I have one fragment where are three (default) images and when user click on them, they will change to another. But when i swipe to another fragment and back to fragment with images there are not default ones as on the start. When I swipe two times so I will pass to another fragment (distance from original with images is 2 fragments) images are resetted to default. I was trying to implement setOffscreenPageLimit() from ViewPager and set it to 1, but minimum "length" when views in fragments are resetted is 2. How can I change that images to default manually after swipe action? Thank you.
Edit: I think that issue why onResume() is not working here: Fragment onResume not called
but i dont know what that means :/ I have three classes FragmentController.class, PagerAdapter.class and class of specific fragment for example FirstFragment.class. I don't know how connect these classes together.
Check that you create the fragments in the getItem() method of the adapter and do not hold any reference to that fragments (only WeakReferences if necessary), otherwise the fragments could not be destroyed.
EDIT:
The first fragment is unloaded only when you are in the third one because setOffscreenPageLimit is at least 1 so a viewpager allways loads the fragments that are at both sides of the selected one.
What you could do is to update your adapter with this code to provide a getFragment(position) method:
private HashMap<Integer, WeakReference<Fragment>> fragmentReferences = new HashMap<>();
#Override
public Fragment getItem(int position) {
Fragment fragment;
switch (position) {
case 0:
fragment = FirstFragment.newInstance();
break;
// etc
}
fragmentReferences.put(position, new WeakReference<>(fragment));
return fragment;
}
public Fragment getFragment(int position) {
WeakReference<Fragment> ref = fragmentReferences.get(position);
return ref == null ? null : ref.get();
}
After then you can get the selected fragment and call the method you want from the first fragment when a page is selected:
viewPager.setOnPageChangeListener(new OnPageChangeListener() {
#Override
public void onPageSelected(int currentPage) {
if (currentPage == 0) {
Fragment firstFragment = adapter.getFragment(0);
if (firstFragment != null) {
// This method resets the images of the first fragment
((FirstFragment) firstFragment).reset();
}
}
}
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
// Do nothing
}
#Override
public void onPageScrollStateChanged(int state) {
// Do nothing
}
});
I have an Android activity that holds and manages six fragments, is fragment is a step in a flow, some of the fragments are replaced and some of them are added.
The Activity just uses a Framelayout as the container for the fragments as follows:
<FrameLayout
android:id="#+id/content"
android:layout_below="#+id/toolbar"
android:layout_width="match_parent"
android:layout_height="match_parent" />
Then the flow of the fragments is like this:
//Activity starts, add first Fragment
fragmentManager.beginTransaction().replace(R.id.content, FirstFragment.newInstance(listOfItems)).commit();
then
//User pressed button, activity got callback from first fragment
FragmentTransaction transaction = fragmentManager.beginTransaction();
transaction.replace(R.id.content, fragment2);
transaction.addToBackStack("frag2");
transaction.commit();
then
//Another callback from Frag2, perform the add of frag 3
FragmentTransaction transaction = fragmentManager.beginTransaction();
transaction.add(R.id.content, fragment3);
transaction.addToBackStack("frag3");
transaction.commit();
And so on....
I also manage the back stack from the Activity like this:
//Controlling the back stack when the user selects the soft back button in the toolbar
#Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
if (fragmentManager.getBackStackEntryCount() == 0) {
super.onBackPressed();
overridePendingTransition(R.anim.no_change, R.anim.slide_down);
} else {
if(!BaseFragment.handleBackPressed(getSupportFragmentManager())){
super.onBackPressed();
Fragment fragment = fragmentManager.getFragments()
.get(fragmentManager.getBackStackEntryCount());
fragment.onResume(); //Make sure the fragment that is currently at the top of the stack calls its onResume method
}
}
return true;
}
return super.onOptionsItemSelected(item);
}
//Controlling the back stack when the user selects the "hardware" back button
#Override
public void onBackPressed() {
if (fragmentManager.getBackStackEntryCount() == 0) {
super.onBackPressed();
overridePendingTransition(R.anim.no_change, R.anim.slide_down);
} else {
if(!BaseFragment.handleBackPressed(getSupportFragmentManager())){
super.onBackPressed();
Fragment fragment = fragmentManager.getFragments()
.get(fragmentManager.getBackStackEntryCount());
fragment.onResume(); //Make sure the fragment that is currently at the top of the stack calls its onResume method
}
}
}
My problem is that I open the app and go to this Activity which loads the fragments and then go through the flow to a certain stage ( I haven't narrowed it down yet) then I press the home button and blank my screen. Now after a certain amount of time when I open the app again it opens on the fragment I left but everything seems to be messed up, when I press back it seems to pop the wrong fragment and the UI becomes mixed up with the different fragments.
