I am using 4 fragments inside a ViewPager ,as ViewPager load the previous and next fragment in advance ,and no lifecycle method is called when navigating between fragments.
So is there any way to detect when Fragment is actually visible.
Thanks in Advance.
as per #Matt's answer setUserVisibleHint is deprecated
so here is alternative way for this.
#Override
public void setMenuVisibility(boolean isvisible) {
super.setMenuVisibility(isvisible);
if (isvisible){
Log.d("Viewpager", "fragment is visible ");
}else {
Log.d("Viewpager", "fragment is not visible ");
}
}
Of course. Assuming that viewPager is your instance of the ViewPager, use: viewPager.getCurrentItem().
Within your Fragment you can check if its instance is visible to the user like so:
#Override
public void setUserVisibleHint(boolean visible) {
super.setUserVisibleHint(visible);
if (visible) {
Log.i("Tag", "Reload fragment");
}
}
Always make sure that you search for answers throughly before asking your question. For instance, the first place you should check would be: https://developer.android.com/reference/android/support/v4/view/ViewPager.html
You can use viewPager.getCurrrentItem() to get the currently selected index, and from that you should be able to extrapolate which fragment is shown. However what you probably want is to use addOnPageChangeListener() to add an OnPageChangeListener. This will let you keep track of what page is selected, as it's selected by implementing the onPageSelected(int selected) method.
Did you try the isVisible method in the fragment?
Nowadays you can override androidx.fragment.app.onResume and androidx.fragment.app.onPauseto detect if it is visible or not respectively.
I have a ViewPager (instantiated with FragmentStatePagerAdapter) with some Fragment attached to it.
In a specific usecase I need to reset instanceBean and UI for most of the fragments in the pager.
After some googling I have tried some solutions like this but the side effects were not easy manageable. Other solution like this doesn't match my needs.
So I decided to go straight with the manual reset of the UI and instanceBean obj like in the code below:
The code
Single fragment reset
public void initFragment() {
notaBean = new NoteFragmentTO();
fromSpinnerListener = false;
}
public void resetFragment() {
initFragment();
NoteFragment.retainInstanceState = false;
}
This is done with the following code from the parent Activity:
Fragment reset from parent
private void resetAfterSaving() {
mIndicator.setCurrentItem(POSITION_F*****);
f*****Info.resetFragment();
mIndicator.setCurrentItem(POSITION_NOTE);
noteInfo.resetFragment();
mIndicator.setCurrentItem(POSITION_M*****);
m*****Info.resetFragment();
mIndicator.setCurrentItem(POSITION_V*****);
v*****.resetFragment();
}
AfterViews method:
#AfterViews
public void afterView() {
if (mSavedInstanceState != null) {
restoreState(mSavedInstanceState);
}
NoteFragment.retainInstanceState = true;
// Inits the adapters
noteAdapter = new NoteArrayAdapter(this, noteDefaultList);
sp_viol_nota_default.setAdapter(noteAdapter);
//sp_viol_nota_default.seton
et_viol_nota.setOnFocusChangeListener(new OnFocusChangeListener() {
#Override
public void onFocusChange(View v, boolean hasFocus) {
if (!hasFocus) {
String readText = et_viol_nota.getText().toString().trim();
notaBean.setNota(readText == "" ? null : readText);
}
}
});
}
OnSavedInstanceState
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putParcelableArrayList(KEY_NOTE_D_LIST, (ArrayList<VlzAnagraficaNoteagente>) noteDefaultList);
outState.putInt(KEY_NOTE_D_POSITION, !NoteFragment.retainInstanceState ? 0 : notePosition);
notaBean.setNota(!NoteFragment.retainInstanceState ? "" : et_viol_nota.getText().toString().trim());
outState.putParcelable(NoteFragmentTO.INTENT_KEY, notaBean);
}
Why do I set every page before resetting them?
Because like explained here:
When pages are not visible to the user, their entire fragment may be destroyed, only keeping the saved state of that fragment.
and because until I don't select the relative fragment the #AfterViews method (that is everything processed right after OnCreateView of the fragment) is not executed.
This throws NullPointerException for a thousand of reason (Usually in the #AfterViews method You launch RestoreState method, initializes adapter, do UI stuff).
Setting the relative page before the reset let #AfterViews method be processed.
Before checking what would happened when rotating the device, all the fragment I need are correcly reset.
When rotating the device, the error comes out:
The views (mainly EditText) go back to their previous state BEFORE my reset.
What happens?
When switching between the page, at a certain point the page will be destroyed and OnSavedInstanceState is called everytime for each page.
I have already handled the OnSavedInstanceState (like above) that when the boolean is false saves the state like if it had just been created.
I found that until within AfterView method the EditText has its text set to blank (like I want) but going on with the debug the EditText goes back to its previous state, so at the end it will show the last text it had.
Question
How can I keep the manually set (in OnSavedInstanceState) EditText text after destroying/recreating a fragment?
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);
}
In my application i have a FragmentPager. Now each Fragment has a next button with which i navigate to the next fragment. Via the next button i know that the user is navigation away from the view. But how do i know if the user has clicked on the tabs. Will the
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putString(KEY_CONTENT, mContent);
}
function be called when a user presses a different tab ? Can i save the state and restore it on the
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if ((savedInstanceState != null)
&& savedInstanceState.containsKey(KEY_CONTENT)) {
mContent = savedInstanceState.getString(KEY_CONTENT);
}
}
will this work ? What other way can i know that the user has clicked on the different tab ?
Kind Regards
First of all, are you using ActionBarSherlock for you actionbar/tabs? I recommend that you do since you'll get a cross-version way of working with the actionbar.
In any case, you should add a listener to each tab before adding it to the actionbar. With the listener implemented you know when a tab has been selected, reselected and unselected
I'm not sure about when the onSaveInstanceState is called (try it using the debugger!), but with the listener implemented you'll get a fool-proof way of knowing what goes on with your tabs.
I'm new to android and I'm facing the following problem. I'm developing for both, Android 2 and 3, and this is why I use fragments. However to make the app working on Android 2 devices I import android.support.v4.app.ListFragment. I need to maintain selection within my ListFragment when orientation of the screen changes. I'm overriding onSaveInstanceState() method and put an int into the bundle. When the screen is rotated, this method is called and the int is added to the bundle. However when onActivityCreated() is called, its bundle is null. I am following the example provided on Android website: http://developer.android.com/reference/android/app/Fragment.html, but as mentioned above - after onSaveInstanceState() is called, the bundle in onActivityCreated() is still null.
Here's the code:
import android.support.v4.app.ListFragment;
public class VisitsHomeFragment extends ListFragment {
private int selectedPosition = -1;
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
if (savedInstanceState != null) {
if (savedInstanceState.containsKey("SELECTED_POSITION")) {
selectedPosition = savedInstanceState.getInt("SELECTED_POSITION");
}
}
}
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt("SELECTED_POSITION", selectedPosition);
}
}
I would appreciate any help with this problem.
I had the same problem, adding android:id to the fragment element in the layout file fixed this issue.
It seems FragmentManager uses the id to send the appropriate bundle when recreating a fragment.
Make sure you're not calling setRetainInstance(true) in the Fragment. After a little experimentation I pinpointed this as being the error in my code. The downside of having to do it this way is one has to manually bundle all instance data.
After removing the method call and updating my onSaveInstanceState to parcel all of my instance variables, I can now restore list position on rotation.
I had the same problem, and I eventually tracked it down to having different android:id attribute values on the fragment elements in the two different layouts (portrait and landscape).