Right now I'm developing an application, which basically uses this components for navigation and visualization:
- Navigation component,
- ViewPager,
- FragmentStatePagerAdapter,
- TabLayout.
In the application there is 7 fixed tab (fragment). Most of them have one RecyclerView and I fetch the data from a server.
I have two problem with this solution:
When I click an item in one of the RecyclerView, I use navigation component's navigate() method. Then I press back button, and the list is 'making a network call again' and scroll to the top (not retain the fragment's state).
When I swiping in the ViewPager it doesn't save the fragment's state and reloading them all the time. Yes, I'm familiar with the setOffscreenPageLimit() method, and it's working, but according to the docummentation: "You should keep this limit low, especially if your pages have complex layouts", so I shouldn't set it to 7.
So basically my question is, how Google do it on Play Store? Play Store has planty of tabs on the bottom navigation, plenty of tabs on the top, but somehow it seems to save all of my previous navigation history (RecyclerView's state etc.).
Thank you.
Adapter for ViewPager:
public class MainAdapter extends FragmentStatePagerAdapter {
private Context mCtx;
public MainAdapter(#NonNull FragmentManager fm, int behavior, Context ctx) {
super(fm, behavior);
mCtx = ctx;
}
#NonNull
#Override
public Fragment getItem(int i) {
return new NewsFragment();
}
#Override
public int getCount() {
return 7;
}
#Override
public CharSequence getPageTitle(int position) {
String tabTitle = "";
if (mCtx != null) {
switch (position) {
case 0:
tabTitle = mCtx.getString(R.string.title_fragment_news);
break;
case 1:
tabTitle = mCtx.getString(R.string.button_city_operation);
break;
case 2:
// TODO
tabTitle = "Tab 2";
break;
case 3:
// TODO
tabTitle = "Tab 3";
break;
case 4:
tabTitle = mCtx.getString(R.string.title_fragment_information);
break;
case 5:
tabTitle = mCtx.getString(R.string.title_fragment_announcement);
break;
case 6:
// TODO
tabTitle = "Tab7";
break;
}
}
return tabTitle;
}
}
Init viewpager and tablayout:
MainAdapter mMainPagerAdapter = new MainAdapter(getChildFragmentManager(), BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT, getApplicationContext());
ViewPager mViewPager = view.findViewById(R.id.pager);
mViewPager.setAdapter(mMainPagerAdapter);
// mViewPager.setOffscreenPageLimit(3);
final TabLayout tabLayout = view.findViewById(R.id.tab_layout);
tabLayout.setupWithViewPager(mViewPager);
Please refer to this question for the setup of fragments:
| A | B |
↓
| C | D |
↓
| E |
I am struggling to figure out why my App is exiting on pressing the back button on a fragment added with addToBackStack().
According to the answer,
Case 1: If I use getSupportFragmentManager() or getFragmentManager(): my fragments vanish after I swipe to a different tab and come back.
Case 2: if I use getChildFragmentManager(): I dynamically add Fragment E to C while using addToBackStack() but when I press back, the app exits. Expectation is that it should return to C instead of exiting.