My guess is that when I open the app again the Activity onResume or the Fragment onResume or some lifecycle event is being called that I am not handling correctly?
So I was wondering is there best practices, guidelines or patterns that should be adhered to when using a Fragment pattern like I am doing so?
Since you have so many fragments in one activity, and they use the same container, that means all fragments are in the same place, and only one fragment will show at a time.
So why don't you use ViewPager and let FragmentPagerAdapter manager these fragments? In this way, you do not need to manager fragment lifecycle by yourself, you just need to override FragmentPagerAdapter methods:
to create fragment instance by getItem,
to update fragment by getItemPosition and Adapter.notifyDataSetChanged(),
to show selected fragment by mViewPager.setCurrentItem(i)
Code snippets, detail refer to https://github.com/li2/Update_Replace_Fragment_In_ViewPager/
private FragmentPagerAdapter mViewPagerAdapter = new FragmentPagerAdapter(getSupportFragmentManager()) {
#Override
public int getCount() {
return PAGE_COUNT;
}
// Return the Fragment associated with a specified position.
#Override
public Fragment getItem(int position) {
Log.d(TAG, "getItem(" + position + ")");
if (position == 0) {
return Page0Fragment.newInstance(mDate);
} else if (position == 1) {
return Page1Fragment.newInstance(mContent);
}
return null;
}
#Override
// To update fragment in ViewPager, we should override getItemPosition() method,
// in this method, we call the fragment's public updating method.
public int getItemPosition(Object object) {
Log.d(TAG, "getItemPosition(" + object.getClass().getSimpleName() + ")");
if (object instanceof Page0Fragment) {
((Page0Fragment) object).updateDate(mDate);
} else if (object instanceof Page1Fragment) {
((Page1Fragment) object).updateContent(mContent);
}
return super.getItemPosition(object);
};
};
I've created tab view using the code example on the android web.
http://developer.android.com/training/implementing-navigation/lateral.html
I've added this code to call a the setTitle method which would set the title.
mViewPager.addOnPageChangeListener(
new ViewPager.SimpleOnPageChangeListener() {
#Override
public void onPageSelected(int position) {
actionBar.setSelectedNavigationItem(position);
FragmentInterface f = (FragmentInterface) mSectionsPagerAdapter
.getItem(position);
f.setTitle();
}
});
In my fragment class, I've define setTitle as
#Override
public void setTitle() {
System.out.println("Title " + cellMain);
if (cellMain != null) {
getActivity().getActionBar()
.setTitle(cellMain.cellData.getIPWithPort());
}
}
and I also have a button which does :
public void connect(View view) {
System.out.println("Connect " + cellMain);
if (cellMain == null) {
cellMain = CellMain.createAndroid(this,
getActivity().getFilesDir().toString());
getActivity().getActionBar()
.setTitle(cellMain.cellData.getIPWithPort());
}
First I click the button which calls connect,
It prints out "Connect null" which is expected as it has not been initialized.
Pressing the button again print out "Connect cell.CellMain#....".
Now I change the view by selecting another tab and changing back to the same tab.
setTitle() method prints out "Title null" which is not expected as cellMain is initialized. Pressing of the button still prints out "Connect cell.CellMain#...."
Why does my setTitle method give a null value for my variable?
Guess it's due to the fragments lifecycle inside the ViewPager.
The ViewPager has a limit of pages that are active, being those the current one and it's closer fragments (e.g: if the limit is 3, you will have active the current fragment shown, it's next and it's previous). The rest will got through the onPause() method.
The same happens when resuming a fragment. When you bring a fragment to the front, the fragments in that ranged that aren't active will go through the onResume method.
Depending on the number of fragments you have, you can think in different solutions.
If you have two or three fragments, change the offsetLimit of the viewPager to contain all of them.
viewPager.setOffscreenPageLimit(3);
If you have more fragments, think about saving it's state on the onPause() method, and restoring it on the onResume() of each fragment.
I've notice the mSectionsPagerAdapter.getItem(position) returns a new instance of the fragment which results in the variable always being null.
I've manually instantiated each fragment in the constructor and return them accordingly.
public class SectionsPagerAdapter extends FragmentPagerAdapter {
String[] classes;
Fragment[] fragments;
public SectionsPagerAdapter(FragmentManager fm) {
super(fm);
classes = new String[]{CellView.class.getName(),
ControlPanelView.class.getName()};
fragments = new Fragment[classes.length];
for (int i = 0; i < classes.length; i++) {
fragments[i] = Fragment.instantiate(context, classes[i]);
}
}
#Override
public Fragment getItem(int position) {
//Used to be this line
//return Fragment.instantiate(context, classes[i])
return fragments[position];
}
I am having problems with fragments or maybe rather the way I want them to work.
