I have five fragments a user can switch between. One of these fragments loads a list of users from the server to populate the UI list on the fragment. I need the list information to persist if a user swipes to a different fragment and then swipes back to the original. I do not want the fragment to reload the users every time a user leaves the fragment and goes back.
I am looking at setRetainInsance(true) and was wondering if this is possible solution? What would be the best way for the fragment to retain the information without being created from scratch each time.
I am using this to switch between fragements -getSupportFragmentManager().beginTransaction().replace(R.id.searchLayout, ratingFragment).commit();
A Fragment is Just like any other object.
on Fragment transaction , the Fragment does not call OnCreate() method instead it starts from onCreateView , therefore , load your users and save it an instance variable and assign it in onCreate()
Example
class MyFragment extends Fragment{
List<users> userList;
void onCreate(){
userList = getUserList();}
//the list is loaded during Oncreate();
now imagine you have replaced the Fragment
now According to Andorid Framework , onCreate() is not Called again
instead onCreateView() is called
void onCreateView(){
//you can check whether instance Variable is initialised or not
if(userList != null) {
listview.setAdapter(new Myadapter(this,userList);
Replace the fragment by adding it to backstack.
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.addToBackStack(tag);
fragmentTransaction.replace(container, fragment, tag);
fragmentTransaction.commit();
Also create object of View and return it if it's not null.
private void View view ;
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
if (view != null)
return view;
view = inflater.inflate(R.layout.fragment_browse_recipe, container, false);
//initialize layout views
return view;
}
I use a FragmentPagerAdapter to switch from fragments. I need some functions to be called when a fragmentswitch is made and had some troubles with OnPause and OnResume, so as suggested by THIS question I have implemented an interface OnPageSelectListener :
public interface OnPageSelectListener {
void onPageSelected();
void onPageNotVisible();
}
It calls the function OnPageSelected whenever this page comes to the foreground. Works nice, except that I want to call a function on my adapter. I thought that would work, except that my adapter returns NULL all the times (even though it is initialized and data is loaded in my listview as prefered).
public class AfterCheckFragment extends Fragment implements OnPageSelectListener{
private ListView listView;
private List<Check> checkList;
private CheckListAdapter adapter;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View view = inflater.inflate(R.layout.fragment_check, container, false);
System.out.println("VIEW create called");
//(.. some other stuff, not relevant for question..)
//initializing the adapter
listView = (ListView) view.findViewById(R.id.listView);
adapter = new CheckListAdapter(checkList,getActivity(),trainPosition);
listView.setAdapter(adapter);
adapter.handleButtonVisibility();
return view;
}
#Override
public void onPageSelected() {
if(this.adapter != null) {
System.out.println("adapter not null");
this.adapter.checkForActive();
}else{
System.out.println("Adapter is NULL");
}
}
#Override
public void onPageNotVisible() { //page is moved to backgroung
System.out.println("AFTER not active any more ");
}
}
Now is my question: Why does adapter (or any other object in the fragment) return null when I return to my fragment? When the fragmentPager is initialized the onActivityCreate function of the fragment is called one time, but after that not any more, and the adapter return null....
you have to call the onPageSelected() after initialization of the adapter and setAdapter() otherwise adapter will return null always
Here is why I think your CheckListAdapter (i'll call it listAdapter) is null:
You give the pagerAdapter to the ViewPager
The ViewPager asks the pagerAdapter for a new Fragment
The ViewPager tells the FragmentManager to use it
onPageSelected gets called
You try and use listAdapter. It hasn't been initialized yet at this point. (NPE)
The FragmentManager drags the Fragment through all its stages.
onCreateView gets called. Your listAdapter is created.
Don't try and use internal data of a fragment outside of it. It is meant to work as a standalone unit, it won't be very good if you use it differently. Since the fragment is initialized at a later stage, you can't use it like you intend.
You can try and do what you want to do in the fragment, rather than the pagerAdapter, or write a method in the hosting Activity and call it from the fragment when ready, or even launch an event.
ViewPager will create and destroy fragments as the user changes pages (see ViewPager.setOffscreenPageLimit()). So onActivityCreated() is only called on the fragment when it is being restored or set up for the first time. Hence, fragments can be created without ever having onActivityCreated() called.
Instead of onActivityCreated(), I would recommend overriding onViewCreated() and setting up your adapter there. No fragment can be displayed without having a view created, so this is a good place to do that kind of stuff.
