My goal is to delete a fragment from a ViewPager upon user button click.
Populating the ViewPager works fine, but when I try to delete it, I get an error indicating a null reference. I incorporated Remove Fragment Page from ViewPager in Android
In my fragment to be deleted I have:
Button delete = (Button) getActivity().findViewById(R.id.dont_show_button_1);
delete.setOnClickListener(new View.OnClickListener() {
#Override
public void onClick(View v) {
db.deletePerson(count); // SQLiteDatabase, works fine
displayActivity.removeCurrentFragment(count-1);
}
});
DisplayActivity is as follows:
public class DisplayActivity extends FragmentActivity {
ViewPager viewPager;
PagerAdapter pagerAdapter;
String TAG = "DisplayActivity";
#Override
protected void onCreate(#Nullable Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.db_layout);
viewPager = (ViewPager) findViewById(R.id.pager);
pagerAdapter = new PagerAdapter(getSupportFragmentManager());
viewPager.setAdapter(pagerAdapter);
}
public void removeCurrentFragment(int position){
pagerAdapter.fragmentArrayList.remove(position);
pagerAdapter.notifyChangeInPosition(1);
pagerAdapter.notifyDataSetChanged();
Log.e(TAG, "in removeCurrentFragment");
}
}
PagerAdapter
public class PagerAdapter extends FragmentPagerAdapter {
long baseId = 0;
public static List<Fragment> fragmentArrayList = new ArrayList<Fragment>();
public PagerAdapter(FragmentManager fm){
super(fm);
fragmentArrayList.add(new FragmentOne());
fragmentArrayList.add(new FragmentTwo());
fragmentArrayList.add(new FragmentThree());
}
#Override
public Fragment getItem(int position) {
return fragmentArrayList.get(position);
}
#Override
public int getCount() {
return fragmentArrayList.size();
}
#Override
public int getItemPosition(Object object){
return PagerAdapter.POSITION_NONE;
}
#Override
public long getItemId(int position) {
// give an ID different from position when position has been changed
return baseId + position;
}
/**
* Notify that the position of a fragment has been changed.
* Create a new ID for each position to force recreation of the fragment
* #param n number of items which have been changed
*/
public void notifyChangeInPosition(int n) {
// shift the ID returned by getItemId outside the range of all previous fragments
baseId += getCount() + n;
}
}
This is the error:
java.lang.NullPointerException: Attempt to invoke virtual method 'void .DisplayActivity.removeCurrentFragment(int)' on a null object reference
Triggered from the fragment
Edit:
public class FragmentOne extends Fragment {
DatabaseHelper db;
WebView mWebView;
DisplayActivity displayActivity;
int count = 1;
This is how I get reference from displayActivity, is this the wrong way to get a reference of it?
if (count > 0) {
displayActivity.removeCurrentFragment(count - 1);
}
My host activity has a viewpager with two fragments A and B.My activity code looks like this:
public class MainActivity extends AppCompatActivity implements
OnDataLoadedListener {
private ViewPager pager;
private MyPagerAdapter adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
pager = (ViewPager) findViewById(R.id.pager);
adapter = new MyPagerAdapter(getSupportFragmentManager());
pager.setAdapter(adapter);
final int pageMargin = (int) TypedValue.applyDimension(
TypedValue.COMPLEX_UNIT_DIP, 4, getResources()
.getDisplayMetrics());
pager.setPageMargin(pageMargin);
tabLayout.setupWithViewPager(pager);
}
public class MyPagerAdapter extends FragmentPagerAdapter {
private final String[] TITLES = { "A",
"B" };
public MyPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public CharSequence getPageTitle(int position) {
return TITLES[position];
}
#Override
public int getCount() {
return TITLES.length;
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return A.getInstance();
case 1:
return B.getInstance();
}
return null;
}
}
public Fragment findFragmentByPosition(int position) {
return getSupportFragmentManager().findFragmentByTag(
"android:switcher:" + pager.getId() + ":"
+ adapter.getItemId(position));
}
Now when activity start viewpager get populated with fragment properly and I try to access fragmentby using following code:
if (AFragment == null)
AFragment = (A) findFragmentByPosition(0);
if (BFragment == null)
BFragment = (B) findFragmentByPosition(1);
But AFragment and BFragment always contains null.I have read other simmilar question but it didn't help either.I need access to fragments as I want to call some methods defined in fragment from host activity.