In my activity I have a layout container (R.id.container1) to which I add a fragment (FragMain) programmatically at startup.
In the fragment I have 2 Fragments (Frag1, Frag2) and a ViewPager which loads several other fragments (FragA, FragB, FragC, FragD, FragE) via a FragmentPagerAdapter.
On a button press I replace the whole content of R.id.container1, so FragMain is replaced with another Fragment (FragSub).
Now when I press the back button, FragMain is loaded again, but the ViewPager isn't fully initialized, some Fragments are missing. From what I observed, it's always FragB and FragD missing, If I scroll to the empty views, the app crashes. The other fragments seem to be fine. What's going wrong here?
This thread suggests using getChildFragmentManager in creation of the PagerAdapter, but I am already doing that... Fragment in ViewPager not restored after popBackStack
I am accessing the fragments via e.g.
((FragA)((PagerAdapter)viewPager.getAdapter()).getItem(0));
Is this the best way?
Some Code :
MainActivity's onCreate
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
pagerFragList = new Vector<Fragment>();
pagerFragList.add(Fragment.instantiate(this, FragA.class.getName()));
pagerFragList.add(Fragment.instantiate(this, FragB.class.getName()));
pagerFragList.add(Fragment.instantiate(this, FragC.class.getName()));
pagerFragList.add(Fragment.instantiate(this, FragD.class.getName()));
pagerFragList.add(Fragment.instantiate(this, FragE.class.getName()));
FragMain fragMain = (FragMain)getSupportFragmentManager().findFragmentByTag(FragMain.debugTag);
if(fragMain==null) fragMain = new FragMain();
FragmentHelper.replaceSupportFragment(this, fragMain, R.id.container1, false, FragMain);
}
Helper
public Vector<Fragment> getFragList() {
return pagerFragList;
}
FragMain's onViewCreated
#Override
public void onViewCreated(View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
pagerAdapter = new PagerAdapter(getChildFragmentManager(), ((MainActivity)getActivity()).getFragList());
viewPager = ((ViewPager)view.findViewById(R.id.viewPager));
viewPager.setAdapter(pagerAdapter);
viewPager.setOffscreenPageLimit(5);
viewPager.setCurrentItem(0, true);
}
The PagerAdapter
public class PagerAdapter extends FragmentPagerAdapter {
private List<Fragment> fragments;
public PagerAdapter(FragmentManager fm, List<Fragment> fragments) {
super(fm);
this.fragments=fragments;
}
#Override
public Fragment getItem(int position) {
return fragments.get(position);
}
#Override
public int getCount() {
return fragments.size();
}
}
Have no idea why this seems to be fixing it on my end, but try commenting out your "viewPager.setOffscreenPageLimit(5);" line.
I'm still investigating and will be back with more if I find anything else useful out.
The other thing it turns out that I had to do was override the "state" methods of a FragmentStatePagerAdapter like this:
#Override
public Parcelable saveState() {
return null;
}
#Override
public void restoreState(Parcelable state, ClassLoader loader) {
//do nothing
}
In order to bypass whatever strange thing that was causing problems (must have had something to do with saving and restoring the states of nested fragments in a ViewPager...
There are alot of permutations involving the state of fragments and backstack transitions. For debug, it may help to isolate the event you are working with (backbutton , orientation change ... ) and to look at the following before and after your event....
state of fragment manager which includes the backstack i believe...
//debug
getFragmentManager().dump("", null,
new PrintWriter(System.out, true), null);
see this thread
Fragments seem to be very nice for separation of UI logic into some modules. But along with ViewPager its lifecycle is still misty to me. So Guru thoughts are badly needed!
Edit
See dumb solution below ;-)
Scope
Main activity has a ViewPager with fragments. Those fragments could implement a little bit different logic for other (submain) activities, so the fragments' data is filled via a callback interface inside the activity. And everything works fine on first launch, but!...
Problem
When the activity gets recreated (e.g. on orientation change) so do the ViewPager's fragments. The code (you'll find below) says that every time the activity is created I try to create a new ViewPager fragments adapter the same as fragments (maybe this is the problem) but FragmentManager already has all these fragments stored somewhere (where?) and starts the recreation mechanism for those. So the recreation mechanism calls the "old" fragment's onAttach, onCreateView, etc. with my callback interface call for initiating data via the Activity's implemented method. But this method points to the newly created fragment which is created via the Activity's onCreate method.
Issue
Maybe I'm using wrong patterns but even Android 3 Pro book doesn't have much about it. So, please, give me one-two punch and point out how to do it the right way. Many thanks!
