Why are my floating action buttons not working properly in my ViewPager? - android-fragments

Question

I have a ViewPager set up with my app and am trying to also set two floating action buttons, a left one and a right one, to do the same thing as the ViewPager, so that the user has a choice in terms of navigation. I'm trying to have it set so that the left button is invisible on the first page, and the right button is invisible on the last page, but the appearances of the buttons seem to be sporadic. I've tried debugging the app, and upon testing each situation, the appropriate code is executed, so I can't understand why this behavior is happening. Any help would be appreciated.
TestFragment:
public class TestFragment extends Fragment {
public static final String ARG_ID = "Id";
private int Id;
private String title;
private TextView titleTV;
private String description;
private TextView descriptionTV;
private int number;
private TextView numberTV;
private FloatingActionButton leftBtn;
private FloatingActionButton rightBtn;
public static TestFragment newInstance(int Id) {
Bundle args = new Bundle();
args.putSerializable(ARG_ID, Id);
TestFragment fragment = new TestFragment();
fragment.setArguments(args);
return fragment;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_test, container, false);
Id = getArguments().getInt(ARG_ID);
title = Test.testData[Id].getTitle();
description = Test.testData[Id].getDescription();
number = Test.testData[Id].getNumber();
titleTV = view.findViewById(R.id.title);
titleTV.setText(title);
descriptionTV = view.findViewById(R.id.description);
descriptionTV.setText(description);
numberTV = view.findViewById(R.id.number);
numberTV.setText(String.valueOf(number));
leftBtn = view.findViewById(R.id.left_btn);
rightBtn = view.findViewById(R.id.right_btn);
toggleButtons();
leftBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
testViewPager.setCurrentItem(--index);
toggleButtons();
}
});
rightBtn.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View view) {
testViewPager.setCurrentItem(++index);
toggleButtons();
}
});
return view;
}
public void toggleButtons() {
if(index == 0) {
leftBtn.setVisibility(View.INVISIBLE);
}
else if(index == Test.testData.length - 1) {
rightBtn.setVisibility(View.INVISIBLE);
}
else {
leftBtn.setVisibility(View.VISIBLE);
rightBtn.setVisibility(View.VISIBLE);
}
}
}
TestPagerActivity:
public class TestPagerActivity extends AppCompatActivity {
public static int index;
public static ViewPager testViewPager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_test_pager);
index = (int) getIntent().getSerializableExtra(EXTRA_ID);
testViewPager = findViewById(R.id.test_view_pager);
FragmentManager fragmentManager = getSupportFragmentManager();
testViewPager.setAdapter(new FragmentStatePagerAdapter(fragmentManager) {
#Override
public Fragment getItem(int position) {
return TestFragment.newInstance(position);
}
#Override
public int getCount() {
return Test.testData.length;
}
});
for(int i = 0; i < Test.testData.length; i++) {
if(i == index) {
testViewPager.setCurrentItem(i);
break;
}
}
}
}