I am aware that when you would like to communicate between fragments you should do so via the parent activity. It makes sense when the two fragments are on the same level. If one is nested within the second It makes little sense to "go up" only to return "down".
In this scenario the pattern makes sense:
Activity
____|____
/ \
Frag A Frag B
It makes little sense to use the pattern when one is nested within the other:
Activity
|
Frag A
|
Frag B
Is it acceptable to communicate directly using findFragmentByTag(FRAG_X_TAG) if one is nested within the other?
The idea of this pattern is to use the Activity as a Controller interface, to which the Fragments are Views - they send UI events to the Controller, which in turn updates them as appropriate.
This means that the real question here should be "Is Frag A a Controller for Frag B" - if so, direct communication would be acceptable. If both are just "dumb Views", they really shouldn't know about each other.
The bottom line is that you want to avoid making spaghetti code, which is possible as long as you enforce separation of concerns.
According to API 4.2 documentation, you should use getChildFragmentManager()
You can always use BusEvent library, it eases communication between components, but you may also lose code intelligibility.
It sounds like you could use an Event Bus. These are some of the most popular choices:
Otto by Square: http://square.github.io/otto/
EventBus by GreenRobot: https://github.com/greenrobot/EventBus
Another option is to use Model–view–viewmodel (MVVM) artchitecture that google promotes in Google Architecture components:
public class SharedViewModel extends ViewModel {
private final MutableLiveData<Item> selected = new MutableLiveData<Item>();
public void select(Item item) {
selected.setValue(item);
}
public LiveData<Item> getSelected() {
return selected;
}
}
public class MasterFragment extends Fragment {
private SharedViewModel model;
public void onViewCreated(#NonNull View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
model = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);
itemSelector.setOnClickListener(item -> {
model.select(item);
});
}
}
public class DetailFragment extends Fragment {
public void onViewCreated(#NonNull View view, Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
SharedViewModel model = new ViewModelProvider(requireActivity()).get(SharedViewModel.class);
model.getSelected().observe(getViewLifecycleOwner(), { item ->
// Update the UI.
});
}
}
More info:
https://developer.android.com/topic/libraries/architecture/viewmodel#sharing
If you want to activte morethan 1 fragment at the same time... then use the method getChildFragmentManager()
eg:
I have a main fragment called "ShareSpace" and has 3 child fragment..
//In ShareSpace Fragment
View view = inflater.inflate(R.layout.fragment_sharespace, container, false);
mTabletSize = getResources().getBoolean(R.bool.isTablet);
mContext=getActivity();
ViewPager pager = (ViewPager) view.findViewById(R.id.pager);
ShareSpaceAdapter pagerAdapter = new ShareSpaceAdapter(mContext,getChildFragmentManager());
pager.setAdapter(pagerAdapter);
mSlidingTabLayout = (SlidingTabLayout) view.findViewById(R.id.sliding_tabs_share);
mSlidingTabLayout.setViewPager(pager);
//In Adapter
public ShareSpaceAdapter(Context mContext, FragmentManager fm) {
super(fm);
this.mContext = mContext;
// TODO Auto-generated constructor stub
try {
if (home == null) {
homeFact = FactoryGenerator.getFactory(Constants.HOME);
home = homeFact.getHomeManagement(Constants.SHARESPACE);
}
local = home.readAssets(mContext);
} catch (Exception e) {
e.printStackTrace();
}
}
#Override
public Fragment getItem(int arg0) {
Fragment frgmt = null;
switch (arg0) {
case 0:
frgmt = new ShareSpaceFiles(mContext);
break;
case 1:
frgmt=new ShareSpaceFolder(mContext);
break;
case 2:
frgmt = new ShareSpaceInbox(mContext);
break;
default:
break;
}
return frgmt;
}
#Override
public int getCount() {
return PAGE_COUNT;
}
#Override
public CharSequence getPageTitle(int position) {
switch (position) {
case 0: // Fragment # 0 - This will show FirstFragment
return local.getmFiles();//"FILES";
case 1: // Fragment # 0 - This will show FirstFragment different title
return local.getmFolders();//"FOLDERS";
case 2:
return local.getmMessages();//"MESSAGES";
default:
return null;
}
}
It will load 3 child fragment at the same time
I've recently tried to use an interface for fragment-activity communication. The idea is that when a button is pressed in a fragment, it retrieves data from an EditText in the same fragment, it then sends the string to the MainActivty - this controls all my fragments - which then starts another fragment and delivers the string to this fragment for use later, however, I'm having trouble initially setting up the first interface which sends the data. Unfortunately nothing happens, and I cannot therefore get to the next fragment which should be displayed. Additionally I have tried using getActivity() but it cannot find the associated method within the fragment, leading me to believe that the fragments somehow aren't directly connected to MainActivity (I've only just grasped basics of Java and a little of Android, just learning.)
