ViewPager - Android Error setCurrentItem(int,boolean) while sending data from fragment to activity

Question

I am using NonSwipeableViewPager

NonSwipeableViewPager.Java

public class NonSwipeableViewPager extends ViewPager {
    public NonSwipeableViewPager(Context context) {
        super(context);
    }

    public NonSwipeableViewPager(Context context, AttributeSet attrs) {
        super(context, attrs);
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent event) {
        // Never allow swiping to switch between pages
        return false;
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        // Never allow swiping to switch between pages
        return false;
    }
}

I have MainActivity in Which I am using this ViewPager with Two Fragments

activity_main.xml

<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"
    tools:context="com.advancetechindia.fragmenttest.MainActivity">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <TextView
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:text="Hello"
            android:textSize="20sp"
            android:textStyle="bold" />

        <com.advancetechindia.fragmenttest.NonSwipeableViewPager
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_gravity="center_horizontal"
            android:id="@+id/viewpager_id"/>

    </LinearLayout>

</RelativeLayout>

MainActivity.java

public class MainActivity extends AppCompatActivity {

private NonSwipeableViewPager viewpager;
private FragmentFirst fragmentFirst=new FragmentFirst();

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    viewpager=(NonSwipeableViewPager)findViewById(R.id.viewpager_id);
    viewpager.setAdapter(new SamplePagerAdapter(
            getSupportFragmentManager()));
}

public void getData(String s) {
    Log.d("TAG",s);
    viewpager.setCurrentItem(1,true);
}

public class SamplePagerAdapter extends FragmentPagerAdapter {

    public SamplePagerAdapter(FragmentManager fm) {
        super(fm);
    }

    @Override
    public Fragment getItem(int position) {
        /** Show a Fragment based on the position of the current screen */

        if (position==0) {
            return new FragmentFirst();
        } else return new FragmentTwo();
    }

    @Override
    public int getCount() {
        return 2;
    }

} }

frag_one.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:orientation="vertical">

        <EditText
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/et_id"
            android:hint="texthere"/>

        <Button
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:id="@+id/btn_id"
            android:text="Fire"
            android:onClick="GetString"/>

    </LinearLayout>

</RelativeLayout>

frag_one.xml

FragmentFirst.java

public class FragmentFirst extends Fragment {

private EditText et;
private Button btn;
private MainActivity mainact;

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    View rootView = inflater.inflate(R.layout.frag_one, container,
            false);
    mainact=new MainActivity();

    et=(EditText)rootView.findViewById(R.id.et_id);
    btn=(Button)rootView.findViewById(R.id.btn_id);

    btn.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            String abc=et.getText().toString();
            Log.d("TAG",abc);
            mainact.getData(abc);
        }
    });

    return rootView;
} }

Also, i have another Fragment--- FragmentTwo.java

when I click on Fire Button it invokes

getData(String s)

method of MainActivity where I got the string but it shows error on

viewpager.setCurrentItem(int,boolean)

Please let me get out of this hurdle. Thanks

Error

10:54:46.205 31492-31492/com.advancetechindia.fragmenttest E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.advancetechindia.fragmenttest, PID: 31492
java.lang.NullPointerException: Attempt to invoke virtual method 'void com.advancetechindia.fragmenttest.NonSwipeableViewPager.setCurrentItem(int, boolean)' on a null object reference
at com.advancetechindia.fragmenttest.MainActivity.getData(MainActivity.java:30) atcom.advancetechindia.fragmenttest.FragmentFirst$1.onClick(FragmentFirst.java:37)at android.view.View.performClick(View.java:5612)at android.view.View$PerformClick.run(View.java:22285)at android.os.Handler.handleCallback(Handler.java:751)at android.os.Handler.dispatchMessage(Handler.java:95)at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6123) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:867) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:757)

Answer 1

mainact=new MainActivity(); is create new object and ViewPager alive in Old object so you need to access old object of MainActivity

((MainActivity)getActivity()).getData(abc);

Answer 2

replace this in your FragmentFirst.java

mainact.getData(abc);

with

((MainActivity)getActivity()).getData(abc);