Develop Reference

Viewpager fragment reference to new copy after activity restore

When my activity containing viewpager is killed by system in background and then restores its state, fragments are correctly created and viewpager adapter can also point to them correctly.
But when I get a fragment reference and try to access its fields, they are all null (checked by using breakpoint).
I checked this by placing breakpoints in fragment onCreateView() and in my activity button's clickListener.
((WelcomeFragment)homeActivityFragmentPageAdapter.getItem(POSITION_HOME)).setdata(myData);
Now this method will through null pointer exception since setdata(data) is internally accessing arraylist field of fragment.
This creates a problem for me since, my activity has to continuously feed network data to the fragment by calling its public method (as suggested by documentation).
How to insure that after state restored; correct instance is pointed in my activity.

Try to use instantiateItem adapter method instead getItem.
((WelcomeFragment)homeActivityFragmentPageAdapter.instantiateItem(mViewPager, POSITION_HOME)).setdata(myData);
Method getItem is overrided method, and common use is creation of child fragments.
EDIT:
In case of the question's scenario, you also need to store the state of FragmentStatePagerAdapter manually:
#Override
public void onSaveInstanceState(Bundle savedInstanceState) {
savedInstanceState
.putParcelable("pages",homeActivityFragmentPageAdapter.saveState());
super.onSaveInstanceState(savedInstanceState);
}
Then you can retrieve the state in oncreate:
#Override
protected void onCreate(final Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (savedInstanceState != null) {
homeActivityFragmentPageAdapter.restoreState(savedInstanceState.getParcelable("pages"),this.getClassLoader());
welcomeFragment = (WelcomeFragment) homeActivityFragmentPageAdapter.instantiateItem(mViewPager, POSITION_HOME);
}
else { //simply create a new instance here}
homeActivityFragmentPageAdapter.addFragmentToAdapter(welcomeFragment);
homeActivityFragmentPageAdapter.notifyDataSetChanged();
}

Android: on screen rotation what should Fragment's onCreate() and onCreateView() do

In my activity I have a check for savedInstanceState, making sure I am not creating multiple fragments
But my question is should I have similar checks in Fragment's onCreate() and onCreateView()
Because when I rotate screen Fragment's onCreate() and onCreateView() are called everytime.
Question is, Is it OK for these 2 methods to re-do there job after everyscreen rotation or they should have a savedInstanceState check as well.
Right now my onCreate() makes a service call and onCreateView inflates a view (Recyclerview)

When an activity or Fragment is recreated, the onCreate() method is first fired, followed by the onRestoreInstanceState() method, which enables you to retrieve the state that you savedpreviously in the onSaveInstanceState() method through the Bundle object in its argument:
# Override
public void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
//---retrieve the information persisted earlier---
String ID = savedInstanceState.getString(“ID”);
}

When is fragment finally attached to activity?

I have a main fragment with a viewpager inside it. This viewpager has 2 pages (list fragments). When I start the activty, the main fragment is shown and I also show the first paged fragment. This paged fragment displays data from a db using AsyncTask.
In the main fragment I have:
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
onPageSelected(0);
}
#Override
public void onPageSelected(int position) {
Fragment fragment = (Fragment) pagerAdapter.instantiateItem(viewPager, position);
if (fragment instanceof IPagedFragment) {
((IPagedFragment) fragment).onShown(getActivity());
}
}
And the interface is:
public interface IPagedFragment {
void onShown(FragmentActivity activity);
}
The first issue I have is that I have to pass the activity as a parameter because when onShown gets called, the activity is still null.
Furthermore, the paged fragments use progressbar logic similar to the LoginActivity sample. I also get the following exception:
IllegalStateException: Fragment PagedFragment1{4201f758} not attached to Activity
at android.support.v4.app.Fragment.getResources(Fragment.java:620)
So what is the correct stage to start retrieving data from db once the paged fragment is fully available to the UI?

Issues like yours is the reason some developers are starting to question if fragments are really that good or useful.
Also "the correct" is debatable as you can do it in a variety of places and different developers will give you different answers, But let me try to supply you some useful info.
The attach/detach callbacks:
public void onAttach(Activity activity);
public void onDetach();
between those two methods any call to getActivity() will return the non-null activity the fragments is connected to. You can override them and use a private boolean isAttached to keep track of that call.
Also useful is the:
public void onActivityCreated (Bundle savedInstanceState)
this method is called AFTER the Activity.onCreate method. That is very important if you rely on some initialisation that happened there.
Also it's important to remember that on the moment the fragment transaction happens, the Fragment.onCreate happens after the Activity.onCreate and during rotation it happens before it.
As a general rule of thumb I use the Fragment.onStart() / Fragment.onStop() for getting/listening to data. On those calls, all the UI have been created, the fragment is attached to the activity and those callbacks don't get called if there's a dialog/popup (pause/resume does)

From the documentation:
public void onActivityCreated (Bundle savedInstanceState)
[...] tells the fragment when it is fully associated with the new activity instance.
source: http://developer.android.com/reference/android/app/Fragment.html#onActivityCreated(android.os.Bundle)

To get the reference of your activity, create a local object of fragmentActivity and get your activity reference as shown below.
private FragmentActivity fragmentActivity;
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
fragmentActivity=activity;
}

How to save custom Objects onSaveInstanceState without implementing parcelable

i need to save a custom object that i use in a fragment so it will not be lost when the screen rotates (when the app calls onDestroy and then recalls onCreate)
now the normal way to do so is to implement Parcelable interface and save it to the bundle as a Parcelable object.
that is a very tedious way of doing things.
is there a way to just pass the object along as "putObject" method?