Code to get an instance of fragment:
public static AFragment getInstance() {
AFragment fragment = new AFragment();
return fragment;
}
I'm think that the problem is that you need to move the method to the Adapter, because you need the original instance of the FragmentManager :
public class MyPagerAdapter extends FragmentPagerAdapter {
FragmentManager fm;
private final String[] TITLES = { "A",
"B" };
public MyPagerAdapter (FragmentManager fm) {
super(fm);
this.fm = fm;
}
#Override
public CharSequence getPageTitle(int position) {
return TITLES[position];
}
#Override
public int getCount() {
return TITLES.length;
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return A.getInstance();
case 1:
return B.getInstance();
}
return null;
}
public Fragment findFragmentByPosition(int position, int pagerId) {
return fm.findFragmentByTag(
"android:switcher:" + pagerId + ":"
+ getItemId(position));
}
}
So now you can call:
adapter.findFragmentByPosition(position, pager.getId());
I have problem with FragmentPagerAdapter ,I have set fragments in viewpager through FragmentPagerAdapter,
I have to show viewpager dynamically,I have listview data , which I need to show in viewpager,
when I click on the listview , I have to load exact position in the viewpager
so i just set the total size of the item to show in FragmentPagerAdapter, But the problem is that when I select the viewpager position through mPager.setCurrentItem(listposition) it show correct position of the viewpager,
but the data load at wrong place, it load in next fragement in viewpager position,after some tracking in FragmentPagerAdapter, I show that instantiateItem method initailize one fragment in advance, like i set the currentitem (from listview)of viewpager 2
then instantiateItem method initalize 0 to 3 fragment, I think that the reason the data load in 3rd fragment,I tried a lot with FragmentStatePagerAdapter also but no any success , please help me , thanks in advance.
Mainactivity class(Fragmnetactivity) :
public class NewsDetail extends FragmentActivity implements OnClickListener {
public static ViewPager mPager;
private static int NUM_PAGES;
private PagerAdapter mPagerAdapter;
public static ArrayList<Integer> exist_detail = new ArrayList<Integer>();
public static ArrayList<PageFragment> detailfragment = new ArrayList<PageFragment>();
mPager = (ViewPager) findViewById(R.id.pager);
mPagerAdapter = new ScreenSlidePagerAdapter(getSupportFragmentManager());
mPager.setAdapter(mPagerAdapter);
NUM_PAGES = topList.size();
PageFragment fragment = new PageFragment();
Bundle args = new Bundle();
args.putInt("page", i);
fragment.setArguments(args);
detailfragment.add(fragment);
mPager.setOnPageChangeListener(new ViewPager.SimpleOnPageChangeListener() {
#Override
public void onPageSelected(int arg0) {
if (PageFragment.getInstance() != null) {
Log.d("LOG","PageFragment || "+ PageFragment.getInstance());
PageFragment.getInstance().startLoadingNews(
MusicList.topMusicList.get(arg0)._id);
}
return;
}
#Override
public void onPageScrolled(int arg0, float arg1, int arg2) {}
#Override
public void onPageScrollStateChanged(int arg0) {}
});
mPagerAdapter.notifyDataSetChanged();
mPager.setCurrentItem(listposition);// setcurrent item from here , it is selected from list. "listposition" indicate list position click
private class ScreenSlidePagerAdapter extends FragmentPagerAdapter {
private FragmentManager mFragmentManager;
private FragmentTransaction mCurTransaction = null;
private Fragment mCurrentPrimaryItem = null;
private static final boolean DEBUG = false;
public ScreenSlidePagerAdapter(FragmentManager fragmentManager) {
super(fragmentManager);
this.mFragmentManager = fragmentManager;
}
#Override
public Fragment getItem(int position) {
return detailfragment.get(position);
}
#Override
public long getItemId(int position) {
// TODO Auto-generated method stub
return super.getItemId(position);
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
Log.v("LOG", "On InstantiateItem " + position);// it indicate that this method initialize one fragment in advance.
