This one is a bit hard to explain and demonstrate. I will try my best.
I have two fragments ItemListFragment and ItemViewFragment : a fragment with a recycleview and listing inside the recycleview and a fragment displaying a single item respectively.
In the ItemListFragment, there is RecyclerViewClickListener to handle clicks on items of the list.
The implementation is as followed:
public class ItemListFragment extends Fragment {
private OnFragmentListClickListener onClickListener = null;
public interface OnFragmentListClickListener {
void OnFragmentListClick(ItemModel Item);
}
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
class RecyclerViewClickListenerImpl implements RecyclerViewClickListener {
#Override
public void onClick(View view, int position) {
if (onClickListener != null) {
onClickListener.OnFragmentListClick(adapter.getItem(position));
}
}
adapter = new ItemListAdapter(getActivity(), ItemModelList, new RecyclerViewClickListenerImpl());
mRecyclerView = getActivity().findViewById(R.id.recycler_view);
RecyclerView.LayoutManager mLayoutManager = new GridLayoutManager(getActivity(), 2);
mRecyclerView.setLayoutManager(mLayoutManager);
mRecyclerView.setItemAnimator(new DefaultItemAnimator());
mRecyclerView.setAdapter(adapter);
.
.
.
}
#Override
public void onAttach(Context context) {
super.onAttach(context);
Toast.makeText(getActivity(), "onAttach", Toast.LENGTH_SHORT).show();
if (context instanceof OnFragmentListClickListener) {
onClickListener = (OnFragmentListClickListener) context;
}
}
.
.
.
}
The list contains thumbnail (loaded with Glide) and a text for each time.
When I add this fragment in my activity implementing the ItemListFragment.OnFragmentListClickListener interface, everything works fine using the code below:
public class MainActivity extends AppCompatActivity
implements ItemListFragment.OnFragmentListClickListener {
.
.
.
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
ItemListFragment fragment_list = ItemListFragment.newInstance();
FragmentManager fragmentManager = getSupportFragmentManager();
FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
fragmentTransaction.replace(R.id.content_frame, fragment_list);
fragmentTransaction.commit();
}
#Override
public void OnFragmentListClick(CameraModel camera) {
// handle the list click
}
.
.
.
}
Things get weird when I try to add a second fragment (ItemViewFragment) in my activity as followed:
When there is a second fragment, the RecyclerViewClickListener's onClick on the ItemListFragment is not called anymore:
class RecyclerViewClickListenerImpl implements RecyclerViewClickListener {
#Override
public void onClick(View view, int position) {
if (onClickListener != null) {
onClickListener.OnFragmentListClick(adapter.getItem(position));
}
}
Also, certain thmbnails in the ItemListFragment stopped working when a second fragment has been added in the activity.
This is a weird one... I tried using fragmentTransaction.add instead of fragmentTransaction.add also and all kind of combinations...
You want put your onClick in item of recycle view. You should do every thing of item (like: load image, make event for view,... ) in ViewHolder class. Beacause that's easier to view source code in your activity or fragment. You can references my ViewHolder class with this link. It will help you.
I have a fragment containing a RecyclerView and a button. The fragment is brought up on pressing a button (which adds some data) in a previous fragment, and the recycler shows correctly populated, the button works. Then I go back to the previous fragmen, press the button again (adding more data) and the same piece of code brings up the same fragment, but the RecyclerView is unpopulated and the button doesn't work. From reading this question my guess is that I am doing something in my Fragment management - because as soon as I change orientation and the Fragment is recreated, the list shows fine and the button works fine.
So here is the management I'm doing on the fragments - I took it from an example on the internet, but I'm worried it's not correct
First there is a Base class which I make for my fragments:
public class BaseFragment extends Fragment {
private AbstractFragmentCallback mCallback;
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
try {
mCallback = (AbstractFragmentCallback) activity;
} catch (ClassCastException e) {
throw new ClassCastException(activity.toString()
+ " must implement " +
AbstractFragmentCallback.class.getCanonicalName());
}
}
/**
* This method replaces the currently shown fragment with a new
fragment of a particular class.
* If a fragment of the required class already shown - does
nothing.
