I've got this strange issue, ViewPager's setCurrentItem(position, false) works perfectly fine, then im switching to another activity, and after I'm back to the first activity, the ViewPager always ends up on the first item. Even though I've added setCurrentItem to onResume method it still ignores it. It's not even throwing any exception when I'm trying to set item to out of bounds index.
Though later on when I call this method, when the button "next" is tapped, it works like expected.
Checked my code 10 times for any possible calls to setCurrentItem(0) or something but it's just not there at all.
i can't really answer WHY exactly this happens, but if you delay the setCurrentItem call for a few milliseconds it should work. My guess is that because during onResume there hasn't been a rendering pass yet, and the ViewPager needs one or something like that.
private ViewPager viewPager;
#Override
public void onResume() {
final int pos = 3;
viewPager.postDelayed(new Runnable() {
#Override
public void run() {
viewPager.setCurrentItem(pos);
}
}, 100);
}
UPDATE: story time
so today i had the problem that the viewpager ignored my setCurrentItem action, and i searched stackoverflow for a solution. i found someone with the same problem and a fix; i implemented the fix and it didn't work. whoa! back to stackoverflow to downvote that faux-fix-provider, and ...
it was me. i implemented my own faulty non-fix, which i came up with the first time i stumbled over the problem (and which was later forgotten). i'll now have to downvote myself for providing bad information.
the reason my initial "fix" worked was not because of of a "rendering pass"; the problem was that the pager's content was controlled by a spinner. both the spinners and the pagers state were restored onResume, and because of this the spinners onItemSelected listener was called during the next event propagation cycle, which did repopulate the viewpager - this time using a different default value.
removing and resetting the listener during the initial state restoration fixed the issue.
the fix above kind-of worked the first time, because it set the pagers current position after the onItemSelected event fired. later, it ceased to work for some reason (probably the app became too slow - in my implementation i didn't use 100ms, but 10ms). i then removed the postDelayed in a cleanup cycle, because it didn't change the already faulty behaviour.
update 2: i can't downvote my own post. i assume, honorable seppuku is the only option left.
I had a similar issue in the OnCreate of my Activity.
The adapter was set up with the correct count and I
applied setCurrentItem after setting the adapter to the
ViewPager however is would return index out of bounds. I think the ViewPager had not loaded all my Fragments at the point i set the current item. By posting a runnable on the ViewPager i was able to work around this. Here is an example with a little bit of context.
// Locate the viewpager in activity_main.xml
final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
// Set the ViewPagerAdapter into ViewPager
viewPager.setAdapter(new ViewPagerAdapter(getSupportFragmentManager()));
viewPager.setOffscreenPageLimit(2);
viewPager.post(new Runnable() {
#Override
public void run() {
viewPager.setCurrentItem(ViewPagerAdapter.CENTER_PAGE);
}
});
I found a very simple workaround for this:
if (mViewPager.getAdapter() != null)
mViewPager.setAdapter(null);
mViewPager.setAdapter(mPagerAdapter);
mViewPager.setCurrentItem(desiredPos);
And, if that doesn't work, you can put it in a handler, but there's no need for a timed delay:
new Handler().post(new Runnable() {
#Override
public void run() {
mViewPager.setCurrentItem(desiredPos);
}
});
ViewTreeObserver can be used to avoid a static delay.
Kotlin:
Feel free to use Kotlin extension as a concise option.
view_pager.doOnPreDraw {
view_pager.currentItem = 1
}
Please, make sure you have a gradle dependency: implementation 'androidx.core:core-ktx:1.3.2' or above
Java
OneShotPreDrawListener.add(view_pager, () -> view_pager.currentItem = 1);
A modern approach in a Fragment or Activity is to call ViewPager.setcurrentItem(Int) function in a coroutine in the context of Dispatchers.Main :
lifecycleScope.launch(Dispatchers.Main) {
val index = 1
viewPager.setCurrentItem(index)
}
I had similar bug in the code, the problem was that I was setting the position before changing the data.
