Develop Reference

i have a dynamic tablayout but every time i push back button and re-enter my app again , my tab doubles , why?

in my TabLayout i create my login TabItem dynamically at the onCreate() method of my MainActivity , but every time i exit from my application with back button and i re-enter my app , it creates that login TabItem again and so it doubles it every time , i tried to check and use :
if(savedInstanceState == null) {
// create the first tab
}
but it didn't work , can you please help me ?
here is my code for the MainActivity :
public class MainActivity extends AppCompatActivity {
TabLayout tabLayout;
ViewPager viewPager;
public static List<Fragment> fragments = new ArrayList<>();
public static List<String> fragmentsTitle = new ArrayList<>();
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tabLayout = findViewById(R.id.myTabLayout);
viewPager = findViewById(R.id.myViewPager);
MyViewPagerAdapter Adapter = new MyViewPagerAdapter(getSupportFragmentManager());
Adapter.createTab(new LoginFragment(), "Login", getSupportFragmentManager(), viewPager);
viewPager.setAdapter(Adapter);
tabLayout.setupWithViewPager(viewPager);
tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
public void onTabSelected(TabLayout.Tab tab) {
}
public void onTabUnselected(TabLayout.Tab tab) {
}
public void onTabReselected(TabLayout.Tab tab) {
}
});
}
}
and this is the code for FragmentPagerAdapter
public class MyViewPagerAdapter extends FragmentPagerAdapter {
public MyViewPagerAdapter(FragmentManager manager) { super(manager);}
public void createTab(Fragment fragment, String title, FragmentManager manager, ViewPager viewPager) {
MyViewPagerAdapter Adapter = new MyViewPagerAdapter(manager);
MainActivity.fragments.add(fragment);
MainActivity.fragmentsTitle.add(title);
Adapter.notifyDataSetChanged();
viewPager.setAdapter(Adapter);
}
public Fragment getItem(int position) {
return MainActivity.fragments.get(position);
}
public CharSequence getPageTitle(int position) {
return MainActivity.fragmentsTitle.get(position);
}
public int getCount() {
return MainActivity.fragments.size();
}
}

Try removing static keyword from your list in MainActivity. Instead use final to prevent reinitialisation of list.
It's creating that tab everytime because static things stay alive as long as they get killed. And the professional way on earth to create tab and store them inside list is to keep that list inside viewpager adaptor.
I am happy it was helpful.

load fragment in ViewPager only when its selected

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

Launching new Fragment Inside ViewPager

I'm on the verge of losing it. Anyone that could help me solve this issue will be showered with coding props for all of eternity.
I have a Tablayout containing 3 Tabs within my Main Activity. Each tab contains their own Fragment(Tasks,Calendar,Contacts). There is a FAB button in the Main Activity that lives on top of all the Fragments and performs a certain action base on what Tab I'm currently in.
My main issue is that, when I'm in Tab1, and the Fab is clicked, I need to replace the Tasks Fragment with a different Fragment called AddContact.
I've been looking up how to solve this for hours and finally settled on an earlier answer from this stack post
The issue is, I'm not quite grasping how they were able to do it.
My understanding is that the swapping of Fragments should be managed by the getItem method within the View Pager Adapter. And that there should be a listener that exists between the ViewPagerAdapter and the buttonClicked action in my Main Activity that tells it to execute.
The problem is that I can't make this link. I've tried a number of things but with no luck. Below I included my MainActivity Class and my ViewPagerAdapter Class. If someone could please explain to me how I could swap out my Tasks Fragment with my AddContacts Fragment in the ViewPager, I would greatly appreciate it
Main Activity:
public class MainActivity extends AppCompatActivity {
private CollapsingToolbarLayout collapsingToolbarLayout;
private ViewPager viewPager;
private ArrayList<Fragment> fragments = new ArrayList<>();
private ArrayList<String> titles = new ArrayList<>();
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
collapsingToolbarLayout = (CollapsingToolbarLayout)findViewById(R.id.collapsing_toolbar);
setSupportActionBar(toolbar);
fragments.addAll(Arrays.asList(new Tasks(),new Calendar(),new Contacts()));
titles.addAll(Arrays.asList(getResources().getString(R.string.fragment_task_title),
getResources().getString(R.string.fragment_cal_title),getResources().getString(R.string.fragment_contacts_title)));
TabLayout tabLayout = (TabLayout)findViewById(R.id.tabs);
final FloatingActionButton fab = (FloatingActionButton)findViewById(R.id.fab);
viewPager = (ViewPager)findViewById(R.id.container);
ViewPagerAdapter viewPagerAdapter = new ViewPagerAdapter(getSupportFragmentManager(),fragments,titles);
viewPager.setAdapter(viewPagerAdapter);
viewPager.setCurrentItem(1);
tabLayout.setupWithViewPager(viewPager);
fab.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
fabAction();
}
});
}
public void fabAction(){
int current = viewPager.getCurrentItem();
switch (current){
case 0:{
//Need to indicate Fragment Swap here somehow. Through Listener?
break;
}
}
}}
ViewPagerAdapter Class:
public class ViewPagerAdapter extends FragmentPagerAdapter {
ArrayList<Fragment> fragments;
ArrayList<String> titles;
private Fragment mFragmentAtPos0;
public ViewPagerAdapter(FragmentManager fm, ArrayList<Fragment> fragments, ArrayList<String>titles) {
super(fm);
this.fragments = fragments;
this.titles = titles;
}
#Override
public Fragment getItem(int position) {
if (position == 0)
{
if (mFragmentAtPos0 == null)
{
//HANDLES THE CHANGING OF FRAGMENTS IN HERE USING THE LISTENER BELOW? BUT I'M NOT GRASPING THE LOGIC
//ON HOW TO IMPLEMENT THIS.
}
}
return fragments.get(position);
}
#Override
public int getCount() {
return fragments.size();
}
#Override
public CharSequence getPageTitle(int position) {
return titles.get(position);
}
//GOT FROM LESSON - ALLOWS VIEWPAGER TO CHANGE IT'S VIEW AND ATTACH NEW FRAGMENT WHEN LAUNCHED
#Override
public int getItemPosition(Object object)
{
if (object instanceof Tasks && mFragmentAtPos0 instanceof AddContact)
return POSITION_NONE;
return POSITION_UNCHANGED;
}
//GOT FROM LESSON. A LISTENER BUT I'M NOT SURE WHERE AND HOW TO IMPLEMENT IT. WHERE IN THE MAIN ACTIVITY SHOULD THIS
//GO? HOW DOES IT COMMUNICATE BACK TO THE ADAPTER?
public interface FirstPageFragmentListener
{
void onSwitchToNextFragment();
}
The post or lesson that Im referring is also from 5 years ago so I don't know if there's a simpler way to implement this, in which case I would love to hear it. Thanks so much.

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.