Code
Main Activity
public class DashboardActivity extends BasePagerActivity implements OnMessageListActionListener {
private MessagesFragment mMessagesFragment;
#Override
protected void onCreate(Bundle savedInstanceState) {
Logger.d("Dash onCreate");
super.onCreate(savedInstanceState);
setContentView(R.layout.viewpager_container);
new DefaultToolbar(this);
// create fragments to use
mMessagesFragment = new MessagesFragment();
mStreamsFragment = new StreamsFragment();
// set titles and fragments for view pager
Map<String, Fragment> screens = new LinkedHashMap<String, Fragment>();
screens.put(getApplicationContext().getString(R.string.dashboard_title_dumb), new DumbFragment());
screens.put(getApplicationContext().getString(R.string.dashboard_title_messages), mMessagesFragment);
// instantiate view pager via adapter
mPager = (ViewPager) findViewById(R.id.viewpager_pager);
mPagerAdapter = new BasePagerAdapter(screens, getSupportFragmentManager());
mPager.setAdapter(mPagerAdapter);
// set title indicator
TitlePageIndicator indicator = (TitlePageIndicator) findViewById(R.id.viewpager_titles);
indicator.setViewPager(mPager, 1);
}
/* set of fragments callback interface implementations */
#Override
public void onMessageInitialisation() {
Logger.d("Dash onMessageInitialisation");
if (mMessagesFragment != null)
mMessagesFragment.loadLastMessages();
}
#Override
public void onMessageSelected(Message selectedMessage) {
Intent intent = new Intent(this, StreamActivity.class);
intent.putExtra(Message.class.getName(), selectedMessage);
startActivity(intent);
}
BasePagerActivity aka helper
public class BasePagerActivity extends FragmentActivity {
BasePagerAdapter mPagerAdapter;
ViewPager mPager;
}
Adapter
public class BasePagerAdapter extends FragmentPagerAdapter implements TitleProvider {
private Map<String, Fragment> mScreens;
public BasePagerAdapter(Map<String, Fragment> screenMap, FragmentManager fm) {
super(fm);
this.mScreens = screenMap;
}
#Override
public Fragment getItem(int position) {
return mScreens.values().toArray(new Fragment[mScreens.size()])[position];
}
#Override
public int getCount() {
return mScreens.size();
}
#Override
public String getTitle(int position) {
return mScreens.keySet().toArray(new String[mScreens.size()])[position];
}
// hack. we don't want to destroy our fragments and re-initiate them after
#Override
public void destroyItem(View container, int position, Object object) {
// TODO Auto-generated method stub
}
}
Fragment
public class MessagesFragment extends ListFragment {
private boolean mIsLastMessages;
private List<Message> mMessagesList;
private MessageArrayAdapter mAdapter;
private LoadMessagesTask mLoadMessagesTask;
private OnMessageListActionListener mListener;
// define callback interface
public interface OnMessageListActionListener {
public void onMessageInitialisation();
public void onMessageSelected(Message selectedMessage);
}
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// setting callback
mListener = (OnMessageListActionListener) activity;
mIsLastMessages = activity instanceof DashboardActivity;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
inflater.inflate(R.layout.fragment_listview, container);
mProgressView = inflater.inflate(R.layout.listrow_progress, null);
mEmptyView = inflater.inflate(R.layout.fragment_nodata, null);
return super.onCreateView(inflater, container, savedInstanceState);
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
// instantiate loading task
mLoadMessagesTask = new LoadMessagesTask();
// instantiate list of messages
mMessagesList = new ArrayList<Message>();
mAdapter = new MessageArrayAdapter(getActivity(), mMessagesList);
setListAdapter(mAdapter);
}
#Override
public void onResume() {
mListener.onMessageInitialisation();
super.onResume();
}
public void onListItemClick(ListView l, View v, int position, long id) {
Message selectedMessage = (Message) getListAdapter().getItem(position);
mListener.onMessageSelected(selectedMessage);
super.onListItemClick(l, v, position, id);
}
/* public methods to load messages from host acitivity, etc... */
}
Solution
The dumb solution is to save the fragments inside onSaveInstanceState (of host Activity) with putFragment and get them inside onCreate via getFragment. But I still have a strange feeling that things shouldn't work like that... See code below:
#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
getSupportFragmentManager()
.putFragment(outState, MessagesFragment.class.getName(), mMessagesFragment);
}
protected void onCreate(Bundle savedInstanceState) {
Logger.d("Dash onCreate");
super.onCreate(savedInstanceState);
...
