I've written up a dummy activity that switches between two fragments. When you go from FragmentA to FragmentB, FragmentA gets added to the back stack. However, when I return to FragmentA (by pressing back), a totally new FragmentA is created and the state it was in is lost. I get the feeling I'm after the same thing as this question, but I've included a complete code sample to help root out the issue:
public class FooActivity extends Activity {
#Override public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
final FragmentTransaction transaction = getFragmentManager().beginTransaction();
transaction.replace(android.R.id.content, new FragmentA());
transaction.commit();
}
public void nextFragment() {
final FragmentTransaction transaction = getFragmentManager().beginTransaction();
transaction.replace(android.R.id.content, new FragmentB());
transaction.addToBackStack(null);
transaction.commit();
}
public static class FragmentA extends Fragment {
#Override public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
final View main = inflater.inflate(R.layout.main, container, false);
main.findViewById(R.id.next_fragment_button).setOnClickListener(new View.OnClickListener() {
public void onClick(View v) {
((FooActivity) getActivity()).nextFragment();
}
});
return main;
}
#Override public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
// Save some state!
}
}
public static class FragmentB extends Fragment {
#Override public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
return inflater.inflate(R.layout.b, container, false);
}
}
}
With some log messages added:
07-05 14:28:59.722 D/OMG ( 1260): FooActivity.onCreate
07-05 14:28:59.742 D/OMG ( 1260): FragmentA.onCreateView
07-05 14:28:59.742 D/OMG ( 1260): FooActivity.onResume
<Tap Button on FragmentA>
07-05 14:29:12.842 D/OMG ( 1260): FooActivity.nextFragment
07-05 14:29:12.852 D/OMG ( 1260): FragmentB.onCreateView
<Tap 'Back'>
07-05 14:29:16.792 D/OMG ( 1260): FragmentA.onCreateView
It's never calling FragmentA.onSaveInstanceState and it creates a new FragmentA when you hit back. However, if I'm on FragmentA and I lock the screen, FragmentA.onSaveInstanceState does get called. So weird...am I wrong in expecting a fragment added to the back stack to not need re-creation? Here's what the docs say:
Whereas, if you do call addToBackStack() when removing a fragment,
then the fragment is stopped and will be resumed if the user navigates
back.
If you return to a fragment from the back stack it does not re-create the fragment but re-uses the same instance and starts with onCreateView() in the fragment lifecycle, see Fragment lifecycle.
So if you want to store state you should use instance variables and not rely on onSaveInstanceState().
Comparing to Apple's UINavigationController and UIViewController, Google does not do well in Android software architecture. And Android's document about Fragment does not help much.
When you enter FragmentB from FragmentA, the existing FragmentA instance is not destroyed. When you press Back in FragmentB and return to FragmentA, we don't create a new FragmentA instance. The existing FragmentA instance's onCreateView() will be called.
The key thing is we should not inflate view again in FragmentA's onCreateView(), because we are using the existing FragmentA's instance. We need to save and reuse the rootView.
The following code works well. It does not only keep fragment state, but also reduces the RAM and CPU load (because we only inflate layout if necessary). I can't believe Google's sample code and document never mention it but always inflate layout.
Version 1(Don't use version 1. Use version 2)
public class FragmentA extends Fragment {
View _rootView;
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (_rootView == null) {
// Inflate the layout for this fragment
_rootView = inflater.inflate(R.layout.fragment_a, container, false);
// Find and setup subviews
_listView = (ListView)_rootView.findViewById(R.id.listView);
...
} else {
// Do not inflate the layout again.
// The returned View of onCreateView will be added into the fragment.
// However it is not allowed to be added twice even if the parent is same.
// So we must remove _rootView from the existing parent view group
// (it will be added back).
((ViewGroup)_rootView.getParent()).removeView(_rootView);
}
return _rootView;
}
}
------Update on May 3 2005:-------
As the comments mentioned, sometimes _rootView.getParent() is null in onCreateView, which causes the crash. Version 2 removes _rootView in onDestroyView(), as dell116 suggested. Tested on Android 4.0.3, 4.4.4, 5.1.0.
Version 2
public class FragmentA extends Fragment {
View _rootView;
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
if (_rootView == null) {
// Inflate the layout for this fragment
_rootView = inflater.inflate(R.layout.fragment_a, container, false);
// Find and setup subviews
_listView = (ListView)_rootView.findViewById(R.id.listView);
...
} else {
// Do not inflate the layout again.
