I am using BottomNavigationView with navigation according to android guidelines, the issue i am facing is new fragment is created everytime I go to another tab. I tried to explore and follow different solutions, but nothing works so far. Is there any work around which anyone has tried to make it work?
You can do this by creating fragment as singleton by using the below code snippet: -
class YourFragment extends Fragment{
private static YourFragment instance;
public static YourFragment getInstance(){
if (instance == null) {
instance = new YourFragment();
}
return instance;
}
}
Now create object of fragment using by YourFragment.getInstance();
It won't create a new object every time.
I used this method.
Fragment currentlyActiveFragment = null;
private void showActiveFragment(Fragment nextFragment){
currentlyActiveFragment = nextFragment;
if (currentlyActiveFragment!=null){
fragmentManager.beginTransaction()
.show(currentlyActiveFragment)
.commitAllowingStateLoss();
}
}
Then keep some references of your fragments:
private FragmentA fragmentA=null;
private FragmentB fragmentB=null;
// ... ...
So whenever you click on your button, you do the following check:
btnToOpenFragmentA.setOnClickListener(v -> {
if (fragmentA == null) {
// create this fragment
fragmentA = new FragmentA();
getSupportFragmentManager().beginTransaction()
.add(R.layout.baseFrameLayout, fragmentA, FragmentA.TAG)
.addToBackStack(null)
.commitAllowingStateLoss();
} else {
showActiveFragment(fragmentA);
}
});
So this basically checks: if the fragment already exists in the stack, don't create it, instead bring it to top, else create a new object.
The name 'getSupportFragmentManager' does not exist in the current context
My Code:
using Android.Views;
using Android.OS;
using Android.Support.V4.App;
using com.refractored;
using Android.Support.V4.View;
namespace XamarinStore
{
public class HomeFragment : Android.App.Fragment
{
BadgeDrawable basketBadge;
int badgeCount;
public override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
RetainInstance = true;
SetHasOptionsMenu(true);
// Create your fragment here
}
public override View OnCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState)
{
var HomePage = inflater.Inflate(Resource.Layout.HomeLayout, container, false);
var pager = HomePage.FindViewById<ViewPager>(Resource.Id.pager);
pager.Adapter = new MyPagerAdapter(SupportFragmentManager);
var tabs = HomePage.FindViewById<PagerSlidingTabStrip>(Resource.Id.tabs);
tabs.SetViewPager(pager);
return HomePage;
}
}
public class MyPagerAdapter : FragmentPagerAdapter{
private string[] Titles = {"Categories", "Home", "Top Paid", "Top Free", "Top Grossing", "Top New Paid",
"Top New Free", "Trending"};
public MyPagerAdapter(Android.Support.V4.App.FragmentManager fm) : base(fm)
{
}
public override Java.Lang.ICharSequence GetPageTitleFormatted (int position)
{
return new Java.Lang.String (Titles [position]);
}
#region implemented abstract members of PagerAdapter
public override int Count {
get {
return Titles.Length;
}
}
#endregion
#region implemented abstract members of FragmentPagerAdapter
public override Android.Support.V4.App.Fragment GetItem (int position)
{
return SuperAwesomeCardFragment.NewInstance (position);
}
#endregion
}
}
How to get access to getSupportFragmentManager in fragment ..
I'am using xamarin cross platform development tool.. with the help of sample project from this source https://xamarin.com/c-sharp-shirt
In the demo project if BackStackEntryCount count equals to zero it switch screen to another fragment.. so i replaced code with new homefragment i decided to add tabs in the that.. so i tried to use this component "Material Pager Sliding Tab Strip" .. while using that component it stops with this error.
the name 'getSupportFragmentManager' does not exist in the current context
http://components.xamarin.com/view/PagerSlidingTabStrip
First i inherit HomeFragment to Android.Support.V4.App.Fragment
Then i used ChildFragmentManager instead of SupportFragmentManager
pager.Adapter = new MyPagerAdapter(ChildFragmentManager);
You can also do:
using Fragment = Android.Support.V4.App.Fragment;
using FragmentManager = Android.Support.V4.App.FragmentManager;
public class YourFragment : Fragment
{
//...
