Develop Reference

Automatic UI configuration change handling in Activity and Fragment sometimes fails

I have written android app now for a long time but now I'm facing a problem that I have never thought about. It is about the android lifecycle of Activitys and Fragments in in relation to configuration changes. For this I have create a small application with this necessary code:
public class MainActivity extends FragmentActivity {
private final String TAG = "TestFragment";
private TestFragment fragment;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
FragmentManager fm = getSupportFragmentManager();
fragment = (TestFragment) fm.findFragmentByTag(TAG);
if (fragment == null) {
fragment = new TestFragment();
fm.beginTransaction().add(R.id.fragment_container, fragment, TAG).commit();
}
}
}
And here is my code for the TestFragment. Note that I'm calling setRetainInstance(true); in the onCreate method so the fragment is not recrated after a configuration change.
public class TestFragment extends Fragment implements View.OnClickListener {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setRetainInstance(true);
}
#Override
public View onCreateView(LayoutInflater li, ViewGroup parent, Bundle bundle) {
View rootView = li.inflate(R.layout.fragment_test, parent, false);
Button button = (Button) rootView.findViewById(R.id.toggleButton);
button.setOnClickListener(this);
return rootView;
}
#Override
public void onClick(View v) {
Button button = (Button) v;
String enable = getString(R.string.enable);
if(button.getText().toString().equals(enable)) {
button.setText(getString(R.string.disable));
} else {
button.setText(enable);
}
}
}
And here is the layout that my fragment is using:
<LinearLayout
...>
<EditText
android:id="#+id/editText"
android:layout_width="match_parent"
android:layout_height="wrap_content" />
<Button
android:id="#+id/toggleButton"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="#string/enable"/>
</LinearLayout>
My problem is that if I rotate the device the text of the Button change back to the default value. Of course the View of the Fragment is new created and inflated but the saved instance for the Views should be restored. I also have an EditText in my layout and there the text and other properties remains after the rotation. So why is the Button not restore from the Bundle by default? I have read on the developer site:
By default, the system uses the Bundle instance state to save information about each View object in your activity layout (such as the text value entered into an EditText object). So, if your activity instance is destroyed and recreated, the state of the layout is restored to its previous state with no code required by you.
I've also read a lot of answers the last days but I do not know how actual they are anymore. Please do not leave a comment or an answer with android:configChanges=... this is very bad practice. I hope someone can bring light into my lack of understanding.

You should save state of your fragment in the onSaveInstanceState(Bundle outState) and restore it in the onViewCreated(View view, Bundle savedState) method. This way you will end up with the UI just as it was before configuration change.

TextView subclasses don't save their text by default. You need to enable freezesText="true" in the layout, or setFreezesText(true) at runtime for it to save its state.

As per documentation, views should maintain their state without using setRetainInstance(true). Try to remove it from your onCreate, this should force the fragment to be recreated on screen rotation, hence all of it's views should be saved before rotation and restored after.

This stack overflow should answer your question:
setRetainInstance not retaining the instance
setRetainInstance does tell the fragment to save all of its data, and for ui elements where the user has manipulated the state (EditText, ScrollView, ListView, etc) the state gets restored. That being said, normal read-only UI components get reinflated from scratch in onCreateView and have to be set again - my guess would be that their properties are not considered "data" that needs to be retained and restored - Google probably does this for performance reasons. So things like a normal Button, ImageView, or TextView need their contents set manually when they are reinflated if it differs from the initial state in the XML. (TextView's android:freezesText basically puts the TextView in a mode that uses an implementation to save it's state and restore it).
PS: According to this stack overflow Save and restore a ButtonText when screen orientation is switched, you may be able to set android:freezesText on the button to have it keep the text you set - I haven't tried it, but it makes sense.