// The returned View of onCreateView will be added into the fragment.
// However it is not allowed to be added twice even if the parent is same.
// So we must remove _rootView from the existing parent view group
// in onDestroyView() (it will be added back).
}
return _rootView;
}
#Override
public void onDestroyView() {
if (_rootView.getParent() != null) {
((ViewGroup)_rootView.getParent()).removeView(_rootView);
}
super.onDestroyView();
}
}
WARNING!!!
This is a HACK! Though I am using it in my app, you need to test and read comments carefully.
I guess there is an alternative way to achieve what you are looking for.
I don't say its a complete solution but it served the purpose in my case.
What I did is instead of replacing the fragment I just added target fragment.
So basically you will be going to use add() method instead replace().
What else I did.
I hide my current fragment and also add it to backstack.
Hence it overlaps new fragment over the current fragment without destroying its view.(check that its onDestroyView() method is not being called. Plus adding it to backstate gives me the advantage of resuming the fragment.
Here is the code :
Fragment fragment=new DestinationFragment();
FragmentManager fragmentManager = getFragmentManager();
android.app.FragmentTransaction ft=fragmentManager.beginTransaction();
ft.add(R.id.content_frame, fragment);
ft.hide(SourceFragment.this);
ft.addToBackStack(SourceFragment.class.getName());
ft.commit();
AFAIK System only calls onCreateView() if the view is destroyed or not created.
But here we have saved the view by not removing it from memory. So it will not create a new view.
And when you get back from Destination Fragment it will pop the last FragmentTransaction removing top fragment which will make the topmost(SourceFragment's) view to appear over the screen.
COMMENT: As I said it is not a complete solution as it doesn't remove the view of Source fragment and hence occupying more memory than usual. But still, serve the purpose. Also, we are using a totally different mechanism of hiding view instead of replacing it which is non traditional.
So it's not really for how you maintain the state, but for how you maintain the view.
I would suggest a very simple solution.
Take the View reference variable and set view in OnCreateView. Check if view already exists in this variable, then return same view.
private View fragmentView;
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
if (fragmentView != null) {
return fragmentView;
}
View view = inflater.inflate(R.layout.yourfragment, container, false);
fragmentView = view;
return view;
}
I came across this problem in a Fragment containing a map, which has too many setup details to save/reload.
My solution was to basically keep this Fragment active the whole time (similar to what #kaushal mentioned).
Say you have current Fragment A and wants to display Fragment B.
Summarizing the consequences:
replace() - remove Fragment A and replace it with Fragment B. Fragment A will be recreated once brought to the front again
add() - (create and) add a Fragment B and it overlap Fragment A, which is still active in the background
remove() - can be used to remove Fragment B and return to A. Fragment B will be recreated when called later on
Hence, if you want to keep both Fragments "saved", just toggle them using hide()/show().
Pros: easy and simple method to keep multiple Fragments running
Cons: you use a lot more memory to keep all of them running. May run into problems, e.g. displaying many large bitmaps
onSaveInstanceState() is only called if there is configuration change.
Since changing from one fragment to another there is no configuration change so no call to onSaveInstanceState() is there. What state is not being save? Can you specify?
If you enter some text in EditText it will be saved automatically. Any UI item without any ID is the item whose view state shall not be saved.
first: just use add method instead of replace method of FragmentTransaction class then you have to add secondFragment to stack by addToBackStack method
second :on back click you have to call popBackStackImmediate()
Fragment sourceFragment = new SourceFragment ();
final Fragment secondFragment = new SecondFragment();
final FragmentTransaction ft = getChildFragmentManager().beginTransaction();
ft.add(R.id.child_fragment_container, secondFragment );
ft.hide(sourceFragment );
ft.addToBackStack(NewsShow.class.getName());
ft.commit();
((SecondFragment)secondFragment).backFragmentInstanceClick = new SecondFragment.backFragmentNewsResult()
{
#Override
public void backFragmentNewsResult()
{
getChildFragmentManager().popBackStackImmediate();
}
};
Kotlin and ViewBinding Solution
I am using replace() and backstack() method for FragmentTransaction. The problem is that the backstack() method calls the onCreateView of the Previous Fragment which causes in re-built of Fragment UI. Here is a solution for that:
private lateinit var binding: FragmentAdRelevantDetailsBinding
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,savedInstanceState: Bundle?