The solution was simply to set the position afterwards and notify the data changed
notifyDataSetChanged()
setCurrentItem()
I have the same problem and I edit
#Override
public int getCount() { return NUM_PAGES; }
I set NUM_PAGES be mistake to 1 only.
some guy wrote on forums here. https://code.i-harness.com/en/q/126bff9 worked for me
if (mViewPager.getAdapter() != null)
mViewPager.setAdapter(null);
mViewPager.setAdapter(mPagerAdapter);
mViewPager.setCurrentItem(desiredPos);
Solution (in Kotlin with ViewModel etc.) for those trying to set the current item in the onCreate of Activity without the hacky Runnable "solutions":
class MyActivity : AppCompatActivity() {
lateinit var mAdapter: MyAdapter
lateinit var mPager: ViewPager
// ...
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.fragment_pager)
// ...
mainViewModel = ViewModelProviders.of(this).get(MainViewModel::class.java)
mAdapter = MyAdapter(supportFragmentManager)
mPager = findViewById(R.id.pager)
mainViewModel.someData.observe(this, Observer { items ->
items?.let {
// first give the data to the adapter
// this is where the notifyDataSetChanged() happens
mAdapter.setItems(it)
mPager.adapter = mAdapter // assign adapter to pager
mPager.currentItem = idx // finally set the current page
}
})
This will obviously do the correct order of operations without any hacks with Runnable or delays.
For the completeness, you usually implement the setItems() of the adapter (in this case FragmentStatePagerAdapter) like this:
internal fun setItems(items: List<Item>) {
this.items = items
notifyDataSetChanged()
}
I've used the post() method described here and sure enough it was working great under some scenarios but because my data comes from the server, it was not the holy grail.
My problem was that i want to have
notifyDataSetChanged
called at an arbitrary time and then switch tabs on my viewPager. So right after the notify call i have this
ViewUtilities.waitForLayout(myViewPager, new Runnable() {
#Override
public void run() {
myViewPager.setCurrentItem(tabIndex , false);
}
});
and
public final class ViewUtilities {
public static void waitForLayout(final View view, final Runnable runnable) {
view.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
#Override
public void onGlobalLayout() {
//noinspection deprecation
view.getViewTreeObserver().removeGlobalOnLayoutListener(this);
runnable.run();
}
});
}
}
Fun fact: the //noinspection deprecation at the end is because there is a spelling mistake in the API that was fixed after API 16, so that should read
removeOnGlobalLayoutListener
^^
ON Global
instead of
removeGlobalOnLayoutListener
^^
ON Layout
This seems to be covering all cases for me.
I was working on this problem for one week and I realized that this problem happens because I was using home activity context in view pager fragments and we can only use context in fragment after it gets attached to activity..
When a view pager gets created, activity only attach to the first (0) and second (1) page. When you open the second page, the third page gets attached and so on! When you use setCurrentItem() method and the argument is greater than 1, it wants to open that page before it is attached, so the context in fragment of that page will be null and the application gets crashed! That's why when you delay setCurrentItem(), it works! At first it gets attached and then it'll open the page...
This is a lifecycle issue, as pointed out by several posters here. However, I find the solutions with posting a Runnable to be unpredictable and probably error prone. It seems like a way to ignore the problem by posting it into the future.
I am not saying that this is the best solution, but it definitely works without using Runnable. I keep a separate integer inside the Fragment that has the ViewPager. This integer will hold the page we want to set as the current page when onResume is called next. The integer's value can be set at any point and can thus be set before a FragmentTransaction or when resuming an activity. Also note that all the members are set up in onResume(), not in onCreateView().
public class MyFragment extends Fragment
{
private ViewPager mViewPager;
private MyPagerAdapter mAdapter;
private TabLayout mTabLayout;
private int mCurrentItem = 0; // Used to keep the page we want to set in onResume().
