java - Android addToBackStack(null) not working, closing the app -

in app using fragments in 1 activity, , trying replace them. works fine, on press want switch previous fragment. found addtobackstack() method not working. here code in mainactivity:

mainactivity.java:

import android.support.v4.app.fragment; import android.support.v4.app.fragmentmanager; import android.support.v4.app.fragmenttransaction; import android.support.v7.app.appcompatactivity; import android.os.bundle;  public class mainactivity extends appcompatactivity {  @override protected void oncreate(bundle savedinstancestate) {     super.oncreate(savedinstancestate);     fragment1 fragment1 = new fragment1();     fragmentmanager fragmentmanager = getsupportfragmentmanager();     fragmenttransaction fragmenttransaction = fragmentmanager.begintransaction();     fragmenttransaction.replace(android.r.id.content, fragment1);     fragmenttransaction.addtobackstack(null);     fragmenttransaction.commit(); }  public void changefragment(fragment f) {     fragmentmanager fragmentmanager = getsupportfragmentmanager();     fragmenttransaction fragmenttransaction = fragmentmanager.begintransaction();     fragmenttransaction.add(android.r.id.content, f);     fragmenttransaction.commit(); }  @override public void onbackpressed() {     if (getsupportfragmentmanager().getbackstackentrycount() > 0 )     {         getsupportfragmentmanager().popbackstackimmediate();     }     else     {         super.onbackpressed();     } } } 

fragment1.java:

import android.os.bundle; import android.support.v4.app.fragment; import android.view.layoutinflater; import android.view.view; import android.view.viewgroup; import android.widget.button;  public class fragment1 extends fragment { private button buttonfragment1;  public fragment1() {     // required empty public constructor }   @override public view oncreateview(layoutinflater inflater, viewgroup container,                          bundle savedinstancestate) {     // inflate layout fragment     return inflater.inflate(r.layout.fragment_fragment1, container, false); }  @override public void onactivitycreated(bundle savedinstancestate) {     super.onactivitycreated(savedinstancestate);     buttonfragment1 = (button)getactivity().findviewbyid(r.id.buttonfragment1);     buttonfragment1.setonclicklistener(new view.onclicklistener()     {         @override         public void onclick(view v)         {             fragment2 fragment2 = new fragment2();             ((mainactivity) getactivity()).changefragment(fragment2);         }     }); } } 

fragment2.java:

import android.os.bundle; import android.support.v4.app.fragment; import android.view.layoutinflater; import android.view.view; import android.view.viewgroup;  public class fragment2 extends fragment {   public fragment2() {     // required empty public constructor }   @override public view oncreateview(layoutinflater inflater, viewgroup container,                          bundle savedinstancestate) {     // inflate layout fragment     return inflater.inflate(r.layout.fragment_fragment2, container, false); }  } 

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?> <relativelayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:paddingbottom="@dimen/activity_vertical_margin" android:paddingleft="@dimen/activity_horizontal_margin" android:paddingright="@dimen/activity_horizontal_margin" android:paddingtop="@dimen/activity_vertical_margin" tools:context="com.example.asteam.myapplication.mainactivity">  <fragment     android:layout_width="match_parent"     android:layout_height="match_parent"     android:id="@+id/fraggment" /> </relativelayout> 

fragment_fragment1.xml:

<framelayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context="com.example.asteam.myapplication.fragment1">  <relativelayout     android:layout_width="match_parent"     android:layout_height="match_parent"     android:background="@color/colorprimarydark">      <button         android:layout_width="wrap_content"         android:layout_height="wrap_content"         android:id="@+id/buttonfragment1"         android:text="send fragment2"/>  </relativelayout>  </framelayout> 

fragment_fragment2.xml:

<framelayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" tools:context="com.example.asteam.myapplication.fragment2">  <relativelayout     android:layout_width="match_parent"     android:layout_height="match_parent"     android:background="@color/colorprimary">      <textview         android:layout_width="match_parent"         android:layout_height="match_parent"         android:text="fragment2" />  </relativelayout>  </framelayout> 

and manifest xml:

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

i tried override onbackpressed() method:

@override public void onbackpressed() {     if (getsupportfragmentmanager().getbackstackentrycount() > 0 )     {         getsupportfragmentmanager().popbackstackimmediate();     }     else     {         super.onbackpressed();     } } 

but not working, if show stack number after click button 1. tried changing android.support.v4. android. java fragment files , main activity , changed mainactivity extend activity didn't worked either. doing wrong? app supports api 14 , above. appreciated.

edited

plus logcat:

02-08 14:38:49.191 10417-10417/? i/art: not late-enabling -xcheck:jni (already on) 02-08 14:38:49.266 10417-10417/com.example.asteam.myapplication w/system:  classloader referenced unknown path: /data/app/com.example.asteam.myapplication-2/lib/x86 02-08 14:38:49.322 10417-10432/com.example.asteam.myapplication d/openglrenderer: use egl_swap_behavior_preserved: true 02-08 14:38:49.452 10417-10432/com.example.asteam.myapplication i/openglrenderer: initialized egl, version 1.4 02-08 14:38:49.489 10417-10432/com.example.asteam.myapplication w/egl_emulation: eglsurfaceattrib not implemented 02-08 14:38:49.489 10417-10432/com.example.asteam.myapplication w/openglrenderer: failed set egl_swap_behavior on surface 0xabebfe80, error=egl_success 02-08 14:38:55.915 10417-10432/com.example.asteam.myapplication e/surface: getslotfrombufferlocked: unknown buffer: 0xab852fc0 

change method this

public void changefragment(fragment f) {     fragmentmanager fragmentmanager = getsupportfragmentmanager();     fragmenttransaction fragmenttransaction = fragmentmanager.begintransaction();     fragmenttransaction.replace(android.r.id.content, f);     fragmenttransaction.addtobackstack(null);     fragmenttransaction.commit(); } 

then should remove fragmenttransaction.addtobackstack(null); oncreate of mainactivity.

also, in fragment1 code inside onactivitycreated should moved oncreateview.