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My app crashes in landscape mode

I don’t know what happened when I run my application on the emulator and I switch to landscape mode, it crashes. But it works great in portrait mode. Please, what can I do to solve this problem. Thank you in advance! here are my codes ...

MainActivity.class

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); } }

This snippet is displayed in the activity_main layout.

MAFragment.class

 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<?> parent, View view, int position, long id) { Intent intent = new Intent(getActivity(), SubTopicsActivity.class); intent.putExtra("index", position); startActivity(intent); } }); } }

Activity Layout

 <?xml version="1.0" encoding="utf-8"?> <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"> <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"/> </LinearLayout>

Here's the error that I get whenever the application crashes.

 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.<init>(ToolbarWidgetWrapper.java:94) at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:87) at android.support.v7.internal.app.ToolbarActionBar.<init>(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)
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3 answers

See if this is missing in the manifest activity declaration

 android:configChanges="orientation|screenSize|keyboardHidden"
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check if you missed this property by declaring in AndroidManifest.

Android: configChanges = "orientation | keyboardHidden"

updated:

 <activity android:name=".SlideNewActivity" android:configChanges="orientation|keyboardHidden" android:launchMode="singleTask" />
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Add these lines to your activity in .manifest

  <activity android:name=".MainActivity" android:configChanges="orientation|keyboardHidden" />

Also add this override method to your MainActivity

 @Override public void onConfigurationChanged(Configuration newConfig) { // TODO Auto-generated method stub super.onConfigurationChanged(newConfig); }

What is it.

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Source: https://habr.com/ru/post/1238702/

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