* #param clazz the class of the fragment to show
* #param addToBackStack whether the replacement should be added
to back-stack
* #param args arguments for the newly created fragment (can be
null)
*/
public void replaceFragment(Class<? extends Fragment> clazz,
boolean addToBackStack,
Bundle args) {
mCallback.replaceFragment(clazz, addToBackStack, args);
}
public interface AbstractFragmentCallback {
/**
* Call to this method replaces the currently shown fragment
with a new one
*
* #param clazz the class of the new fragment
* #param addToBackStack whether the old fragment should be
added to the back stack
* #param args arguments to be set for the new fragment
*/
void replaceFragment(Class<? extends Fragment> clazz, boolean addToBackStack,
Bundle args);
}
}
So then my MainActivity implements the BaseFragment.AbstractfragmentCallback so:
public class MainActivity extends AppCompatActivity implements BaseFragment.AbstractFragmentCallback {
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(....);
if (null == savedInstanceState) {
replaceFragment(WelcomeFragment.class, false, null);
}
}
// ---------------------------------------------------------------------------------------------
//
// Fragments management
#Override
public void replaceFragment(Class<? extends Fragment> clazz, boolean addToBackStack,
Bundle args) {
FragmentTransaction ft = getSupportFragmentManager().beginTransaction();
Fragment newFragment;
try {
// Create new fragment
newFragment = clazz.newInstance();
if (args != null) newFragment.setArguments(args);
} catch (InstantiationException e) {
e.printStackTrace();
return;
} catch (IllegalAccessException e) {
e.printStackTrace();
return;
}
if (addToBackStack) {
ft.addToBackStack(null);
}
// Change to a new fragment
ft.replace(R.id.container, newFragment, clazz.getName());
ft.commit();
}
// End of fragments management
//
// ---------------------------------------------------------------------------------------------
}
and when my fragment with the button wants to bring up the list fragment it calls
replaceFragment(ListFragment.class, true, null);
So - to be clear, the ListFragemnt comes up, and all its code fires including recrersating the RecyclerView and repopulating it - I even see all the code in the adapter being called for each item - but the items do not appear in the list
public class ListFragment extends BaseFragment implements ListFragmentMvc.ListViewMvcListener {
private List<MyStuff> stuffList;
#Override
public View onCreateView(#NonNull LayoutInflater inflater, ViewGroup container, Bundle savedInstance) {
stuffList = new ArrayList<>();
return inflater.inflate(R.layout.list_activity, container, true);
}
#Override
public void onResume() {
super.onResume();
recyclerView = mRootView.findViewById(R.id.recycler_view);
letsGoButton = mRootView.findViewById(R.id.lets_go_button);
letsGoButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Activity activity = getActivity();
if (activity != null) {
getActivity().onBackPressed();
}
}
});
recyclerView.setItemAnimator(new DefaultItemAnimator());
DividerItemDecoration itemDecor = new DividerItemDecoration(context, HORIZONTAL);
recyclerView.addItemDecoration(itemDecor);
RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(context);
recyclerView.setLayoutManager(mLayoutManager);
setData(MyApplication.getAllStuffItems());
}
public void setData(List<MyStuff> stuff) {
stuffList = stuff;
mAdapter = new StuffAdapter(stuffList);
recyclerView.setAdapter(mAdapter);
mAdapter.notifyDataSetChanged();
}
}
So, anyone have a clue why this doesn't work until I change orientation on re-entering the listFragment?
Thanks
Can you try to move the code which sets/updates the recyclerView and letsGoButton from the onResume method to onViewCreated method as below:
#Override
public void onViewCreated(#NonNull View view, #Nullable Bundle savedInstanceState) {
super.onViewCreated(view, savedInstanceState);
recyclerView = view.findViewById(R.id.recycler_view);
letsGoButton = view.findViewById(R.id.lets_go_button);
letsGoButton.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
Activity activity = getActivity();
if (activity != null) {
getActivity().onBackPressed();
}
}
});
recyclerView.setItemAnimator(new DefaultItemAnimator());
DividerItemDecoration itemDecor = new DividerItemDecoration(context, HORIZONTAL);
recyclerView.addItemDecoration(itemDecor);
RecyclerView.LayoutManager mLayoutManager = new LinearLayoutManager(context);
recyclerView.setLayoutManager(mLayoutManager);
setData(MyApplication.getAllStuffItems());
}
Wow, that was a wild waste of a day.
In the end I had a couple of errors which were pasting over and hiding each other.
The real real reason this wasn't working, I think was because I should have had
return inflater.inflate(R.layout.list_activity, container, false);
instead of
return inflater.inflate(R.layout.list_activity, container, true);
I lied a little in my code because I wasn't really directly returning the result of inflater.inflate... I was calling it (with the wrong parameter) and then returning null.
I guess that will teach me to be more honest in the posting
If we have 4 pages in a View pager and swipe from positions 0 do 3
Item at position 0 is destroyed when we get to position 2, item at position 1 is destroyed when we get to position 4.
I need them to be destroyed right away, because I want the view to be recreated if I go back to it, which doesnt happen at the moment.
public class ViewPagerTutorialAdapter extends FragmentStatePagerAdapter {
public ViewPagerTutorialAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
Bundle args = new Bundle();
args.putInt("page", position);
TutorialPageFragment fragment = new TutorialPageFragment();
fragment.setArguments(args);
return fragment;
}
#Override
public int getCount() {
return 4;
}
}
public class TutorialPageFragment extends android.support.v4.app.Fragment {
private ImageView ivTutorialPage;
private TransitionDrawable myTransitionDrawable;
private View rootView;
public TutorialPageFragment() {
}
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
rootView = inflater.inflate(R.layout.fragment_tutorial_page, container, false);
return rootView;
}
#Override
public void onResume() {
super.onResume();
ivTutorialPage = (ImageView) rootView.findViewById(R.id.ivTutorialPage);
ivTutorialPage.setImageResource(R.drawable.fadein);
myTransitionDrawable = (TransitionDrawable) ivTutorialPage.getDrawable();
new Timer().schedule(new TimerTask() {
#Override
public void run() {
getActivity().runOnUiThread(new Runnable() {
#Override
public void run() {
myTransitionDrawable.startTransition(1000);
}
});
}
}, 1000);
}
}
While this is not exactly answer to asked question, a better practice is not recreate Views if not necessary because it can be expensive to do on more complicated layouts + cause stuttering / extra lag which makes user experience worse.
In this case (running animations when fragment becomes visible) it's better to override setUserVisibleHint in fragment with code to run animation which will trigger when user visits the screen. The main advantage is of course no need to recreate Views and allows Android to perform it's internal optimization naturally.
