Develop Reference

Interface in fragment in ViewPager.OnPageChangeListener

In my viewpager i set listener from which i call methods from my interface in tab fragments.
But variable in this tab fragments in my interfaces methods always return null.
Tell me why ?
p.s. sorry for my english)
Parent fragment:
public class MyFragment
extends Fragment {
protected Context mContext;
#Override
public void onAttach(Context context) {
super.onAttach(context);
mContext = context;
}
#Override
public void onDetach() {
super.onDetach();
mContext = null;
} }
Container fragment with PagerAdapter:
public class FragmentContainer
extends MyFragment {
private ViewPager viewPager;
private ViewPager.OnPageChangeListener onPageChangeListener;
public interface IPageSelected {
void onPageSelected();
void onPageUnselected();
}
public static FragmentContainer newInstance() {
return new FragmentContainer();
}
#Override
public View onCreateView(#NonNull LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(
R.layout.fragment_container, container, false);
viewPager = view.findViewById(R.id.pager);
PagerAdapter pagerAdapter = new PagerAdapter(getFragmentManager());
viewPager.setAdapter(pagerAdapter);
TabLayout tabLayout = view.findViewById(R.id.tab_layout);
tabLayout.setupWithViewPager(viewPager);
onPageChangeListener = new ViewPager.OnPageChangeListener() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
for(int x = 0; x < pagerAdapter.getCount(); x++) {
((IPageSelected) pagerAdapter.getItem(x)).onPageUnselected();
}
((IPageSelected) pagerAdapter.getItem(position)).onPageSelected();
}
#Override
public void onPageScrollStateChanged(int state) {
}
};
viewPager.addOnPageChangeListener(onPageChangeListener);
return view;
}
#Override
public void onResume() {
super.onResume();
setCurrentItem();
}
private void setCurrentItem() {
viewPager.post(() -> {
viewPager.setCurrentItem(0);
onPageChangeListener.onPageSelected(0);
});
}
class PagerAdapter
extends FragmentStatePagerAdapter {
PagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return TestFragment1.newInstance();
case 1:
return TestFragment2.newInstance();
}
return null;
}
#Override
public int getCount() {
return 2;
}
#Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "Tab1";
case 1:
return "Tab2";
default:
return null;
}
}
} }
Tab fragments.
Question: why variable mContext in interface methods always return null ?
public class TestFragment1
extends MyFragment
implements FragmentContainer.IPageSelected {
public static TestFragment1 newInstance() {
return new TestFragment1();
}
#Override
public View onCreateView(#NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment1, container, false);
}
#Override
public void onPageSelected() {
Log.d("myLog", "TestFragment1 onPageSelected: " + mContext); // WHY NULL ???
}
#Override
public void onPageUnselected() {
Log.d("myLog", "TestFragment1 onPageUnselected: " + mContext); // WHY NULL ???
} }
public class TestFragment2
extends MyFragment
implements FragmentContainer.IPageSelected {
public static TestFragment2 newInstance() {
return new TestFragment2();
}
#Override
public View onCreateView(#NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment2, container, false);
}
#Override
public void onPageSelected() {
Log.d("myLog", "TestFragment2 onPageSelected: " + mContext); // WHY NULL ???
}
#Override
public void onPageUnselected() {
Log.d("myLog", "TestFragment2 onPageUnselected: " + mContext); // WHY NULL ???
} }

In your fragment container :
PagerAdapter pagerAdapter = new PagerAdapter(getFragmentManager()); here is the fault.
In order to attach your child fragments to your container fragment, consider passing child fragment manager getChildFragmentManager() to your viewpager adapter. (Right now your fragments are attached to same level as your container fragment).

