load fragment in ViewPager only when its selected - android

I have a ViewPager with 3 tabs.
I'm loading big data in every fragments.
The app load every fragments but I want to load fragment only when its selected.
How can I do that? I have no idea.
I'm waiting for your help. Thank you
my code:
public class Fragments extends AppCompatActivity {
private TabLayout tabLayout;
private ViewPager viewPager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_tabs);
viewPager = (ViewPager) findViewById(R.id.viewpager);
setupViewPager(viewPager);
tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(viewPager);
}
private void setupViewPager(ViewPager viewPager) {
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFragment(new FirstFragment(), "1");
adapter.addFragment(new SecondFragment(), "2");
adapter.addFragment(new ThirdFragment(), "3");
viewPager.setAdapter(adapter);
}
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 CharSequence getPageTitle(int position) {
return mFragmentTitleList.get(position);
}
}
}


If no one has given you a good answer I know this is 5 years later, but anyone reading this. I'm actually having the opposite problem. I need to load all tabs at the same time. What is happening to me now is only one tab is loading at a time. I need to use this adapter for viewpager2 with tablayout so that I can disable the viewpager swiping left to right for my specific usecase.
Here is my code:
WARNING CODE IS IN KOTLIN NOT JAVA
class RecipeTabAdapter internal constructor(fm: FragmentManager, lifecycle: Lifecycle) : FragmentStateAdapter(fm, lifecycle) {
val fragmentsList: ArrayList<Fragment> = arrayListOf()
fun addFragment(fragment: Fragment) {
fragmentsList.add(fragment)
}
override fun getItemCount(): Int {
return fragmentsList.size
}
override fun createFragment(position: Int): Fragment {
when (position) {
position -> fragmentsList[position]
position -> fragmentsList[position]
}
return fragmentsList[position]
}
}


Is it possible to disable the offscreen page limit?
No. It is already set to the minimum possible value: one page to each side of the viewed page. This is necessary to have the animation effects work -- you see parts of two fragments (original and new) at the same time.


In
OncreateView(){
//.... dont initialize your view here
if(isMenuVisible()) { // menu should be visible if current fragment is visible right now
setUserVisibleHint(true); // manually set value to true
}
}
in
oncreate(){
setHasOptionsMenu(true);
}
Finally there is method called setuservisiblehint() which is only called when the fragment is visible to the user this is the only method where you shud initialize all your views.
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if(isVisibleToUser && v != null) {
// initialize your view here and call you fetch_data_function()
}


Here's my solution and it works as expected. In all of your child fragments create a boolean variable:
private boolean loadFragmentExecuted = false;
in the child fragments create a generic method called loadFragment and move all of the logic you added in onCreateView to that method:
public void loadFragment()
{
if(!loadFragmentExecuted)
{
//Add your logic to manipulate the UI or load data etc...
loadFragmentExecuted = true;
}
}
in your pageview logic create the fragments dynamically like:
//add the fragment
String fragmentName = "com.something." + fragmentId;
//check if the class exists
try
{
Class myFragmentClass = Class.forName(fragmentName);
Fragment myFragment = (Fragment) myFragmentClass.newInstance();
mFragments.add(myFragment);
}
catch (ClassNotFoundException e)
{
e.printStackTrace();
}
catch (IllegalAccessException e)
{
e.printStackTrace();
}
catch (InstantiationException e)
{
e.printStackTrace();
}
then set your pager adapter and attach a tablayout with it:
//set our pager adapter that contains different fragments
mPagerAdapter = new BasePagerAdapter(mFragmentManager, mFragments);
//link the adapter to the viewpager
mViewPager.setAdapter(mPagerAdapter);
//cache fragments
int limit = (mPagerAdapter.getCount() > 0 ? mPagerAdapter.getCount() : 1);
mViewPager.setOffscreenPageLimit(limit);
//add the page listner to the viewPager and link it to the tabLayout
mViewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(mTabLayout));
//on tab selected select current viewpager item
mTabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener()
{
#Override
public void onTabSelected(TabLayout.Tab tab)
{
mViewPager.setCurrentItem(tab.getPosition());
//get fragment for the selected tab
Fragment f = mPagerAdapter.getItem(tab.getPosition());
//load the content of the fragment
try
{
Class c = f.getClass();
Method loadFragment = c.getMethod("loadFragment");
loadFragment.invoke(f);
}
catch (IllegalAccessException e){}
catch (InvocationTargetException e){}
catch (NoSuchMethodException e){}
}
#Override
public void onTabUnselected(TabLayout.Tab tab)
{
}
#Override
public void onTabReselected(TabLayout.Tab tab)
{
}
});


