java.lang.Class java.lang.Object.getClass()' on a null object reference

Question

I try to use viewPager with the tablayout but when i set adapter with the view pager i'm getting error "java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass() on a null object reference" i don't understand why this error is show.

view pager set Adapter:

viewPager= (ViewPager) findViewById(R.id.viewPager_id);
  viewPager.setAdapter(newViewPagerAdapterUseThisClass(getSupportFragmentManager(),14));

Adapter clss:

class ViewPagerAdapterUseThisClass extends FragmentPagerAdapter {
    int countTabItem;
     ViewPagerAdapterUseThisClass(FragmentManager fm,int contTabItem) {
        super(fm);

        this.countTabItem=contTabItem;
    }

    @Override
    public Fragment getItem(int position) {

        if(position==0){
            EnthusamTab enthusamTab=new EnthusamTab();
            return enthusamTab;
        }

        return null;
    }

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

view pager xml file:

 <android.support.v4.view.ViewPager
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:layout_below="@id/tab_layout_id"
            android:id="@+id/viewPager_id"/>

Error log:

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference
                                                                                  at android.support.v4.app.BackStackRecord.doAddOp(BackStackRecord.java:380)
                                                                                  at android.support.v4.app.BackStackRecord.add(BackStackRecord.java:375)
                                                                                  at android.support.v4.app.FragmentPagerAdapter.instantiateItem(FragmentPagerAdapter.java:103)
                                                                                  at android.support.v4.view.ViewPager.addNewItem(ViewPager.java:1034)
                                                                                  at android.support.v4.view.ViewPager.populate(ViewPager.java:1248)
                                                                                  at android.support.v4.view.ViewPager.populate(ViewPager.java:1116)
                                                                                  at android.support.v4.view.ViewPager.onMeasure(ViewPager.java:1642)
                                                                                  at android.view.View.measure(View.java:19861)
                                                                                  at android.widget.RelativeLayout.measureChildHorizontal(RelativeLayout.java:715)
                                                                                  at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:461)
                                                                                  at android.view.View.measure(View.java:19861)
                                                                                  at android.support.v4.widget.DrawerLayout.onMeasure(DrawerLayout.java:1081)
                                                                                  at android.view.View.measure(View.java:19861)
                                                                                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
                                                                                  at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
                                                                                  at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
                                                                                  at android.view.View.measure(View.java:19861)
                                                                                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
                                                                                  at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
                                                                                  at android.widget.LinearLayout.measureVertical(LinearLayout.java:758)
                                                                                  at android.widget.LinearLayout.onMeasure(LinearLayout.java:640)
                                                                                  at android.view.View.measure(View.java:19861)
                                                                                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
                                                                                  at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
                                                                                  at android.view.View.measure(View.java:19861)
                                                                                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
                                                                                  at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1464)
                                                                                  at android.widget.LinearLayout.measureVertical(LinearLayout.java:758)
                                                                                  at android.widget.LinearLayout.onMeasure(LinearLayout.java:640)
                                                                                  at android.view.View.measure(View.java:19861)
                                                                                  at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:6083)
                                                                                  at android.widget.FrameLayout.onMeasure(FrameLayout.java:185)
                                                                                  at com.android.internal.policy.DecorView.onMeasure(DecorView.java:689)
                                                                                  at android.view.View.measure(View.java:19861)
                                                                                  at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2275)
                                                                                  at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1366)
                                                                                  at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1619)
                                                                                  at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1254)
                                                                                  at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6343)
                                                                                  at android.view.Choreographer$CallbackRecord.run(Choreographer.java:874)
                                                                                  at android.view.Choreographer.doCallbacks(Choreographer.java:686)
                                                                                  at android.view.Choreographer.doFrame(Choreographer.java:621)
                                                                                  at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:860)
                                                                                  at android.os.Handler.handleCallback(Handler.java:751)
                                                                                  at android.os.Handler.dispatchMessage(Handler.java:95)
                                                                                  at android.os.Looper.loop(Looper.java:154)
                                                                                  at android.app.ActivityThread.main(ActivityThread.java:6126)
                                                                                  at java.lang.reflect.Method.invoke(Native Method)
                                                                                  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)
                                                                                  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

You're telling the Adapter that it's got 14 items, but you're returning null for all of them except position 0. — Mike M., Jan 24 '17 at 11:10

score 50 · Answer 1 · answered Jun 10 '17 at 19:08

This exception occurs when you return null at getItem(int position) method of PagerAdapter.

You have to set a return value(n) at getCount() method and return a Fragment at getItem(int position) method for all (0 .. n-1) positions.

For instance, if you return 3 from getCount() method, then you must return a not-null Fragment for positions 0, 1 and 2 at getItem(int position) method. If you return a null for position 0, 1 or 2, you'll get:

java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Class java.lang.Object.getClass()' on a null object reference

private static class MyPagerAdapter extends FragmentPagerAdapter {
    ...