Code for adding tabs C and D is:
public class MyProfileTabFragmentPagerAdapter extends FragmentPagerAdapter {
private String tabTitles[];
private Context context;
private String userID;
private static final String TAG = makeLogTag(MyProfileTabFragmentPagerAdapter.class);
public MyProfileTabFragmentPagerAdapter(FragmentManager fm, Context context) {
super(fm);
tabTitles = context.getResources().getStringArray(R.array.profileTabs);
this.context = context;
SharedPreferences prefs =
PreferenceManager.getDefaultSharedPreferences(context);
userID = prefs.getString("token", "");
}
#Override
public int getCount() {
return tabTitles.length;
}
#Override
public Fragment getItem(int position) {
switch (position){
case 0:
{
return UserProfileFragment.getInstance(userID);
}
case 1:
{
return new MySnapsFragment();
}
default:
{
LOGI(TAG, "Invalid tab" + position);
return null;
}
}
}
#Override
public CharSequence getPageTitle(int position) {
// Generate title based on item position
return tabTitles[position];
}
}
This is how I setup my tabs in B which I call in its onCreateView():
private void setupTabs() {
// Get the ViewPager and set it's PagerAdapter so that it can display items
vpProfileTab.setAdapter(new MyProfileTabFragmentPagerAdapter(getChildFragmentManager(), ctx));
// Give the TabLayout the ViewPager
slidingProfileTabs.setDistributeEvenly(true);
slidingProfileTabs.setBackgroundColor(colorAccent2);
slidingProfileTabs.setSelectedIndicatorColors(colorTabIndicator);
slidingProfileTabs.setViewPager(vpProfileTab);
}
I setup C from B using in onCreateView():
private void setupUserProfileFeed() {
if(feedFragment==null){
feedFragment = new FeedFragment();
this.getFragmentManager().beginTransaction().replace(R.id.feed_fragment, feedFragment).addToBackStack()
.commit();
}
}
I setup E from C when I click a button:
#Override
public void onProfileClick(View v) {
UserProfileFragment userProfileFragment = UserProfileFragment.getInstance(userID);
this.getFragmentManager().beginTransaction().replace(R.id.feedContent, userProfileFragment)
.addToBackStack(null).commit();
}
I am using SlidingTabLayout from Google github here.
I have the following questions:
What is the reason for Case 1. Which FM should be used, as per my understanding: getFM() should be used for top level and getChildFM() should be used for adding fragments to a fragment?
Why is the App exiting in Case 2? Do I need to do anything else?
How to solve this problem either way? Have been stuck for a while, any help is highly appreciated.
override onBackPressed and make a switch statement for the different view pager positions (0,1,2,3...) and tell it what to do in each case. Add this to the main activity where you are attaching the viewPager adapter. This example code is a simple way to do it if you want more complex behavior use the switch statement as previously described.
#Override
public void onBackPressed() {
if (mViewPager.getCurrentItem() == 0) {
// If the user is currently looking at the first page, allow android to handle the
// Back button. This exits the app because you are on the first fragment.
super.onBackPressed();
} else {
// Otherwise, select the fragment in the viewPager
mViewPager.setCurrentItem(mViewPager.getCurrentItem() - 1);
}
}
I am using viewpager in order to load images from the server, each fragment should load the image based on positon of the fragment in the adapter. so for example position 0 will load image 0 position 1 load image 1 etc. for the last two days I am struggeling with getting the correct fragment position, in total I have 3 fragments however from print outs I have added to the code I can see only position 0 and 2 and thus the image is duplicated in position 1.
the main question is how can I resolve this? I would like to get the correct position and based on that the correct image. below is the viewpager code and adapter code, it was modified several times based on several solutions however none of them seems to work
public class LoadCarFullSizeImage extends AppCompatActivity{
private ViewPager viewPager;
protected String imagePath;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.car_images);
imagePath=getIntent().getStringExtra("imagePath");
viewPager=(ViewPager)findViewById(R.id.vp_carViewPager);
CirclePageIndicator titleIndicator = (CirclePageIndicator)findViewById(R.id.titles);
PagerAdapter mPagerAdapter = new ScreenSlidePagerAdapter(getSupportFragmentManager(),imagePath);
viewPager.setAdapter(mPagerAdapter);
titleIndicator.setViewPager(viewPager);
}
#Override
public void onBackPressed() {
if (viewPager.getCurrentItem() == 0) {
// If the user is currently looking at the first step, allow the system to handle the
// Back button. This calls finish() on this activity and pops the back stack.
super.onBackPressed();
} else {
// Otherwise, select the previous step.
viewPager.setCurrentItem(viewPager.getCurrentItem() - 1);
}
}
private static class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter{
private String imgPath;
public ScreenSlidePagerAdapter(android.support.v4.app.FragmentManager fm, String _imagePath) {
super(fm);
this.imgPath=_imagePath;
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0: // Fragment # 0 - This will show FirstFragment
return CarImageFragment.newInstance(0, imgPath);
case 1: // Fragment # 0 - This will show FirstFragment different title
return CarImageFragment.newInstance(1, imgPath);
case 2: // Fragment # 1 - This will show SecondFragment
return CarImageFragment.newInstance(2, imgPath);
default:
return null;
}
}
#Override
public int getCount() {
return 3;
}
}
}
Since you are using the indicator.. you have to getthe current page from it... and set current page using it too...