I've listed the relevant information below, thanks for the assistance!
Fragment
public class CreateWorkoutFragment extends Fragment implements OnClickListener {
View rootViewCreateWorkoutFragment;
EditText editTextWorkoutName;
// Using an ImageView for custom button
ImageView buttonNext;
String valueCreateWorkoutEditText;
OnDataPass dataPasser;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
rootViewCreateWorkoutFragment = inflater.inflate(R.layout.fragment_create_workout, container, false);
buttonNext = (ImageView) rootViewCreateWorkoutFragment.findViewById(R.id.button_workout_name_next);
editTextWorkoutName = (EditText) rootViewCreateWorkoutFragment.findViewById(R.id.edit_text_workout_name);
buttonNext.setOnClickListener(this);
return rootViewCreateWorkoutFragment;
}
public interface OnDataPass {
public void onDataPass(String data);
}
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
dataPasser = (OnDataPass) activity;
}
public void passData(String data) {
dataPasser.onDataPass(data);
}
#Override
public void onClick(View v) {
switch (v.getId()) {
case R.id.button_workout_name_next:
valueCreateWorkoutEditText = editTextWorkoutName.getText().toString();
passData(valueCreateWorkoutEditText);
break;
}
}
}
Main Activity
public class MainActivity extends FragmentActivity implements OnClickListener, CreateWorkoutFragment.OnDataPass {
ImageView buttonCreate;
Fragment newFragment;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setTheme(R.style.AppThemeBlue);
setContentView(R.layout.activity_main);
buttonCreate = (ImageView) findViewById(R.id.create_foreground);
buttonCreate.setOnClickListener(this);
FragmentManager fragManager = getSupportFragmentManager();
FragmentTransaction tranManager = fragManager.beginTransaction();
CreateWorkoutFragment createWorkoutFrag = new CreateWorkoutFragment();
// fragment_change is just the area in XML where fragments switch
tranManager.add(R.id.fragment_change, createWorkoutFrag);
tranManager.commit();
newFragment = null;
}
#Override
public void onDataPass(String data) {
// CreateFragment is not to be confused with CreateWorkoutFragment
// CreateFragment is the fragment I'm trying to start when any strings
// are obtained from CreateWorkoutFragment
newFragment = new CreateFragment();
}
#Override
public void onClick(View v) {
switch (v.getId()) {
// create_foreground is just an ImageView used as a button
// Additionaly, other buttons are used to create other fragments,
// I've cut them out currently as they are not nessesary which is
// why CreateWorkoutFragment is only button and default currently
case R.id.create_foreground:
newFragment = new CreateWorkoutFragment();
break;
default:
newFragment = new CreateWorkoutFragment();
}
FragmentTransaction tranManager = getSupportFragmentManager().beginTransaction();
tranManager.replace(R.id.fragment_change, newFragment);
tranManager.addToBackStack(null);
tranManager.commit();
}
}
Sorry the code isn't exactly tidy, however, it was the most relevant code cut out from a large class. As I said, I have tried other methods yet cannot get any response from MainActivity either way. Thanks in advance!
Just before I posted: Got the app to write logcat messages to me, it manages to pass the data when the button is clicked - at least I think, and is something to do with the fragment not starting! At MainActivity>onDataPass()>new Fragment = new CreateFragment() Any ideas? As mentioned before, other buttons do exist and manage to change the fragment. However, were cutout to reduce amount of code posted.
getActivity() but it cannot find the associated method within the fragment
This is because getActivity() returns an Activity, not a MainActivity which is your custom subclass. You can easily fix this with a cast. For example, in your fragment, you can do this:
OnDataPass main = (OnDataPass) getActivity();
main.onDataPass(message);
Since such a cast is required, the interface seems to get in the way in my opinion. You can just as easily cast directly to MainActivity:
MainActivity main = (MainActivity) getActivity();
main.onDataPass(message);
I am trying to implement fragment communication in android like the one in the android guide http://developer.android.com/guide/components/fragments.html#CommunicatingWithActivity
but my application is crashing as the getSupportFragmentManager().findFragmentById() returns null. What is the issue with my implementation.
