Unable to access View of Fragment with ViewPager and FragmentPagerAdapter

Question

Trying to learn Android development by poking around so please forgive if the query is too simple.

I have the following code which keeps crashing due to NullPointerException - I hve tried several ways to access the View of the Fragment but I always get null. Can anyone help me out with what I'm doing wrong?

What I'm trying to do is save the contents of the EditText to SharedPreferences when the page is scrolled. For the life of me, I can't seem to access the View of the fragment that is loaded when the tab is displayed.

public class ViewPagerAdapter extends FragmentPagerAdapter {

    final int PAGE_COUNT = 3;
    // Tab Titles
    private String tabtitles[] = new String[] { "Profile", "Address", 
    "Security"};
    Context context;

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

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

    @Override
    public Fragment getItem(int position) {
        switch (position) {
            // Open FragmentTab1.java
            case 0:
                CreateUserFragmentProfile fragmenttab1 = new 
                CreateUserFragmentProfile();
                return fragmenttab1;
            // Open FragmentTab2.java
            case 1:
                CreateUserFragmentLocation fragmenttab2 = new 
                CreateUserFragmentLocation();
                return fragmenttab2;
            // Open FragmentTab3.java
            case 2:
                CreateUserFragmentSecurity fragmenttab3 = new 
                CreateUserFragmentSecurity();
                return fragmenttab3;

        }
        return null;
    }

    @Override
    public CharSequence getPageTitle(int position) {
        return tabtitles[position];
    }

}

The Fragment code extends Fragment, and does pretty much nothing.

public class CreateUserFragmentSecurity extends Fragment {

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup 
    container, @Nullable Bundle savedInstanceState) {
        //return super.onCreateView(inflater, container, 
    savedInstanceState);
        View view = inflater.inflate(R.layout.create_fragment_security, 
    container, false);


        return view;

    }

    public void  storeData(){

    }
}

The Activity code is as follows:

public class CreateUser extends AppCompatActivity {


    public SharedPreferences preferences;
    public SharedPreferences.Editor editor;
    public View currView;
    public String fname, lname, dob, gender, email, addr1, addr2, addr3, 
    addrstate, city, passwd, passwdPlain;
    public Long mobile, pin;
    //public FragmentPagerAdapter adapter;

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

        preferences = getSharedPreferences("Reviv", MODE_PRIVATE);
        editor = preferences.edit();

        // Locate the viewpager in activity_create_user.xml
        final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);

        // Set the ViewPagerAdapter into ViewPager

        final FragmentPagerAdapter adapter = new 
        ViewPagerAdapter(getSupportFragmentManager());
        viewPager.setAdapter(adapter);
        viewPager.setOffscreenPageLimit(3);

        viewPager.addOnPageChangeListener(new 
            ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, 
            int positionOffsetPixels) {
                boolean hasChanged = false;
                switch (position){ // store data on tab switch
                    case 0: // Profile tab
                        //currView = 
               viewPager.getChildAt(viewPager.getCurrentItem());  // returns 
               null
                        currView = 
               adapter.getItem(viewPager.getCurrentItem()).getView();  // 
               crashes, returns null
                        EditText etFname = 
               currView.findViewById(R.id.etFname);


                        fname = etFname.getText().toString();

                        hasChanged = false;

                        if(!StringUtils.isEmpty(fname)) {
                            editor.putString("fname", fname);
                            hasChanged = true;
                        }

                        if(hasChanged == true) editor.commit();

                        break;
                    case 1: // Address tab
                        // currView = 
             viewPager.getChildAt(viewPager.getCurrentItem()); // returns 
             null
                        currView = 
             adapter.getItem(viewPager.getCurrentItem()).getView();
                        EditText etAddr1 = 
             currView.findViewById(R.id.etAddr1);



                        addr1 = etAddr1.getText().toString();


                        hasChanged = false;

                        if(!StringUtils.isEmpty(addr1)) {
                            editor.putString("addr1", addr1);
                            hasChanged = true;
                        }


                        if(hasChanged == true) editor.commit();


                        break;
                    case 2: // Security tab
                        //currView = 
          viewPager.getChildAt(viewPager.getCurrentItem()); // returns null
                        currView = 
          adapter.getItem(viewPager.getCurrentItem()).getView();

                        EditText etPasswd = 
          currView.findViewById(R.id.etPasswd);