): View {
if (!this::binding.isInitialized)
binding = FragmentAdRelevantDetailsBinding.inflate(layoutInflater, container, false)
return binding.root
}
Here, since onSaveInstanceState in fragment does not call when you add fragment into backstack. The fragment lifecycle in backstack when restored start onCreateView and end onDestroyView while onSaveInstanceState is called between onDestroyView and onDestroy. My solution is create instance variable and init in onCreate. Sample code:
private boolean isDataLoading = true;
private ArrayList<String> listData;
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
isDataLoading = false;
// init list at once when create fragment
listData = new ArrayList();
}
And check it in onActivityCreated:
public void onViewCreated(View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
if(isDataLoading){
fetchData();
}else{
//get saved instance variable listData()
}
}
private void fetchData(){
// do fetch data into listData
}
getSupportFragmentManager().addOnBackStackChangedListener(new FragmentManager.OnBackStackChangedListener()
{
#Override
public void onBackStackChanged()
{
if (getSupportFragmentManager().getBackStackEntryCount() == 0)
{
//setToolbarTitle("Main Activity");
}
else
{
Log.e("fragment_replace11111", "replace");
}
}
});
YourActivity.java
#Override
public void onBackPressed()
{
Fragment fragment = getSupportFragmentManager().findFragmentById(R.id.Fragment_content);
if (fragment instanceof YourFragmentName)
{
fragmentReplace(new HomeFragment(),"Home Fragment");
txt_toolbar_title.setText("Your Fragment");
}
else{
super.onBackPressed();
}
}
public void fragmentReplace(Fragment fragment, String fragment_name)
{
try
{
fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.Fragment_content, fragment, fragment_name);
fragmentTransaction.setCustomAnimations(R.anim.enter_from_right, R.anim.exit_to_left, R.anim.enter_from_left, R.anim.exit_to_right);
fragmentTransaction.addToBackStack(fragment_name);
fragmentTransaction.commitAllowingStateLoss();
}
catch (Exception e)
{
e.printStackTrace();
}
}
My problem was similar but I overcame me without keeping the fragment alive. Suppose you have an activity that has 2 fragments - F1 and F2. F1 is started initially and lets say in contains some user info and then upon some condition F2 pops on asking user to fill in additional attribute - their phone number. Next, you want that phone number to pop back to F1 and complete signup but you realize all previous user info is lost and you don't have their previous data. The fragment is recreated from scratch and even if you saved this information in onSaveInstanceState the bundle comes back null in onActivityCreated.
Solution:
Save required information as an instance variable in calling activity. Then pass that instance variable into your fragment.
#Override
public void onActivityCreated(#Nullable Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
Bundle args = getArguments();
// this will be null the first time F1 is created.
// it will be populated once you replace fragment and provide bundle data
if (args != null) {
if (args.get("your_info") != null) {
// do what you want with restored information
}
}
}
So following on with my example: before I display F2 I save user data in the instance variable using a callback. Then I start F2, user fills in phone number and presses save. I use another callback in activity, collect this information and replace my fragment F1, this time it has bundle data that I can use.
#Override
public void onPhoneAdded(String phone) {
//replace fragment
F1 f1 = new F1 ();
Bundle args = new Bundle();
yourInfo.setPhone(phone);
args.putSerializable("you_info", yourInfo);
f1.setArguments(args);
getFragmentManager().beginTransaction()
.replace(R.id.fragmentContainer, f1).addToBackStack(null).commit();
}
}
More information about callbacks can be found here: https://developer.android.com/training/basics/fragments/communicating.html
Replace a Fragment using following code:
Fragment fragment = new AddPaymentFragment();
getSupportFragmentManager().beginTransaction().replace(R.id.frame, fragment, "Tag_AddPayment")
.addToBackStack("Tag_AddPayment")
.commit();
Activity's onBackPressed() is :
#Override
public void onBackPressed() {
android.support.v4.app.FragmentManager fm = getSupportFragmentManager();
if (fm.getBackStackEntryCount() > 1) {
fm.popBackStack();
} else {
finish();
}
Log.e("popping BACKSTRACK===> ",""+fm.getBackStackEntryCount());
}
Public void replaceFragment(Fragment mFragment, int id, String tag, boolean addToStack) {
FragmentTransaction mTransaction = getSupportFragmentManager().beginTransaction();
mTransaction.replace(id, mFragment);
hideKeyboard();
if (addToStack) {
mTransaction.addToBackStack(tag);
}
mTransaction.commitAllowingStateLoss();
}
replaceFragment(new Splash_Fragment(), R.id.container, null, false);
Perfect solution that find old fragment in stack and load it if exist in stack.