Try viewPager.setOffscreenPageLimit(1);. This should save only one page near selected one. There is not way to only load selected item at a time according to this.
I have my main activity actionbaractivity One where you can screenslide through some fragmets, on each fragment you have an imageView and a ListView where you can click any item and the image will change. Also in the menu options you have a button where you change to an almost exact activity: actiobbaractivity Two which also have this button to change to activity One
What I'm able to do is to keep the image when sliding the fragments, but unable to keep the fragments state's through the change of activities.
For example
I'm in activity One on fragment 3 with the image: "something". I click on the button to change to activity Two, I do things here and then, I click on the button to change to activity One and I want to see my fragment 3 with the image: "something" and not the default fragment 1 and default image
Im using ActionBarActivity, FragmentStatePagerAdapter and Fragment for each activity
Thanks for the help
According to the Activity and Fragment lifecycles (http://developer.android.com/reference/android/app/Activity.html#ActivityLifecycle and http://developer.android.com/guide/components/fragments.html#Lifecycle), the most reliable way of persisting states between activity/fragment changes is to use the default API for saving and restoring states:
When the activity/fragment is being dismissed (either because of a configuration change such as screen rotation or because the user requested to go to another activity/fragment), you can save its state in a Bundle object. When it is being created, you can restore its saved state, thus recreating a new instance exactly like the one the user left - so the user feels nothing has changed. This does not depend on the specific subclass of activity/fragment you are using.
I have implemented something like what you want: in my case, a fragment containing a menu with buttons that would each lead the user to another fragment containing a submenu with a "back" button. So if the user went from menu to submenu 1, then back to menu, then to submenu 2, then back to menu and finally again to submenu 1, I wanted that submenu 1 to appear just like the user has left it in the first time.
For that I have created:
1) an interface defining my submenu types, implemented by my activities so they could change between my submenus
2) a master generic class, which all my submenus would extend, that had a Bundle object to store their state
3) in my activities, I had an array of Bundle capable of storing one instance of each of my submenus (because I am only interested in restoring the last state, so I don't need more than one)
The interface (item 1):
public interface SubmenusManager {
public static enum Submenus {
ROOTMENU,
SUBMENU1,
SUBMENU2;
private static final int size = Submenus.values().length;
public static int size() {
return size;
}
public static int getId(Submenus test) {
switch(test) {
case SUBMENU1:
return 1;
case SUBMENU2:
return 2;
case ROOTMENU:
default:
return 0;
}
}
}
public void cloneCurrentSubmenuState(Parcelable toOverwrite);
public Bundle getLastStoredSubmenuState(Submenus submenu);
public void setCurrentSubmenuTo(Submenus submenu);
}
The generic class (item 2):
public class MenuFragment extends Fragment {
private Bundle menuData = new Bundle();
public static String RESTORE_MAIN_OBJECT = "restore_main";
public Bundle getMenuData() {
return menuData;
}
public Bundle cloneMenuData() {
return new Bundle(menuData);
}
public void setMenuData(Bundle menuData) {
this.menuData = menuData;
}
}
One of the activities (item 3):
public class ExampleAct extends FragmentActivity implements SubmenusManager {
/**
* instance variables
*/
private MenuFragment mMenu;
private Bundle [] menuData; // the Array of Bundles!
private static final String CONTAINER = "parcelable_container";
private static final String SUBMENU = "saved_submenu";
private Submenus curSubmenu = Submenus.ROOTMENU; // the default state is the ROOTMENU
private boolean restoreLastSavedState = false;
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
if (savedInstanceState == null) { // first time creating this activity
menuData = new Bundle[Submenus.size()];
} else { // this activity has a saved state from before
// restore all the data from all the submenus
menuData = (Bundle[]) savedInstanceState.getParcelableArray(CONTAINER);
// restore the info about which is the current active submenu
curSubmenu = (Submenus) savedInstanceState.getSerializable(SUBMENU);
}
buildMenuFragment(true);
//(...) stuff
}
private void buildMenuFragment(boolean restoreState) {
// (re)builds fragment inside menu.
// restoreState flags whether activity should look for
// saved state data and restore it
restoreLastSavedState = restoreState;
switch(curSubmenu) {
// Eclipse warns you about which are the constants in your enum
case ROOTMENU:
mMenu = new FragmentRootMenu();
break;
case SUBMENU1:
mMenu = new FragmentSubmenu1();
break;
case SUBMENU2:
mMenu = new FragmentSubmenu2();
break;
}
getSupportFragmentManager()
.beginTransaction()
.replace(R.id.menu_frame, mMenu)
.commit();
}
#Override
public void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
outState.putSerializable(SUBMENU, curSubmenu);
cloneCurrentSubmenuState(mMenu.getMenuData().
getParcelable(MenuFragment.RESTORE_MAIN_OBJECT));
outState.putParcelableArray(CONTAINER, menuData);
// (...) stuff
}
#Override
public void cloneCurrentSubmenuState(Parcelable toOverwrite) {
if (menuData == null) menuData = new Bundle[Submenus.size()];
if (toOverwrite != null)
mMenu.getMenuData().putParcelable(MenuFragment.RESTORE_MAIN_OBJECT, toOverwrite);
menuData[Submenus.getId(curSubmenu)] = mMenu.cloneMenuData();
}
#Override
public Bundle getLastStoredSubmenuState(Submenus forThisSubmenu) {
return
(menuData == null || !restoreLastSavedState) ? new Bundle() : menuData[Submenus.getId(forThisSubmenu)];
}
#Override
public void setCurrentSubmenuTo(Submenus toThisSubmenu) {
if (mMenu != null) {
cloneCurrentSubmenuState(mMenu.getMenuData().