I have a solution that does not require subclassing, and it's easy to introduce into existing projects. It uses the child fragment mechanism.
The basic idea is to replace your content fragment with an almost empty fragment, and add your content fragment as a child fragment when it is really visible to the user
The gist of the code is like this
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
boolean hasFragment = getChildFragmentManager().findFragmentById(R.id.container) != null;
if (hasFragment) {
return;
}
if (getUserVisibleHint()) {
addFragment("onViewCreated");
}
}
#Override
public void onResume() {
super.onResume();
if (getUserVisibleHint()) {
addFragment("onResume");
}
}
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (isVisibleToUser && isResumed()) {
addFragment("setUserVisibleHint");
}
}
private void addFragment(String cause) {
if (getChildFragmentManager().findFragmentById(R.id.container) == null) {
getChildFragmentManager().beginTransaction()
.setCustomAnimations(android.R.animator.fade_in, android.R.animator.fade_out)
.add(R.id.container, createFragment()).commit();
}
}
Check out my full solution here, which also contains a progressbar, and the option to automatically start loading of background fragments with a specified delay: Lazy Load Fragment

Related

How to call fragment method from activity

I'm populating fragments in a tablayout. I have a method in one of my fragments, and i want to call it from an activity. But when i tried to have reference of the fragment by doing like this Fragment myFragment = (Fragment ) getSupportFragmentManager().findFragmentById(R.id.my_fragment), myFragment is null. I'm new to android. (Sorry for the bad english)
My code so far.
public class DashboardActivity extends AppCompatActivity {
private ViewPager pager;
private TabLayout tabLayout;
private Toolbar dashboardToolbar;
public static int position;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_dashboard_activity);
HomeFragment myFragment = new HomeFragment ();
if(getSupportFragmentManager().findFragmentById(R.id.homeFragment) == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.homeFragment, myFragment).commit();
}
pager = (ViewPager) findViewById(R.id.view_pager);
setupViewPager(pager);
tabLayout = (TabLayout) findViewById(R.id.tab_layout);
tabLayout.setupWithViewPager(pager);
pager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));
tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
#Override
public void onTabSelected(TabLayout.Tab tab) {
// Toast.makeText(DashboardActivity.this, "tabSelected: " + tab.getText()+" "+ tab.getPosition(), Toast.LENGTH_SHORT).show();
// no where in the code it is defined what will happen when tab is tapped/selected by the user
// this is why the following line is necessary
// we need to manually set the correct fragment when a tab is selected/tapped
// and this is the problem in your code
pager.setCurrentItem(tab.getPosition());
position = tab.getPosition();
}
#Override
public void onTabUnselected(TabLayout.Tab tab) {
}
#Override
public void onTabReselected(TabLayout.Tab tab) {
// Toast.makeText(DashboardActivity.this, "tabReSelected: " + tab.getText(), Toast.LENGTH_SHORT).show();
position = tab.getPosition();
// Reload your recyclerView here
}
});
}
private void setupViewPager(ViewPager viewPager) {
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFragment(new HomeFragment(), "FOR YOU");
adapter.addFragment(new NotificationFragment(), "NOTIF");
adapter.addFragment(new ChatFragment(), "CHAT");
adapter.addFragment(new ProfileFragment(), "PROFILE");
viewPager.setAdapter(adapter);
}
}
Fragment
public class HomeFragment extends Fragment {
// Objects Declaration
public HomeFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.homeFragment, container, false);
}
public void myMethod(){ //method to be called
//do something
}
}
Activity
public class MyActivity extends AppCompatActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_activity_filter);
HomeFragment myFragment= (HomeFragment ) getSupportFragmentManager().findFragmentById(R.id.homeFragment);
if(myFragment!= null) {
Toast.makeText(ActivityFilter.this, "Not null.", Toast.LENGTH_SHORT).show();
home.myMethod(); // this line is not accessed since myFragment is null
}else{
Toast.makeText(ActivityFilter.this, "Null fragment.", Toast.LENGTH_SHORT).show();
}
}
}