//To access to FragmentManager use base.FragmentManager
//Example:
base.FragmentManager.BeginTransaction()
.Replace(Resource.Id.content_frame, fragment)
.Commit();
//...
}
The first two lines (using...) are very useful if
you work only with Fragment and FragmentManager from Support
and you have clear about not mixing them with normal Fragment and FragmentManager.
In Xamarin Android you should be able to access this using FragmentManager and you need to inherit from Android.Support.V4.App.Fragment
like so:
public class HomeFragment : Android.Support.V4.App.Fragment
{
BadgeDrawable basketBadge;
int badgeCount;
public override void OnCreate(Bundle savedInstanceState)
{
base.OnCreate(savedInstanceState);
RetainInstance = true;
SetHasOptionsMenu(true);
var count = FragmentManager.BackStackEntryCount;
// Create your fragment here
}
getActivity 's equivalent in Xamarin is Activity (when used in a class that inherits from Android.Support.V4.App.Fragment for example)
I am not familiar with Xamarin but in native android development you cannot access FragmentManager from a Fragment using getFragmentManager or getSupportFragmentManager methods. From API 17 you can call getChildFragmentManager method to get a FragmentManager instance that allows you to manage fragments from another fragment.
getChildFragmentManager().beginTransaction().add(...).commit();
getChildFragmentManager().executePendingTransactions();
public class HomeFragment : FragmentActivity
Extend your class using FragmentActivity will solve your problem
I have a MainActivity (FragmentActivity) that has a FragmentTabHost.
public class FragmentTabs extends FragmentActivity {
private FragmentTabHost mTabHost;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.fragment_tabs);
mTabHost = (FragmentTabHost)findViewById(android.R.id.tabhost);
mTabHost.setup(this, getSupportFragmentManager(), R.id.realtabcontent);
mTabHost.addTab(mTabHost.newTabSpec("classA").setIndicator("Class A"),
ClassA.class, null);
mTabHost.addTab(mTabHost.newTabSpec("classB").setIndicator("Class B"),
ClassB.class, null);
mTabHost.addTab(mTabHost.newTabSpec("classC").setIndicator("Class C"),
ClassC.class, null);
}
}
ClassA, ClassB and ClassC are all Fragments (android.support.v4.app.Fragment).
I need to pass data (and call methods) on the Fragments. How can I get a reference of each of the Fragments, like this:
ClassA mClassAFragment = ???;
I’ve tried using getSupportFragmentManager().findFragmentByTag() and I’ve also tried exploring the capabilities of mTabHost. Nothing can get them.
Can you suggest a way to do this or suggest an alternative approach?
And i tried used this...
Bundle arguments = new Bundle();
arguments.putString("some id string", "your data");
YourFragment fragment = new YourFragment();
fragment.setArguments(arguments);
getSupportFragmentManager().beginTransaction().add(R.id.fragmentid, fragment).commit();
but i dont know how can use this R.id.fragmentid if my add tabs is well:
mTabHost.addTab(mTabHost.newTabSpec("classA").setIndicator("Class A"),
ClassA.class, null);
Anyone help me?
Define the Fragments in your Activity as public. Then in each Fragment you also reference the Activity.
In your Activity:
public ClassAFragment aFragment;
...
// during initialization:
aFragment = new ClassAFragment();
// or you get it from your TabHost
FragmentManager fm = getFragmentManager();
aFragment = fm.findFragmentByTag("ClassA");
aFragment.mActivity = this;
// same with B and C
In your Fragments:
public MainActivity mActivity;
...
// in Fragment C
String newText = mActivity.aFragment.editText.getText().toString() + mActivity.bFragment.editText.getText().toString();
textView.setText(newText);
I am following the example FragmentTabsPager under the Samples from ActionBarSherlock.
In my case, I have created a simple SherlockActivity with the TabsPager and the same code from the sample for the FragmentPagerAdapter.
I created two fragments (different classes). The first one contains just four buttons. Depending of which one is clicked, the main Activity gets a code (e.g. 1,2,3,4). I get correctly the code for the pressed button.
Now, in the second Fragment I want to draw something depending on that code, or what is the same, update dynamically its view.