getParcelable(MenuFragment.RESTORE_MAIN_OBJECT));
}
curSubmenu = toThisSubmenu;
buildMenuFragment(true);
}
One of the submenus (extension of item 2):
public class FragmentSubmenu1 extends MenuFragment {
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
return inflater.inflate(R.layout.fragment_submenu1, null);
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
init();
}
public void init() {
// (...) stuff
MyParcelableObject tmp = null; // MyParcelableObject is a class
// that implements Parcelable and stores
// relevant info to rebuild this menu
// from a saved state
SubmenusManager m = (SubmenusManager) getActivity(); // remember activity implements SubmenusManager
Bundle bnd = m.getLastStoredSubmenuState(SubmenusManager.Submenus.SUBMENU1);
if (bnd != null) tmp = bnd.getParcelable(MenuFragment.RESTORE_MAIN_OBJECT);
if (tmp == null) {
tmp = new MyParcelableObject();
tmp.buildFromScratch(); // initializes with default data
}
// back button
Button backToMainMenu = (Button) getView().findViewById(R.id.submenu1_back);
backToMainMenu.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
((SubmenusManager) getActivity()).
setCurrentSubmenuTo(SubmenusManager.Submenus.ROOTMENU);
}
});
// (...) stuff
}
}
The Root menu (extension of item 2):
public class FragmentRootMenu extends MenuFragment {
View myView;
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
myView = inflater.inflate(R.layout.fragment_rootmenu, null);
return myView;
}
#Override
public void onActivityCreated(Bundle savedInstanceState) {
super.onActivityCreated(savedInstanceState);
init();
}
public void init() {
Button btnSubmenu1 = (Button) myView.findViewById(R.id.btn_call_submenu1);
btnSubmenu1.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
((SubmenusManager) getActivity()).
setCurrentSubmenuTo(SubmenusManager.Submenus.SUBMENU1);
}
});
Button btnSubmenu2 = (Button) myView.findViewById(R.id.btn_call_submenu2);
btnSubmenu2.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
((SubmenusManager) getActivity()).
setCurrentSubmenuTo(SubmenusManager.Submenus.SUBMENU2);
}
});
}
}
For that to work between activities, all you need to do is pass that object that stores the last state of all fragments (in my case, that would be Bundle [] menuData) to the activity that is being called through its Intent; you would recover it the same way as my ExampleAct did in its onCreate(). You could also wrap that Bundle [] inside a custom Parcelable object (very similar to my example MyParcelableObject; inside that one I had stuff like HashMap) if using an array is a problem.
Here how to pass a Parcelable between activities:
How to send an object from one Android Activity to another using Intents?
I have narrowed my problem down to being a problem with the FragmentManager retaining instances of old fragments and my viewpager being out of sync with my FragmentManager. See this issue: http://code.google.com/p/android/issues/detail?id=19211#makechanges. I still have no clue how to solve this. Any suggestions?
I have tried to debug this for a long time and any help would be greatly appreciated. I am using a FragmentPagerAdapter which accepts a list of fragments like so:
List<Fragment> fragments = new Vector<Fragment>();
fragments.add(Fragment.instantiate(this, Fragment1.class.getName()));
...
new PagerAdapter(getSupportFragmentManager(), fragments);
The implementation is standard. I am using ActionBarSherlock and v4 computability library for Fragments.
My problem is that after leaving the app and opening several other applications and coming back, the fragments lose their reference back to the FragmentActivity (ie. getActivity() == null). I can not figure out why this is happening. I tried to manually set setRetainInstance(true); but this does not help. I figured that this happens when my FragmentActivity gets destroyed, however this still happens if I open the app before I get the log message. Are there any ideas?
#Override
protected void onDestroy(){
Log.w(TAG, "DESTROYDESTROYDESTROYDESTROYDESTROYDESTROYDESTROY");
super.onDestroy();
}
The adapter:
public class PagerAdapter extends FragmentPagerAdapter {
private List<Fragment> fragments;
public PagerAdapter(FragmentManager fm, List<Fragment> fragments) {
super(fm);
this.fragments = fragments;
}
#Override
public Fragment getItem(int position) {
return this.fragments.get(position);
}
#Override
public int getCount() {
return this.fragments.size();
}
}
One of my Fragments stripped but I commented everything out that's stripped and it still doesn't work.
public class MyFragment extends Fragment implements MyFragmentInterface, OnScrollListener {
...