You should use a Callback.
Create a public interface in your fragment.
public interface iCommunicateListener{
void communicate(String msg);
}
You also have to make the activity your listener.
(You can have many listeners, but fragments are supposed to be reusable, so if you have many listeners it will not be as reusable as it could and should be)
private iCommunicateListener listener;
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// This makes sure that the container activity has implemented
// the callback interface. If not, it throws an exception
try {
listener = (iCommunicateListener) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement iCommunicateListener");
}
}
Now you have active listener.
In your onClicks or whenever you want send information to your activity, you have to call listener.communicate("doSomething");
Your Activity must implement the iCommunicateListener.
After implementation of the method communicate you can choose your logic for the different Strings or whatever you want to send through the callback.
There are many other ways for communication between Activities and Fragments, but since you are just beggining learn this one. After you implement it and you see the result you can take a look at this library which will definately help you in your android development. EventBus
With EventBus you will not have to use the callbacks which will make your fragments even more reusable and flexible, but first learn the normal Callbacks. It is a basic pattern and you will use it in many different situations.
More on Fragments: Fragments
Hope this helps!

Refresh fragment when change between tabs

App open on first fragment and there is 2 tabs i want to refresh second fragment
when i move to it but i don't want to refresh first fragment
MainActivity
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
viewPager = (ViewPager) findViewById(R.id.viewpager);
setupViewPager(viewPager);
tabLayout = (TabLayout) findViewById(R.id.tabs);
tabLayout.setupWithViewPager(viewPager);
}
private void setupViewPager(ViewPager viewPager) {
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFragment(new Main_Button(), "Main");
adapter.addFragment(new TwoFragment(), "Main2");
viewPager.setAdapter(adapter);
}
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 CharSequence getPageTitle(int position) {
return mFragmentTitleList.get(position);
}
}
please explain your answer because i'm new in android and i don't know how i can do that

When a Fragment is made visible (i.e., the selected page in your ViewPager), its setUserVisibleHint() method is called. You can override that method in your TwoFragment and use it to trigger a refresh.
public class TwoFragment extends Fragment {
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (isVisibleToUser) {
// Refresh your fragment here
}
}

Inside Your fragment class use the below code:
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (isVisibleToUser) {
getFragmentManager().beginTransaction().detach(this).attach(this).commit();
}
}

Try This
ViewPager mViewPager = (ViewPager)findViewById(R.id.pager);
mViewPager.setOffscreenPageLimit(2);

As of 2020 it is advisable to use architecture components(MVVM) such as LiveData and viewModel
This way all Fragments can share the same state
see docs here https://developer.android.com/jetpack/guide

Try this - it works for me
This code reloads current fragment, when it visible to user. Works when swiping and when back button pressed on next fragment.
#Override
public void setUserVisibleHint(boolean isVisible) {
super.setUserVisibleHint(isVisible);
if (isVisible) {
FragmentTransaction ftr = getFragmentManager().beginTransaction();
ftr.detach(this).attach(this).commit();
}
}

If you wouldn't mind refreshing every fragment every time a tab changes, you could simply override the getItemPosition() method of your FragmentPagerAdapter and make it return always the value POSITION_NONE. Example:
#Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
By doing that, you tell android to refresh the fragment each time the view pager tries to get it. Performance wise, it isn't the best practice. So there is a second approach:
First, create an interface to be called when your need refresh:
public interface Updatable {
public void update();
}
Then, make your fragments implement this interface:
public class MyFragment extends Fragment implements Updateable {
...
#Override
public void update() {
// refresh your fragment, if needed
}
}
If your really wish to not update your first fragment, do nothing in its update() method.
Third, override the getItemPosition method and call update(). This will be called every time a fragment gets selected:
#Override
public int getItemPosition(Object object) {
Updatable f = (Updatable) object;
if (f != null) {
f.update();
}
return super.getItemPosition(object);
}
Most of this code came from this answer.

you could use ViewPager.addOnPageChangeListener to listen to when the fragments are swiped and incorporate some type of action there.