If you have your OnPageSelectListener logic working, that's good. I found the best way to know when your fragment is actually in front of the user is by overriding setPrimaryItem() in the FragmentPagerAdapter. Getting the page out of view event is a little trickier, since you have to keep a reference to the fragment from the previous setPrimaryItem() call.
This is because Viewpager calls OnpageSelected way before Fragments in oncreateView()/onActivityCreated() is called .
The best way for you is to inflate your views in the constructor of the Fragment and set the Adapters.
Or
Use a member variable to store whether the Fragment is active or not. And use the variable in oncreateview() to call function on your adapter.
Why don't you use a viewpager.addOnPageChangeListener, in you pager , after setting its adapter and the setOffscreenPageLimit() instead of implements it on your fragment?
Heres a sample code:
viewpager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
if(position == 1){ // if you want the second page, for example
//Your code here
}
}
#Override
public void onPageScrollStateChanged(int state) {
}
});
Make it in your Activity, where you setup your ViewPager, of course.
for me i had to call this on my viewpager:
myViewPager.setSaveFromParentEnabled(false);
in my app I'm using one activity and two fragments. The app uses a layout with a container so the fragments are added via transactions. The first fragment contains a listview and the other fragment a detail view for the listview items.
Both fragments use setRetainInstance(true). The fragments are added via a replace transaction and addToBackStack(null) is set. The listfragment contains an instance variable which holds some infos for the list. Now I'm changing to detail and press back and the instance variable is null. I read about setRetainInstance and addToBackStack and removed addToBackStack, but even then the instance variable is null.
Does anyone know what I might be doing wrong?
regards,
Thomas
setRetainInstance(true) will tell the FragmentManager to keep the fragment around when the containing Activity is killed and rebuilt for some reason. It doesn't guarantee that the Fragment instance will stick around after a transaction to add or replace. It sounds like your adapter is being garbage collected and you're not creating a new one.
A more generally easy solution would be to make a viewless Fragment to retain your ListAdapter. The way you do this is to create the Fragment, set the retain instance to true, and return null in the method onCreateView(). To add it, just called addFragment(Fragment, String) via the FragmentTransaction. You never remove or replace it, so it will always stay in memory for the length of the app. Screen rotations won't kill it.
Whenever your ListFragment is created, in onCreateView() get the FragmentManager and use either the method findFragmentById() or FindFragmentByTag() to retrieve your retained fragment from memory. Then get the adapter from that fragment and set it as your adapter for the list.
public class ViewlessFragment extends Fragment {
public final static string TAG = "ViewlessFragment";
private ListAdapter mAdapter;
#Override
public ViewlessFragment() {
mAdapter = createAdater();
setRetainInstance(true);
}
#Override
public void onCreateView (LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return null;
}
public ListAdapter getAdapter() {
return mAdapter;
}
}
public class MyListFragment extends ListFragment {
final public static String TAG = "MyListFragment";
#Override
public void onCreateView (LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
final View returnView = getMyView();
final ViewlessFragment adapterFragment = (ViewlessFragment) getFragmentManager().findFragmentByTag(ViewlessFragment.TAG);
setListAdapter(ViewlessFragment.getAdapter());
return returnView;
}
}
public class MainActivity extends FragmentActivity {
#Override
public void onCreate(Bundle icicle) {
// ... setup code...
final FragmentManager fm = getSupportFragmentManager();
final FragmentTransaction ft = fm.beginTransaction();
ViewlessFragment adapterFragment = fm.findFragmentByTag(ViewlessFragment.TAG);
if(adapterFragment == null) {
ft.add(new ViewlessFragment(), ViewlessFragment.TAG);
}
ft.add(R.id.fragmentContainer, new MyListFragment(), MyListFragment.TAG);
ft.commit();
}
}
I have a ViewPager with two Fragments which I instantiate in onCreate of my FragmentActivity.
private List<Fragment> fragments = new Vector<Fragment>();
fragments.add(Fragment.instantiate(this,Frag_1.class.getName()));
fragments.add(Fragment.instantiate(this,Frag_2.class.getName()));
this.vPagerAdapter = new Adapt(super.getSupportFragmentManager(),fragments);
vPager = (ViewPager) super.findViewById(R.id.pager);
vPager.setAdapter(vPagerAdapter);
My second Fragment has a method inside that I call to update my ListView - refreshList():
public class Frag_2 extends Fragment {
private ListView list;
private ArrayList<data> data;
private boolean firstCreation=true;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.setRetainInstance(false);
}
public void onAttach(Activity activity) {
// TODO Auto-generated method stub
super.onAttach(activity);
}
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.layout, container, false);
list = (ListView) view.findViewById(R.id.lst);
//this.setRetainInstance(true);
return view;
}
public void refreshList(ArrayList <data> data){
if(data!=null){
ArrayAdapter<data> adapter = new Item_data_adapter(getActivity(),data);
list.setAdapter(adapter);}
}
}
Called from my FragmentActivity
//Something
Frag_2 fr = (Frag_2) vPagerAdapter.getItem(1);
if (fr.getView() != null) {
fr.refreshList(data);
}
It works fine until I change the orientation of the screen. Correct me if I'm wrong, but I was searching for hours and I didn't find a solution or a good explanation, the FragmentActivity is created only one time and the Fragments are attached to it but the Fragments recreate on configuration changes.