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View view = inflater.inflate(R.layout.my_layout, container, false);
mViewPager = (ViewPager) view.findViewById(R.id.my_viewpager);
mTabLayout = (TabLayout) view.findViewById(R.id.my_tablayout);
return view;
}
#Override
public void onResume()
{
super.onResume();
MyActivity myActivity = (MyActivity) getActivity();
myActivity.getSupportActionBar().setTitle(getString(R.string.my_title));
mAdapter = new MyPagerAdapter(getChildFragmentManager(), myActivity);
mViewPager.setAdapter(mAdapter);
mViewPager.setOffscreenPageLimit(PagerConstants.OFFSCREEN_PAGE_LIMIT);
mViewPager.setCurrentItem(mCurrentItem); // <-- Note the use of mCurrentItem here!
mTabLayout.setupWithViewPager(mViewPager);
}
/**
* Call this at any point before needed, for example before performing a FragmentTransaction.
*/
public void setCurrentItem(int currentItem)
{
mCurrentItem = currentItem;
// This should be called in cases where onResume() is not called later,
// for example if you only want to change the page in the ViewPager
// when clicking a Button or whatever. Just omit if not needed.
mViewPager.setCurrentItem(mCurrentItem);
}
}
For me this worked setting current item after setting adapter
viewPager.setAdapter(new MyPagerAdapter(getSupportFragmentManager()));
viewPager.setCurrentItem(idx);
pagerSlidingTabStrip.setViewPager(viewPager);// assign viewpager to tabs
I've done it this way to restore the current item:
#Override
protected void onSaveInstanceState(Bundle outState) {
if (mViewPager != null) {
outState.putInt(STATE_PAGE_NO, mViewPager.getCurrentItem());
}
super.onSaveInstanceState(outState);
}
#Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
if (savedInstanceState != null) {
mCurrentPage = savedInstanceState.getInt(STATE_PAGE_NO, 0);
}
super.onRestoreInstanceState(savedInstanceState);
}
#Override
protected void onRestart() {
mViewPager.setCurrentItem(mCurrentPage);
super.onRestart();
}
By the time I call setCurrentItem() the view is about to be recreated. So in fact I invoke setCurrentItem() for the viewpager and afterwards the system calls onCreateView() and hence creates a new viewpager.
This is the reason for me why I do not see any changes. And this is the reason why a postDelayed() may help.
Theoretical solution: Postpone the setCurrentItem() invocation until the view has been recreated.
Practical solution: I have no clue for a stable and simple solution. We should be able to check if the class is about to recreate it's view and if that is the case postpone the invocation of setCurrentItem() to the end of onCreateView()
I use the dsalaj code as a reference. If necessary I share the code with the complete solution.
I also strongly recommend using ViewPager2
Solution
Both cases have to go within the Observer {}:
First case: Initialize the adapter only when we have the first data set and not before, since this would generate inconsistencies in the paging. To the first data set we have to pass it as the argument of the Adapter.
Second case: From the first change in the observable we would have from the second data sets onwards which have to be passed to the Adapter through a public method only if we have already initialized the adapter with a first data set.
GL
I was confused with the onActivityCreated() getting invoked for unrelated tab #Mahdi Arabpour was an eye opener for me :)
For me the problem was the third page (as elaborated by #Mahdi Arabpour above) was getting reconstructed when I click the second tab, etc and it was losing its data adapter, setting it again in onActivityCreted solves my problems:
if (myXXRecyclerAdapter != null) {
myXXRecyclerAdapter = new MyXXRecyclerAdapter(myStoredData);
mRecyclerView.setAdapter(myXXRecyclerAdapter );
return;
}
You need to call pager.setCurrentItem(activePage) right after pager.setAdapter(buildAdapter())
#Override
public void onResume() {
if (pager.getAdapter() != null) {
activePage=pager.getCurrentItem();
Log.w(getClass().getSimpleName(), "pager.getAdapter()!=null");
pager.setAdapter(null);
}
pager.setAdapter(buildAdapter());
pager.setCurrentItem(activePage);
}
Related
I'm using a ViewPager to cycle through a set of fragments, and I want to update each fragment after it slides onto the screen. Basically, I want the text to "fade in" after the fragment has settled.
