.lang.RuntimeException: Unable to start activity ComponentInfo{com.actgeek.android.myapplication/com.actgeek.android.studypack.MainActivity}: java.lang.NullPointerException
                                                                                         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2360)
                                                                                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2412)
                                                                                         at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3919)
                                                                                         at android.app.ActivityThread.access$700(ActivityThread.java:162)
                                                                                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1370)
                                                                                         at android.os.Handler.dispatchMessage(Handler.java:107)
                                                                                         at android.os.Looper.loop(Looper.java:194)
                                                                                         at android.app.ActivityThread.main(ActivityThread.java:5388)
                                                                                         at java.lang.reflect.Method.invokeNative(Native Method)
                                                                                         at java.lang.reflect.Method.invoke(Method.java:525)
                                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
                                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
                                                                                         at dalvik.system.NativeStart.main(Native Method)
                                                                                      Caused by: java.lang.NullPointerException
                                                                                         at android.support.v7.internal.widget.ToolbarWidgetWrapper.&lt;init&gt;(ToolbarWidgetWrapper.java:94)
                                                                                         at android.support.v7.internal.widget.ToolbarWidgetWrapper.&lt;init&gt;(ToolbarWidgetWrapper.java:87)
                                                                                         at android.support.v7.internal.app.ToolbarActionBar.&lt;init&gt;(ToolbarActionBar.java:77)
                                                                                         at android.support.v7.app.AppCompatDelegateImplV7.setSupportActionBar(AppCompatDelegateImplV7.java:198)
                                                                                         at android.support.v7.app.AppCompatActivity.setSupportActionBar(AppCompatActivity.java:96)
                                                                                         at com.actgeek.android.studypack.MainActivity.onCreate(MainActivity.java:28)
                                                                                         at android.app.Activity.performCreate(Activity.java:5141)
                                                                                         at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1084)
                                                                                         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2307)
                                                                                         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2412) 
                                                                                         at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3919) 
                                                                                         at android.app.ActivityThread.access$700(ActivityThread.java:162) 
                                                                                         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1370) 
                                                                                         at android.os.Handler.dispatchMessage(Handler.java:107) 
                                                                                         at android.os.Looper.loop(Looper.java:194) 
                                                                                         at android.app.ActivityThread.main(ActivityThread.java:5388) 
                                                                                         at java.lang.reflect.Method.invokeNative(Native Method) 
                                                                                         at java.lang.reflect.Method.invoke(Method.java:525) 
                                                                                         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833) 
                                                                                         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600) 
                                                                                         at dalvik.system.NativeStart.main(Native Method) 
  </code></pre>