/**
* replace or add fragment to the container
*
* #param fragment pass android.support.v4.app.Fragment
* #param bundle pass your extra bundle if any
* #param popBackStack if true it will clear back stack
* #param findInStack if true it will load old fragment if found
*/
public void replaceFragment(Fragment fragment, #Nullable Bundle bundle, boolean popBackStack, boolean findInStack) {
FragmentManager fm = getSupportFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
String tag = fragment.getClass().getName();
Fragment parentFragment;
if (findInStack && fm.findFragmentByTag(tag) != null) {
parentFragment = fm.findFragmentByTag(tag);
} else {
parentFragment = fragment;
}
// if user passes the #bundle in not null, then can be added to the fragment
if (bundle != null)
parentFragment.setArguments(bundle);
else parentFragment.setArguments(null);
// this is for the very first fragment not to be added into the back stack.
if (popBackStack) {
fm.popBackStack(null, FragmentManager.POP_BACK_STACK_INCLUSIVE);
} else {
ft.addToBackStack(parentFragment.getClass().getName() + "");
}
ft.replace(R.id.contenedor_principal, parentFragment, tag);
ft.commit();
fm.executePendingTransactions();
}
use it like
Fragment f = new YourFragment();
replaceFragment(f, null, boolean true, true);
Calling the Fragment lifecycle methods properly and using onSavedInstanceState() can solve the problem.
i.e Call onCreate(), onCreateView(), onViewCreated() and onSavedInstanceState() properly and save Bundle in onSaveInstanceState() and resotre it in onCreate() method.
I don't know how but it worked for me without any error.
If anyone can explain it will very much appreciated.
public class DiagnosisFragment extends Fragment {
private static final String TITLE = "TITLE";
private String mTitle;
private List mList = null;
private ListAdapter adapter;
public DiagnosisFragment(){}
public DiagnosisFragment(List list, String title){
mList = list;
mTitle = title;
}
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if(savedInstanceState != null){
mList = savedInstanceState.getParcelableArrayList(HEALTH_ITEMS);
mTitle = savedInstanceState.getString(TITLE);
itemId = savedInstanceState.getInt(ID);
mChoiceMode = savedInstanceState.getInt(CHOICE_MODE);
}
getActivity().setTitle(mTitle);
adapter = (ListAdapter) new HealthAdapter(mList, getContext()).load(itemId);
}
#Nullable
#Override
public View onCreateView(#NonNull LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
return inflater.inflate(R.layout.diagnosis_fragment, container, false);
}
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
ListView lv = view.findViewById(R.id.subLocationsSymptomsList);
lv.setAdapter(adapter);
}
#Override
public void onSaveInstanceState(#NonNull Bundle outState) {
outState.putParcelableArrayList(HEALTH_ITEMS, (ArrayList) mList);
outState.putString(TITLE, mTitle);
}
}
For who has looking for solution :
#Override
public void onDestroyView() {
Bundle savedState=new Bundle();
// put your data in bundle
// if you have object and want to restore you can use gson to convert it
//to sring
if (yourObject!=null){
savedState.putString("your_object_key",new Gson().toJson(yourObject));
}
if (getArguments()==null){
setArguments(new Bundle());
}
getArguments().putBundle("saved_state",savedState);
super.onDestroyView();
}
and in onViewCreated() method :
Bundle savedState=null;
if (getArguments()!=null){
savedState=getArguments().getBundle("saved_state");
}
if (savedState!=null){
// set your restored data to your view
}
In my application, I have a ViewPager which holds many swipeable Tabs with Fragments inside. I use the setUserVisibleHint method to detect when a Fragment comes to the screen. This works great when the user swipes between tabs but it does not work on the first load. To run the code in the method I have to swipe to left and then back to the first Fragment because the setUserVisibleHint method is called before the onCreateView method.
Do you have any ideas how I can run this code after the first Fragment is visible? Is there a method in the ViewPager or something else?
You can't (and shouldn't) rely on setUserVisibleHint for this. Instead, you should be using a ViewPager.OnPageChangeListener to get callbacks for when a page becomes visible. E.g.
viewPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
#Override
public void onPageSelected(int position) {
// do your work
}
});
Note: You can use ViewPager.SimpleOnPageChangeListener if you don't need to listen for all callbacks.