Edit after Op feedback
Although this fails to answer the question, after consultation with the OP, I've decided to leave it here as a reference point of information on the topic for people who land here. Hope you find it helpful.
Try putting your setRetainInstance in onCreateView. See here
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// setRetainInstance(true);
}
#Override
public View onCreateView(LayoutInflater li, ViewGroup parent, Bundle bundle) {
setRetainInstance(true);
View rootView = li.inflate(R.layout.fragment_test, parent, false);
Button button = (Button) rootView.findViewById(R.id.toggleButton);
button.setOnClickListener(this);
return rootView;
}
Called when the fragment's activity has been created and this
fragment's view hierarchy instantiated. It can be used to do final
initialization once these pieces are in place, such as retrieving
views or restoring state. It is also useful for fragments that use
setRetainInstance(boolean) to retain their instance, as this
callback tells the fragment when it is fully associated with the new
activity instance. This is called after onCreateView(LayoutInflater,
ViewGroup, Bundle) and before onViewStateRestored(Bundle).
developer.android.com/reference/android/app/Fragment.html#onActivityCreated
Control whether a fragment instance is retained across Activity
re-creation (such as from a configuration change). This can only be
used with fragments not in the back stack. If set, the fragment
lifecycle will be slightly different when an activity is recreated:
onDestroy() will not be called (but onDetach() still will be, because
the fragment is being detached from its current activity).
onCreate(Bundle) will not be called since the fragment is not being
re-created.
onAttach(Activity) and onActivityCreated(Bundle) will
still be called.
developer.android.com/reference/android/app/Fragment.html#setRetainInstance
And taken from here:
onCreate : It is called on initial creation of the fragment. You do
your non graphical initializations here. It finishes even before the
layout is inflated and the fragment is visible.
onCreateView : It is called to inflate the layout of the fragment i.e
graphical initialization usually takes place here. It is always called
sometimes after the onCreate method.
onActivityCreated : If your view is static, then moving any code to
the onActivityCreated method is not necessary. But when you - for
instance, fill some lists from the adapter, then you should do it in
the onActivityCreated method as well as restoring the view state when
setRetainInstance used to do so. Also accessing the view hierarchy of
the parent activity must be done in the onActivityCreated, not sooner.
Let me know if this helps.

Activity recreates Fragments on Orientation Change because reference is lost, how to avoid that?