Now, when the orientation changes I don't get the View from onCreateso when I try to get the View from the Fragment it returns null and my refreshList() method isn't called. How can I fix this?
I fixed the problem this way:
In the onCreate of the FragmentActivity
if(savedInstanceState!=null){
frag1 = (frag_1) getSupportFragmentManager().getFragment(savedInstanceState, frag_1.class.getName());
frag2 = (frag_2) getSupportFragmentManager().getFragment(savedInstanceState, frag_2.class.getName());
}
else{
frag1 = (frag_1) Fragment.instantiate(this,frag_1.class.getName());
frag2 = (frag_2) Fragment.instantiate(this,frag_2.class.getName());
}
fragments.add(frag1);
fragments.add(frag2);
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
getSupportFragmentManager().putFragment(outState, frag_1.class.getName(), frag1);
getSupportFragmentManager().putFragment(outState, frag_2.class.getName(), frag2);
}
Maybe it's not the best solution in the universe, but it looks like it works...
When u want to refresh the List do something like this :
public void setView() {
Frag_2 fr = (Frag_2) vPagerAdapter.getItem(1);
fragmentManager.beginTransaction().detach(fr).commit();
fragmentManager.beginTransaction().attach(fr).commit();
}
If you are using a dynamic fragment, you need to test first to prevent creating a second instance of a fragment.
To test whether the system is re-creating the activity, check whether the Bundle argument passed to your activity’s
onCreate() is null.
If it is non-null, the system is re-creating the activity. In this case, the activity automatically re-instantiates existing
fragments.
If it's null you can safely instantiate your dynamic fragment. For example:
public void onCreate(Bundle savedInstanceState) {
// ...
if (savedInstanceState != null) {
FragmentManager fragmentManager = getFragmentManager()
// Or: FragmentManager fragmentManager = getSupportFragmentManager()
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
ExampleFragment fragment = new ExampleFragment();
fragmentTransaction.add(R.id.fragment_container, fragment);
fragmentTransaction.commit();
}
}
The Fragment class supports the onSaveInstanceState(Bundle) method (but not the onRestoreInstanceState() method) in much the same way as the Activity class.
The default implementation saves the state of all the fragment’s views that have IDs.
You can override this method to store additional fragment state information.
If the system is re-creating the fragment from a previous saved state, it provides a reference to the Bundle containing that state to the onCreate(), onCreateView(), and onActivityCreated() methods; otherwise, the
argument is set to null.
If you want a detailed info, here's a good talk by Ken Jones of Marakana
I can't update the content in ViewPager.
What is the correct usage of methods instantiateItem() and getItem() in FragmentPagerAdapter class?
I was using only getItem() to instantiate and return my fragments:
#Override
public Fragment getItem(int position) {
return new MyFragment(context, paramters);
}
This worked well. Except I can't change the content.
So I found this: ViewPager PagerAdapter not updating the View
"My approach is to use the setTag() method for any instantiated view in the instantiateItem() method"
Now I want to implement instantiateItem() to do that. But I don't know what I have to return (the type is Object) and what is the relation with getItem(int position)?
I read the reference:
public abstract Fragment getItem (int position)
Return the Fragment associated with a specified position.
public Object instantiateItem (ViewGroup container, int position)
Create the page for the given position. The adapter is responsible for adding the view to the container given here, although it only must ensure this is done by the time it returns from finishUpdate(ViewGroup).
Parameters
container The containing View in which the page will be shown.
position The page position to be instantiated.
Returns
Returns an Object representing the new page. This does not need to be a View, but can be some other container of the page.
but I still don't get it.
Here's my code. I'm using support package v4.