return super.instantiateItem(container, position);
}
public String makeFragmentName(int viewId, long index) {
return "android:switcher:" + viewId + ":" + index;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
if (DEBUG)
Log.e("LOG", "Detaching item #" + position + ": f=" + object
+ " v=" + ((Fragment) object).getView());
mCurTransaction.detach((Fragment) object);
}
#Override
public void restoreState(Parcelable state, ClassLoader loader) {
}
#Override
public int getCount() {
return NUM_PAGES;
}
}
}
PageFragment
public class PageFragment extends Fragment implements OnClickListener {
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mPageNumber = getArguments().getInt(ARG_PAGE);
mDetailPageFragment = this;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout containing a title and body text.
rootView = (ViewGroup) inflater.inflate(R.layout.newsdetail, container,
false);
//init();
return rootView;
}
public void startLoadingNews(String _id) {
if (NetworkUtil.cheackNetwork(mActivity)) {
executeTask(_id);
} else {
showRetryCancelDialog();
}
}
}
I can see two issues in the code you've posted:
Only instantiate your fragments in FragmentPagerAdapter.getItem. Don't instantiate them and save them to some list or array, let the FragmentPagerAdapter do that for you. In FragmentPagerAdapter.instantiateItem it checks if the Fragment was already created and if so it returns it, if not, it'll call your getItem to create the fragment.
Don't use the Singleton scheme for your fragment, create a new fragment using a constructor or a .newInstance() static helper.
I'm using the v4 compatibility ViewPager in Android. My FragmentActivity has a bunch of data which is to be displayed in different ways on different pages in my ViewPager. So far I just have 3 instances of the same ListFragment, but in the future I will have 3 instances of different ListFragments. The ViewPager is on a vertical phone screen, the lists are not side-by-side.
Now a button on the ListFragment starts an separate full-page activity (via the FragmentActivity), which returns and FragmentActivity modifies the data, saves it, then attempts to update all views in its ViewPager. It is here, where I am stuck.
public class ProgressMainActivity extends FragmentActivity
{
MyAdapter mAdapter;
ViewPager mPager;
#Override
public void onCreate(Bundle savedInstanceState)
{
...
mAdapter = new MyAdapter(getSupportFragmentManager());
mPager = (ViewPager) findViewById(R.id.viewpager);
mPager.setAdapter(mAdapter);
}
#Override
protected void onActivityResult(int requestCode, int resultCode, Intent data)
{
...
updateFragments();
...
}
public void updateFragments()
{
//Attempt 1:
//mAdapter.notifyDataSetChanged();
//mPager.setAdapter(mAdapter);
//Attempt 2:
//HomeListFragment fragment = (HomeListFragment) getSupportFragmentManager().findFragmentById(mAdapter.fragId[0]);
//fragment.updateDisplay();
}
public static class MyAdapter extends FragmentPagerAdapter implements
TitleProvider
{
int[] fragId = {0,0,0,0,0};
public MyAdapter(FragmentManager fm)
{
super(fm);
}
#Override
public String getTitle(int position){
return titles[position];
}
#Override
public int getCount(){
return titles.length;
}
#Override
public Fragment getItem(int position)
{
Fragment frag = HomeListFragment.newInstance(position);
//Attempt 2:
//fragId[position] = frag.getId();
return frag;
}
#Override
public int getItemPosition(Object object) {
return POSITION_NONE; //To make notifyDataSetChanged() do something
}
}
public class HomeListFragment extends ListFragment
{
...
public static HomeListFragment newInstance(int num)
{
HomeListFragment f = new HomeListFragment();
...
return f;
}
...
Now as you can see, my first attempt was to notifyDataSetChanged on the entire FragmentPagerAdapter, and this showed to update the data sometimes, but others I got an IllegalStateException: Can not perform this action after onSaveInstanceState.