I tried using the fragment's onStart and onResume methods, and while this works for most of the pages, it does NOT work for the second page, because for whatever dumb reason, the first page AND the second page have their onStart/onResume methods called at the same time (before the second page ever hits the screen).
Now I'm trying to get it to work with the onPageChangeListener's onPageSelected callback. That method looks like this:
#Override
public void onPageSelected(final int position) {
mCurrentPosition = position;
PageFragment fragment = (PageFragment) ((MainActivity.ScreenSlidePagerAdapter) mViewPager.getAdapter()).getItem(position);
fragment.onSelect();
}
And the onSelect method in the fragment looks like this:
public void onSelect(){
new android.os.Handler().postDelayed(
new Runnable() {
public void run() {
mSwitcher.setText("");
mNum = getArguments() != null ? getArguments().getInt("num") : 1;
Media currentMedia = slideshow.getMedia().get(mNum);
mSwitcher.setText(currentMedia.getDisplayName());
}
},
4000);
}
The problem with this way is that the line mSwitcher.setText(""); throws a NullPointerException
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextSwitcher.setText(java.lang.CharSequence)' on a null object reference
Which would suggest that the onCreateView method in that class has yet to run since that's where the mSwitcher variable is instantiated. Which seems bananas to me, since the view is already sliding onto the screen at this point.
Any ideas about how to solve this problem would be greatly appreciated. This is my first Android experience, and I've been trying to solve this stupid text-fade-in issue for a full week with no luck. At this point I'm almost ready to abandon mobile as a platform because of how painful every minor change has been so far.
ViewPager keeps the next page in memory & this is it's default behaviour. You could adjust it by calling like:
viewPager.setOffscreenPageLimit(2);
However this might not be useful as if you pass 0 in above method, viewPager will ignore it.
You are going in right direction. I believe now problem is in your ScreenSlidePagerAdapter. In getItem(int position) you might have something like
if(position == 1)
return new PageFragment();
instead change the adapter to something like following,
public class ScreenSlidePagerAdapter extends FragmentPagerAdapter {
private List<Fragment> mFragments = new ArrayList<>();
public ScreenSlidePagerAdapter(FragmentManager fm, List<Item> items) {
super(fm);
for (Item item : items) {
mFragments.add(new PageFragment());
}
}
#Override
public int getCount() {
return mFragments.size();
}
#Override
public Fragment getItem(int position) {
return mFragments.get(position); // Return from list instead of new PagerFragment()
}
}
I have the similar problem as yours, onPageSelected() is called before the fragments are initialized, but your description is not detailed enough, such as how you select the second page.
When adapter is fed with Fragments, or we say getCount() > 0, getItem() will whatever returns a Fragment, which is not null. But this doesn't mean it is initialized, at least it doesn't if you extend from FragmentStatePagerAdapter.
when adapter is fed with data and called notifyDataSetChange(), adapter will initialize the first two pages by default. If you call setCurrentItem() to move to other pages immediately after notifyDataSetChange() the issue might happen. During the runtime, setCurrentItem() -> onPageSelected() might be called before the fragments are initialized.
my solution is using view.post() when setCurrentItem(). e.g.
viewPager.post(() -> viewPager.setCurrentItem(index));
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);
I have a ViewPager with 10 pages. When I start the last (10th) page onCreateView() method of my fragment is called. When I swipe to the 9th page onCreateView() is called also. But when I back to the 10th page onCreateView() isn't called. What's wrong?
Try Extending FragmentStatePagerAdapter
That is because a FragmentPagerAdapter keeps in memory every fragment. Hence, when you visit the first time the fragment, onCreate will be invoked but the second time Android will looking for in memory, so it not need invoke onCreate.