Update
setOnPageChangeListener method is now deprecated, use addOnPageChangeListener instead
viewPager.addOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
#Override
public void onPageSelected(int position) {
// do your work
}
});
BELOW WORKED FOR ME
Please create a global view like this
View view;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState)
{
//inflate view layout
view =inflater.inflate(R.layout.your_fragment, container, false);
// return view
return view;
}
and use this
#Override
public void setUserVisibleHint(boolean isUserVisible)
{
super.setUserVisibleHint(isUserVisible);
// when fragment visible to user and view is not null then enter here.
if (isUserVisible && view != null)
{
onResume();
}
}
and In OnResume method
#Override
public void onResume() {
super.onResume();
if (!getUserVisibleHint()) {
return;
}
//do your stuff here
}
You have to call manually mViewPagerListener.onPageSelected(0); in onCreateView in your root activity/fragment.
I dont understand what you need exactly but you can detect the page of the current fragment by calling ViewPager.getCurrentItem that return integer.
Hope it helps.
Good luck.
Well, its workaround more, and maybe its better to setup OnPageChangeListener, but it works for me. The task is to determine whether the current fragment is visible at creation. You can use the menu to do this. In your fragment:
#Override
public void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setHasOptionsMenu(true); // set current fragment has its own options menu
}
and this
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
...
if(isMenuVisible()) { // menu should be visible if current fragment is visible right now
setUserVisibleHint(true); // manually set value to true
}
...
return view;
Maybe someone will find it usefull. This works for me.
I check your problem，but I find out the onCreateView method is called before the
setUserVisibleHint method
enter code here
because the setUserVisibleHint method is called before the onCreateView method
What I ought to do is change the view/layout of Fragment without creating another class for fragment on click of a button.
For example I have an activity - ContactsActivity and I have a fragment - ContactsFragment.
The Standard way of using Fragments:
From ContactsActivity I call ContactsFragment by -
getFragmentManager().beginTransaction().replace(android.R.id.content, new ContactsFragment())
.commit();
Code for setting View in ContactsFragment class -
#Override
public View onCreateView(final LayoutInflater inflater, final ViewGroup container, final Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.contacts_primary, container, false);
return rootView;
}
**Now comes how I do what I want to do ** (Change the view of fragment)
I change only the view of ContactsFragment by doing a bad kind of hack.
I change the onCreateView() shown above to this -
#Override
public View onCreateView(final LayoutInflater inflater, final ViewGroup container, final Bundle savedInstanceState) {
//Set the view to R.layout.contacts_primary
rootView = inflater.inflate(R.layout.contacts_primary, container, false);
//Set the view to R.layout.contacts_secondary
if(getActivity().getIntent()!=null && getActivity().getIntent().getBooleanExtra("s", false)) {
rootView = inflater.inflate(R.layout.contacts_secondary, container, false);
Log.e(tag,getActivity().getIntent().getExtras().toString());
return rootView;
}
//This is the onClickListener which again calls the ContactsActivity class,
//this time with an Intent which I used above to change the view from
//R.layout.contacts_primary to R.layout.contacts_secondary
Button button = (Button)rootView.findViewById(R.id.button1);
button.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
startActivity(new Intent(getActivity(), ContactsActivity.class).putExtra("s",true));
}
});
Now everything works as I want and flawlessly.
But I have a very strong feeling that either all of it is wrong and Fragments aren't supposed to work this way or I am using a hectic hack to achieve what can be done by few lines of code.
So please let me know what is it? And if there is a standard way of doing what I am trying to do.
For me passing additional argument on which base fragment decides wich layout to use seems totally ok. But there is cleaner way of doing what you want to achieve without starting another activity.
First of all pass argument to fragment by making standard static new instance method in fragment (we cannot pass this argument in constructor as android always recreates fragments using empty constructor). Something like this:
public static ContactsFragment newInstance(boolan firstView) {
ContactsFragment fragment = new ContactsFragment();
Bundle args = new Bundle();
args.putBoolean("yourArg", firstView);
fragment.setArguments(args);
return fragment;
}
Every time you have to initiate your fragment do this with this method.
Then declare interface in your fragment to communicate with your activity. Like this
public interface NewViewListener {
public void showNewView(boolen firstView);
}
Than make your activity implement it so your activity han a method where it can place new fragment in container view. In your fragments onAttach and onDetach methodsmake sure your activity implements this interface and hold reference to your activity in private NewViewListener field in your fragment. Like this:
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
mListener = (NewViewListener ) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement NewViewListener ");
}
}
#Override
public void onDetach() {
super.onDetach();
mListener = null;
}
Then in on button click method call showNewView method on your activity with whatever argument you want indicating which view you want in new fragment instance. And in your activity method showNewVew fragment in the container. Like this:
#Override
public void showNewView(boolean firstView) {
getFragmentManager().beginTransaction().replace(android.R.id.content, ContactsFragment.newInstance(firstView)
.commit();
}
In your fragments onCreateView you may get passed arguments and decide which view you want to use.