I'm trying to learn Android Fragments and I have a very specific problem concerning Fragment management, because screen orientation screws up my implementation.
EDIT: Already solved my problem, see the "Update" below.
Short version:
Using static Fragments, if I change screen orientation, the reference to R.id.fragment is lost and the Activity re-creates the Fragment causing problems because another Fragment is still present on the Layout (because they're defined on the XML maybe).
Context:
I have a Master/Detail workflow using the default Eclipse template and I have a different type of Fragment for every tab on the ItemList. Ideally, what I want to do is switch between fragments, but I want to retain their current state without using the BackStack, since I want to navigate with the ItemList, and using the Back button to close the App.
I couldn't find any solutions for this specific problem and I tried with a lot of different approaches. Right now I'm using static fragments defined in the main Layout:
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="#+id/item_detail_container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".ItemDetailActivity"
tools:ignore="MergeRootFrame" >
<fragment android:name="com.example.pintproject.DevicesFragment"
android:id="#+id/devices"
android:layout_weight="1"
android:layout_width="0dp"
android:layout_height="match_parent"
/>
<fragment android:name="com.example.pintproject.ItemDetailFragment"
android:id="#+id/detail"
android:layout_weight="1"
android:layout_width="0dp"
android:layout_height="match_parent"
/>
</FrameLayout>
In the ItemListActivity onCreate(), I look for the Fragments in the layout, and add them if they aren't created yet, and I hold a reference to the current active Detail Fragment so I can hide it / show the fragment I switch to.
I'm using hide/show instead of replace because replace destroys the Fragment:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_item_list);
if (findViewById(R.id.item_detail_container) != null) {
// The detail container view will be present only in the
// large-screen layouts (res/values-large and
// res/values-sw600dp). If this view is present, then the
// activity should be in two-pane mode.
mTwoPane = true;
// In two-pane mode, list items should be given the
// 'activated' state when touched.
((ItemListFragment) getSupportFragmentManager().findFragmentById(
R.id.item_list)).setActivateOnItemClick(true);
}
df = (DevicesFragment) getSupportFragmentManager().findFragmentById(R.id.devices);
if (df==null){
df = new DevicesFragment();
getSupportFragmentManager().beginTransaction().add(R.id.item_detail_container,df).commit();
getSupportFragmentManager().beginTransaction().hide(df).commit();
}
idf = (ItemDetailFragment) getSupportFragmentManager().findFragmentById(R.id.detail);
if (idf==null){
idf = new ItemDetailFragment();
getSupportFragmentManager().beginTransaction().add(R.id.item_detail_container,idf).commit();
getSupportFragmentManager().beginTransaction().hide(idf).commit();
}
mContent = df;
#Override
public void onItemSelected(String id) {
if (mTwoPane) {
// In two-pane mode, show the detail view in this activity by
// adding or replacing the detail fragment using a
// fragment transaction.
switch (Integer.valueOf(id)){
case 1:{
if (idf!=null){
getSupportFragmentManager().beginTransaction().hide(mContent).commit();
getSupportFragmentManager().beginTransaction().show(idf).commit();
mContent = idf;
}
}break;
case 2:{
if (df!=null){
getSupportFragmentManager().beginTransaction().hide(mContent).commit();
getSupportFragmentManager().beginTransaction().show(df).commit();
mContent = df;
}
}break;
}
} else {
// In single-pane mode, simply start the detail activity
// for the selected item ID.
Intent detailIntent = new Intent(this, ItemDetailActivity.class);
detailIntent.putExtra(ItemDetailFragment.ARG_ITEM_ID, id);
startActivity(detailIntent);
}
}
Problem:
With this approach, the Fragments hide/show without any problems and hold the status, but if I make an Orientation Change, they are destroyed and recreated again.
I know they are destroyed because I'm not using setRetainInstance(), but the problem is when I change orientation, the Activity loses the reference to the Fragment, and
df = (DevicesFragment) getSupportFragmentManager().findFragmentById(R.id.devices);
is null, so the program creates another Fragment. If I change the orientation again, not only the program re-creates two new Fragments, but two more Fragments are somehow added to the layout and they aren't even hidden, they are shown one above another.
If I use setRetainInstance(), the Fragment holds the state when Orientation is changed, but still, the activity reference to the Fragment is null, and creates a new Fragment above the existing one, having two of each Fragment.
Example:
I create Fragment A and Fragment B in Landscape orientation. Both work fine and I can switch between them.
I change orientation to Portrait, Fragment A and Fragment B are destroyed and a new Fragment A' and Fragment B' are created, still, they work fine.
I change orientation again to Landscape, Fragment A' and Fragment B' are destroyed, a new Fragment A'' and Fragment B'' are created, but the screen shows another Fragment A and Fragment B, both at the same time (one above another, let's call them residual), and these new A'' and B'' work fine but are shown above residual A and B.
From this point on, every time I change orientation, 2 new Fragments are added to the previous ones, but they don't even hold the previous state.
I hope the example is clear enough. I think the problem is the Activity not holding view references when the orientation is changed, creates them again and I don't really know how to work around that.
UPDATE:
I solved my problem by using findFragmentByTag instead of findFragmentById. Since I can now retrieve Fragment s already created, I have to add them to the container adding a specific tag to search for.
So my test code looks like this:
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_item_list);
if (findViewById(R.id.item_detail_container) != null) {
// The detail container view will be present only in the
// large-screen layouts (res/values-large and
// res/values-sw600dp). If this view is present, then the
// activity should be in two-pane mode.
mTwoPane = true;
// In two-pane mode, list items should be given the
// 'activated' state when touched.
((ItemListFragment) getSupportFragmentManager().findFragmentById(
R.id.item_list)).setActivateOnItemClick(true);
}
df = (DevicesFragment) getSupportFragmentManager().findFragmentByTag("df");
idf = (ItemDetailFragment) getSupportFragmentManager().findFragmentByTag("idf");
if (savedInstanceState==null){
if (df==null){
df = new DevicesFragment();
getSupportFragmentManager().beginTransaction().add(R.id.item_detail_container,df, "df").commit();
getSupportFragmentManager().beginTransaction().hide(df).commit();
}
if (idf==null){
idf = new ItemDetailFragment();
getSupportFragmentManager().beginTransaction().add(R.id.item_detail_container,idf,"idf").commit();
getSupportFragmentManager().beginTransaction().hide(idf).commit();
}
} else {
Log.i("OUT","INSTANCE NOT NULL");
}
mContent = df;
}
This is fully functional, also have to setRetainInstance(true) for every Fragment and they hold their current state no matter how many times we change the orientation.