The code is given below:
The program is just to send an input text from one fragment to another fragment textView area through a button click from first fragmnet.I have an activity_main.xml and two fragment layout (two separate xml files rather than part of in activity_main.xml)
Frag1.java
public class Frag1 extends Fragment {
public Frag1(){
}
buttonClickListener buttonListener;
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
buttonListener = (buttonClickListener) getActivity();
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString() + " must implement OnButtonPressListener");
}
}
View myFragmentView;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
myFragmentView = inflater.inflate(R.layout.frag1, container, false);
//SetValue Button
Button setValueButton = (Button) myFragmentView.findViewById(R.id.setValueButton);
setValueButton.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
buttonListener.onButtonPressed("Message received");
}
});
return myFragmentView;
}
}
Frag2.java
public class Frag2 extends Fragment {
View myFragmentView;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
myFragmentView = inflater.inflate(R.layout.frag2, container, false);
return myFragmentView;
}
void setMessage(String msg){
TextView txt=(TextView)myFragmentView.findViewById(R.id.textView1);
txt.setText(msg);
}
}
buttonClickListener.java
public interface buttonClickListener {
public void onButtonPressed(String msg);
}
MainActivity.java
public class MainActivity extends FragmentActivity implements
ActionBar.TabListener, buttonClickListener {
SectionsPagerAdapter mSectionsPagerAdapter;
#Override
public void onButtonPressed(String msg) {
// TODO Auto-generated method stub
Frag2 fragmentObj=(Frag2) getSupportFragmentManager().findFragmentById(R.layout.frag2);
fragmentObj.setMessage(msg);
}
Please tell me where did I go wrong?
EDIT:
I am using fragment creation using the template generated by Android Plug-in eclipse IDE.
So the fragments are created using android.support.v4.app.Fragment
#Override
public Fragment getItem(int position) {
Fragment fragment = null;
switch(position)
{
case 0:
return new Frag1();
case 1:
return new Frag2();
}
return fragment;
}
The codebase is kept here for reference
https://skydrive.live.com/redir?resid=D37E0F56FEC9B499!259
Try This it works for me How to put Google Maps V2 on a Fragment Using ViewPager
<fragment
android:id="#+id/map"
android:layout_width="wrap_content"
android:layout_height="match_parent"
class="com.google.android.gms.maps.SupportMapFragment" />
GoogleMap mGoogleMap = ((SupportMapFragment) getChildFragmentManager().findFragmentById(R.id.map)).getMap();
You should have added the fragment Frag2 by calling
getSupportFragmentManager().beginTransaction().add(R.id.frag2_view, new Frag2(), "tag").commit();
at your MainActivity, where R.id.frag2_view is a layout defined in your main_layout.
To get that Fragment, you should then call
Frag2 obj = (Frag2)getSupportFragmentManager().findFragmentById(R.id.frag2_view);
passing the layout id you used to add the fragment in the main_layout.
Hope it helps.
EDIT:
Since you use a ViewPager, you should use R.id.pager as the ID.
I just tried with your example and it worked.
Frag2 fragmentObj=(Frag2) getSupportFragmentManager().findFragmentById(R.id.pager);
EDIT 2:
Despite it worked, I don't really think this is the correct way, since R.id.pager its from ViewPager and you can't find, let's say, frag4 or frag5.
Ignore my answer please. I'm not sure how to do that with ViewPager, sorry.
I was having a similar problem and here is the solution.
To get the reference to the proper fragment inside the viewpager just call:
getSupportFragmentManager().findFragmentByTag(tag);
The tag param you can build it using the following syntax: "android:switcher:pager_id:index", where pager_id is the id of the ViewPager in the XML layout and the index is the position of your fragment inside the ViewPager starting by zero. See the original response here: https://stackoverflow.com/a/7393477/2423274
Found the right solution for this question.
Hope more people see this.
Frag2 fragmentObj=(Frag2) mSectionsPagerAdapter.getItem(2);
You should use your Adapter (where you populate your fragments) as a source for get the Fragment reference.
I used this to get a child fragment from a fragment adapter...
Fragment parent = MainActivity.this.getSupportFragmentManager().findFragmentById(R.id.main_container);
if (parent instanceof PagerFragment) {
// do something with parent
Fragment child = ((PagerFragment) f).adapter.getItem(childPosition);
}
Firstly, I know these subjects have been created a lot of time on stackoverflow, but I don't have found the solution to my problems. Secondly, I'm french, so my english is not perfect, sorry per advance and tell me if you don't understand something. And to finish this introduction, it's the first time that I'm dealing with fragments, so, sorry if there is something that I don't have well understand !
I have three buttons, that allow to switch between three fragments.