I have been searched for a solution but I haven´t got anything. In this case I have this:
[MainActivity.java]
public static class TabsAdapter extends FragmentPagerAdapter
implements TabHost.OnTabChangeListener, ViewPager.OnPageChangeListener {
private final Context mContext;
private final TabHost mTabHost;
private final ViewPager mViewPager;
private final ArrayList<TabInfo> mTabs = new ArrayList<TabInfo>();
[...]
#Override
public Fragment getItem(int position) {
TabInfo info = mTabs.get(position);
return Fragment.instantiate(mContext, info.clss.getName(), info.args);
}
I managed to update the Bundle info.args with the new value, but I don´t know how to pass it to the fragment correctly and order it to update its dynamic View.
Is this possible?
Thanks in advance.
UPDATE
Finally, I used what Sunny kindly explained. I kept an SparseArray with my Fragments so I could definitely access them as I know its position inside MainActivity:
[MainActivity.java]
//Once the user presses the button on the first fragment, the callback calls
// this function
public void onImageSelected(int iNumber){
MySecondFragment msf = (MySecondFragment)mTabsAdapter.getFragment(POS_1);
if(msf != null){
msf.setNumImage(iNumber);
msf.updateView();
}
}
And finally in MySecondFragment.java I can access my Layout components (e.g. a GridView), as they were initialized during onCreateView, so I put all the code I needed inside my updateView() method.
For instance, I update the content of a GridView:
[MySecondFragment.java]
myGridView.setBackground(getResources().getDrawable(iCode));
HTH
UPDATE 2
I have included the following code in order to save the fragments into the state bundle of the main activity. When the application changes from portrait to landscape or viceversa (it is recreated) the function getItem is not being called, so the SparseArray map is not refilled again with the necessary Fragments:
#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putString(CURRENT_TAB, mTabHost.getCurrentTabTag());
getSupportFragmentManager().putFragment(outState, MyFirstFragment.class.getName(), mTabsAdapter.getFragment(POS_1));
getSupportFragmentManager().putFragment(outState, MySecondFragment.class.getName(),
mTabsAdapter.getFragment(POS_2));
}
#Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
if (savedInstanceState != null) {
MyFirstFragment mff = (MyFirstFragment) getSupportFragmentManager().getFragment(savedInstanceState, MyFirstFragment.class.getName());
if(mff != null)
mTabsAdapter.setFragment(POS_1, mff);
MySecondFragment msf = (MySecondFragment) getSupportFragmentManager().getFragment(
savedInstanceState, MySecondFragment.class.getName());
if(msf != null)
mTabsAdapter.setFragment(POS_2, msf);
mTabHost.setCurrentTabByTag(savedInstanceState
.getString(CURRENT_TAB));
}
}
Also, inside the TabsAdapter class:
public Fragment getFragment(int pos) {
return map.get(pos);
}
public void setFragment (int position, Fragment fragment) {
map.put(position, fragment);
}
HTH
The source for FragmentPagerAdapter shows that Fragments are given the following tag:
"android:switcher:" + viewId + ":" + id;
Where viewId is the R.id of your ViewPager and id is the page number.
Therefore you can retrieve the second page's Fragment by using:
activity.getSupportFragmentManager().findFragmentByTag(
"android:switcher:" + pager.getId() + ":2")
Where pager is your ViewPager. You'd then want to cast that returned Fragment to whatever specific class you have, then call a method to pass in the information you need.
anhanniballake answer might work. But This might break in future.
To actually get the fragment you can define a sparesArray in your TabAdapter class
private SparseArray<Fragment> map;
and add your fragments in this array
#Override
public Fragment getItem(int position) {
TabInfo info = mTabs.get(position);
Fragment fragment = Fragment.instantiate(mContext, info.clss.getName(), info.args);
map.put(position, fragment);
return fragment;
}
You also need to remove the fragment from map when fragment get destroy
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
map.remove(position);
super.destroyItem(container, position, object);
}
Now define a public method in TabAdapter class which can get Fragments
public Fragment getFragment(int pos) {
return map.get(pos);
}
Now in Your Main SherlockFragementActivity you can get the instance of any fragment
MyFragment f = (MyFragment) mTabsAdapter.getFragment(1); // 1 means second fragment from left
Now call any method in your fragments using the fragment instance you got above
f.doAnyThingInMySecondFragment();
doAnyThingInMySecondFragment must be declared public :)
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" })