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