My second attempt involed trying to call an update function in my ListFragment, but getId in getItem returned 0. As per the docs I tried by
acquiring a reference to the Fragment from FragmentManager, using
findFragmentById() or findFragmentByTag()
but I don't know the tag or id of my Fragments! I have an android:id="#+id/viewpager" for ViewPager, and a android:id="#android:id/list" for my ListView in the ListFragment layout, but I don't think these are useful.
So, how can I either:
a) update the entire ViewPager safely in one go (ideally returning the user to the page he was on before) - it is ok that the user see the view change.
Or preferably,
b) call a function in each affected ListFragment to update the ListView manually.
Any help would be gratefully accepted!
Barkside's answer works with FragmentPagerAdapter but doesn't work with FragmentStatePagerAdapter, because it doesn't set tags on fragments it passes to FragmentManager.
With FragmentStatePagerAdapter it seems we can get by, using its instantiateItem(ViewGroup container, int position) call. It returns reference to fragment at position position. If FragmentStatePagerAdapter already holds reference to fragment in question, instantiateItem just returns reference to that fragment, and doesn't call getItem() to instantiate it again.
So, suppose, I'm currently looking at fragment #50, and want to access fragment #49. Since they are close, there's a good chance the #49 will be already instantiated. So,
ViewPager pager = findViewById(R.id.viewpager);
FragmentStatePagerAdapter a = (FragmentStatePagerAdapter) pager.getAdapter();
MyFragment f49 = (MyFragment) a.instantiateItem(pager, 49)
OK, I think I've found a way to perform request b) in my own question so I'll share for others' benefit. The tag of fragments inside a ViewPager is in the form "android:switcher:VIEWPAGER_ID:INDEX", where VIEWPAGER_ID is the R.id.viewpager in XML layout, and INDEX is the position in the viewpager. So if the position is known (eg 0), I can perform in updateFragments():
HomeListFragment fragment =
(HomeListFragment) getSupportFragmentManager().findFragmentByTag(
"android:switcher:"+R.id.viewpager+":0");
if(fragment != null) // could be null if not instantiated yet
{
if(fragment.getView() != null)
{
// no need to call if fragment's onDestroyView()
//has since been called.
fragment.updateDisplay(); // do what updates are required
}
}
I've no idea if this is a valid way of doing it, but it'll do until something better is suggested.
Try to record the tag each time a Fragement is instantiated.
public class MPagerAdapter extends FragmentPagerAdapter {
private Map<Integer, String> mFragmentTags;
private FragmentManager mFragmentManager;
public MPagerAdapter(FragmentManager fm) {
super(fm);
mFragmentManager = fm;
mFragmentTags = new HashMap<Integer, String>();
}
#Override
public int getCount() {
return 10;
}
#Override
public Fragment getItem(int position) {
return Fragment.instantiate(mContext, AFragment.class.getName(), null);
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
Object obj = super.instantiateItem(container, position);
if (obj instanceof Fragment) {
// record the fragment tag here.
Fragment f = (Fragment) obj;
String tag = f.getTag();
mFragmentTags.put(position, tag);
}
return obj;
}
public Fragment getFragment(int position) {
String tag = mFragmentTags.get(position);
if (tag == null)
return null;
return mFragmentManager.findFragmentByTag(tag);
}
}
If you ask me, the second solution on the below page, keeping track of all the "active" fragment pages, is better: http://tamsler.blogspot.nl/2011/11/android-viewpager-and-fragments-part-ii.html
The answer from barkside is too hacky for me.
you keep track of all the "active" fragment pages. In this case, you keep track of the fragment pages in the FragmentStatePagerAdapter, which is used by the ViewPager.
private final SparseArray<Fragment> mPageReferences = new SparseArray<Fragment>();
public Fragment getItem(int index) {
Fragment myFragment = MyFragment.newInstance();
mPageReferences.put(index, myFragment);
return myFragment;
}
To avoid keeping a reference to "inactive" fragment pages, we need to implement the FragmentStatePagerAdapter's destroyItem(...) method:
public void destroyItem(View container, int position, Object object) {
super.destroyItem(container, position, object);
mPageReferences.remove(position);
}
... and when you need to access the currently visible page, you then call:
int index = mViewPager.getCurrentItem();
MyAdapter adapter = ((MyAdapter)mViewPager.getAdapter());
MyFragment fragment = adapter.getFragment(index);
... where the MyAdapter's getFragment(int) method looks like this:
public MyFragment getFragment(int key) {
return mPageReferences.get(key);
}
"
Okay, after testing the method by #barkside above, I could not get it to work with my application. Then I remembered that the IOSched2012 app uses a viewpager as well, and that is where I found my solution. It does not use any fragment ID's or Tags as these are not stored by viewpager in an easily accessible way.