You must never hold a reference to the fragment. Instead. Whenever you need something from it, retrieve the reference for a short moment.
public ItemListFragment getItemListFragment() {
return ((ItemListFragment) getSupportFragmentManager().findFragmentById(
R.id.item_list));
}
Then, whenever you need to get data from it, use
final ItemListFragment listFragment = getItemListFragment();
if (listFragment != null) {
// do something
}
And avoid calling setters. You can define the setters, but it's a better practice to either pass an arguments when creating a Fragment or retrieve the data by getActivity() from the Fragment itself, as described below.
This is done because the Fragment lifecycle not always matches the Activity one.
If you ever have to call setter from Activity, don't forget to save the value in Fragment's onSaveInstanceState(), if needed.
So instead of calling
setActivateOnItemClick(true);
From Activity, do it from the Fragment.
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
final YourActivity activity = (Activtity) getYourActivity();
setActivateOnItemClick(activity.isMultiPane());
}
This way when the Fragment is re-created after Activity onCreate() (only in which you handle the value setting), it will has always access to the value
And define isMultiPane method from Activity, of course
public boolean isMultiPane() {
return mTwoPane;
}

Since there are no answer yet, here is my opinion :
When your orientation changes, your fragment is being recreated and you loose your data, right ? I think this is exactly whete the "savedInstanceState" is made for :
Caution: Your activity will be destroyed and recreated each time the user rotates the screen. When the screen changes orientation, the system destroys and recreates the foreground activity because the screen configuration has changed and your activity might need to load alternative resources (such as the layout).
Here is a link that can explain you how to handle that recreation
Hope this is useful to you ! =)

Fragment switching views being reused?

I have an Activity with a FrameLayout and need to show different fragments based on user input.
The code I use for showing a fragment is this:
private void showFragment(Fragment fragment, Bundle args, boolean addToBackStack) {
if (args != null) {
fragment.setArguments(args);
}
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.setCustomAnimations(R.anim.activity_open_translate, R.anim.activity_close_scale);
fragmentTransaction.replace(R.id.main_frame, fragment);
if (addToBackStack) {
fragmentTransaction.addToBackStack(fragment.getClass().getName());
}
fragmentTransaction.commit();
}
This is called as :
if (contactPickFragment == null) {
contactPickFragment = new ContactPickFragment();
}
showFragment(contactPickFragment, args, true);
All this works fine. Now if the user goes into one fragment presses back and returns back to the same fragment, all my views inside stay the same. For example, I have an EditText inside the fragment and the user edits something inside. If the user comes back to the fragment, the same text persists. I do not want this to happen. How do I reset everything in the view?
I have added code within the Fragment's onCreateView() to clear the text, and from debugging I see that this is being called, but the text never gets cleared. What am I doing wrong here?