ViewPagerTest
public class ViewPagerTest extends FragmentActivity {
private ViewPager pager;
private MyFragmentAdapter adapter;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.pager1);
pager = (ViewPager)findViewById(R.id.slider);
String[] data = {"page1", "page2", "page3", "page4", "page5", "page6"};
adapter = new MyFragmentAdapter(getSupportFragmentManager(), 6, this, data);
pager.setAdapter(adapter);
((Button)findViewById(R.id.button)).setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
reload();
}
});
}
private void reload() {
String[] data = {"changed1", "changed2", "changed3", "changed4", "changed5", "changed6"};
//adapter = new MyFragmentAdapter(getSupportFragmentManager(), 6, this, data);
adapter.setData(data);
adapter.notifyDataSetChanged();
pager.invalidate();
//pager.setCurrentItem(0);
}
}
MyFragmentAdapter
class MyFragmentAdapter extends FragmentPagerAdapter {
private int slideCount;
private Context context;
private String[] data;
public MyFragmentAdapter(FragmentManager fm, int slideCount, Context context, String[] data) {
super(fm);
this.slideCount = slideCount;
this.context = context;
this.data = data;
}
#Override
public Fragment getItem(int position) {
return new MyFragment(data[position], context);
}
#Override
public int getCount() {
return slideCount;
}
public void setData(String[] data) {
this.data = data;
}
#Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
}
MyFragment
public final class MyFragment extends Fragment {
private String text;
public MyFragment(String text, Context context) {
this.text = text;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.slide, null);
((TextView)view.findViewById(R.id.text)).setText(text);
return view;
}
}
Here is also somebody with a similar problem, no answers
http://www.mail-archive.com/android-developers#googlegroups.com/msg200477.html
When using FragmentPagerAdapter or FragmentStatePagerAdapter, it is best to deal solely with getItem() and not touch instantiateItem() at all. The instantiateItem()-destroyItem()-isViewFromObject() interface on PagerAdapter is a lower-level interface that FragmentPagerAdapter uses to implement the much simpler getItem() interface.
Before getting into this, I should clarify that
if you want to switch out the actual fragments that are being displayed, you need to avoid FragmentPagerAdapter and use
FragmentStatePagerAdapter.
An earlier version of this answer made the mistake of using FragmentPagerAdapter for its example - that won't work because FragmentPagerAdapter never destroys a fragment after it's been displayed the first time.
I don't recommend the setTag() and findViewWithTag() workaround provided in the post you linked. As you've discovered, using setTag() and findViewWithTag() doesn't work with fragments, so it's not a good match.
The right solution is to override getItemPosition(). When notifyDataSetChanged() is called, ViewPager calls getItemPosition() on all the items in its adapter to see whether they need to be moved to a different position or removed.
By default, getItemPosition() returns POSITION_UNCHANGED, which means, "This object is fine where it is, don't destroy or remove it." Returning POSITION_NONE fixes the problem by instead saying, "This object is no longer an item I'm displaying, remove it." So it has the effect of removing and recreating every single item in your adapter.
This is a completely legitimate fix! This fix makes notifyDataSetChanged behave like a regular Adapter without view recycling. If you implement this fix and performance is satisfactory, you're off to the races. Job done.
If you need better performance, you can use a fancier getItemPosition() implementation. Here's an example for a pager creating fragments off of a list of strings:
ViewPager pager = /* get my ViewPager */;
// assume this actually has stuff in it
final ArrayList<String> titles = new ArrayList<String>();
FragmentManager fm = getSupportFragmentManager();
pager.setAdapter(new FragmentStatePagerAdapter(fm) {
public int getCount() {
return titles.size();
}
public Fragment getItem(int position) {
MyFragment fragment = new MyFragment();
fragment.setTitle(titles.get(position));
return fragment;
}
public int getItemPosition(Object item) {
MyFragment fragment = (MyFragment)item;
String title = fragment.getTitle();
int position = titles.indexOf(title);
if (position >= 0) {
return position;
} else {
return POSITION_NONE;
}
}
});
With this implementation, only fragments displaying new titles will get displayed. Any fragments displaying titles that are still in the list will instead be moved around to their new position in the list, and fragments with titles that are no longer in the list at all will be destroyed.
What if the fragment has not been recreated, but needs to be updated anyway? Updates to a living fragment are best handled by the fragment itself. That's the advantage of having a fragment, after all - it is its own controller. A fragment can add a listener or an observer to another object in onCreate(), and then remove it in onDestroy(), thus managing the updates itself. You don't have to put all the update code inside getItem() like you do in an adapter for a ListView or other AdapterView types.
One last thing - just because FragmentPagerAdapter doesn't destroy a fragment doesn't mean that getItemPosition is completely useless in a FragmentPagerAdapter. You can still use this callback to reorder your fragments in the ViewPager. It will never remove them completely from the FragmentManager, though.