                        passwd = etPasswd.getText().toString();

                        hasChanged = false;

                        if(!StringUtils.isEmpty(passwd)) {
                            editor.putString("passwd", passwd);
                            hasChanged = true;
                        }



                        if(hasChanged == true) editor.commit();

                        break;
                }

            }

            @Override
            public void onPageSelected(int position) {
               // do nothing
            }

            @Override
            public void onPageScrollStateChanged(int state) {
                // do nothing
            }
        });
    }
}

My Stack trace is as follows:

java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.View android.view.View.findViewById(int)' on a null object reference at com.portmanteau.reviv.CreateUser$1.onPageScrolled(CreateUser.java:58) at android.support.v4.view.ViewPager.dispatchOnPageScrolled(ViewPager.java:1921) at android.support.v4.view.ViewPager.onPageScrolled(ViewPager.java:1895) at android.support.v4.view.ViewPager.pageScrolled(ViewPager.java:1833) at android.support.v4.view.ViewPager.scrollToItem(ViewPager.java:690) at android.support.v4.view.ViewPager.onLayout(ViewPager.java:1777) at android.view.View.layout(View.java:19678) at android.view.ViewGroup.layout(ViewGroup.java:6057) at android.support.constraint.ConstraintLayout.onLayout(ConstraintLayout.java:1197) at android.view.View.layout(View.java:19678) at android.view.ViewGroup.layout(ViewGroup.java:6057) at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323) at android.widget.FrameLayout.onLayout(FrameLayout.java:261) at andr oid.view.View.layout(View.java:19678) at android.view.ViewGroup.layout(ViewGroup.java:6057) at android.support.v7.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:434) at android.view.View.layout(View.java:19678) at android.view.ViewGroup.layout(ViewGroup.java:6057) at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323) at android.widget.FrameLayout.onLayout(FrameLayout.java:261) at android.view.View.layout(View.java:19678) at android.view.ViewGroup.layout(ViewGroup.java:6057) at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1791) at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1635) at android.widget.LinearLayout.onLayout(LinearLayout.java:1544) at android.view.View.layout(View.java:19678) at android.view.ViewGroup.layout(ViewGroup.java:6057) at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323) at android.widget.FrameLayout.onLayout(FrameLayout.java:261) at com.android.internal.policy.DecorView.onLayout(DecorVie w.java:758) at android.view.View.layout(View.java:19678) at android.view.ViewGroup.layout(ViewGroup.java:6057) at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2510) at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2219) at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1405) at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6829) at android.view.Choreographer$CallbackRecord.run(Choreographer.java:966) at android.view.Choreographer.doCallbacks(Choreographer.java:778) at android.view.Choreographer.doFrame(Choreographer.java:713) at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:952) at android.os.Handler.handleCallback(Handler.java:789) at android.os.Handler.dispatchMessage(Handler.java:98) at android.os.Looper.loop(Looper.java:164) at android.app.ActivityThread.main(ActivityThread.java:6803) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygo te.java:240) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

Answer 1

Try something like this:

@Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
    boolean hasChanged = false;
    if (positionOffset > 0) {
        currView = getSupportFragmentManager().findFragmentByTag("android:switcher:" + R.id.pager + ":" + position).getView();
        if (currView != null) {
            EditText editText = null;
            if (position == 0) editText = currView.findViewById(R.id.etPasswdPlain);
            else if (position == 1) editText = currView.findViewById(R.id.etAddr1);
            else if (position ==2) editText = currView.findViewById(R.id.etFname);
            if (editText != null) {
                String value = editText.getText().toString();
                Log.d("TAG", "Value is " + value);
            }
        }
    }
}

Note that this will work only if you are doing left to right swipe ( from page 1 to page 2 and page 2 to page 3).

ie when you are swiping from page 1 to page 2 , data in page 1 is saved and

when you are swiping from page 2 to page 3 , data in page 2 will be saved.

For right to left swipe assuming that you have to save page 3 data when swiping from page 3 to page 2 and save page 2 data when swiping from page 2 to page 1 , you have to do some logic but you can get the idea from here.

Answer 2

Try calling

((EditText) viewPager.getChildAt(viewPager.getCurrentItem())
    .findViewById(R.id.etFname)).getText().toString()

rather than

adapter.getItem(viewPager.getCurrentItem()).getView();