I found solution.
Adapter class.
Old:
class PagerAdapter
extends FragmentStatePagerAdapter {
PagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return TestFragment1.newInstance();
case 1:
return TestFragment2.newInstance();
}
return null;
}
#Override
public int getCount() {
return 2;
}
#Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0:
return "Tab1";
case 1:
return "Tab2";
default:
return null;
}
}
}
New:
class PagerAdapter
extends FragmentStatePagerAdapter {
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
PagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}
#Override
public int getCount() {
return mFragmentList.size();
}
void addFragment(Fragment fragment, String title) {
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
}
#Override
public CharSequence getPageTitle(int position) {
return mFragmentTitleList.get(position);
}
}
Adapter initialization.
Old:
PagerAdapter pagerAdapter = new PagerAdapter(getFragmentManager());
viewPager.setAdapter(pagerAdapter);
New:
PagerAdapter pagerAdapter = new PagerAdapter(getFragmentManager());
pagerAdapter.addFragment(TestFragment1.newInstance(), "tab1");
pagerAdapter.addFragment(TestFragment2.newInstance(), "tab2");
viewPager.setAdapter(pagerAdapter);
And now new question: what's the differense with the first option ?
Now i initializing adapter in container fragment, it's a cause ?
Why didn't work when initializing was in the adapter ?

TabLayout addOnTabSelectedListener is not working properly when I reopen the application

I am working with TabLayout which shows tab icon red according to fragment selected in ViewPager. But I have been facing this problem for 2 weeks and I have been searching a lot to resolve this issue.
The problem is if I am at fragment user account and when I close the application, my user tab icon is selected. Now when I reopen the application fragment, my tab restaurant is loaded, but the user account tab icon is still selected, although restaurant tab icon should be selected.
I have attached screenshots for reference:
user account image
restaurant image after re open
public class PagerMainActivity extends Fragment {
//This is our tablayout
public TabLayout tabLayout;
public static CustomViewPager viewPager;
AdapterPager adapter;
public int tabIconColor_Selected;
public int tabIconColor_DeSelected;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// tabSelection();
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.activity_pager, container, false);
tabLayout = (TabLayout) v.findViewById(R.id.tab_layout);
viewPager = v.findViewById(R.id.pager);
tabLayout.addTab(tabLayout.newTab().setIcon(R.drawable.restaurent).setText("Restaurant"));
tabLayout.addTab(tabLayout.newTab().setIcon(R.drawable.order).setText("Order"));
tabLayout.addTab(tabLayout.newTab().setIcon(R.drawable.deals).setText("Deals"));
tabLayout.addTab(tabLayout.newTab().setIcon(R.drawable.account).setText("Account"));
viewPager = v.findViewById(R.id.pager);
adapter = new AdapterPager(getActivity().getSupportFragmentManager(), tabLayout.getTabCount());
adapter.getRegisteredFragment(viewPager.getCurrentItem());
viewPager.setAdapter(adapter);
viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.addOnTabSelectedListener(new TabLayout.ViewPagerOnTabSelectedListener(viewPager));
viewPager.setAllowedSwipeDirection(SwipeDirection.none);
// setupTabIcons();
tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener()
{
#Override
public void onTabSelected(TabLayout.Tab tabSelected)
{
viewPager.setCurrentItem(tabSelected.getPosition());
if(UserAccountFragment.LOG_OUT_FLAG || UserAccountFragment.LOG_IN_FLAG){
tabIconColor_Selected = ContextCompat.getColor(getContext(), R.color.colorDeal);
tabSelected.getIcon().setColorFilter(tabIconColor_Selected, PorterDuff.Mode.SRC_IN);
UserAccountFragment.LOG_OUT_FLAG=false;
UserAccountFragment.LOG_IN_FLAG=false;
}
tabIconColor_Selected = ContextCompat.getColor(getContext(), R.color.colorRed);
tabSelected.getIcon().setColorFilter(tabIconColor_Selected, PorterDuff.Mode.SRC_IN);
}
#Override
public void onTabUnselected(TabLayout.Tab tabSelected){
viewPager.setCurrentItem(tabSelected.getPosition());
tabIconColor_DeSelected = ContextCompat.getColor(getContext(), R.color.colorDeal);
tabSelected.getIcon().setColorFilter(tabIconColor_DeSelected, PorterDuff.Mode.SRC_IN);
}
#Override
public void onTabReselected(TabLayout.Tab tabSelected){
}
});
return v;
}
#Override
public void onResume() {
super.onResume();
}
#Override
public void onPause() {
super.onPause();
}
#Override
public void onStop() {
super.onStop();
}
#Override
public void onDestroyView() {
super.onDestroyView();
}
Adapter
SparseArray<Fragment> registeredFragments = new SparseArray<Fragment>();
int mNumOfTabs;
public AdapterPager(FragmentManager fragmentManager, int tabCount) {
super(fragmentManager);
this.mNumOfTabs=tabCount;
}
#Override
public Fragment getItem(int position) {
Fragment fm=null;
switch (position) {
case 0:
fm = new RestaurantsFragment();
break;
case 1:
fm = new OrdersFragment();
break;
case 2:
fm = new DealsFragment();
break;
case 3:
fm = new UserAccountFragment();
break;
}
return fm;
}
#Override
public int getCount() {
return mNumOfTabs;
}
/* #Override
public Parcelable saveState() {
// Do Nothing
return saveState();
}*/
#Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
Fragment fragment = (Fragment) super.instantiateItem(container, position);
registeredFragments.put(position, fragment);
return fragment;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
registeredFragments.remove(position);
super.destroyItem(container, position, object);
}
public Fragment getRegisteredFragment(int position) {
return registeredFragments.get(position);
}
}
Your views and solution will be appreciated. Thanks in advance