Instead of returning POSITION_NONE from getItemPosition() and causing full view recreation, do this:
//call this method to update fragments in ViewPager dynamically
public void update(UpdateData xyzData) {
this.updateData = xyzData;
notifyDataSetChanged();
}
#Override
public int getItemPosition(Object object) {
if (object instanceof UpdateableFragment) {
((UpdateableFragment) object).update(updateData);
}
//don't return POSITION_NONE, avoid fragment recreation.
return super.getItemPosition(object);
}
Your fragments should implement UpdateableFragment interface:
public class SomeFragment extends Fragment implements
UpdateableFragment{
#Override
public void update(UpdateData xyzData) {
// this method will be called for every fragment in viewpager
// so check if update is for this fragment
if(forMe(xyzData)) {
// do whatever you want to update your UI
}
}
}
and the interface:
public interface UpdateableFragment {
public void update(UpdateData xyzData);
}
Your data class:
public class UpdateData {
//whatever you want here
}
for those who still face the same problem which i faced before when i have a ViewPager with 7 fragments. the default for these fragments to load the English content from API service but the problem here that i want to change the language from settings activity and after finish
settings activity i want ViewPager in main activity to refresh the fragments to match the language selection from the user and load the Arabic content if user chooses Arabic here what i did to work from the first time
1- You must use FragmentStatePagerAdapter as mentioned above.
2- on mainActivity i override the onResume and did the following
if (!(mPagerAdapter == null)) {
mPagerAdapter.notifyDataSetChanged();
}
3-i overrided the getItemPosition() in mPagerAdapter and make it return POSITION_NONE.
#Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
works like charm
I have encountered this problem and finally solved it today, so I write down what I have learned and I hope it is helpful for someone who is new to Android's ViewPager and update as I do. I'm using FragmentStatePagerAdapter in API level 17 and currently have just 2 fragments. I think there must be something not correct, please correct me, thanks.
Serialized data has to be loaded into memory. This can be done using a CursorLoader/AsyncTask/Thread. Whether it's automatically loaded depends on your code. If you are using a CursorLoader, it's auto-loaded since there is a registered data observer.
After you call viewpager.setAdapter(pageradapter), the adapter's getCount() is constantly called to build fragments. So if data is being loaded, getCount() can return 0, thus you don't need to create dummy fragments for no data shown.
After the data is loaded, the adapter will not build fragments automatically since getCount() is still 0, so we can set the actually loaded data number to be returned by getCount(), then call the adapter's notifyDataSetChanged(). ViewPager begin to create fragments (just the first 2 fragments) by data in memory. It's done before notifyDataSetChanged() is returned. Then the ViewPager has the right fragments you need.
If the data in the database and memory are both updated (write through), or just data in memory is updated (write back), or only data in the database is updated. In the last two cases if data is not automatically loaded from the database to memory (as mentioned above).
The ViewPager and pager adapter just deal with data in memory.
So when data in memory is updated, we just need to call the adapter's notifyDataSetChanged(). Since the fragment is already created, the adapter's onItemPosition() will be called before notifyDataSetChanged(） returns. Nothing needs to be done in getItemPosition(). Then the data is updated.
Try destroyDrawingCache() on ViewPager after notifyDataSetChanged() in your code.
After hours of frustration while trying all the above solutions to overcome this problem and also trying many solutions on other similar questions like this, this and this which all FAILED with me to solve this problem and to make the ViewPager to destroy the old Fragment and fill the pager with the new Fragments. I have solved the problem as following:
1) Make the ViewPager class to extends FragmentPagerAdapter as following:
public class myPagerAdapter extends FragmentPagerAdapter {
2) Create an Item for the ViewPager that store the title and the fragment as following:
public class PagerItem {
private String mTitle;
private Fragment mFragment;
public PagerItem(String mTitle, Fragment mFragment) {
this.mTitle = mTitle;
this.mFragment = mFragment;
}
public String getTitle() {
return mTitle;
}
public Fragment getFragment() {
return mFragment;
}
public void setTitle(String mTitle) {
this.mTitle = mTitle;
}
public void setFragment(Fragment mFragment) {
this.mFragment = mFragment;
}
}
3) Make the constructor of the ViewPager take my FragmentManager instance to store it in my class as following:
private FragmentManager mFragmentManager;
private ArrayList<PagerItem> mPagerItems;
public MyPagerAdapter(FragmentManager fragmentManager, ArrayList<PagerItem> pagerItems) {
super(fragmentManager);
mFragmentManager = fragmentManager;
mPagerItems = pagerItems;
}
4) Create a method to re-set the adapter data with the new data by deleting all the previous fragment from the fragmentManager itself directly to make the adapter to set the new fragment from the new list again as following:
public void setPagerItems(ArrayList<PagerItem> pagerItems) {
if (mPagerItems != null)
for (int i = 0; i < mPagerItems.size(); i++) {
mFragmentManager.beginTransaction().remove(mPagerItems.get(i).getFragment()).commit();
}
mPagerItems = pagerItems;
}
5) From the container Activity or Fragment do not re-initialize the adapter with the new data. Set the new data through the method setPagerItems with the new data as following:
ArrayList<PagerItem> pagerItems = new ArrayList<PagerItem>();
pagerItems.add(new PagerItem("Fragment1", new MyFragment1()));
pagerItems.add(new PagerItem("Fragment2", new MyFragment2()));
mPagerAdapter.setPagerItems(pagerItems);
mPagerAdapter.notifyDataSetChanged();
I hope it helps.