// create fragments to use
if (savedInstanceState != null) {
mMessagesFragment = (MessagesFragment) getSupportFragmentManager().getFragment(
savedInstanceState, MessagesFragment.class.getName());
StreamsFragment.class.getName());
}
if (mMessagesFragment == null)
mMessagesFragment = new MessagesFragment();
...
}
When the FragmentPagerAdapter adds a fragment to the FragmentManager, it uses a special tag based on the particular position that the fragment will be placed. FragmentPagerAdapter.getItem(int position) is only called when a fragment for that position does not exist. After rotating, Android will notice that it already created/saved a fragment for this particular position and so it simply tries to reconnect with it with FragmentManager.findFragmentByTag(), instead of creating a new one. All of this comes free when using the FragmentPagerAdapter and is why it is usual to have your fragment initialisation code inside the getItem(int) method.
Even if we were not using a FragmentPagerAdapter, it is not a good idea to create a new fragment every single time in Activity.onCreate(Bundle). As you have noticed, when a fragment is added to the FragmentManager, it will be recreated for you after rotating and there is no need to add it again. Doing so is a common cause of errors when working with fragments.
A usual approach when working with fragments is this:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
...
CustomFragment fragment;
if (savedInstanceState != null) {
fragment = (CustomFragment) getSupportFragmentManager().findFragmentByTag("customtag");
} else {
fragment = new CustomFragment();
getSupportFragmentManager().beginTransaction().add(R.id.container, fragment, "customtag").commit();
}
...
}
When using a FragmentPagerAdapter, we relinquish fragment management to the adapter, and do not have to perform the above steps. By default, it will only preload one Fragment in front and behind the current position (although it does not destroy them unless you are using FragmentStatePagerAdapter). This is controlled by ViewPager.setOffscreenPageLimit(int). Because of this, directly calling methods on the fragments outside of the adapter is not guaranteed to be valid, because they may not even be alive.
To cut a long story short, your solution to use putFragment to be able to get a reference afterwards is not so crazy, and not so unlike the normal way to use fragments anyway (above). It is difficult to obtain a reference otherwise because the fragment is added by the adapter, and not you personally. Just make sure that the offscreenPageLimit is high enough to load your desired fragments at all times, since you rely on it being present. This bypasses lazy loading capabilities of the ViewPager, but seems to be what you desire for your application.
Another approach is to override FragmentPageAdapter.instantiateItem(View, int) and save a reference to the fragment returned from the super call before returning it (it has the logic to find the fragment, if already present).
For a fuller picture, have a look at some of the source of FragmentPagerAdapter (short) and ViewPager (long).
I want to offer a solution that expands on antonyt's wonderful answer and mention of overriding FragmentPageAdapter.instantiateItem(View, int) to save references to created Fragments so you can do work on them later. This should also work with FragmentStatePagerAdapter; see notes for details.
Here's a simple example of how to get a reference to the Fragments returned by FragmentPagerAdapter that doesn't rely on the internal tags set on the Fragments. The key is to override instantiateItem() and save references in there instead of in getItem().
public class SomeActivity extends Activity {
private FragmentA m1stFragment;
private FragmentB m2ndFragment;
// other code in your Activity...
private class CustomPagerAdapter extends FragmentPagerAdapter {
// other code in your custom FragmentPagerAdapter...
public CustomPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
// Do NOT try to save references to the Fragments in getItem(),
// because getItem() is not always called. If the Fragment
// was already created then it will be retrieved from the FragmentManger
// and not here (i.e. getItem() won't be called again).
switch (position) {
case 0:
return new FragmentA();
case 1:
return new FragmentB();
default:
// This should never happen. Always account for each position above
return null;
}
}
// Here we can finally safely save a reference to the created
// Fragment, no matter where it came from (either getItem() or
// FragmentManger). Simply save the returned Fragment from
// super.instantiateItem() into an appropriate reference depending
// on the ViewPager position.
#Override
public Object instantiateItem(ViewGroup container, int position) {
Fragment createdFragment = (Fragment) super.instantiateItem(container, position);
// save the appropriate reference depending on position
switch (position) {
case 0:
m1stFragment = (FragmentA) createdFragment;
break;
case 1:
m2ndFragment = (FragmentB) createdFragment;
break;
}
return createdFragment;
}
}
public void someMethod() {
// do work on the referenced Fragments, but first check if they
// even exist yet, otherwise you'll get an NPE.
if (m1stFragment != null) {
// m1stFragment.doWork();
}
if (m2ndFragment != null) {
// m2ndFragment.doSomeWorkToo();
}
}
}
or if you prefer to work with tags instead of class member variables/references to the Fragments you can also grab the tags set by FragmentPagerAdapter in the same manner:
NOTE: this doesn't apply to FragmentStatePagerAdapter since it doesn't set tags when creating its Fragments.