How to re create the fragment in viewpager

I have a viewpager with 5 tabs , each tab is fragment showing different data to user , each fragment have recycleview inside itself , and i need to re insert updated data into the recyclerview when user change the tab, and I need to update the view
Every time I swipe to a tab, a new instance of the fragment in that tab needs to load so that data will be updated.
I have tried:
1- I used FragmentStatePagerAdapter (nothing happens)
2- I Override getItemPosition method to return PagerAdapter.POSITION_NONE; (nothing happens)
3- setOffscreenPageLimit(0) (Nothing happens)
4- refresh function inside each fragment to be called onTabSelected
(gives nullPointerException)
How can i recreate fragment from scratch each time user change the tab
i really need to know.
I have been struggling with this problem for a week with no progress. I appreciate any help, be it a hint, a comment, a suggestion.
Let me know what code should I post, Thanks.
Edit:
my codes:
MainActivity:
public class Sefaresh_activity3 extends AppCompatActivity implements Serializable, Sefaresh3_interface {
Context context;
Toolbar mtoolbar;
private List<Food> food_list = new ArrayList<>();
MyPagerAdapter adapter;
Custom_TabLayout mTabLayout;
ViewPager mpager;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_sefaresh_activity3);
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.JELLY_BEAN_MR1) {
getWindow().getDecorView().setLayoutDirection(View.LAYOUT_DIRECTION_LTR);
}
context = this;
sqlHelper = new SqlHelper(this);
setupTabs();
private void setupTabs() {
mtoolbar = (Toolbar) findViewById(R.id.app_bar);
setSupportActionBar(mtoolbar);
SpannableString s = new SpannableString(getTitle());
s.setSpan(new TypefaceSpan(this, "IRAN Sans Bold.ttf"), 0, s.length(),
Spannable.SPAN_EXCLUSIVE_EXCLUSIVE);
setTitle(s);
try {
getSupportActionBar().setHomeButtonEnabled(true);
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
} catch (Exception e) {
L.m("something is wrong in toolbar section");
}
adapter = new MyPagerAdapter(getSupportFragmentManager());
mTabLayout = (Custom_TabLayout) findViewById(R.id.tab_layout);
mpager = (ViewPager) findViewById(R.id.viewpager);
mpager.setAdapter(adapter);
mTabLayout.setTabsFromPagerAdapter(adapter);
mTabLayout.setupWithViewPager(mpager);
mpager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(mTabLayout));
mTabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
#Override
public void onTabSelected(TabLayout.Tab tab) {
L.m("tab selected" + tab.getPosition());
mpager.setCurrentItem(tab.getPosition());
// Sefaresh3_fragment all_fragment = (Sefaresh3_fragment) adapter.getFragment_all();
// sefaresh3_fragment.onRefresh();
// Sefaresh3_fragment sefaresh3_fragment = (Sefaresh3_fragment) adapter.fragment_all;
// adapter.notifyDataSetChanged();
}
#Override
public void onTabUnselected(TabLayout.Tab tab) {
}
#Override
public void onTabReselected(TabLayout.Tab tab) {
}
});
}
class MyPagerAdapter extends FragmentStatePagerAdapter {
// public ArrayList<Fragment> fragmentArrayList = new ArrayList<>();
Fragment fragment_all;
Fragment fragment_pizza;
Fragment fragment_sandwich;
Fragment fragment_salad;
Fragment fragment_coca;
public Fragment getFragment_coca() {
return fragment_coca;
}
public Fragment getFragment_all() {
return fragment_all;
}
public Fragment getFragment_pizza() {
return fragment_pizza;
}
public Fragment getFragment_sandwich() {
return fragment_sandwich;
}
public Fragment getFragment_salad() {
return fragment_salad;
}
String[] tabs = {
"products",
"new products",
"featured",
"star",
"star2"
};
#Override
public int getItemPosition(Object object) {
return PagerAdapter.POSITION_NONE;
}
public MyPagerAdapter(FragmentManager fm) {
super(fm);
tabs = getResources().getStringArray(R.array.sefaresh3_tabs);
}
#Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
#Override
public Fragment getItem(int num) {
Fragment fragment = null;
orders = new Orders();
orders.setOrders(all_orders);
switch (num) {
case 0:
// fragment_all = Sefaresh3_fragment.newInstance("all", "");
// return new Sefaresh3_fragment().newInstance("all","");
return Sefaresh3_fragment.newInstance("all","");
case 1:
fragment_pizza = Sefaresh3_fragment.newInstance("pizza", "");
return fragment_pizza;
case 2:
fragment_sandwich = Sefaresh3_fragment.newInstance("sandwich", "");
return fragment_sandwich;
case 3:
fragment_salad = Sefaresh3_fragment.newInstance("salad", "");
return fragment_salad;
case 4:
fragment_coca = Sefaresh3_fragment.newInstance("coca", "");
return fragment_coca;
default:
return fragment;
}
}
#Override
public CharSequence getPageTitle(int position) {
return tabs[position];
}
#Override
public int getCount() {
return 5;
}
}

thanks for everybody suggestions , after one week struggling with this problem I found the solution.
I tried several methods but finally I just found the solution.
I used Broadcast receiver to tell the fragment update the list , and every time I need to update the fragments to update the data list , I call the broadcaster. its awesome and it works well
If anyone had the same problem I will be happy to help him :) thanks.