If you need run the code in OnCreate every time fragment is displayed, you should move it to getItem(int id)
See offical documentation: http://developer.android.com/reference/android/support/v4/app/FragmentPagerAdapter.html
Nothing is wrong. The ViewPager already has the page, and so it does not need to create it.
I had the same problem, my solution was to assign again the adapter of the ViewPager instance, just like:
pager.setAdapter(adapter);
This causes a restart of the "mItems" property from the viewPager and removes the cache.
But I don't know if it's a safe solution
You can call the adapter getItem from onPageSelect, which is called also on swipes, and place your code inside the getItem, or even in the onPageSeelect itself.
CommonWare's answer is the best and works like charm:
simple add OnPageChangeListener to your ViewPager item, something like this:
ViewPager viewPager = null;
PagerAdapter pagerAdapter = null;
//Some code come here...
pagerAdapter = new PagerAdapter(); //Or any class derived from it
viewPager = (ViewPager)findViewById(R.id.container);//Connect it to XML
viewPager.setAdapter (mPagerAdapter); //Connect the two
//Next two lines are simply for fun...
//viewager.setPageTransformer(true, new DepthPageTransformer());
//viewPager.setPageTransformer(true, new PaymentZoomOutPageTransformer());
viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
//This is the right place to connect the pages with a data struct!!!
#Override
public void onPageSelected(int position) {
// Here you can connect the current displayed page with some data..
}
#Override
public void onPageScrollStateChanged(int state) {
}
});
//Here use the inflater to add views/pages
//Don't forget to do:
pagerAdapter.notifyDataSetChanged();
//When you're done...
Using SDK 19, min 13, and support.v4.app Fragments.
I have searched SO and found similiar threads which should help, but everything I have tried has not addressed my issue yet. Furthermore, many people seem to have the issue of the ViewPager restarting when they don't want it to, whereas my problem seems to be the opposite.
These posts do not seem to have helped me yet:
PagerAdapter start position
ViewPager PagerAdapter not updating the View
How to force ViewPager to re-instantiate its items
Here is my setup:
A (support.v4) Fragment in memory, which contains a ViewPager, inflated from a layout file, thus not added programmatically. The Fragment itself is not recreated, but in memory for the life of the app; it is being attached/detached to the root FragmentActivity's FragmentManager.
When the user visits this Fragment sometime during the app's lifetime, it is attached and the onCreateView is called, where I findViewById the ViewPager and assign a new FragmentStatePagerAdapter to it.
Here is my problem:
The first time the user visits this pager, everything works fine. The next time they visit it, I expect it to "start over" from page 0, meaning that I expect to not be able to scroll left immediately, but must start scrolling right. I also expect the getItem() of the FragmentStatePagerAdapter to start back at position 0. I basically want it to function the same as the first time the user visited it. However, this is not the case.
I have tried several things, but it always seems to start at the previous index of page I left it at. So if the first time I scrolled 5 pages over, and then left the Fragment and returned later, the ViewPager starts at that same page index, meaning I can scroll 5 pages left. I don't want this.
It may have something to do with the ViewPager or FragmentStatePagerAdapter storing pages internally, which are not being released. But I thought the commented out code I tried would have done that. There might be another way that I have not tried. Perhaps it is related to not recreating my Fragment, but doing so at this point in my architecture will not be great. I was hoping I could restart the ViewPager without doing this.
Here is my code:
My Fragment's onCreateView code. Everything commented out I have tried without success.