    @Override
    public int getCount() {
        return 3;
    }

    @Override
    public Fragment getItem(int position) {
        switch (position) {
            case 0:
                return new XFragment();
            case 1:
                return new YFragment();
            case 2:
                return new ZFragment();
            default:
                return null; // Problem occurs at this condition!
        }
    }
}

May be it's late but I want to ask how you know that is that exact reason? I just curious to know how you get the exact reason. The log is not so helpful. — Ankur_009, Aug 25 '17 at 06:49
@Ankur_009 FragmentPagerAdapter.instantiateItem (it is at shared log) calls getItem method. If getItem returns null NPE occurs. — Devrim, Aug 25 '17 at 07:42
I think from my understanding, first you have check onMeasue() -> populate() -> addNewItem() -> instantiateItem() will call getItem(). That was your thoughtprocess? — Ankur_009, Aug 25 '17 at 08:52

score 11 · Answer 2 · answered Nov 16 '17 at 16:02

11

This error usually comes when you have few fragments to return than the count specified. Like for example, returning count=3, and you return null on the second position. Please note that count is a zero based index.

answered Nov 16 '17 at 16:02

BYISHIMO Audace

585
1
8
18

score 3 · Answer 3 · answered Jan 24 '17 at 11:12

3

Return for all counts. Try this:

Override
    public Fragment getItem(int position) {
            EnthusamTab enthusamTab=new EnthusamTab();
            return enthusamTab;

    }

answered Jan 24 '17 at 11:12

Pushpendra

2,791
4
26
49

score 3 · Answer 4 · answered Sep 13 '18 at 21:06

Problem is occurring to return null in Fragment count function

 @Override
public Fragment getItem(int position) {
    switch (position) {
        case 0:
            return new XFragment();
        case 1:
            return new YFragment();
        case 2:
            return new ZFragment();
        default:
            return null; // Problem occurs at this condition!
    }
}

Here outer bracket occurs error.

So the above-mentioned Answer is right and it's working.

public Fragment getItem(int position) {
    if (position == 0) {

        Tab1 tab1 = new Tab1();
        return tab1;
    }
    if (position == 2) {
        Tab2 tab2 = new Tab2();
        return tab2;
    } else {
        Tab3 tab3 = new Tab3();
        return tab3;
    }

}

it right answers.

score 2 · Answer 5 · answered Jan 24 '17 at 11:10

According to what i see you are returning null in this method:

@Override
    public Fragment getItem(int position) {

        if(position==0){
            EnthusamTab enthusamTab=new EnthusamTab();
            return enthusamTab;
        }

        return null;
    }

score 2 · Answer 6 · edited Jun 18 '18 at 02:08

2

Try to do this in getCount do count of all fragments you have: like 1..5

@Override
public int getCount() {
    return 5; //her 
}

edited Jun 18 '18 at 02:08

pushkin

9,575
15
51
95

answered Jun 18 '18 at 01:22

mouad zizi

307
2
9

score 2 · Answer 7 · answered Aug 10 '18 at 07:13

2

This type of exception only occurs when you try to use method getCount() to return value more than you intialize in tabs. Change your return value.

answered Aug 10 '18 at 07:13

Syed Muhammad Zeejah Hashmi ze

276
2
8

score 2 · Answer 8 · edited Jul 06 '19 at 08:34

2

Just use the code given below. It avoids null error and runs smoothly

@Override
public Fragment getItem(int position) {

      return new Tab1( );
}

edited Jul 06 '19 at 08:34

Suraj Rao

29,388
11
94
103

answered Jul 06 '19 at 08:10

Sahil Choudhary

181
1
7

score 0 · Answer 9 · answered May 28 '19 at 16:58

I got this error because I forget to set break command. Check your break operators at first.

Now I have this code:

@Override
    public Fragment getItem(int position) {
        switch (position) {
            case 0:
                return new FollowersFragment();
            case 1:
                return new PostsFragment();
            case 2:
                return new ReactsFragment();
            case 3:
                return new StoriesFragment();
            case 4:
                return new FollowersFragment();
            case 5:
                return new FollowersFragment();
            case 6:
                return new FollowersFragment();
        }
        return null;
    }

score -1 · Answer 10 · edited Mar 09 '18 at 19:10

-1

public Fragment getItem(int position) {
        if (position == 0) {

            Tab1 tab1 = new Tab1();
            return tab1;
        }
        if (position == 2) {
            Tab2 tab2 = new Tab2();
            return tab2;
        } else {
            Tab3 tab3 = new Tab3();
            return tab3;
        }

    }

edited Mar 09 '18 at 19:10

ADM

20,406
11
52
83

answered Mar 09 '18 at 16:27

Mohammad Eslim

19
2

3

How does this relate to the original question? Please provide more context – Nico Haase Mar 09 '18 at 16:48
i just had the same problem and that code worked for me – Mohammad Eslim Oct 10 '19 at 21:06

java.lang.Class java.lang.Object.getClass()' on a null object reference

10 Answers10