My Android application has an ActionBar that changes which Fragment occupies a certain FrameLayout. I am trying to use onSaveInstanceState to save the state of a Fragment when the tab is changed, so that it can be recovered in onCreateView.
The problem is, onSaveInstanceState is never called. The Fragment's onDestroyView and onCreateView methods are called, but the Bundle supplied to onCreateView remains null.
Can someone please explain to me when onSaveInstanceState is actually called, how I can make sure it gets called when switching tabs, or the best practice for saving and restoring the state of a Fragment when it is detached and re-attached?
Fragment:
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.event_log, container, false);
// Retrieve saved state
if (savedInstanceState != null){
System.out.println("log retrieved");
} else {
System.out.println("log null");
}
return view;
}
#Override
public void onSaveInstanceState(Bundle outState) {
System.out.println("log saved");
super.onSaveInstanceState(outState);
// more code
}
Activity:
/**
* Detach the current Fragment, because another one is being attached.
*/
#Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
if (tab.getText().equals(getString(R.string.tab_events))){
if (frEventLog != null) {
ft.detach(frEventLog);
}
}
Fragment#onSaveInstanceState is only called when the Activity hosting the Fragment is destroyed AND there is a chance that you can come back to the same activity AND the fragment is still added to the FragmentManager. The most common case would be screen rotation.
I think your Fragment will also need to do setRetainInstance(true) in onCreate for example. Not exactly sure about that point though.
You should also see this method being called when you press the home button for example. That will destroy the activity but you can go back to it by using the task list for example.
If you just detach() the fragment all you need to do to get it back is to ask the FragmentManager for it.
There are two examples you should have a look at:
ActionBar FragmentTabs and TabHost FragmentTabs
The TabHost example uses
ft.add(containerId, fragment, tag);
// later
fragment = mActivity.getSupportFragmentManager().findFragmentByTag(tag);
to find the instances of previously added Fragments, works until you remove() a Fragment
Regarding onCreateView / onDestroyView: That is called once a fragment gets detached because the next time you attach it needs to create a new View. Note that Fragment#onDetached() is not called when you detach() the fragment because it is still attached to the Activity. It is only detached from the view-hierarchy.
There is another nice example on how to retain fragment state / how to use fragments to retain state in Android Training - Caching Bitmaps.
That example is missing a critical line though:
public static RetainFragment findOrCreateRetainFragment(FragmentManager fm) {
RetainFragment fragment = (RetainFragment) fm.findFragmentByTag(TAG);
if (fragment == null) {
fragment = new RetainFragment();
fm.beginTransaction().add(fragment, TAG).commit(); // << add this
}
return fragment;
}
Related
I am working on an application and there is one specific thing that is bothering me. Let's just say I have one activity and 2 fragments.FragmentA and FragmentB and FragmentA gets attached when activity starts.
I want to save the fragment data and fragment state when orientation changes occur.I have successfully saved fragment data using OnSavedInstanceState method. Now I want to save fragment state in the activity so that if orientation change occurs I want to be on the fragment I was (in my case either FragmentA or FragmentB depends on which was showing before config changes occur).
This is how I am saving the fragment state in the Activity:
#Override
protected void onSaveInstanceState(Bundle outState) {
// Save the values you need into "outState"
super.onSaveInstanceState(outState);
outState.putLong(SS_DATE, userDate.getTime());
android.support.v4.app.FragmentManager manager = getSupportFragmentManager();
Fragment currentFragment = this.getSupportFragmentManager().findFragmentById(R.id.content_container);
manager.putFragment(outState, "currentFragment", currentFragment);
}
And this is how I am retrieving on which fragment I was when the orientation change occurred:
#Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
FragmentManager manager = getSupportFragmentManager();
#SuppressLint("CommitTransaction")
FragmentTransaction transaction = manager.beginTransaction();
if (savedInstanceState != null) {
Fragment MyFragment = (Fragment) manager.getFragment(savedInstanceState, "currentFragment");
if (MyFragment instanceof FragListStudentsAttendance) {
Log.v("onRestore", FragListStudentsAttendance.TAG);
}else if (MyFragment instanceof FragGetClassesForAttendance){
Log.v("onRestore", FragGetClassesForAttendance.TAG);
if(MyFragment!=null) {
mFragGetClassesForAttendance = (FragGetClassesForAttendance) MyFragment;
}else{
mFragGetClassesForAttendance = new FragGetClassesForAttendance();
FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
// mFragGetClassesForAttendanceNew.setRetainInstance(true);
// transaction.replace(R.id.content_ssadmin_container, mFragGetClassesForAttendanceNew, "FragGetClassesForAttendance").addToBackStack(null);
transaction.add(R.id.content_ssadmin_container, mFragGetClassesForAttendance, FragGetClassesForAttendance.TAG);
//transaction.replace(R.id.newEnrollmentMainContainer, mFragNewEnrollmentResults).addToBackStack("FragNewEnrollments");
transaction.commit();
mFragGetClassesForAttendance.setDate(userDate);
}
}
}
}
Now
Scenario 1:
If I am on fragment A and I rotate the device every thing works fine as it should. Like fragment have web services which loads the data into listview so I check if data exist then there is no need to run the web service and that working for now
Scenario 2:
If I am on fragment B and orientation change occurs everything works fine as it is supposed to be on fragment B. Now When I press back button Fragment A gets called again and all the data also comes from service. I think this shouldn't happen because it was supposed to be in BackStack and it's data was saved. So what Should I do now here?