Access Fragment viewPager in Parent Activity

I have a problem in my Application, I load a fragment in my activity and in the fragment i used the ViewPager(for TabLayout) so i want to handle the BackPressed of ViewPager.
Because there is no OnKeyDown override method is available in fragment so i want the refrence of my Fragment ViewPager in my Parent Activty so i can handle this situation in onBackPressed() method Activity.
Activity Code :
fragment= new TabFragment();
if (fragment != null) {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.replace(R.id.containerView, fragment);
ft.commitAllowingStateLoss();
// ft.commit();
}
#Override
public void onBackPressed() {
if (isMainShown) {
// want the refrence of view pager so i can handle ViewPager on backPress
}
else {
//display tab fragment
}
//super.onBackPressed();
}
TabFragment :
public class TabFragment extends Fragment {
public TabFragment() {
// Required empty public constructor
}
public static TabLayout tabLayout;
public static ViewPager viewPager;
public static int int_items = 2 ; View x;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
x=inflater.inflate(R.layout.content_main_menu,null);
tabLayout=(TabLayout) x.findViewById(R.id.tabs);
viewPager =(ViewPager) x.findViewById(R.id.viewpager);
setupViewPager(viewPager);
//viewPager.setAdapter(new MyAdapter(getChildFragmentManager()));
viewPager.setOffscreenPageLimit(1);
tabLayout.post(new Runnable() {
#Override
public void run() {
tabLayout.setupWithViewPager(viewPager);
}
});
return x;
}
#RequiresApi(api = Build.VERSION_CODES.KITKAT)
#Override
public void onDetach() {
super.onDetach();
try {
Field childFragmentManager = Fragment.class.getDeclaredField("mChildFragmentManager");
childFragmentManager.setAccessible(true);
childFragmentManager.set(this, null);
} catch (NoSuchFieldException | IllegalAccessException e) {
throw new RuntimeException(e);
}
}
private void setupViewPager(ViewPager viewPager) {
MyAdapter adapter = new MyAdapter(getChildFragmentManager());
adapter.addFragment(new TabOne(), "TAb1");
adapter.addFragment(new TabTwo(), "Tab2");
viewPager.setAdapter(adapter);
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
final InputMethodManager imm = (InputMethodManager)getActivity().getSystemService(Context.INPUT_METHOD_SERVICE);
imm.hideSoftInputFromWindow(x.getWindowToken(), 0);
}
#Override
public void onPageSelected(int position) {
}
#Override
public void onPageScrollStateChanged(int state) {
}
});
}
private class MyAdapter extends FragmentPagerAdapter{
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public MyAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}
#Override
public int getCount() {
return mFragmentList.size();
}
void addFragment(Fragment fragment, String title) {
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
}
#Override
public CharSequence getPageTitle(int position) {
return mFragmentTitleList.get(position);
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
return super.instantiateItem(container, position);
}
}
}......