#Override
public Object instantiateItem(ViewGroup container, int position) {
Fragment createdFragment = (Fragment) super.instantiateItem(container, position);
// get the tags set by FragmentPagerAdapter
switch (position) {
case 0:
String firstTag = createdFragment.getTag();
break;
case 1:
String secondTag = createdFragment.getTag();
break;
}
// ... save the tags somewhere so you can reference them later
return createdFragment;
}
Note that this method does NOT rely on mimicking the internal tag set by FragmentPagerAdapter and instead uses proper APIs for retrieving them. This way even if the tag changes in future versions of the SupportLibrary you'll still be safe.
Don't forget that depending on the design of your Activity, the Fragments you're trying to work on may or may not exist yet, so you have to account for that by doing null checks before using your references.
Also, if instead you're working with FragmentStatePagerAdapter, then you don't want to keep hard references to your Fragments because you might have many of them and hard references would unnecessarily keep them in memory. Instead save the Fragment references in WeakReference variables instead of standard ones. Like this:
WeakReference<Fragment> m1stFragment = new WeakReference<Fragment>(createdFragment);
// ...and access them like so
Fragment firstFragment = m1stFragment.get();
if (firstFragment != null) {
// reference hasn't been cleared yet; do work...
}
I found another relatively easy solution for your question.
As you can see from the FragmentPagerAdapter source code, the fragments managed by FragmentPagerAdapter store in the FragmentManager under the tag generated using:
String tag="android:switcher:" + viewId + ":" + index;
The viewId is the container.getId(), the container is your ViewPager instance. The index is the position of the fragment. Hence you can save the object id to the outState:
#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putInt("viewpagerid" , mViewPager.getId() );
}
#Override
protected void onCreate(Bundle savedInstanceState) {
setContentView(R.layout.activity_main);
if (savedInstanceState != null)
viewpagerid=savedInstanceState.getInt("viewpagerid", -1 );
MyFragmentPagerAdapter titleAdapter = new MyFragmentPagerAdapter (getSupportFragmentManager() , this);
mViewPager = (ViewPager) findViewById(R.id.pager);
if (viewpagerid != -1 ){
mViewPager.setId(viewpagerid);
}else{
viewpagerid=mViewPager.getId();
}
mViewPager.setAdapter(titleAdapter);
If you want to communicate with this fragment, you can get if from FragmentManager, such as:
getSupportFragmentManager().findFragmentByTag("android:switcher:" + viewpagerid + ":0")
I want to offer an alternate solution for perhaps a slightly different case, since many of my searches for answers kept leading me to this thread.
My case
- I'm creating/adding pages dynamically and sliding them into a ViewPager, but when rotated (onConfigurationChange) I end up with a new page because of course OnCreate is called again. But I want to keep reference to all the pages that were created prior to the rotation.
Problem
- I don't have unique identifiers for each fragment I create, so the only way to reference was to somehow store references in an Array to be restored after the rotation/configuration change.
Workaround
- The key concept was to have the Activity (which displays the Fragments) also manage the array of references to existing Fragments, since this activity can utilize Bundles in onSaveInstanceState
public class MainActivity extends FragmentActivity
So within this Activity, I declare a private member to track the open pages
private List<Fragment> retainedPages = new ArrayList<Fragment>();
This is updated everytime onSaveInstanceState is called and restored in onCreate
#Override
protected void onSaveInstanceState(Bundle outState) {
retainedPages = _adapter.exportList();
outState.putSerializable("retainedPages", (Serializable) retainedPages);
super.onSaveInstanceState(outState);
}
...so once it's stored, it can be retrieved...
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
if (savedInstanceState != null) {
retainedPages = (List<Fragment>) savedInstanceState.getSerializable("retainedPages");
}
_mViewPager = (CustomViewPager) findViewById(R.id.viewPager);
_adapter = new ViewPagerAdapter(getApplicationContext(), getSupportFragmentManager());
if (retainedPages.size() > 0) {
_adapter.importList(retainedPages);
}
_mViewPager.setAdapter(_adapter);
_mViewPager.setCurrentItem(_adapter.getCount()-1);
}
These were the necessary changes to the main activity, and so I needed the members and methods within my FragmentPagerAdapter for this to work, so within
public class ViewPagerAdapter extends FragmentPagerAdapter
an identical construct (as shown above in MainActivity )
private List<Fragment> _pages = new ArrayList<Fragment>();
and this syncing (as used above in onSaveInstanceState) is supported specifically by the methods
public List<Fragment> exportList() {
return _pages;
}
public void importList(List<Fragment> savedPages) {
_pages = savedPages;
}
And then finally, in the fragment class
public class CustomFragment extends Fragment
in order for all this to work, there were two changes, first
public class CustomFragment extends Fragment implements Serializable
and then adding this to onCreate so Fragments aren't destroyed
setRetainInstance(true);
I'm still in the process of wrapping my head around Fragments and Android life cycle, so caveat here is there may be redundancies/inefficiencies in this method. But it works for me and I hope might be helpful for others with cases similar to mine.