Scenario 3: On FragmentB I have noticed that when I rotates the device the saveInstanceState function of FragmentA also gets called. Why it is so? where as I was replacing the FragmentB with FragmentA ?
Some Confusions:
Let me talk about some of the confusions also , maybe someone clear it to me although I have searched and read a lot about fragment and activity life cycle,
Actually I want to save the data per activity and fragment on device rotation. I know how to do it with activity(how to save states) so I also know how to do it in the fragment (save state of fragment views) now I am confused how to tell activity which fragment was showing and which to go after config changes(rotation) ? also what happens to FragmentA if I am on FragmentB Does its get attach and detach again and again in background?
I got your problems and confusions. I think the life cycle of fragment is confusing you. and indeed it will confuse you.
You need to learn different situations.
1. Fragment Life cycle when it is in foreground (attaching and detaching with activity) . Please keenly observe all the methods that will call i.e OnSaveInstance,onCreateView,OnDestroyView,onDestroy
2. Fragment life cycle when it is in background (observe the methods stated above)
3. Fragment life cycle when it is added to backstack (and not in foreground)
I am quite sure you are confused with the point number 3. As when the fragment is added to backstack it never gets destroy. So rotating device twice will set the ffragment data to null. I think you are restoring data on ActivityCreated or on onViewCreated ,
Ill suggest you to restore the fragment data in the oncreate. this will work for you when your fragment is coming back to foreground from the backstack .
Example
private List<String> mCountries;</pre>
#Override
public void onCreate(Bundle savedInstanceState)
{
if (savedInstanceState != null)
{
// Populate countries from bundle
}
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
View view = inflater.inflate(R.layout.fragment_countries, container, false);
if (mCountries == null)
{
// Populate countries by calling AsyncTask
}
return view;
}
public void onSaveInstanceState(Bundle outState)
{
// Save countries into bundle
}
Hope this will clear your confusions.
I have a Fragment inside a ViewPager. The Fragment contains a RecyclerView (think ListView). When the user pages away and then returns to the fragment, no matter where the user left the list, the list always restarts at the top. So I need to retain the currPosition somehow. Would savedInstanceState be a good place to store it? If yes, in which callback do I read the data? Again this is inside a ViewPager and I am using a FragmentPagerAdapter and so not many callbacks are called. Still my broader question stands: What causes a Fragment's savedInstanceState to be non-empty?
To give further breadth to the question. Imagine I have an activity with two fragments. I detach and attach the fragments when needed. Say I navigate away from the activity. Would the savedInstanceState of the fragment be empty in this case if the activity's savedInstanceState is not empty? To be exact here is some code for this second case
private void addMainFragment() {
FragmentManager fm=getSupportFragmentManager();
FragmentTransaction transaction = fm.beginTransaction();
Fragment removeFragment = fm.findFragmentByTag(getString(R.string.fragment_a));
if(null != removeFragment){
transaction.detach(removeFragment);
}
Fragment fragment = fm.findFragmentByTag(getString(R.string.fragment_b));
if(null != fragment){
transaction.attach(fragment);
}else{
fragment=MainFragment.newInstance(null,null);
transaction.
add(R.id.fragment_container,fragment,getString(R.string.fragment_b));
}
transaction.commit();
}
savedInstanceState is the best place to save information like current postion, selected items etc.
View pagers have an offscreen page limit that handles how many pages (in this case fragments) are kept idle either side of the current visible page. If the page is outside this limit the pages are destroyed. This is to keep memory usage lower. This setting defaults to 1. So when a fragment goes out side this limit and then comes back its savedInstanceState will be non-null.