Updating the contents on tab changed in view pager

I am scracthing my head for past 1 day but unable to find the solution.
In mine application there are two tabs under the toolbar
First tab is USER-TAB
the second one is ADMIN-TAB
In both the tabs there are the listView. When a ListItem on the USER-TAB is clicked a dialog appears and user take some action.
Now after this when the ADMIN-TAB is Selected the Admin should get refreshed with new sets of data. But It's not. On selecting the ADMIN-TAB the onResume() method and everyting is getting called but it is not able to update the list.
I wont be able to write the Whole code, I am giving some snippet.
Basically I have taken the code from this link
https://github.com/codepath/android_guides/wiki/Sliding-Tabs-with-PagerSlidingTabStrip
In My Main Activity I have written the OpPageChangeListener.
public class MaterialTab extends FragmentActivity {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.material_main_sample);
// Get the ViewPager and set it's PagerAdapter so that it can display items
ViewPager viewPager = (ViewPager) findViewById(R.id.viewpager);
viewPager.setAdapter(new SampleFragmentPagerAdapter(getSupportFragmentManager()));
// Give the PagerSlidingTabStrip the ViewPager
PagerSlidingTabStrip tabsStrip = (PagerSlidingTabStrip) findViewById(R.id.tabs);
// Attach the view pager to the tab strip
tabsStrip.setViewPager(viewPager);
tabsStrip.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
if(position == 0){
MileUserFragment userFragment = new MileUserFragment();
final FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.detach(userFragment);
ft.attach(userFragment);
ft.commit();
} if(position == 1){
MileAdminFragment adminFragment = new MileAdminFragment();
final FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
ft.detach(adminFragment);
ft.attach(adminFragment);
ft.commit();
}
}
#Override
public void onPageScrollStateChanged(int state) {
}
});
}
}
OnPageSelected You can see I am detaching and reattaching the fragment.Everything is working fine. Both Fragments OnResume() are getting called but the List is not getting changed. I don't undrstand why
For additional assistance i am adding snippet one Fragment. Hope this will give some Idea where i might be going wrong
public class MileUserFragment extends Fragment {
#Override
public void onResume() {
super.onResume();
new GetAdminDbTask().execute();
if(!internetUtil.isConnectedToInternet(getActivity())){
mSwipeRefreshLayout.setRefreshing(false);
mSwipeRefreshLayout.setEnabled(false);
}
}
public class GetAdminDbTask extends AsyncTask<Admin, Void, String> {
#Override
protected String doInBackground(Admin... parmas) {
_adminList = shipmentDbHandler.getAllAdmin();
return "";
}
#Override
protected void onPostExecute(String str) {
mAdminAdapter = new AdminAdapter(getActivity(), _adminList);
adminListView.setAdapter(mAdminAdapter);
mAdminAdapter.notifyDataSetChanged();
// Set the refresh Listener to false after the list has been loaded with new set of data
if (mSwipeRefreshLayout.isRefreshing()) {
mSwipeRefreshLayout.setRefreshing(false);
}
if(_adminList.size() > 0 ){
mAdminAdapter = new AdminAdapter(getActivity(), _adminList);
adminListView.setAdapter(mAdminAdapter);
mAdminAdapter.notifyDataSetChanged();
}
}
}
}
public class SampleFragmentPagerAdapter extends FragmentPagerAdapter {
final int PAGE_COUNT = 2;
private String tabTitles[] = new String[] { "Tab1", "Tab2" };
private FragmentManager fragmentManager;
public SampleFragmentPagerAdapter(FragmentManager fm) {
super(fm);
this.fragmentManager = fm;
}
#Override
public int getCount() {
return PAGE_COUNT;
}
#Override
public Fragment getItem(int position) {
FragmentTransaction ft = null;
if(position == 0){
MileUserFragment userFragment = new MileUserFragment();
return userFragment;
}
if(position == 1){
MileAdminFragment adminFragment = new MileAdminFragment();
return archiveFragment;
}
}
#Override
public CharSequence getPageTitle(int position) {
// Generate title based on item position
return tabTitles[position];
}
}