Inside one of these fragments, I have a view pager with two fragments. For the moment, each fragments (there are 5), only contains a TextView.
I'm using the latest version of android-support-v4 (I have read a lot of subject in stackoverflow that say that the latest version of support solve the "Recursive entry to executePendingTransactions" error that I have).
My two problems :
When I click two times in one button, I have an IllegaleStateException "can't change tag of fragment". I was able to fix that by creating a new fragment on onButtonSelected method, but I don't want to recreate fragment each time, for memory reasons and for functional reasons : fragment have to keep her state. This problem is not my main problem, indeed, i know that to disable the button when user is already on fragment is possible, but it's strange to have an exception when this management is not done, no ?.
When I go out from the fragment with the view pager, and I go back to this fragment, I have an IllegalStateException "Recursive entry to executePendingTransactions". I can fix this by setting my adapter on an handler, or use FragmentStatePagerAdapter instead of FragmentPageAdapter (see Display fragment viewpager within a fragment), but even if my application don't crash, when I go back to my fragment with the view pager, the view pager has disapear !
Can you help me ?
Java source code is bellow, layout source code is, I think, useless.
MainActivity :
public class MainActivity extends SherlockFragmentActivity{
private SherlockFragment fragmentOne, fragmentTwo, fragmentThree;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// this.fragmentOne = new fragmentOne();
// this.fragmentTwo = new fragmentTwo();
// this.fragmentThree = new fragmentThree();
// Call new or instanciate ? What's the correct way ?
this.fragmentOne = (SherlockFragment) SherlockFragment.instantiate(this, FragmentOne.class.getName());
this.fragmentTwo = (SherlockFragment) SherlockFragment.instantiate(this, FragmentTwo.class.getName());
this.fragmentThree = (SherlockFragment) SherlockFragment.instantiate(this, FragmentThree.class.getName());
// Add fragment
FragmentTransaction transaction = (
this.getSupportFragmentManager().beginTransaction()
);
transaction.add(
R.id.tab_fragment,
this.fragmentOne,
this.fragmentOne.toString()
);
transaction.commit();
}
public void onButtonSelected(View v){
switch (v.getId()){
case R.id.button_one_tab:{
showFragment(this.fragmentThree);
break;
}
case R.id.button_two_tab:{
showFragment(this.fragmentOne);
break;
}
case R.id.button_three_tab:{
showFragment(this.fragmentTwo);
break;
}
default:{
break;
}
}
}
public void showFragment(SherlockFragment fragmentToShow){
FragmentTransaction transaction = (
this.getSupportFragmentManager().beginTransaction()
);
transaction.replace(R.id.tab_fragment, fragmentToShow, fragmentToShow.toString());
transaction.commit();
}
}
Fragment two and three only inflate a layout that only contains a TextView.
Fragment one (note that i'm using a DirectionalViewPager - a lib - instead of a ViewPager):
public class FragmentOne extends SherlockFragment{
private FragmentOneAdapter fragmentOneAdapter;
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
// Set up the pager
final DirectionalViewPager pager = (DirectionalViewPager)getActivity().findViewById(R.id.pager);
if (this.fragmentOneAdapter== null){
this.fragmentOneAdapter= new FragmentOneAdapter (getActivity().getSupportFragmentManager());
}
pager.setAdapter(fragmentOneAdapter);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_landing_page, container, false);
}
FragmentOneAdapter :
public class FragmentOneAdapter extends FragmentPagerAdapter{
private ArrayList<SherlockFragment> fragmentsList;
public FragmentOneAdapter(FragmentManager fragmentManager) {
super(fragmentManager);
SherlockFragment fragmentFour = new FragmentFour();
SherlockFragment fragmentFive = new FragmentFive();
this.fragmentsList = new ArrayList<SherlockFragment>();
this.fragmentsList.add(fragmentFour);
this.fragmentsList.add(fragmentFive);
}
#Override
public Fragment getItem(int position) {
return this.fragmentsList.get(position);
}
#Override
public int getCount() {
return this.fragmentsList.size();
}
}
Thanks per advance for your help !
I have solved my problem !
I have simply replace getSupportFragmentManager() on FragmentOne to getChildFragmentManager(). Then, I have edited my onButtonSelected's method by creating a new instance of fragment each time instead of using my three different instances (if I don't do that, I have an exception : java.lang.IllegalStateException: Activity has been destroyed).
I have still a problem with this solution : I lose the state of each fragment each time I'm switching between fragmentOne, fragmentTwo and fragmentThree. Do you have a solution for that ?
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" })