To answer your second question. Im not quite sure what you mean by navigate away from the activity. If you navigate away from the activity (e.g press the back / home button) then come back. The activities savedInstanceState will be null.
If you start another activity on top of the current then onSavedInstance will be called.
Here is a snippet of code I use in one of my projects for restoring a fragments state in a viewpager.
You can override onSaveInstanceState to save some information about the fragment.
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
// restore state
mListState = mLayoutManager.onSaveInstanceState();
state.putParcelable("list_state", mListState);
}
Then in the fragments onCreateView you can restore the state of the recycelerview
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
...
if (savedInstanceState != null) {
// save list state
mListState = state.getParcelable("list_state");
mLayoutManager.onRestoreInstanceState(mListState);
}
return root;
}
My viewpager is set with offscreenpagelimit 1 (default)
When i scroll my viewpager to the right, oncreateview is called on the fragment with the current position +1 to prepare the next fragment.
But when i swipe to the 3rd fragment and go back to the second, the first fragment's oncreateview is not called.
Why is the viewpager behaving like this and how can i preload previous fragments
if they were removed from memory?
The viewPager behaves like this because the fragmentStatePagerAdapter is saving its views. On the first run, you will alyways see the onCreateView() is called for the n+1 fragment. But if you have swiped over all the Fragments, their views are already in the FragmentStatePagerAdapter.
Of course, is could happen that the PagerAdapter will destroy some views(and the Fragment) because of memmory management reasons.
Lets assume this happens: the fragment X gets destroyed.
So if you swipe over you fragments, and you are on fragment Y. fragment X is in your offscreenpagelimit.
The FragmentStatePagerAdapter will notice that there is no fragment availible and will recreate it. In this case, the onCreateView() will be called again.
If you want to preload the state, which was before the Fragment got destroyed, then you need to use the callback onSaveInstanceState().
Here is an example:
to save the state of the Fragment:
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
Log.v(TAG, "In frag's on save instance state ");
outState.putSerializable("starttime", startTime); //saves the object variable
}
to restore the state:
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
Log.v(TAG, "In frag's on create view");
View view = inflater.inflate(R.layout.fragment_data_entry, container,
false);
timeTV = (TextView) view.findViewById(R.id.time_tv);
if ((savedInstanceState != null)
&& (savedInstanceState.getSerializable("starttime") != null)) {
startTime = (Calendar) savedInstanceState
.getSerializable("starttime");
}
return view;
}
This code is taken from here. You get more information about this on this site.
I have a problem reloading an activity with tabs and fragments when I change the orientation of my device.
Here's the situation:
I have an activity which has 3 tabs in the action bar. Each tab loads a different fragment in a FrameLayout in main view. Everything works fine if I don't change the orientation of the device. But when I do that Android tries to initialize the currently selected fragment twice which produce the following error:
E/AndroidRuntime(2022): Caused by: android.view.InflateException: Binary XML file line #39: Error inflating class fragment
Here's the sequence of steps that produce the error:
I load the activity, select tab nr 2. and change the orientation of the device.
Android destroys the activity and the instance of the fragment loaded by tab nr 2 (from now on, 'Fragment 2'). Then it proceeds to create new instances of the activity and the fragment.
Inside Activity.onCreate() I add the first tab to the action bar. When I do that, this tab gets automatically selected. It may represent a problem in the future, but I don't mind about that now. onTabSelected gets called and a new instance of the first fragment is created and loaded (see code below).
I add all the other tabs without any event being triggered, which is fine.
I call ActionBar.selectTab(myTab) to select Tab nr 2.
onTabUnselected() gets called for the first tab, and then onTabSelected() for the second tab. This sequence replaces the current fragment for an instance of Fragment 2 (see code below).
Next, Fragment.onCreateView() is called on Fragment 2 instance and the fragment layout gets inflated.
Here is the problem. Android Calls onCreate() and then onCreateView() on the fragment instance ONCE AGAIN, which produces the exception when I try to inflate (a second time) the layout.
Obviously the problem is Android is initializing the fragment twice, but I don't know why.
I tried NOT selecting the second tab when I reaload the activity but the second fragment gets initialized anyway and it is not shown (since I didn't select its tab).
I found this question: Android Fragments recreated on orientation change
The user asks basically the same I do, but I don't like the chosen answer (it's only a workaroud). There must be some way to get this working without the android:configChanges trick.
