Heelp me for using viewmodel with radio group,when i rotate it was unchecked - radio-button

Question

FirstPage.java
'viewModel = new ViewModelProvider(requireActivity()).get(PagesVM.class);
radioGroup.setOnCheckedChangeListener((group, checkedId) -> {
checkedId = group.getCheckedRadioButtonId();
invisibleBtn.setVisibility(View.INVISIBLE);
switch (checkedId) {
case 0:
case 1:
case 2:
case 3:
count += 0;
break;
case 4:
count += 1;
break;
}
viewModel.getSelectedValue().observe(getViewLifecycleOwner(),check -> {
radioGroup.setSelected(check);
});
});'
FirstPageVm.java
public class PagesVM extends ViewModel {
MutableLiveData<Boolean> setItem=new MutableLiveData<Boolean>();
LiveData<Boolean> getSelectedValue(){
return setItem;
}
RadioGroup radioGroup;
public void slectItem(){
setItem.setValue(radioGroup.isSelected());
}
}
Error
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2307)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:246)
at android.app.ActivityThread.main(ActivityThread.java:8512)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:602)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1130)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'boolean android.widget.RadioGroup.isSelected()' on a null object reference
at mening.dasturim.mytest.ui.pages.PagesVM.slectItem(PagesVM.java:21)
at mening.dasturim.mytest.ui.pages.FirstPage.onDestroy(FirstPage.java:115)
at androidx.fragment.app.Fragment.performDestroy(Fragment.java:3219)
at androidx.fragment.app.FragmentStateManager.destroy(FragmentStateManager.java:774)
at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:350)
at androidx.fragment.app.FragmentStore.moveToExpectedState(FragmentStore.java:112)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1647)
at androidx.fragment.app.FragmentManager.dispatchStateChange(FragmentManager.java:3128)
at androidx.fragment.app.FragmentManager.dispatchDestroy(FragmentManager.java:3107)
android.app.ActivityThread.performDestroyActivity(ActivityThread.java:5587)
at android.app.ActivityThread.handleDestroyActivity(ActivityThread.java:5647) 
at android.app.ActivityThread.handleRelaunchActivityInner(ActivityThread.java:5939) 
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:5869) 
at android.app.servertransaction.ActivityRelaunchItem.execute(ActivityRelaunchItem.java:69) 
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2307) 
at android.os.Handler.dispatchMessage(Handler.java:106) 
at android.os.Looper.loop(Looper.java:246) 
at android.app.ActivityThread.main(ActivityThread.java:8512) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:602) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1130) 
2021-08-14 02:21:59.001 4226-4548/? E/BufferQueueProducer: com.samsung.android.app.cocktailbarservice/com.samsung.android.app.cocktailbarservice.CocktailBarService$_11743#0 disconnect: not connected (req=1)
2021-08-14 02:21:59.011 4900-4900/? E/ndroid.systemu: Invalid ID 0x00000000.

Answer 1

you should omit
RadioGroup radioGroup;
public void slectItem(){
setItem.setValue(radioGroup.isSelected());
}
and run again