You can save your data in fragment, retained during a configuration change like in example.
Extend the Fragment class and declare references to your stateful
objects.
public class RetainedFragment extends Fragment {
// data object we want to retain
private MyDataObject data;
// this method is only called once for this fragment
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// retain this fragment
setRetainInstance(true);
}
.. getter and setter
}
Then use FragmentManager to add the fragment to the activity.
public class MyActivity extends Activity {
private RetainedFragment dataFragment;
#Override
public void onCreate(Bundle savedInstanceState) {
..
// find the retained fragment on activity restarts
FragmentManager fm = getFragmentManager();
dataFragment = (RetainedFragment) fm.findFragmentByTag(“data”);
// create the fragment and data the first time
if (dataFragment == null) {
// add the fragment
dataFragment = new DataFragment();
fm.beginTransaction().add(dataFragment, “data”).commit();
} else {
// available dataFragment.getData()
..
// save data in onDestroy dataFragment.setData(yourData);

The best way is to implement Parcelable (Faster).
Easier (not efficient) way is to implement Serializable and add the object into the bundle as serializable.

well searching i found no official way of doing so, so here are two "hacks" i found around the problem:
1)create a class that extends Application class, in it add an arrayList of objects.
inside onSaveInstanceState call:
getApplication().getObjectArray().add(YourObject);
save the Object index inside the bundle using putInt.
extract it inside the method onReturnestoreInstanceState.
2)my less favorite one:
android automatically saves the states of its views
therefor a way to save an object will be to create a view set its visibility to none so it wont show on the screen and then add each object we want to the view using the methods:
view.setTag(key,Object); or view.setTag(Object);
now inside onReturnestoreInstanceState get the view and extract the tags.
unfortunately i couldn't find a more simple way of saving an object
hope this one helps you out (in my app i ended up using the first method)

SavedInstanceState is always null in fragment

I have a fragment attached to the activity using XML (and setContentView() in activity). A have a problem because I have very dynamic views in my fragment, so when orientation changes
I must restore all states of views.
I have problem because I'm using something like that:
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putBoolean("restore", true);
outState.putInt("nAndroids", 2);
}
But after orientation change when methods with param Bundle savedInstanceState are called (like onCreateView etc) my savedInstanceState is always null.
I'm not a noob in the Android but now I'm very angry because of this problem...
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
if (savedInstanceState == null) {
//smth
} else {
// smthelse THIS IS NEVER REACHED BECAUSE BUNDLE IS ALWAYS NULL
}
getListView().setDivider(getResources().getDrawable(R.drawable.list_divider));
}

All the problem was in that I don't declare android:id for the fragment in XML. Android needs ID or TAG to recognize stored fragment and reproduce all elements in it. So guys, remember - every instance of fragment needs unique id or tag!
Also, when setRetainInstance(true) is declared then bundle should always return null.

I had a similar problem where I was always getting savedInstanceState as null inspite of supplying the bundle to the Fragment.
The only solution that worked for me was to do
myFragment.setArguments(bundle)
with my bundle from the Activity and do a
Bundle bundle = this.getArguments();
in onCreateView of the fragment.
Hope this helps someone else.

For Fragment :-
use this for save state of fragment on orientation.
onCreate(Bundle save)
{
super.onCreate(save);
setRetainInstance(true);
}
See this tutorial :-
http://techbandhu.wordpress.com/2013/07/02/android-headless-fragment/
For Activity:-
When you start your application, in onCreate, your bundle object is null, so you have to put a check like below and when you rotate your screen then onSaveInstance is called and your bundle object is initialized
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_game);
if (savedInstanceState != null) {
boolean t = outState.getBoolean("restore");
int s = outState.getInt("nAndroids");
}
}

First you should put your data, then call super.onSaveInstanceState(outState);
public void onSaveInstanceState(Bundle outState) {
outState.putBoolean("restore", true);
outState.putInt("nAndroids", 2);
super.onSaveInstanceState(outState);
}
And be sure that activity has not nohistory property in AndroidManifest.xml or set it to false.
<activity
android:noHistory="false">

If you are trying to use outState to save the state and destroy the fragment by navigating to another fragment, it will not work, you have in this case to save your state permanently in either sharedPreferences or if it's big and you want to be more organized you can use any persistence lib like Room, Realm, ...etc.
When should use outState and savedInstanceState only to make Fargment/Activity survive config change(rotation for example) or processes being killed by the OS when the app is in background for example.

Ok I know this is an old post but I couldn't find the right answer for me here nor many other places, so I am posting how I fixed my case.
So My Fragment is inside an Activity. And I originally tried to save Bundle only in Fragment and retrieve it at onCreateView. However that was the problem.
I fixed this by initiating myFragment object in activity and put that object to activity Bundle at onSaveInstanceState(). Then retrieved it at onRestoreInstanceState(). I used getSupportFragmentManager().putFragment/getFragment. Then the savedInstanceState in fragment was no longer null.