When using indicator stop using the pager or pager listener... any listener should be set to the indicator.
titleIndicator.getCurrentItem()==0...
and
titleIndicator.setCurrent.....
I'm developing an application in which i use a ViewPager.
Underneath the ViewPager, there are some bullet points that should indicate which page is displayed, but their behaviour is wrong.
Here's the activity part:
ind1 = (ImageView)findViewById(R.id.page1);
ind2 = (ImageView)findViewById(R.id.page2);
ind3 = (ImageView)findViewById(R.id.page3);
ind4 = (ImageView)findViewById(R.id.page4);
mPager = (ViewPager) findViewById(R.id.pager);
mPagerAdapter = new ScreenSlidePagerAdapter(getSupportFragmentManager());
mPager.setAdapter(mPagerAdapter);
Here's the Adapter:
/*Adapter for ViewPager*/
private class ScreenSlidePagerAdapter extends FragmentStatePagerAdapter{
public ScreenSlidePagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
switch(position){
case 0:
ind1.setImageResource(on);
ind2.setImageResource(off);
ind3.setImageResource(off);
ind4.setImageResource(off);
return Frag1.newInstance();
case 1:
ind1.setImageResource(off);
ind2.setImageResource(on);
ind3.setImageResource(off);
ind4.setImageResource(off);
return Frag2.newInstance();
case 2:
ind1.setImageResource(off);
ind2.setImageResource(off);
ind3.setImageResource(on);
ind4.setImageResource(off);
return Frag3.newInstance();
case 3:
ind1.setImageResource(off);
ind2.setImageResource(off);
ind3.setImageResource(off);
ind4.setImageResource(on);
return Frag4.newInstance();
default:
ind1.setImageResource(on);
ind2.setImageResource(off);
ind3.setImageResource(off);
ind4.setImageResource(off);
return Frag1.newInstance();
}
}
#Override
public int getCount() {
return NUM_PAGES; /*NUM_PAGES = 4*/
}
}
Here's Frag1 (the other Fragments are equal to Frag1, the only differences are the layout and the loaded HTML file):
public class Frag1 extends Fragment{
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
ViewGroup rootView = (ViewGroup) inflater.inflate(R.layout.frag_page_1, container, false);
WebView wv = (WebView) rootView.findViewById(R.id.webView1);
wv.loadUrl("file:///android_asset/html/tabel1.html");
wv.setBackgroundColor(0x00000000);
wv.setLayerType(WebView.LAYER_TYPE_SOFTWARE, null);
return rootView;
}
public static Frag1 newInstance(){
Frag1 f = new Frag1();
return f;
}
}
The wrong behaviour is the following: when activity starts, the first fragment is displayed but the 'active' bullet point is the second, for the second page the active point is the third, for the third page is active the fourth, for the fourth page the fourth point remains active. If i swipe back to the third page the second bullet point is active.
In simple terms, the active bullet point doesn't match with the displayed page.
I tried to print the position in the Adapter, like following, under each case::
Toast.makeText(context, String.valueOf(position), Toast.LENGTH_SHORT).show();
When activity starts, are printed two consecutive message, 0 and 1, without interacting with the ViewPager.
When i change page, the position is always wrong, but the relative fragment are displayed correctly.
I tried to set the bullet point state in the fragments class, but nothing changed.
Why the adapter indicates the wrong position? How can i make that the correct bullet point indicates the right displayed page?
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" })