In case it's not clear, what I want to know how whether to prevent the recreation of the fragment or to avoid the double initialization of it. It would be nice to know why is this happening also. :P
Here is the relevant code:
public class MyActivity extends Activity implements ActionBar.TabListener {
private static final String TAG_FRAGMENT_1 = "frag1";
private static final String TAG_FRAGMENT_2 = "frag2";
private static final String TAG_FRAGMENT_3 = "frag3";
Fragment frag1;
Fragment frag2;
Fragment frag3;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// my_layout contains a FragmentLayout inside
setContentView(R.layout.my_layout);
// Get a reference to the fragments created automatically by Android
// when reloading the activity
FragmentManager fm = getFragmentManager();
this.frag1 = fm.findFragmentByTag(MyActivity.TAG_FRAGMENT_1);
this.frag2 = fm.findFragmentByTag(MyActivity.TAG_FRAGMENT_2);
this.frag3 = fm.findFragmentByTag(MyActivity.TAG_FRAGMENT_3)
ActionBar actionBar = getActionBar();
// snip...
// This triggers onTabSelected for the first tab
actionBar.addTab(actionBar.newTab()
.setText("Tab1").setTabListener(this)
.setTag(MyActivity.TAG_FRAGMENT_1));
actionBar.addTab(actionBar.newTab()
.setText("Tab2").setTabListener(this)
.setTag(MyActivity.TAG_FRAGMENT_2));
actionBar.addTab(actionBar.newTab()
.setText("Tab3").setTabListener(this)
.setTag(MyActivity.TAG_FRAGMENT_3));
Tab t = null;
// here I get a reference to the tab that must be selected
// snip...
// This triggers onTabUnselected/onTabSelected
ab.selectTab(t);
}
#Override
protected void onDestroy() {
// Not sure if this is necessary
this.frag1 = null;
this.frag2 = null;
this.frag3 = null;
super.onDestroy();
}
#Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
Fragment curFrag = getFragmentInstanceForTag(tab.getTag().toString());
if (curFrag == null) {
curFrag = createFragmentInstanceForTag(tab.getTag().toString());
if(curFrag == null) {
// snip...
return;
}
}
ft.replace(R.id.fragment_container, curFrag, tab.getTag().toString());
}
#Override
public void onTabUnselected(Tab tab, FragmentTransaction ft)
{
Fragment curFrag = getFragmentInstanceForTag(tab.getTag().toString());
if (curFrag == null) {
// snip...
return;
}
ft.remove(curFrag);
}
private Fragment getFragmentInstanceForTag(String tag)
{
// Returns this.frag1, this.frag2 or this.frag3
// depending on which tag was passed as parameter
}
private Fragment createFragmentInstanceForTag(String tag)
{
// Returns a new instance of the fragment requested by tag
// and assigns it to this.frag1, this.frag2 or this.frag3
}
}
The code for the Fragment is irrelevant, it just returns an inflated view on onCreateView() method override.
I got a simple answer for that:
Just add setRetainInstance(true); to the Fragment's onAttach(Activity activity) or onActivityCreated(Bundle savedInstanceState).
These two are call-backs in the Fragment Class.
So basically, what setRetainInstance(true) does is:
It maintains the state of your fragment as it is, when it goes through:
onPause();
onStop();
It maintains the instance of the Fragment no matter what the Activity goes through.
The problem with it could be, if there are too many Fragments, it may put a strain on the System.
Hope it helps.
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
setRetainInstance(true);
}
Open for Correction as always. Regards, Edward Quixote.
It seems that, when the screen is rotated and the app restarted, it is recreating each Fragment by calling the default constructor for the Fragment's class.
I have encountered the same issue and used the following workaround:
in the fragment's onCreateView begining of:
if (mView != null) {
// Log.w(TAG, "Fragment initialized again");
((ViewGroup) mView.getParent()).removeView(mView);
return mView;
}
// normal onCreateView
mView = inflater.inflate(R.layout...)
I think this is a fool proof way to avoid re-inflating of the root view of the fragment:
private WeakReference<View> mRootView;
private LayoutInflater mInflater;
/**
* inflate the fragment layout , or use a previous one if already stored <br/>
* WARNING: do not use in any function other than onCreateView
* */
private View inflateRootView() {
View rootView = mRootView == null ? null : mRootView.get();
if (rootView != null) {
final ViewParent parent = rootView.getParent();
if (parent != null && parent instanceof ViewGroup)
((ViewGroup) parent).removeView(rootView);
return rootView;
}
rootView = mFadingHelper.createView(mInflater);
mRootView = new WeakReference<View>(rootView);
return rootView;
}
#Override
public View onCreateView(final LayoutInflater inflater, final ViewGroup container, final Bundle savedInstanceState) {
mInflater=inflater!=null?inflater:LayoutInflater.from(getActivity());
final View view = inflateRootView();
... //update your data on the views if needed
}
add
android:configChanges="orientation|screenSize"
in the manifest file
To protect activity recreate try to add configChanges in your Activity tag (in manifest), like:
android:configChanges="keyboardHidden|orientation|screenSize"
My code was a little different, but I believe our problem is the same.