Haah.. Finally i got an answer to after an heck of losing almost 1 and half days. It might be not completely good answer but atleast it is one of the closest I got.
First of all MainActivity.java looks like:
tabs.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
int scrollPosition = 0;
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
if(position == 0){
scrollPosition = 0;
}
if(position == 1){
scrollPosition = 1;
}
}
#Override
public void onPageSelected(int position) {
}
#Override
public void onPageScrollStateChanged(int state) {
if(state == pager.SCROLL_STATE_IDLE){
if(scrollPosition == 0 && application.isActiveAction()){
viewPagerAdapter.notifyDataSetChanged();
application.setActiveAction(false);
}
if(scrollPosition == 1 && application.isArchiveAction()){
viewPagerAdapter.notifyDataSetChanged();
application.setArchiveAction(false);
}
}
}
});
Now what I have done here is I have set OnPageChangeListener and in this I am keeping track of the position whenever the tabs are changing. For my needs what i have done is i have created two boolean variables and setting it when any content on those tab are changing in Application scope. Now when the contents on one tab has been changed or some Action are done I am calling
viewPagerAdapter.notifyDataSetChanged() // Now this is the real gem
after invoking this it will make a call to the ViewPagerAdapter function
#Override
public int getItemPosition(Object object) {
return PagerAdapter.POSITION_NONE; // This will get invoke as soon as you call notifyDataSetChanged on viewPagerAdapter.
}
Also the Point is your ViewPagerAdapter should extend FragmentStatePageAdapter. Now the Point is
PagerAdapter.POSITION_NONE
will not cache the fragment and reload a new fragment for that tab position.
Basic idea is we should not make or retutn PagerAdapter.POSITION_NONE everytime on sliding of tab since it destroys the cached element and reload the fragment which affects UI performance.
So finally the basic thing is always check that whether on calling viewPagerAdapter.notifyDataSetChanged() the function getItemPosition() should also gets invoked. Hope it will help somebody. For better perfomance you can make changes according to your requirement.
I got the needed breakthrough and understanding from this post : #Louth Answer
Remove Fragment Page from ViewPager in Android

Just put
viewPager.setCurrentItem(tab.getPosition());
in your onTabSelected method like:
tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
#Override
public void onTabSelected(TabLayout.Tab tab) {
viewPager.setCurrentItem(tab.getPosition());
}
#Override
public void onTabUnselected(TabLayout.Tab tab) {
}
#Override
public void onTabReselected(TabLayout.Tab tab) {
}
});

ViewPager.setOffscreenPageLimit(0) doesn't work as expected

The fragments I use in my ViewPager instance are quite resource intensive, so I'd only like to load one at a time. When I try the following:
mViewPager.setOffscreenPageLimit(0);
mViewPager.setAdapter(mPagerAdapter);
My FragmentStatePagerAdapter.getItem(int position) override function is called 3 times, which is what happens when I call mViewPager.setOffscreenPageLimit(1). I would expect it to only be called once, because I specified 0 offscreen pages.
I believe I'm calling everything correctly, because if I call mViewPager.setOffscreenPageLimit(2), FragmentStatePagerAdapter.getItem(int position) is called 5 times as I would expect.
Does ViewPager require a minimum of 1 offscreen pages, or am I doing something wrong here?

The best way that I found was setUserVisibleHint
add this to your fragment
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (isVisibleToUser) {
// load data here
}else{
// fragment is no longer visible
}
}

Does ViewPager require a minimum of 1 offscreen pages
Yes. If I am reading the source code correctly, you should be getting a warning about this in LogCat, something like:
Requested offscreen page limit 0 too small; defaulting to 1

You can try like this :
public abstract class LazyFragment extends Fragment {
protected boolean isVisible;
/**
* 在这里实现Fragment数据的缓加载.
* #param isVisibleToUser
*/
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if(getUserVisibleHint()) {
isVisible = true;
onVisible();
} else {
isVisible = false;
onInvisible();
}
}
protected void onVisible(){
lazyLoad();
}
protected abstract void lazyLoad();
protected void onInvisible(){}
protected abstract void lazyLoad();
protected void onInvisible(){}

First Add
boolean isFragmentLoaded = false;
than
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (isVisibleToUser && !isFragmentLoaded) {
//Load Your Data Here like.... new GetContacts().execute();
isFragmentLoaded = true;
}
else{
}
}

this may be old thread but this seems to work for me. Override this function :
#Override
public void setMenuVisibility(boolean menuVisible) {
super.setMenuVisibility(menuVisible);
if ( menuVisible ) {
/**
* Load your stuffs here.
*/
} else {
/**
* Fragment not currently Visible.
*/
}
}
happy codings...