We all know that when using ViewPager with Fragment and FragmentPagerAdapter we get 3 Fragment loaded: the visible one, and both on each of its sides.
So, if I have 7 Fragments and I'm iterating through them to see which 3 of them are the ones that are loaded, and by that I mean onCreateView() has already been called, how can I determine this?
EDIT: The Fragment doesn't have to be the one that the ViewPager is showing, just that onCreateView() has already been called.
Well logically, this would be a reasonable test if onCreateView has been called:
myFragment.getView() != null;
Assuming you a have a reference to all of the fragments in the pager iterate, them and check if they have a view.
http://developer.android.com/reference/android/app/Fragment.html#getView()
Update
The above answer assumes that your fragments always create a view, and are not viewless fragments. If they are then I suggest sub classing the fragment like so:
public abstract class SubFragment extends Fragment
{
protected boolean onCreateViewCalled = false;
public boolean hasOnCreateViewBeenCalled()
{
return onCreateViewCalled;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup Container, Bundle state){
onCreateViewCalled = true;
return null;
}
}
Just bear in mind that further sub classes will have to call super or set the flag themselves should they override onCreateView as well.
I added an interface to Fragment. Looks like:
protected OnCreateViewCallback createViewCallback = null;
public void setCreateViewCallback(OnCreateViewCallback createViewCallback) {
this.createViewCallback = createViewCallback;
}
public interface OnCreateViewCallback {
void onCreateView();
}
In my onCreateView():
//initialize your view.
if (createViewCallback != null) {
createViewCallback.onCreateView();
createViewCallback = null;
}
return mainView;
From my activity:
if (ocrFragment.getView() == null) {
ocrFragment.setCreateViewCallback(new MainScreenFragment.OnCreateViewCallback() {
#Override
public void onCreateView() {
ocrFragment.ocrImage(picture, false);
}
});
} else {
ocrFragment.ocrImage(picture, false);
}
If you are trying to perform something after onCreateView is called, use onViewCreated:
Called immediately after onCreateView(LayoutInflater, ViewGroup,
Bundle) has returned, but before any saved state has been restored in
to the view. This gives subclasses a chance to initialize themselves
once they know their view hierarchy has been completely created. The
fragment's view hierarchy is not however attached to its parent at
this point.
public void onViewCreated(View view, Bundle savedInstanceState) {
MyActivity myActivity = (MyActivity) getActivity();
MyActivity.newAsyncTask(mPar);
}
You could also check for Fragment.isVisible() because a Fragment is in visible state when it's in the offscreen page limit of a ViewPager.
Edit: But it just really depends on what you really want to achieve with your question. Perhaps some kind of update to all UIs in your Fragments when their UI is ready?
EDIT:
Just another addition, you could listen to onViewCreated() and set a flag. Or notify your Activity and do further work (getActivity() will return your Activity at this point). But really, better state what you want to accomplish with your question.
I have a ViewPager. My FragmentPageAdapter returns the position of the Viewpager in the getItem() methode. But after rotating the Screen the methode returns no value. Why? If I understood it right, everytime you rotate the screen OnCreateView() is called, but why doesn't it return the value any more? Could someone point out how to solve this? Thank you
Edit: My FragmentPageAdapter:
public Fragment getItem(int position) {
return Fragment_results.newInstance(position);
}
My Fragment:
public static Fragment_results newInstance(int i) {
Fragment_results fragment = new Fragment_results();
fragment.mContent = i +"";
return fragment;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.layout_result, null);
((TextView) view.findViewById(R.id.text)).setText(mContent);
The position is set to 0 upon creating of the ViewPager instance and whenever you set a new adapter. When onCreateView() is called, you're rebuilding the entire app essentially. In order to revert back to the position it was, you must first use onSavedInstanceState(Bundle savedInstanceState) and store the item position via the Bundle.
#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt("pageItem", myViewPager.getCurrentItem());
}
Then in onCreate, restore the viewPager's state like so:
if (savedInstanceState != null) {
myViewPager.setCurrentItem(savedInstanceState.getInt("pageItem", 0));
}