In the onTabSelected I didn't use replace, I use add when is the first time creating the fragment and attach if isn't. In the onTabUnselected I use detach.
The problem is that when the view is destroyed, my Fragment was attached to the FragmentManager and never destroyed. To solve that I implemented on the onSaveInstanceBundle to detach the fragment from the FragmentManager.
The code was something like that:
FragmentTransition ft = getSupportFragmentManager().begin();
ft.detach(myFragment);
ft.commit();
In the first try I put that code in the onDestroy, but I get a exception telling me that I couldn't do it after the onSaveInstanceBundle, so I moved the code to the onSaveInstanceBundle and everything worked.
Sorry but the place where I work don't allow me to put the code here on StackOverflow. This is what I remember from the code. Feel free to edit the answer to add the code.
I think you are facing what I faced. I had a thread downloader for json which starts in onCreate() , each time I changed the orientation the thread is called and download is fired. I fixed this using onSaveInstance() and onRestoreInstance() to pass the json response in a list, in combination of checking if the list is not empty, so the extra download is not needed.
I hope this gives you a hint.
I solved this problem by using below code.
private void loadFragment(){
LogUtil.l(TAG,"loadFragment",true);
fm = getSupportFragmentManager();
Fragment hf = fm.findFragmentByTag("HOME");
Fragment sf = fm.findFragmentByTag("SETTING");
if(hf==null) {
homeFragment = getHomeFragment();// new HomeFragment();
settingsFragment = getSettingsFragment();// new Fragment();
fm.beginTransaction().add(R.id.fm_place, settingsFragment, "SETTING").hide(settingsFragment).commit();
fm.beginTransaction().add(R.id.fm_place, homeFragment, "HOME").commit();
activeFragment = homeFragment;
}else{
homeFragment = hf;
settingsFragment = sf;
activeFragment = sf;
}
}
Initiate this method in OnCreate();
Can I use savedInstanceState() to save the state when removing a fragment, then restore the state when I pop the fragment off the back stack? When I restore the fragment from the back stack, savedInstanceState bundle is always null.
Right now, the app flow is: fragment created -> fragment removed (added to back stack) -> fragment restored from back stack (savedInstanceState bundle is null).
Here is the relevant code:
public void onActivityCreated(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
Bundle bundle = getArguments();
Long playlistId = bundle.getLong(Constants.PLAYLIST_ID);
int playlistItemId = bundle.getInt(Constants.PLAYLISTITEM_ID);
if (savedInstanceState == null) {
selectedVideoNumber = playlistItemId;
} else {
selectedVideoNumber = savedInstanceState.getInt("SELECTED_VIDEO");
}
}
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt(Constants.SELECTED_VIDEO, selectedVideoNumber);
}
I think the problem is that onSavedInstanceState() is never called when being removed and being added to back stack. If I cant use onsavedInstanceState(), is there another way to fix this?
onSaveInstanceState is (unfortunately) not called in normal back-stack re-creation of a fragment. Check out http://developer.android.com/guide/components/fragments.html#Creating and the answer on How can I maintain fragment state when added to the back stack?
I like to store the View I return in onCreateView as a global variable and then when I return I simply check this:
if(mBaseView != null) {
// Remove the view from the parent
((ViewGroup)mBaseView.getParent()).removeView(mBaseView);
// Return it
return mBaseView;
}
The problem is that the fragment needs to have an Id or Tag associated with it in order for the FragmentManager to keep track of it.
There are at least 3 ways to do this:
In xml layout declare an Id for your fragment:
android:id=#+id/<Id>
If your fragments container View has an Id, use FragmentTransaction:
FragmentTransaction add (int containerViewId, Fragment fragment)
If your fragment is not associated with any View (e.g. headless fragment), give it a Tag:
FragmentTransaction add (Fragment fragment, String tag)
Also, see this SO answer.
FWIW, I hit this as well, but in my case onSaveInstanceState was called properly and I pushed in my state data when a new activity fragment was brought up on the smartphone. Same as you, the onActivityCreated was called w/ savedInstanceState always null. IMHO, I think it's a bug.
I worked around it by creating a static MyApplication state and putting the data there for the equivalent of "global variables"...