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View view = inflater.inflate(R.layout.fragment_playscreen, container, false);
//while (getChildFragmentManager().popBackStackImmediate()) {}
mAdapter = new AdapterPlayPages(this, getChildFragmentManager());
mPager = (ViewPlayPager) view.findViewById(R.id.pagerPlayScreen);
//mPager.setAdapter(null);
mPager.storeAdapter(mAdapter);
//mPager.setCurrentItem(0);
//mPager.removeAllViews();
return view;
}
My ViewPager, which has been overridden like so to get around a completely unrelated bug, as suggested here: https://stackoverflow.com/a/19900206/1002098. This does not effect the problem; I removed these changes so that I could call setAdapter(null) as suggested, but it did not address my question.
public class ViewPlayPager extends ViewPager
{
PagerAdapter mPagerAdapter;
public ViewPlayPager(Context context)
{
super(context);
}
public ViewPlayPager(Context context, AttributeSet attrs)
{
super(context, attrs);
}
#Override
protected void onAttachedToWindow()
{
super.onAttachedToWindow();
if (mPagerAdapter != null)
{
//super.setAdapter(null); // did not help
super.setAdapter(mPagerAdapter);
}
}
#Override
public void setAdapter(PagerAdapter adapter)
{
// do nothing
}
public void storeAdapter(PagerAdapter adapter)
{
mPagerAdapter = adapter;
}
}
My FragmentStatePagerAdapter. I've removed some unrelated logic and members.
public class AdapterPlayPages extends FragmentStatePagerAdapter
{
private FragmentPlayScreen mParent;
public AdapterPlayPages(FragmentPlayScreen parent, FragmentManager fragmentManager)
{
super(fragmentManager);
mParent = parent;
}
#Override
public int getCount()
{
// some logic from parent to determine true count
// the count shouldn't effect the position to start at
return Integer.MAX_VALUE;
}
#Override
public Fragment getItem(int position)
{
// logic to determine type of page to display,
// which is not changing based on position at the moment
return new FragmentPlayPage();
}
// this did not seem to help me
//#Override
//public int getItemPosition(Object object)
//{
// //return super.getItemPosition(object);
// return POSITION_NONE;
//}
}
I had to change my architecture to recreate the Fragments - add/remove them from FragmentManager, as opposed to attach/detach them while kept in memory.
It is not clear to me why the Fragment would have to be recreated for the ViewPager to reset. Android FragmentManager and FragmentTransaction supports keeping Fragments in memory and simply attaching/detaching them, or showing/hiding them, so it should be possible to simply reset the ViewPager from the in-memory Fragment's onCreateView event, but again, none of the commented out calls above seemed to work.
If anyone else has a solution, I'd still consider it. It will help me understand this issue.
I have a ViewPager (extends FragmentPagerAdapter) which holds two Fragments. What I need is just refresh a ListView for each Fragment when I swipe among them. For this I have implemented ViewPager.OnPageChangeListener interface (namely onPageScrollStateChanged). In order to hold references to Fragments I use a HashTable. I store references to Fragments in HashTable in getItem() method:
#Override
public Fragment getItem(int num) {
if (num == 0) {
Fragment itemsListFragment = new ItemsListFragment();
mPageReferenceMap.put(num, itemsListFragment);
return itemsListFragment;
} else {
Fragment favsListFragment = new ItemsFavsListFragment();
mPageReferenceMap.put(num, favsListFragment);
return favsListFragment;
}
}
So when I swipe from one Fragment to another the onPageScrollStateChanged triggers where I use the HashTable to call required method in both Fragments (refresh):
public void refreshList() {
((ItemsListFragment) mPageReferenceMap.get(0)).refresh();
((ItemsFavsListFragment) mPageReferenceMap.get(1)).refresh();
}
Everything goes fine until orientation change event happens. After it the code in refresh() method, which is:
public void refresh() {
mAdapter.changeCursor(mDbHelper.getAll());
getListView().setItemChecked(-1, true); // The last row from a exception trace finishes here (my class).
}
results in IllegalStateException:
java.lang.IllegalStateException: Content view not yet created
at android.support.v4.app.ListFragment.ensureList(ListFragment.java:328)
at android.support.v4.app.ListFragment.getListView(ListFragment.java:222)
at ebeletskiy.gmail.com.passwords.ui.ItemsFavsListFragment.refresh(ItemsFavsListFragment.java:17)
Assuming the Content view is not created indeed I set the boolean variable in onActivityCreated() method to true and used if/else condition to call getListView() or not, which shown the activity and content view successfully created.