My solution is very rude but works: being my fragments dynamically created from retained data, I simply remove all fragment from the PageAdapter before calling super.onSaveInstanceState() and then recreate them on activity creation:
#Override
protected void onSaveInstanceState(Bundle outState) {
outState.putInt("viewpagerpos", mViewPager.getCurrentItem() );
mSectionsPagerAdapter.removeAllfragments();
super.onSaveInstanceState(outState);
}
You can't remove them in onDestroy(), otherwise you get this exception:
java.lang.IllegalStateException: Can not perform this action after onSaveInstanceState
Here the code in the page adapter:
public void removeAllfragments()
{
if ( mFragmentList != null ) {
for ( Fragment fragment : mFragmentList ) {
mFm.beginTransaction().remove(fragment).commit();
}
mFragmentList.clear();
notifyDataSetChanged();
}
}
I only save the current page and restore it in onCreate(), after the fragments have been created.
if (savedInstanceState != null)
mViewPager.setCurrentItem( savedInstanceState.getInt("viewpagerpos", 0 ) );
What is that BasePagerAdapter? You should use one of the standard pager adapters -- either FragmentPagerAdapter or FragmentStatePagerAdapter, depending on whether you want Fragments that are no longer needed by the ViewPager to either be kept around (the former) or have their state saved (the latter) and re-created if needed again.
Sample code for using ViewPager can be found here
It is true that the management of fragments in a view pager across activity instances is a little complicated, because the FragmentManager in the framework takes care of saving the state and restoring any active fragments that the pager has made. All this really means is that the adapter when initializing needs to make sure it re-connects with whatever restored fragments there are. You can look at the code for FragmentPagerAdapter or FragmentStatePagerAdapter to see how this is done.
If anyone is having issues with their FragmentStatePagerAdapter not properly restoring the state of its fragments...ie...new Fragments are being created by the FragmentStatePagerAdapter instead of it restoring them from state...
Make sure you call ViewPager.setOffscreenPageLimit() BEFORE you call ViewPager.setAdapter(fragmentStatePagerAdapter)
Upon calling ViewPager.setOffscreenPageLimit()...the ViewPager will immediately look to its adapter and try to get its fragments. This could happen before the ViewPager has a chance to restore the Fragments from savedInstanceState(thus creating new Fragments that can't be re-initialized from SavedInstanceState because they're new).
I came up with this simple and elegant solution. It assumes that the activity is responsible for creating the Fragments, and the Adapter just serves them.
This is the adapter's code (nothing weird here, except for the fact that mFragments is a list of fragments maintained by the Activity)
class MyFragmentPagerAdapter extends FragmentStatePagerAdapter {
public MyFragmentPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
return mFragments.get(position);
}
#Override
public int getCount() {
return mFragments.size();
}
#Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
#Override
public CharSequence getPageTitle(int position) {
TabFragment fragment = (TabFragment)mFragments.get(position);
return fragment.getTitle();
}
}
The whole problem of this thread is getting a reference of the "old" fragments, so I use this code in the Activity's onCreate.
if (savedInstanceState!=null) {
if (getSupportFragmentManager().getFragments()!=null) {
for (Fragment fragment : getSupportFragmentManager().getFragments()) {
mFragments.add(fragment);
}
}
}
Of course you can further fine tune this code if needed, for example making sure the fragments are instances of a particular class.
To get the fragments after orientation change you have to use the .getTag().