add this code in your onBackPressed()
fragobjTab = (TabFragment) getSupportFragmentManager().findFragmentById(R.id.containerView);
try {
fragobjTab.onBackPressed();
}catch (Exception e){
e.printStackTrace();
}
And create a onBackPressed method in your tabFragment and setCurrentItem to the ViewPager:
public void onBackPressed()
{
// set page to your viewPager
// 0 is your first viewpager fragment
viewPager.setCurrentItem(0,true);
}

Refresh Fragment View on Tab Change

Hello I'm implementing a dynamic TabLayout using a single fragment, i have manage to create the tabs so far but there is a problem using a single fragment. When im changing the tabs the fragment view is not updating repeatedly, although im updating the data in the fragment's onCreateView method based on the tab selection. I have a recyclerview in the that fragment which should change according to the tab selection. SO can anyone help me with it or do anyone have a better way of approach?
TabView Activity
public class SubCategory extends AppCompatActivity {
private Toolbar toolbar;
private TabLayout tabLayout;
private ViewPager viewPager;
Activity a;
String url;
List<CategoryEncapsulation> categories = new ArrayList<>();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sub_category);
a=this;
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
viewPager = (ViewPager) findViewById(R.id.viewpager);
tabLayout = (TabLayout) findViewById(R.id.tabs);
categories=((MyshinzGlobal)getApplicationContext()).getCategoryList();
setupViewPager(viewPager);
((MyshinzGlobal)getApplicationContext()).setCategory_id(categories.get(0).getCategory_id());
}
private void setupViewPager(ViewPager viewPager) {
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
try {
for (int i = 0; i < categories.size(); i++) {
try {
adapter.addFragment(new ListFragment(), categories.get(i).getCategory_name());
} catch (Exception e) {
e.printStackTrace();
}
}
}catch (Exception e) {
e.printStackTrace();
}
viewPager.setAdapter(adapter);
tabLayout.setupWithViewPager(viewPager);
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
((MyshinzGlobal)getApplicationContext()).setCategory_id(categories.get(position).getCategory_id());
}
#Override
public void onPageScrollStateChanged(int state) {
}
});
}
class ViewPagerAdapter extends FragmentPagerAdapter {
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public ViewPagerAdapter(FragmentManager manager) {
super(manager);
}
#Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}
#Override
public int getCount() {
return mFragmentList.size();
}
public void addFragment(Fragment fragment, String title) {
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
}
#Override
public int getItemPosition(Object object) {
return super.getItemPosition(object);
}
#Override
public CharSequence getPageTitle(int position) {
return mFragmentTitleList.get(position);
}
}
}
Fragment class
public class ListFragment extends Fragment{
String category_id;
Activity a;
RecyclerView rv;
SubCategoryAdapter sca;
List<ParentListItem> parentListItems;
List<CategoryEncapsulation> categories = new ArrayList<>();
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
}
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View view =inflater.inflate(R.layout.sub_category_fragment, container, false);
a=getActivity();
categories=((MyshinzGlobal)a.getApplicationContext()).getCategoryList();
category_id=((MyshinzGlobal)a.getApplicationContext()).getCategory_id();
parentListItems= new ArrayList<>();
Toast.makeText(getActivity(), String.valueOf(category_id), Toast.LENGTH_SHORT).show();
rv= (RecyclerView) view.findViewById(R.id.recycler_view);
for (int i=0; i<categories.size();i++){
if(categories.get(i).getCategory_id().equals(category_id)){
parentListItems=categories.get(i).getParentListItems();
}
}
sca=new SubCategoryAdapter(a,parentListItems);
rv.setAdapter(sca);
rv.setLayoutManager(new LinearLayoutManager(a));
//new GetAllSubCategoryTask(a,url,"1001").execute();
return view;
}
}

I have two solution for this.
1) make your view pager offset limit 0. Which default 1. If you are switching another fragment which not in offset, that fragment re-creating.
viewPager.setOffscreenPageLimit(0);
2) Tell your adapter, fragment has been changed. So your adapter will re-create its views again.
rv.notifyDataSetChanged();
I hope these will solve your problem.