For some reason none of the answers worked for me so I had to override the restoreState method without calling super in my fragmentStatePagerAdapter. Code:
private class MyAdapter extends FragmentStatePagerAdapter {
// [Rest of implementation]
#Override
public void restoreState(Parcelable state, ClassLoader loader) {}
}
I slightly modified the solution provided by Bill Phillips to suit my needs
private class PagerAdapter extends FragmentStatePagerAdapter{
Bundle oBundle;
FragmentManager oFragmentManager;
ArrayList<Fragment> oPooledFragments;
public PagerAdapter(FragmentManager fm) {
super(fm);
oFragmentManager=fm;
}
#Override
public int getItemPosition(Object object) {
Fragment oFragment=(Fragment)object;
oPooledFragments=new ArrayList<>(oFragmentManager.getFragments());
if(oPooledFragments.contains(oFragment))
return POSITION_NONE;
else
return POSITION_UNCHANGED;
}
}
so that the getItemPosition() returns POSITION_NONE only for those fragments which are currently in the FragmentManager when getItemPosition is called.
(Note that this FragmentStatePager and the ViewPager associated with it are contained in a Fragment not in a Activity)
I had a similar problem but don't want to trust on the existing solutions (hard coded tag names etc.) and I couldn't make M-WaJeEh's solution work for me. Here is my solution:
I keep references to the fragments created in getItem in an array. This works fine as long as the activity is not destroyed due to configurationChange or lack of memory or whatever (--> when coming back to the activity, fragments return to their last state without 'getItem' being called again and thus without updating the array).
To avoid this problem I implemented instantiateItem(ViewGroup, int) and update my array there, like this:
#Override
public Object instantiateItem(ViewGroup container, int position) {
Object o = super.instantiateItem(container, position);
if(o instanceof FragmentX){
myFragments[0] = (FragmentX)o;
}else if(o instanceof FragmentY){
myFragments[1] = (FragmentY)o;
}else if(o instanceof FragmentZ){
myFragments[2] = (FragmentZ)o;
}
return o;
}
So, on the one hand I'm happy that I found a solution that works for me and wanted to share it with you, but I also wanted to ask whether somebody else tried something similar and whether there is any reason why I shouldn't do it like that? So far it works very good for me...
I have lived same problem and I have searched too much times. Any answer given in stackoverflow or via google was not solution for my problem. My problem was easy. I have a list, I show this list with viewpager. When I add a new element to head of the list and I refresh the viewpager nothings changed. My final solution was very easy anybody can use. When a new element added to list and want to refresh the list. Firstly set viewpager adapter to null then recreate the adapter and set i to it to viewpager.
myVPager.setAdapter(null);
myFragmentAdapter = new MyFragmentAdapter(getSupportFragmentManager(),newList);
myVPager.setAdapter(myFragmentAdapter);
Be sure your adapter must extend FragmentStatePagerAdapter
I use EventBus library to update Fragment content in ViewPager. The logic is simple, just like document of EventBus how to do. It is no need to control FragmentPagerAdapter instance. The code is here:
1: Define events
Define which message which is needed to update.
public class UpdateCountEvent {
public final int count;
public UpdateCountEvent(int count) {
this.count = count;
}
}
2.Prepare subscribers
Write below code in the Fragment which is needed update.