ViewPager is default to load the next page(Fragment) which you can't change by setOffscreenPageLimit(0). But you can do something to hack.
You can implement onPageSelected function in Activity containing the ViewPager. In the next Fragment(which you don't want to load), you write a function let's say showViewContent() where you put in all resource consuming init code and do nothing before onResume() method. Then call showViewContent() function inside onPageSelected. Hope this will help.

in my case i wanted to start some animations in views, but with setUserVisibleHint got some issues ...
my solution is :
1/ addOnPageChangeListener for your adapter :
mViewPager.addOnPageChangeListener(this);
2/ implement OnPageChangeListener :
public class PagesFragment extends Fragment implements ViewPager.OnPageChangeListener
3/ override the 3 methodes :
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels)
{
}
#Override
public void onPageSelected(int position)
{
}
#Override
public void onPageScrollStateChanged(int state)
{
}
4/ declare and initialize this variable on your class
private static int mTabState = 1;
notice : i have three fragments in my adapter, and use mTabState for setCurrentItem and current position of adapter which recognize which fragment is show to user in time ...
5/ in onPageSelected method add this codes :
if (mTabState == 0 || position == 0)
{
Intent intent = new Intent("animation");
intent.putExtra("current_position", position);
LocalBroadcastManager.getInstance(mContext).sendBroadcast(intent);
}
if previous page or current page is page 0(fragment in position 0) then do this stuff
6/ now in your fragment class (fragment in position 0 of adapter), you must create broadcast receiver and register it in onResume method and unregister it onPause methos :
BroadcastReceiver broadcastReceiver = new BroadcastReceiver()
{
#Override
public void onReceive(Context context, Intent intent)
{
if (Objects.equals(intent.getAction(), "animation"))
{
int currentPosition = intent.getIntExtra("current_position", 0);
if (currentPosition == 0)
{
startAnimation();
setViewsVisible();
} else
{
setViewsInvisible();
}
}
}
};
#Override
public void onResume()
{
super.onResume();
LocalBroadcastManager.getInstance(mContext).registerReceiver(broadcastReceiver, new IntentFilter("animation"));
}
#Override
public void onPause()
{
super.onPause();
LocalBroadcastManager.getInstance(mContext).unregisterReceiver(broadcastReceiver);
}
summary : i have Fragment Pager Adapter witch shows Three Fragments in it, I want show some Animations on Views in Fragment in Position 0 of Adapter, For this I use BroadcastReceiver. When Fragment is Picked I start the Animation method and shows the Views to User, When Fragment is not Showing to User I try to Invisible Views...