#Override
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
handler = new Handler();
setHasOptionsMenu(true);
}
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
Log.w(TAG,"ATTACHATTACHATTACHATTACHATTACH");
context = activity;
if(context== null){
Log.e("IS NULL", "NULLNULLNULLNULLNULLNULLNULLNULLNULLNULLNULL");
}else{
Log.d("IS NOT NULL", "NOTNOTNOTNOTNOTNOTNOTNOT");
}
}
#Override
public void onActivityCreated(Bundle savedState) {
super.onActivityCreated(savedState);
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View v = inflater.inflate(R.layout.my_fragment,container, false);
return v;
}
#Override
public void onResume(){
super.onResume();
}
private void callService(){
// do not call another service is already running
if(startLoad || !canSet) return;
// set flag
startLoad = true;
canSet = false;
// show the bottom spinner
addFooter();
Intent intent = new Intent(context, MyService.class);
intent.putExtra(MyService.STATUS_RECEIVER, resultReceiver);
context.startService(intent);
}
private ResultReceiver resultReceiver = new ResultReceiver(null) {
#Override
protected void onReceiveResult(int resultCode, final Bundle resultData) {
boolean isSet = false;
if(resultData!=null)
if(resultData.containsKey(MyService.STATUS_FINISHED_GET)){
if(resultData.getBoolean(MyService.STATUS_FINISHED_GET)){
removeFooter();
startLoad = false;
isSet = true;
}
}
switch(resultCode){
case MyService.STATUS_FINISHED:
stopSpinning();
break;
case SyncService.STATUS_RUNNING:
break;
case SyncService.STATUS_ERROR:
break;
}
}
};
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
menu.clear();
inflater.inflate(R.menu.activity, menu);
}
#Override
public void onPause(){
super.onPause();
}
public void onScroll(AbsListView arg0, int firstVisible, int visibleCount, int totalCount) {
boolean loadMore = /* maybe add a padding */
firstVisible + visibleCount >= totalCount;
boolean away = firstVisible+ visibleCount <= totalCount - visibleCount;
if(away){
// startLoad can now be set again
canSet = true;
}
if(loadMore)
}
public void onScrollStateChanged(AbsListView arg0, int state) {
switch(state){
case OnScrollListener.SCROLL_STATE_FLING:
adapter.setLoad(false);
lastState = OnScrollListener.SCROLL_STATE_FLING;
break;
case OnScrollListener.SCROLL_STATE_IDLE:
adapter.setLoad(true);
if(lastState == SCROLL_STATE_FLING){
// load the images on screen
}
lastState = OnScrollListener.SCROLL_STATE_IDLE;
break;
case OnScrollListener.SCROLL_STATE_TOUCH_SCROLL:
adapter.setLoad(true);
if(lastState == SCROLL_STATE_FLING){
// load the images on screen
}
lastState = OnScrollListener.SCROLL_STATE_TOUCH_SCROLL;
break;
}
}
#Override
public void onDetach(){
super.onDetach();
if(this.adapter!=null)
this.adapter.clearContext();
Log.w(TAG, "DETACHEDDETACHEDDETACHEDDETACHEDDETACHEDDETACHED");
}
public void update(final int id, String name) {
if(name!=null){
getActivity().getSupportActionBar().setTitle(name);
}
}
}
The update method is called when a user interacts with a different fragment and the getActivity is returning null. Here is the method the other fragment is calling:
((MyFragment) pagerAdapter.getItem(1)).update(id, name);
I believe that when the app is destroyed then created again instead of just starting the app up to the default fragment the app starts up and then viewpager navigates to the last known page. This seems strange, shouldn't the app just load to the default fragment?
You are running into a problem because you are instantiating and keeping references to your fragments outside of PagerAdapter.getItem, and are trying to use those references independently of the ViewPager. As Seraph says, you do have guarantees that a fragment has been instantiated/added in a ViewPager at a particular time - this should be considered an implementation detail. A ViewPager does lazy loading of its pages; by default it only loads the current page, and the one to the left and right.
If you put your app into the background, the fragments that have been added to the fragment manager are saved automatically. Even if your app is killed, this information is restored when you relaunch your app.
Now consider that you have viewed a few pages, Fragments A, B and C. You know that these have been added to the fragment manager. Because you are using FragmentPagerAdapter and not FragmentStatePagerAdapter, these fragments will still be added (but potentially detached) when you scroll to other pages.
Consider that you then background your application, and then it gets killed. When you come back, Android will remember that you used to have Fragments A, B and C in the fragment manager and so it recreates them for you and then adds them. However, the ones that are added to the fragment manager now are NOT the ones you have in your fragments list in your Activity.
The FragmentPagerAdapter will not try to call getPosition if there is already a fragment added for that particular page position. In fact, since the fragment recreated by Android will never be removed, you have no hope of replacing it with a call to getPosition. Getting a handle on it is also pretty difficult to obtain a reference to it because it was added with a tag that is unknown to you. This is by design; you are discouraged from messing with the fragments that the view pager is managing. You should be performing all your actions within a fragment, communicating with the activity, and requesting to switch to a particular page, if necessary.
Now, back to your problem with the missing activity. Calling pagerAdapter.getItem(1)).update(id, name) after all of this has happened returns you the fragment in your list, which has yet to be added to the fragment manager, and so it will not have an Activity reference. I would that suggest your update method should modify some shared data structure (possibly managed by the activity), and then when you move to a particular page it can draw itself based on this updated data.
I found simple solution which worked for me.
Make your fragment adapter extends FragmentStatePagerAdapter instead of FragmentPagerAdapter and override method onSave to return null
#Override
public Parcelable saveState()
{
return null;
}
This prevent android from recreating fragment
One day later I found another and better solution.
Call setRetainInstance(true) for all your fragments and save references to them somewhere. I did that in static variable in my activity, because it's declared as singleTask and fragments can stay the same all the time.
This way android not recreate fragments but use same instances.
