Android addToBackStack(null) not working, closing the app

Question

In my app I am using Fragments in one Activity, and I am trying to replace them. This works fine, but on back press I want to switch to previous fragment. I found addToBackStack() method but it is not working. Here is the 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 the layout for this 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 the layout for this 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 to 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 to override the onBackPressed() method:

@Override
public void onBackPressed()
{
    if (getSupportFragmentManager().getBackStackEntryCount() > 0 )
    {
        getSupportFragmentManager().popBackStackImmediate();
    }
    else
    {
        super.onBackPressed();
    }
}

but it is not working, if I show the stack number after I click the button I get 1. I tried changing from android.support.v4. to android. to java fragment files and main activity and changed MainActivity to extend from Activity but that didn't worked either. What am I doing wrong? My app supports API 14 and above. Any help would be 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 to 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

It's great you included all this code, but the crash log would have been perfect — OneCricketeer
– OneCricketeer, Commented Feb 8, 2016 at 13:33
@ASTeam: Try adding fragmentTransaction.addToBackStack(null); in changeFragment method. — Rohit5k2
– Rohit5k2, Commented Feb 8, 2016 at 13:48

Rohit5k2 · Accepted Answer · 2016-02-08 14:28:05Z

1

Change your method like 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 you should remove fragmentTransaction.addToBackStack(null); from onCreate of MainActivity.

Also, in Fragment1 code inside onActivityCreated should be moved to onCreateView.

edited Feb 8, 2016 at 14:28

answered Feb 8, 2016 at 13:50

Rohit5k2

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6 Comments

Mr. Nobody Over a year ago

After the changes if I press back after i clicked the button it goes back but then if I click the button again it doesn't do anything, if i continue clicking it crashes the app with expectation : java.lang.NullPointerException: Attempt to invoke virtual method 'void com.example.asteam.myapplication.MainActivity.changeFragment(android.support.v4.app.Fragment)' on a null object reference at com.example.asteam.myapplication.Fragment1$1.onClick(Fragment1.java:38)

Rohit5k2 Over a year ago

you should remove fragmentTransaction.addToBackStack(null); from onCreate of MainActivity.

Mr. Nobody Over a year ago

It still "disables" the button after first back pressed so I can't get to fragment 2 anymore, but it doesn't crash the app anymore...

Rohit5k2 Over a year ago

In Fragment1 code inside onActivityCreated should be moved to onCreateView

Mr. Nobody Over a year ago

I tried that cause the fragment gets created every time that i press back button and Activity once, so onclick() method its not related to button anymore, and it works thank you. But while trying in changeFragment(Fragment f) method I used fragmentTransaction.add(android.R.id.content, f) instead of replace() and it works too. Which is better?

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