#Override
public void onStart() {
super.onStart();
EventBus.getDefault().register(this);
}
#Override
public void onStop() {
EventBus.getDefault().unregister(this);
super.onStop();
}
public void onEvent(UpdateCountEvent event) {//get update message
Toast.makeText(getActivity(), event.count, Toast.LENGTH_SHORT).show();
}
3.Post events
Write below code in other Activity or other Fragment which needs to update parameter
//input update message
EventBus.getDefault().post(new UpdateCountEvent(count));
I had been trying so many different approaches, none really sove my problem. Below are how I solve it with a mix of solutions provided by you all. Thanks everyone.
class PagerAdapter extends FragmentPagerAdapter {
public boolean flag_refresh=false;
public PagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int page) {
FragmentsMain f;
f=new FragmentsMain();
f.page=page;
return f;
}
#Override
public int getCount() {
return 4;
}
#Override
public int getItemPosition(Object item) {
int page= ((FragmentsMain)item).page;
if (page == 0 && flag_refresh) {
flag_refresh=false;
return POSITION_NONE;
} else {
return super.getItemPosition(item);
}
}
#Override
public void destroyItem(View container, int position, Object object) {
((ViewPager) container).removeView((View) object);
}
}
I only want to refresh page 0 after onResume().
adapter=new PagerAdapter(getSupportFragmentManager());
pager.setAdapter(adapter);
#Override
protected void onResume() {
super.onResume();
if (adapter!=null) {
adapter.flag_refresh=true;
adapter.notifyDataSetChanged();
}
}
In my FragmentsMain, there is public integer "page", which can tell me whether it is the page I want to refresh.
public class FragmentsMain extends Fragment {
private Cursor cursor;
private static Context context;
public int page=-1;
I know am late for the Party. I've fixed the problem by calling TabLayout#setupWithViewPager(myViewPager); just after FragmentPagerAdapter#notifyDataSetChanged();
If you want to use FragmentStatePagerAdapter, please take a look at https://code.google.com/p/android/issues/detail?can=2&start=0&num=100&q=&colspec=ID%20Type%20Status%20Owner%20Summary%20Stars&groupby=&sort=&id=37990.
There are issues with FragmentStatePagerAdapter that may or may not trouble your use case.
Also, link has few solutions too..few may suit to your requirement.
This might be of help to someone - in my case when inserting a new page the view pager was asking for the position of an existing fragment twice, but not asking for the position of the new item, causing incorrect behaviour and data not displaying.
Copy the source for for FragmentStatePagerAdapter (seems to have not been updated in ages).
Override notifyDataSetChanged()
#Override
public void notifyDataSetChanged() {
mFragments.clear();
super.notifyDataSetChanged();
}
Add a sanity check to destroyItem() to prevent crashes:
if (position < mFragments.size()) {
mFragments.set(position, null);
}
Here is my implementation that incorporates the info from #Bill Phillips
One gets fragment caching most of the time, except when the data has changed. Simple, and seems to work fine.
MyFragmentStatePagerAdapter.java
private boolean mIsUpdating = false;
public void setIsUpdating(boolean mIsUpdating) {
this.mIsUpdating = mIsUpdating;
}
#Override
public int getItemPosition(#NonNull Object object) {
if (mIsUpdating) {
return POSITION_NONE;
}
else {
return super.getItemPosition(object);
}
}
MyActivity.java
mAdapter.setIsUpdating(true);
mAdapter.notifyDataSetChanged();
mAdapter.setIsUpdating(false);
Using ViewPager2 and FragmentStateAdapter:
Updating data dynamically is supported by ViewPager2.
There is an important note in the docs on how to get this working:
Note: The DiffUtil utility class relies on identifying items by ID. If you are using ViewPager2 to page through a mutable collection, you must also override getItemId() and containsItem(). (emphasis mine)
Based on ViewPager2 documentation and Android's Github sample project there are a few steps we need to take:
Set up FragmentStateAdapter and override the following methods: getItemCount, createFragment, getItemId, and containsItem (note: FragmentStatePagerAdapter is not supported by ViewPager2)
Attach adapter to ViewPager2
Dispatch list updates to ViewPager2 with DiffUtil (don't need to use DiffUtil, as seen in sample project)
Example:
private val items: List<Int>
get() = viewModel.items
private val viewPager: ViewPager2 = binding.viewPager
private val adapter = object : FragmentStateAdapter(this#Fragment) {
override fun getItemCount() = items.size
override fun createFragment(position: Int): Fragment = MyFragment()
override fun getItemId(position: Int): Long = items[position].id
override fun containsItem(itemId: Long): Boolean = items.any { it.id == itemId }
}
viewPager.adapter = adapter
private fun onDataChanged() {
DiffUtil
.calculateDiff(object : DiffUtil.Callback() {
override fun getOldListSize(): Int = viewPager.adapter.itemCount
override fun getNewListSize(): Int = viewModel.items.size
override fun areItemsTheSame(oldItemPosition: Int, newItemPosition: Int) =
viewPager.adapter?.getItemId(oldItemPosition) == viewModel.items[newItemPosition].id
override fun areContentsTheSame(oldItemPosition: Int, newItemPosition: Int) =
areItemsTheSame(oldItemPosition, newItemPosition)
}, false)
.dispatchUpdatesTo(viewPager.adapter!!)