First thing as you are using ViewPager, onCreateView() of Fragment will be called only when getItem() of FragmentPagerAdapter will be called.
If need to create a method in Fragment which will call RecyclerView.notifyDataSetChanged().
Check out updated code for both classes
TabView Activity
public class SubCategory extends AppCompatActivity {
//....
#Override
protected void onCreate(Bundle savedInstanceState) {
//...
}
private void setupViewPager(ViewPager viewPager) {
//...
viewPager.setAdapter(adapter);
tabLayout.setupWithViewPager(viewPager);
viewPager.setOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
((MyshinzGlobal)getApplicationContext()).setCategory_id(categories.get(position).getCategory_id());
adapter.getItem(position).listUpdated();
}
#Override
public void onPageScrollStateChanged(int state) {
}
});
}
class ViewPagerAdapter extends FragmentPagerAdapter {
private final List<ListFragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public ViewPagerAdapter(FragmentManager manager) {
super(manager);
}
#Override
public ListFragment getItem(int position) {
return mFragmentList.get(position);
}
//...
}
}
Fragment class
public class ListFragment extends Fragment {
//...
public void listUpdated() {
for (int i = 0; i < categories.size(); i++) {
if (categories.get(i).getCategory_id().equals(category_id)) {
parentListItems.clear();
parentListItems.addAll(categories.get(i).getParentListItems());
}
}
sca.notifyDataSetChanged();
}
}

Using viewpager with radiogroup to switch between fragments

I have a viewpager with swipeable fragments and also a radiogroup that shows which view is selected. When I start the application, the first radiobutton is not selected, it is only selected when I swipe another view and get back. I am a beginner, so please share your knowledge. Here's my code:
Viewpager Adapter:
public class ViewPagerAdapter extends FragmentPagerAdapter {
public static int int_items = 3;
public ViewPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return new WelcomeOneFragment();
case 1:
return new WelcomeTwoFragment();
case 2:
return new WelcomeThreeFragment();
}
return null;
}
#Override
public int getCount() {
return int_items;
}
Fragment with the radiogroup:
public class TabFragment extends BaseFragment implements ViewPager.OnPageChangeListener, View.OnClickListener {
public static ViewPager mViewPager;
private Button mButtonMassage;
private RadioGroup mRadioGroup;
public static TabFragment newInstance() {
return new TabFragment();
}
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_tab, container, false);
initUi(rootView);
return rootView;
}
#Override
public void initUi(View rootView) {
mRadioGroup = (RadioGroup) rootView.findViewById(R.id.radio_group);
mViewPager = (ViewPager) rootView.findViewById(R.id.view_pager);
mButtonMassage = (Button) rootView.findViewById(R.id.buttonMassage);
initListeners();
}
#Override
public void initListeners() {
mButtonMassage.setOnClickListener(this);
mViewPager.addOnPageChangeListener(this);
initData();
}
#Override
public void initData() {
mViewPager.setAdapter(new ViewPagerAdapter(getChildFragmentManager()));
mViewPager.setCurrentItem(0);
}
#Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.buttonMassage:
Intent i = new Intent(getActivity(), MassageActivity.class);
startActivity(i);
break;
default:
break;
}
}
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
mRadioGroup.check(mRadioGroup.getChildAt(position).getId());
}
#Override
public void onPageScrollStateChanged(int state) {
}
}

just call this
mRadioGroup.check(mRadioGroup.getChildAt(0).getId());
after
mViewPager.setCurrentItem(0);
as listner will not callup in starting and you have to set it for manually after setting adapter to viewpager
hope it will work for you!! :)

This is a pretty common issue with ViewPager. onPageSelected is not called upon start, so I would just call:
mRadioGroup.check(mRadioGroup.getChildAt(0).getId());
In your initUi() method.