I solved this issue by accessing my fragments directly through the FragmentManager instead of via the FragmentPagerAdapter like so. First I need to figure out the tag of the fragment auto generated by the FragmentPagerAdapter...
private String getFragmentTag(int pos){
return "android:switcher:"+R.id.viewpager+":"+pos;
}
Then I simply get a reference to that fragment and do what I need like so...
Fragment f = this.getSupportFragmentManager().findFragmentByTag(getFragmentTag(1));
((MyFragmentInterface) f).update(id, name);
viewPager.setCurrentItem(1, true);
Inside my fragments I set the setRetainInstance(false); so that I can manually add values to the savedInstanceState bundle.
#Override
public void onSaveInstanceState(Bundle outState) {
if(this.my !=null)
outState.putInt("myId", this.my.getId());
super.onSaveInstanceState(outState);
}
and then in the OnCreate i grab that key and restore the state of the fragment as necessary. An easy solution which was hard (for me at least) to figure out.
Global working tested solution.
getSupportFragmentManager() keeps the null reference some times and View pager does not create new since it find reference to same fragment. So to over come this use getChildFragmentManager() solves problem in simple way.
Don't do this:
new PagerAdapter(getSupportFragmentManager(), fragments);
Do this:
new PagerAdapter(getChildFragmentManager() , fragments);
Do not try to interact between fragments in ViewPager. You cannot guarantee that other fragment attached or even exists. Istead of changing actionbar title from fragment, you can do it from your activity. Use standart interface pattern for this:
public interface UpdateCallback
{
void update(String name);
}
public class MyActivity extends FragmentActivity implements UpdateCallback
{
#Override
public void update(String name)
{
getSupportActionBar().setTitle(name);
}
}
public class MyFragment extends Fragment
{
private UpdateCallback callback;
#Override
public void onAttach(SupportActivity activity)
{
super.onAttach(activity);
callback = (UpdateCallback) activity;
}
#Override
public void onDetach()
{
super.onDetach();
callback = null;
}
public void updateActionbar(String name)
{
if(callback != null)
callback.update(name);
}
}
You can remove the fragments when destroy the viewpager, in my case, I removed them on onDestroyView() of my fragment:
#Override
public void onDestroyView() {
if (getChildFragmentManager().getFragments() != null) {
for (Fragment fragment : getChildFragmentManager().getFragments()) {
getChildFragmentManager().beginTransaction().remove(fragment).commitAllowingStateLoss();
}
}
super.onDestroyView();
}
After a few hours of looking for a similar issue I think a have another solution. This one at least it worked for me and I only have to changed a couple of lines.
This is the problem I had, I have an activity with a view pager that uses a FragmentStatePagerAdapter with two Fragments. Everything works fine until I force the activity to get destroyed (developer options) or I rotate the screen. I do keep a reference to the two fragments after they get created inside the method getItem.
At that point the activity will be created again and everything works fine at this point but I have lost the reference to my fragmetns as getItem doesn't' get called again.
This is how I fixed that problem, inside the FragmentStatePagerAdapter:
#Override
public Object instantiateItem(ViewGroup container, int position) {
Object aux = super.instantiateItem(container, position);
//Update the references to the Fragments we have on the view pager
if(position==0){
fragTabOne = (FragOffersList)aux;
}
else{
fragTabTwo = (FragOffersList) aux;
}
return aux;
}
You won't get a call on getItem again if the adapter already has a reference to it internally, and you shouldn't change that. Instead you can get the fragment it's being used by looking at this other method instantiateItem() which will be called for each of your fragments.
Hope that helps anyone.
Since people don't tend to read comments, here is an answer that mostly duplicates what I wrote here:
the root cause of the issue is the fact that android system does not call getItem to obtain fragments that are actually displayed, but instantiateItem. This method first tries to lookup and reuse a fragment instance for a given tab in FragmentManager. Only if this lookup fails (which happens only the first time when FragmentManager is newly created) then getItem is called. It is for obvious reasons not to recreate fragments (that may be heavy) for example each time a user rotates his device.
To solve this, instead of creating fragments with Fragment.instantiate in your activity, you should do it with pagerAdapter.instantiateItem and all these calls should be surrounded by startUpdate/finishUpdate method calls that start/commit fragment transaction respectively. getItem should be the place where fragments are really created using their respective constructors.
List<Fragment> fragments = new Vector<Fragment>();
#Override protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.myLayout);
ViewPager viewPager = (ViewPager) findViewById(R.id.myViewPager);
MyPagerAdapter adapter = new MyPagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(adapter);
((TabLayout) findViewById(R.id.tabs)).setupWithViewPager(viewPager);
adapter.startUpdate(viewPager);
fragments.add(adapter.instantiateItem(viewPager, 0));
fragments.add(adapter.instantiateItem(viewPager, 1));
// and so on if you have more tabs...
adapter.finishUpdate(viewPager);
}
class MyPagerAdapter extends FragmentPagerAdapter {
public MyPagerAdapter(FragmentManager manager) {super(manager);}
#Override public int getCount() {return 2;}
#Override public Fragment getItem(int position) {
if (position == 0) return new Fragment0();
if (position == 1) return new Fragment1();
return null; // or throw some exception
}
#Override public CharSequence getPageTitle(int position) {
if (position == 0) return getString(R.string.tab0);
if (position == 1) return getString(R.string.tab1);
return null; // or throw some exception
}
}
Since the FragmentManager will take care of restoring your Fragments for you as soon as the onResume() method is called I have the fragment call out to the activity and add itself to a list. In my instance I am storing all of this in my PagerAdapter implementation. Each fragment knows it's position because it is added to the fragment arguments on creation. Now whenever I need to manipulate a fragment at a specific index all I have to do is use the list from my adapter.