If you don't want the data from the previous instance to appear, simply create a new instance of ContactPickFragment each time you show it.
Clearing data in onCreateView() has no effect because view state is restored AFTER onCreateView(). Your Fragment has no view before onCreateView() and so Android cannot possibly apply the previous state any earlier. Values set on the views during onCreateView() will be overwritten by their previous values.

As a general answer, there is no way to "refresh" the view of a Fragment, other than replacing the fragment with another instance of itself (possibly initialized with the parameters that you want to refresh/update).

You can reuse your fragments and refresh the state of your views. You just can't do it from onCreateView as #antonyt correctly points out.
Instead, override onViewStateRestored and set up the state of your views the way you'd like from there.
Something like:
#Override
public void onViewStateRestored(Bundle savedInstanceState) {
super.onViewStateRestored(savedInstanceState);
View view = getView();
// Code to call view.findViewById to grab the views you want
// and set them to a specific state goes here
}
There are advantages to reusing fragments. Not the least of which is that if you have a memory leak with your fragment (which is easier than you may think to accomplish,) you will exacerbate the problem by creating myriads of them.

Save state of custom view inside Fragment

First, some background information. I have an Activity that hosts several Fragments; these are hidden and shown such that only one Fragment is visible at a time. Each Fragment hosts several custom Views that I call IncrementCounters. Those views display a number and increment that number by 1 when tapped.
Each of the Fragments has setRetainInstance(true) called on it when it is created in my Activity. When the Activity is created, I check to see if the Fragments exist; if they do, I store a reference to them; if not, I create a new instance, like this:
autonFragment = (AutonomousScoutingFragment) getFragmentManager()
.findFragmentByTag("auton");
teleopFragment = (TeleoperatedScoutingFragment) getFragmentManager()
.findFragmentByTag("teleop");
postMatchFragment = (PostMatchScoutingFragment) getFragmentManager()
.findFragmentByTag("post_match");
FragmentManager fm = getFragmentManager();
FragmentTransaction ft = fm.beginTransaction();
if (autonFragment == null) {
Log.d("onCreate", "autonFragment is null!");
autonFragment = new AutonomousScoutingFragment();
autonFragment.setRetainInstance(true);
ft.add(R.id.scouting_fragment_container, autonFragment, "auton")
.hide(autonFragment);
}
if (teleopFragment == null) {
Log.d("onCreate", "teleopFragment is null!");
teleopFragment = new TeleoperatedScoutingFragment();
teleopFragment.setRetainInstance(true);
ft.add(R.id.scouting_fragment_container, teleopFragment, "teleop")
.hide(teleopFragment);
}
if (postMatchFragment == null) {
Log.d("onCreate", "postMatchFragment is null!");
postMatchFragment = new PostMatchScoutingFragment();
postMatchFragment.setRetainInstance(true);
ft.add(R.id.scouting_fragment_container, postMatchFragment,
"post_match").hide(postMatchFragment);
}
ft.commit();
One problem I have is that after every orientation change, it seems as though the Fragments aren't actually being retained, as ever time I see debug prints stating that they are all null. This may be realted to my bigger problem; I'm not sure.
I am trying to figure out how to maintain the value of the number stored in each IncrementCounter across configuration changes, specifically rotation. I have overridden onSaveInstanceState() and onRestoreInstanceState() in IncrementCounter. When I rotate my device, I see that onSaveInstanceState() is called on all of the IncrementCounters I have in my Fragments. However, the corresponding onRestoreInstanceState() is never called, and my IncrementCounters do not have their states restored. What is the proper way to handle something like this? I've been banging my head against my desk for hours about this problem.

Since the Fragments have the setRetainInstance(true), they will not be destroyed on a rotation. The Activity will be destroyed, and the Fragments will be detached until a new Activity is created. However, the Fragments will go through the onCreateView() method again, so you would need to restore their IncrementCounters.
Also, you can save state in onSaveInstanceState(), and then restore it in onCreate(), onCreateView(), and several other methods that are all passed that same bundle as a parameter.

savedInstanceState when restoring fragment from back stack

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"...