getSupportFragmentManager().findFragmentByTag("android:switcher:" + viewPagerId + ":" + positionOfItemInViewPager)
For a bit more handling i wrote my own ArrayList for my PageAdapter to get the fragment by viewPagerId and the FragmentClass at any Position:
public class MyPageAdapter extends FragmentPagerAdapter implements Serializable {
private final String logTAG = MyPageAdapter.class.getName() + ".";
private ArrayList<MyPageBuilder> fragmentPages;
public MyPageAdapter(FragmentManager fm, ArrayList<MyPageBuilder> fragments) {
super(fm);
fragmentPages = fragments;
}
#Override
public Fragment getItem(int position) {
return this.fragmentPages.get(position).getFragment();
}
#Override
public CharSequence getPageTitle(int position) {
return this.fragmentPages.get(position).getPageTitle();
}
#Override
public int getCount() {
return this.fragmentPages.size();
}
public int getItemPosition(Object object) {
//benötigt, damit bei notifyDataSetChanged alle Fragemnts refrehsed werden
Log.d(logTAG, object.getClass().getName());
return POSITION_NONE;
}
public Fragment getFragment(int position) {
return getItem(position);
}
public String getTag(int position, int viewPagerId) {
//getSupportFragmentManager().findFragmentByTag("android:switcher:" + R.id.shares_detail_activity_viewpager + ":" + myViewPager.getCurrentItem())
return "android:switcher:" + viewPagerId + ":" + position;
}
public MyPageBuilder getPageBuilder(String pageTitle, int icon, int selectedIcon, Fragment frag) {
return new MyPageBuilder(pageTitle, icon, selectedIcon, frag);
}
public static class MyPageBuilder {
private Fragment fragment;
public Fragment getFragment() {
return fragment;
}
public void setFragment(Fragment fragment) {
this.fragment = fragment;
}
private String pageTitle;
public String getPageTitle() {
return pageTitle;
}
public void setPageTitle(String pageTitle) {
this.pageTitle = pageTitle;
}
private int icon;
public int getIconUnselected() {
return icon;
}
public void setIconUnselected(int iconUnselected) {
this.icon = iconUnselected;
}
private int iconSelected;
public int getIconSelected() {
return iconSelected;
}
public void setIconSelected(int iconSelected) {
this.iconSelected = iconSelected;
}
public MyPageBuilder(String pageTitle, int icon, int selectedIcon, Fragment frag) {
this.pageTitle = pageTitle;
this.icon = icon;
this.iconSelected = selectedIcon;
this.fragment = frag;
}
}
public static class MyPageArrayList extends ArrayList<MyPageBuilder> {
private final String logTAG = MyPageArrayList.class.getName() + ".";
public MyPageBuilder get(Class cls) {
// Fragment über FragmentClass holen
for (MyPageBuilder item : this) {
if (item.fragment.getClass().getName().equalsIgnoreCase(cls.getName())) {
return super.get(indexOf(item));
}
}
return null;
}
public String getTag(int viewPagerId, Class cls) {
// Tag des Fragment unabhängig vom State z.B. nach bei Orientation change
for (MyPageBuilder item : this) {
if (item.fragment.getClass().getName().equalsIgnoreCase(cls.getName())) {
return "android:switcher:" + viewPagerId + ":" + indexOf(item);
}
}
return null;
}
}
So just create a MyPageArrayList with the fragments:
myFragPages = new MyPageAdapter.MyPageArrayList();
myFragPages.add(new MyPageAdapter.MyPageBuilder(
getString(R.string.widget_config_data_frag),
R.drawable.ic_sd_storage_24dp,
R.drawable.ic_sd_storage_selected_24dp,
new WidgetDataFrag()));
myFragPages.add(new MyPageAdapter.MyPageBuilder(
getString(R.string.widget_config_color_frag),
R.drawable.ic_color_24dp,
R.drawable.ic_color_selected_24dp,
new WidgetColorFrag()));
myFragPages.add(new MyPageAdapter.MyPageBuilder(
getString(R.string.widget_config_textsize_frag),
R.drawable.ic_settings_widget_24dp,
R.drawable.ic_settings_selected_24dp,
new WidgetTextSizeFrag()));
and add them to the viewPager:
mAdapter = new MyPageAdapter(getSupportFragmentManager(), myFragPages);
myViewPager.setAdapter(mAdapter);
after this you can get after orientation change the correct fragment by using its class:
WidgetDataFrag dataFragment = (WidgetDataFrag) getSupportFragmentManager()
.findFragmentByTag(myFragPages.getTag(myViewPager.getId(), WidgetDataFrag.class));
A bit different opinion instead of storing the Fragments yourself just leave it to the FragmentManager and when you need to do something with the fragments look for them in the FragmentManager:
//make sure you have the right FragmentManager
//getSupportFragmentManager or getChildFragmentManager depending on what you are using to manage this stack of fragments
List<Fragment> fragments = fragmentManager.getFragments();
if(fragments != null) {
int count = fragments.size();
for (int x = 0; x < count; x++) {
Fragment fragment = fragments.get(x);
//check if this is the fragment we want,
//it may be some other inspection, tag etc.
if (fragment instanceof MyFragment) {
//do whatever we need to do with it
}
}
}
If you have a lot of Fragments and the cost of instanceof check may be not what you want, but it is good thing to have in mind that the FragmentManager already keeps account of Fragments.
add:
#SuppressLint("ValidFragment")
before your class.
it it doesn´t work do something like this:
#SuppressLint({ "ValidFragment", "HandlerLeak" })