The following is an example of an Adapter for a custom ViewPager that will grow the fragment as it moves into focus, and scale it down as it moves out of focus. Besides the Adapter and Fragment classes I have here all you need is for the parent activity to be able to reference the adapter variable and you are set.
Adapter
public class GrowPagerAdapter extends FragmentPagerAdapter implements OnPageChangeListener, OnScrollChangedListener {
public final String TAG = this.getClass().getSimpleName();
private final int COUNT = 4;
public static final float BASE_SIZE = 0.8f;
public static final float BASE_ALPHA = 0.8f;
private int mCurrentPage = 0;
private boolean mScrollingLeft;
private List<SummaryTabletFragment> mFragments;
public int getCurrentPage() {
return mCurrentPage;
}
public void addFragment(SummaryTabletFragment fragment) {
mFragments.add(fragment.getPosition(), fragment);
}
public GrowPagerAdapter(FragmentManager fm) {
super(fm);
mFragments = new ArrayList<SummaryTabletFragment>();
}
#Override
public int getCount() {
return COUNT;
}
#Override
public Fragment getItem(int position) {
return SummaryTabletFragment.newInstance(position);
}
#Override
public void onPageScrollStateChanged(int state) {}
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
adjustSize(position, positionOffset);
}
#Override
public void onPageSelected(int position) {
mCurrentPage = position;
}
/**
* Used to adjust the size of each view in the viewpager as the user
* scrolls. This provides the effect of children scaling down as they
* are moved out and back to full size as they come into focus.
*
* #param position
* #param percent
*/
private void adjustSize(int position, float percent) {
position += (mScrollingLeft ? 1 : 0);
int secondary = position + (mScrollingLeft ? -1 : 1);
int tertiary = position + (mScrollingLeft ? 1 : -1);
float scaleUp = mScrollingLeft ? percent : 1.0f - percent;
float scaleDown = mScrollingLeft ? 1.0f - percent : percent;
float percentOut = scaleUp > BASE_ALPHA ? BASE_ALPHA : scaleUp;
float percentIn = scaleDown > BASE_ALPHA ? BASE_ALPHA : scaleDown;
if (scaleUp < BASE_SIZE)
scaleUp = BASE_SIZE;
if (scaleDown < BASE_SIZE)
scaleDown = BASE_SIZE;
// Adjust the fragments that are, or will be, on screen
SummaryTabletFragment current = (position < mFragments.size()) ? mFragments.get(position) : null;
SummaryTabletFragment next = (secondary < mFragments.size() && secondary > -1) ? mFragments.get(secondary) : null;
SummaryTabletFragment afterNext = (tertiary < mFragments.size() && tertiary > -1) ? mFragments.get(tertiary) : null;
if (current != null && next != null) {
// Apply the adjustments to each fragment
current.transitionFragment(percentIn, scaleUp);
next.transitionFragment(percentOut, scaleDown);
if (afterNext != null) {
afterNext.transitionFragment(BASE_ALPHA, BASE_SIZE);
}
}
}
#Override
public void onScrollChanged(int l, int t, int oldl, int oldt) {
// Keep track of which direction we are scrolling
mScrollingLeft = (oldl - l) < 0;
}
}
Fragment
public class SummaryTabletFragment extends BaseTabletFragment {
public final String TAG = this.getClass().getSimpleName();
private final float SCALE_SIZE = 0.8f;
private RelativeLayout mBackground, mCover;
private TextView mTitle;
private VerticalTextView mLeft, mRight;
private String mTitleText;
private Integer mColor;
private boolean mInit = false;
private Float mScale, mPercent;
private GrowPagerAdapter mAdapter;
private int mCurrentPosition = 0;
public String getTitleText() {
return mTitleText;
}
public void setTitleText(String titleText) {
this.mTitleText = titleText;
}
public static SummaryTabletFragment newInstance(int position) {
SummaryTabletFragment fragment = new SummaryTabletFragment();
fragment.setRetainInstance(true);
Bundle args = new Bundle();
args.putInt("position", position);
fragment.setArguments(args);
return fragment;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
super.onCreateView(inflater, container, savedInstanceState);
mRoot = inflater.inflate(R.layout.tablet_dummy_view, null);
setupViews();
configureView();
return mRoot;
}
#Override
public void onViewStateRestored(Bundle savedInstanceState) {
super.onViewStateRestored(savedInstanceState);
if (savedInstanceState != null) {
mColor = savedInstanceState.getInt("color", Color.BLACK);
}
configureView();
}
#Override
public void onSaveInstanceState(Bundle outState) {
outState.putInt("color", mColor);
super.onSaveInstanceState(outState);
}
#Override
public int getPosition() {
return getArguments().getInt("position", -1);
}
#Override
public void setPosition(int position) {
getArguments().putInt("position", position);
}
public void onResume() {
super.onResume();
mAdapter = mActivity.getPagerAdapter();
mAdapter.addFragment(this);
mCurrentPosition = mAdapter.getCurrentPage();
if ((getPosition() == (mCurrentPosition + 1) || getPosition() == (mCurrentPosition - 1)) && !mInit) {
mInit = true;
transitionFragment(GrowPagerAdapter.BASE_ALPHA, GrowPagerAdapter.BASE_SIZE);
return;
}
if (getPosition() == mCurrentPosition && !mInit) {
mInit = true;
transitionFragment(0.00f, 1.0f);
}
}
private void setupViews() {
mCover = (RelativeLayout) mRoot.findViewById(R.id.cover);
mLeft = (VerticalTextView) mRoot.findViewById(R.id.title_left);