View Pager With only one Page :
This is February 2021: I have able to add only one page with viewPager. The approach is with ViewPager, FragmentPagerAdapter, Tablayout, and a fragment. In my case, I can populate many Pages with many tabs, or only one Page with one Tab. When one tab and one page, on swipe left or right, I can manage to change the chapter of my document (which I want to show next). And when many pages and many tabs, I can change the entire book of documents.
In main Activity Oncreate: (Here is my working code approach, I have changed nothing here from my working code):
if(getIntent()!=null){
if(getIntent().getStringExtra("ONLY_TAFHEEM")!=null)
sectionsPagerAdapter = new SectionsPagerAdapter(this, getSupportFragmentManager(), suraName, suraId, ayatId, true);
else
sectionsPagerAdapter = new SectionsPagerAdapter(this, getSupportFragmentManager(), suraName, suraId, ayatId, false);
}else {
sectionsPagerAdapter = new SectionsPagerAdapter(this, getSupportFragmentManager(), suraName, suraId, ayatId, false);
}
final ViewPager viewPager = findViewById(R.id.view_pager);
viewPager.setAdapter(sectionsPagerAdapter);
tabsLayout = findViewById(R.id.tabs);
tabsLayout.animate();
tabsLayout.setupWithViewPager(viewPager);
In Adapter :
#NonNull
#Override
public Fragment getItem(int position) {
// getItem is called to instantiate the fragment for the given page.
// Return a PlaceholderFragment (defined as a static inner class below).
return PlaceholderFragment.sendData(mContext, postion, suraName, suraId, ayahId, ARABIC_AYAH, BENGALI_AYAH, actualDbNames[position], tafsirDisplayNames[position]);
}
#Nullable
#Override
public CharSequence getPageTitle(int position) {
return tafsirDisplayNames[position];
}
#Override
public int getCount() {
// this is the tricky part // Show pages according to array length. // this may only one // this is the tricky part :
return tafsirDisplayNames.length;
}
And at last the fragments public constructor :
public static PlaceholderFragment sendData(Context mContext, int tabIndex, String suraName, String suraId, String ayahNumber, String arabicAyah, String bengaliAyah, String actualDbName, String displayDbName) {
Log.i("PlaceHolder", "Tafhim sendData: " + bengaliAyah);
PlaceholderFragment fragment = new PlaceholderFragment();
Bundle bundle = new Bundle();
mContext_ = mContext;
BENGALI_AYAH = bengaliAyah;
_DISPLAY_DB_NAME = displayDbName;
bundle.putInt(ARG_SECTION_NUMBER, tabIndex);
bundle.putString(SURA_NAME, suraName);
bundle.putString(SURA_ID, suraId);
bundle.putString(AYAH_NUMBER, ayahNumber);
bundle.putString(ARABIC_AYAH, arabicAyah);
bundle.putString(ACTUAL_DB_NAME, actualDbName);
bundle.putString(DISPLAY_DB_NAME, displayDbName);
fragment.setArguments(bundle);
return fragment;
}
That's all, just passing the array (of Tab Labels) to the adapter, (it may only one element, in case, for one page), with my need, I can populate one page or more page, and according to this it populate one tab or many tabs : in the above code the array is: tafsirDisplayNames. I can also create the array manually in adapter, when the adapter first called, Or, recreate the array with +-elements, on recreate the MainActivity.

Please Try This Code for resolve issue of refreshing view in Viewpager....
/* DO NOT FORGET! The ViewPager requires at least “1” minimum OffscreenPageLimit */
int limit = (mAdapter.getCount() > 1 ? mAdapter.getCount() - 1 : 1);
mViewPager.setOffscreenPageLimit(limit);

for the "instantiateItem" function, just prepare the fragment, but don't load the heavy content.
Use "onPageChangeListener" , so that each time you go to a specific page, you load its heavy content and show it.

I kind of have the same problem. I found some useful code on this site and transform it.
The min int for mViewPager.setOffscreenPageLimit(...); is 1, so even if you change it to 0 you will still have 2 pages loaded.
First thing to do is to create a static int we will call maxPageCount and override FragmentStatePagerAdapter method getCount() to return maxPageCount:
#Override
public int getCount() {
return maxPageCount;
}
Create then a static method accessible from any where in the program that will allow you to change this maxCount:
public static void addPage(){
maxPageCount++; //or maxPageCount = fragmentPosition+2
mFragmentStatePagerAdapter.notifyDataSetChanged(); //notifyDataSetChanged is important here.
}
Now initialize maxPageCount to 1. When ever you want you can add another page.
In my case when I needed the user to treat the current page first before generated the other. He do it and then, without problem can swipe to the next page.
Hope it help someone.

Use This
// create boolean for fetching data
private boolean isViewShown = false;
#Override
public void setUserVisibleHint(boolean isVisibleToUser) {
super.setUserVisibleHint(isVisibleToUser);
if (getView() != null) {
isViewShown = true;
// fetchdata() contains logic to show data when page is selected mostly asynctask to fill the data
fetchData();
} else {
isViewShown = false;
}
}

// step 1: add BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT FragmentPagerAdapter contractor
public class BottomTabViewPager extends FragmentPagerAdapter {
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public BottomTabViewPager(FragmentManager manager) {
super(manager, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT);
}
#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);
}
public void addTabs(String title) {
mFragmentTitleList.add(title);
}
#Override
public CharSequence getPageTitle(int position) {
return mFragmentTitleList.get(position);
// return null;
}
}
// step 2: You can try like this :
public class MyFragment extends Fragment {
public MyFragment() {
// Required empty public constructor
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_ui, container, false);
return view;
}
#Override
public void onResume() {
super.onResume();
/**
* Load your stuffs here.
*/
}
}

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