Then I was debugging to see when FragmentPagerAdapter invokes getItem() and it happens the method is not called after orientation change event. So looks like it ViewPager holds references to old Fragments. This is just my assumption.
So, is there any way to enforce the ViewPager to call getItem() again, so I can use proper references to current Fragments? May be some other solution? Thank you very much.
Then I was debugging to see when FragmentPagerAdapter invokes getItem() and it happens the method is not called after orientation change event. So looks like it ViewPager holds references to old Fragments.
The fragments should be automatically recreated, just like any fragment is on an configuration change. The exception would be if you used setRetainInstance(true), in which case they should be the same fragment objects as before.
So, is there any way to enforce the ViewPager to call getItem() again, so I can use proper references to current Fragments?
What is wrong with the fragments that are there?
I've spent some days searching for a solution for this problem, and many points was figured out:
use FragmentPagerAdapter instead of FragmentStatePagerAdapter
use FragmentStatePagerAdapter instead of FragmentPagerAdapter
return POSITION_NONE on getItemPosition override of FragmentPagerAdapter
don't use FragmentPagerAdapter if you need dynamic changes of Fragments
and many many many others...
In my app, like Eugene, I managed myself the instances of created fragments. I keep that in one HashMap<String,Fragment> inside some specialized class, so the fragments are never released, speeding up my app (but consuming more resources).
The problem was when I rotate my tablet (and phone). The getItem(int) wasn't called anymore for that fragment, and I couldn't change it.
I really spent many time until really found a solution, so I need share it with StackOverflow community, who helps me so many many times...
The solution for this problem, although the hard work to find it, is quite simple:
Just keep the reference to FragmentManager in the constructor of FragmentPagerAdapter extends:
public class Manager_Pager extends FragmentPagerAdapter {
private final FragmentManager mFragmentManager;
private final FragmentActivity mContext;
public Manager_Pager(FragmentActivity context) {
super( context.getSupportFragmentManager() );
this.mContext = context;
this.mFragmentManager = context.getSupportFragmentManager();
}
#Override
public int getItemPosition( Object object ) {
// here, check if this fragment is an instance of the
// ***FragmentClass_of_you_want_be_dynamic***
if (object instanceof FragmentClass_of_you_want_be_dynamic) {
// if true, remove from ***FragmentManager*** and return ***POSITION_NONE***
// to force a call to ***getItem***
mFragmentManager.beginTransaction().remove((Fragment) object).commit();
return POSITION_NONE;
}
//don't return POSITION_NONE, avoid fragment recreation.
return super.getItemPosition(object);
}
#Override
public Fragment getItem( int position ) {
if ( position == MY_DYNAMIC_FRAGMENT_INDEX){
Bundle args = new Bundle();
args.putString( "anything", position );
args.putString( "created_at", ALITEC.Utils.timeToStr() );
return Fragment.instantiate( mContext, FragmentClass_of_you_want_be_dynamic.class.getName(), args );
}else
if ( position == OTHER ){
//...
}else
return Fragment.instantiate( mContext, FragmentDefault.class.getName(), null );
}
}
Thats all. And it will work like a charm...
You can clear the saved instance state
protected void onCreate(Bundle savedInstanceState) {
clearBundle(savedInstanceState);
super.onCreate(savedInstanceState, R.layout.activity_car);
}
private void clearBundle(Bundle savedInstanceState) {
if (savedInstanceState != null) {
savedInstanceState.remove("android:fragments");
savedInstanceState.remove("android:support:fragments");
savedInstanceState.remove("androidx.lifecycle.BundlableSavedStateRegistry.key");
savedInstanceState.remove("android:lastAutofillId");
}
}