mRight = (VerticalTextView) mRoot.findViewById(R.id.title_right);
mBackground = (RelativeLayout) mRoot.findViewById(R.id.root);
mTitle = (TextView) mRoot.findViewById(R.id.title);
}
private void configureView() {
Fonts.applyPrimaryBoldFont(mLeft, 15);
Fonts.applyPrimaryBoldFont(mRight, 15);
float[] size = UiUtils.getScreenMeasurements(mActivity);
int width = (int) (size[0] * SCALE_SIZE);
int height = (int) (size[1] * SCALE_SIZE);
RelativeLayout.LayoutParams params = new RelativeLayout.LayoutParams(width, height);
mBackground.setLayoutParams(params);
if (mScale != null)
transitionFragment(mPercent, mScale);
setRandomBackground();
setTitleText("Fragment " + getPosition());
mTitle.setText(getTitleText().toUpperCase());
mLeft.setText(getTitleText().toUpperCase());
mRight.setText(getTitleText().toUpperCase());
mLeft.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
mActivity.showNextPage();
}
});
mRight.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View v) {
mActivity.showPrevPage();
}
});
}
private void setRandomBackground() {
if (mColor == null) {
Random r = new Random();
mColor = Color.rgb(r.nextInt(255), r.nextInt(255), r.nextInt(255));
}
mBackground.setBackgroundColor(mColor);
}
public void transitionFragment(float percent, float scale) {
this.mScale = scale;
this.mPercent = percent;
if (getView() != null && mCover != null) {
getView().setScaleX(scale);
getView().setScaleY(scale);
mCover.setAlpha(percent);
mCover.setVisibility((percent <= 0.05f) ? View.GONE : View.VISIBLE);
}
}
#Override
public String getFragmentTitle() {
return null;
}
}
My solution: I set almost every View as static. Now my app interacts perfect. Being able to call the static methods from everywhere is maybe not a good style, but why to play around with code that doesn't work? I read a lot of questions and their answers here on SO and no solution brought success (for me).
I know it can leak the memory, and waste heap, and my code will not be fit on other projects, but I don't feel scared about this - I tested the app on different devices and conditions, no problems at all, the Android Platform seems to be able handle this. The UI gets refreshed every second and even on a S2 ICS (4.0.3) device the app is able to handle thousands of geo-markers.
I faced the same issue but my ViewPager was inside a TopFragment which created and set an adapter using setAdapter(new FragmentPagerAdapter(getChildFragmentManager())).
I fixed this issue by overriding onAttachFragment(Fragment childFragment) in the TopFragment like this:
#Override
public void onAttachFragment(Fragment childFragment) {
if (childFragment instanceof OnboardingDiamondsFragment) {
mChildFragment = (ChildFragment) childFragment;
}
super.onAttachFragment(childFragment);
}
As known already (see answers above), when the childFragmentManager recreate itself, it also create the fragments which were inside the viewPager.
The important part is that after that, he calls onAttachFragment and now we have a reference to the new recreated fragment!
Hope this will help anyone getting this old Q like me :)
I solved the problem by saving the fragments in SparceArray:
public abstract class SaveFragmentsPagerAdapter extends FragmentPagerAdapter {
SparseArray<Fragment> fragments = new SparseArray<>();
public SaveFragmentsPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
Fragment fragment = (Fragment) super.instantiateItem(container, position);
fragments.append(position, fragment);
return fragment;
}
#Nullable
public Fragment getFragmentByPosition(int position){
return fragments.get(position);
}
}
Just so you know...
Adding to the litany of woes with these classes, there is a rather interesting bug that's worth sharing.
I'm using a ViewPager to navigate a tree of items (select an item and the view pager animates scrolling to the right, and the next branch appears, navigate back, and the ViewPager scrolls in the opposite direction to return to the previous node).
The problem arises when I push and pop fragments off the end of the FragmentStatePagerAdapter. It's smart enough to notice that the items change, and smart enough to create and replace a fragment when the item has changed. But not smart enough to discard the fragment state, or smart enough to trim the internally saved fragment states when the adapter size changes. So when you pop an item, and push a new one onto the end, the fragment for the new item gets the saved state of the fragment for the old item, which caused absolute havoc in my code. My fragments carry data that may require a lot of work to refetch from the internet, so not saving state really wasn't an option.
I don't have a clean workaround. I used something like this:
public void onSaveInstanceState(Bundle outState) {
IFragmentListener listener = (IFragmentListener)getActivity();
if (listener!= null)
{
if (!listener.isStillInTheAdapter(this.getAdapterItem()))
{
return; // return empty state.
}
}
super.onSaveInstanceState(outState);
// normal saving of state for flips and
// paging out of the activity follows
....
}
An imperfect solution because the new fragment instance still gets a savedState Bundle, but at least it doesn't carry stale data.