}
This solution won't work for everyone, but in my case, every Fragment in my ViewPager is a different class, and only one of them ever exist at a time.
With this constraint, this solution is safe and should be safe to use in production.
private void updateFragment(Item item) {
List<Fragment> fragments = getSupportFragmentManager().getFragments();
for (Fragment fragment : fragments) {
if (fragment instanceof MyItemFragment && fragment.isVisible()) {
((MyItemFragment) fragment).update(item);
}
}
}
If you have multiple versions of the same fragment, you can use this same strategy to call methods on those fragments to determine if it is the fragment you wish to update.
I've gone through all the answers above and a number of others posts but still couldn't find something that worked for me (with different fragment types along with dynamically adding and removing tabs). FWIW following approach is what worked for me (in case anyone else has same issues).
public class MyFragmentStatePageAdapter extends FragmentStatePagerAdapter {
private static final String TAB1_TITLE = "Tab 1";
private static final String TAB2_TITLE = "Tab 2";
private static final String TAB3_TITLE = "Tab 3";
private ArrayList<String> titles = new ArrayList<>();
private Map<Fragment, Integer> fragmentPositions = new HashMap<>();
public MyFragmentStatePageAdapter(FragmentManager fm) {
super(fm);
}
public void update(boolean showTab1, boolean showTab2, boolean showTab3) {
titles.clear();
if (showTab1) {
titles.add(TAB1_TITLE);
}
if (showTab2) {
titles.add(TAB2_TITLE);
}
if (showTab3) {
titles.add(TAB3_TITLE);
}
notifyDataSetChanged();
}
#Override
public int getCount() {
return titles.size();
}
#Override
public Fragment getItem(int position) {
Fragment fragment = null;
String tabName = titles.get(position);
if (tabName.equals(TAB1_TITLE)) {
fragment = Tab1Fragment.newInstance();
} else if (tabName.equals(TAB2_TITLE)) {
fragment = Tab2Fragment.newInstance();
} else if (tabName.equals(TAB3_TITLE)) {
fragment = Tab3Fragmen.newInstance();
}
((BaseFragment)fragment).setTitle(tabName);
fragmentPositions.put(fragment, position);
return fragment;
}
#Override
public CharSequence getPageTitle(int position) {
return titles.get(position);
}
#Override
public int getItemPosition(Object item) {
BaseFragment fragment = (BaseFragment)item;
String title = fragment.getTitle();
int position = titles.indexOf(title);
Integer fragmentPosition = fragmentPositions.get(item);
if (fragmentPosition != null && position == fragmentPosition) {
return POSITION_UNCHANGED;
} else {
return POSITION_NONE;
}
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
super.destroyItem(container, position, object);
fragmentPositions.remove(object);
}
}
Use FragmentStatePagerAdapter instead of FragmentPagerAdapter
if you want to recreate or reload fragment on index basis
For example if you want to reload fragment other than FirstFragment, you can check instance and return position like this
public int getItemPosition(Object item) {
if(item instanceof FirstFragment){
return 0;
}
return POSITION_NONE;
}
You need change instantiateItem's mFragments element getItemPosition.
if (mFragments.size() > position) {
Fragment f = mFragments.get(position);
if (f != null) {
int newPosition = getItemPosition(f);
if (newPosition == POSITION_UNCHANGED) {
return f;
} else if (newPosition == POSITION_NONE) {
mFragments.set(position, null);
} else {
mFragments.set(newPosition, f);
}
}
}
Based AndroidX FragmentStatePagerAdapter.java, because mFragments's elements position do not change when calling notifyDataSetChanged().
Source:
https://github.com/cuichanghao/infivt/blob/master/library/src/main/java/cc/cuichanghao/library/FragmentStatePagerChangeableAdapter.java
Example:
https://github.com/cuichanghao/infivt/blob/master/app/src/main/java/cc/cuichanghao/infivt/MainActivityChangeablePager.kt
You can run this project to confirm how to work.
https://github.com/cuichanghao/infivt