Here's the important parts from the IOSched apps HomeActivity. Pay particular attention to the comment, as therein lies the key.:
#Override
protected void onSaveInstanceState(Bundle outState) {
super.onSaveInstanceState(outState);
// Since the pager fragments don't have known tags or IDs, the only way to persist the
// reference is to use putFragment/getFragment. Remember, we're not persisting the exact
// Fragment instance. This mechanism simply gives us a way to persist access to the
// 'current' fragment instance for the given fragment (which changes across orientation
// changes).
//
// The outcome of all this is that the "Refresh" menu button refreshes the stream across
// orientation changes.
if (mSocialStreamFragment != null) {
getSupportFragmentManager().putFragment(outState, "stream_fragment",
mSocialStreamFragment);
}
}
#Override
protected void onRestoreInstanceState(Bundle savedInstanceState) {
super.onRestoreInstanceState(savedInstanceState);
if (mSocialStreamFragment == null) {
mSocialStreamFragment = (SocialStreamFragment) getSupportFragmentManager()
.getFragment(savedInstanceState, "stream_fragment");
}
}
And store instances of you Fragments in the FragmentPagerAdapter like so:
private class HomePagerAdapter extends FragmentPagerAdapter {
public HomePagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return (mMyScheduleFragment = new MyScheduleFragment());
case 1:
return (mExploreFragment = new ExploreFragment());
case 2:
return (mSocialStreamFragment = new SocialStreamFragment());
}
return null;
}
Also, remember to guard your Fragment calls like so:
if (mSocialStreamFragment != null) {
mSocialStreamFragment.refresh();
}
You can copy FragmentPagerAdapter and modify some source code, add getTag() method
for example
public abstract class AppFragmentPagerAdapter extends PagerAdapter {
private static final String TAG = "FragmentPagerAdapter";
private static final boolean DEBUG = false;
private final FragmentManager mFragmentManager;
private FragmentTransaction mCurTransaction = null;
private Fragment mCurrentPrimaryItem = null;
public AppFragmentPagerAdapter(FragmentManager fm) {
mFragmentManager = fm;
}
public abstract Fragment getItem(int position);
#Override
public void startUpdate(ViewGroup container) {
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
final long itemId = getItemId(position);
String name = getTag(position);
Fragment fragment = mFragmentManager.findFragmentByTag(name);
if (fragment != null) {
if (DEBUG) Log.v(TAG, "Attaching item #" + itemId + ": f=" + fragment);
mCurTransaction.attach(fragment);
} else {
fragment = getItem(position);
if (DEBUG) Log.v(TAG, "Adding item #" + itemId + ": f=" + fragment);
mCurTransaction.add(container.getId(), fragment,
getTag(position));
}
if (fragment != mCurrentPrimaryItem) {
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
}
return fragment;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
if (DEBUG) Log.v(TAG, "Detaching item #" + getItemId(position) + ": f=" + object
+ " v=" + ((Fragment) object).getView());
mCurTransaction.detach((Fragment) object);
}
#Override
public void setPrimaryItem(ViewGroup container, int position, Object object) {
Fragment fragment = (Fragment) object;
if (fragment != mCurrentPrimaryItem) {
if (mCurrentPrimaryItem != null) {
mCurrentPrimaryItem.setMenuVisibility(false);
mCurrentPrimaryItem.setUserVisibleHint(false);
}
if (fragment != null) {
fragment.setMenuVisibility(true);
fragment.setUserVisibleHint(true);
}
mCurrentPrimaryItem = fragment;
}
}
#Override
public void finishUpdate(ViewGroup container) {
if (mCurTransaction != null) {
mCurTransaction.commitAllowingStateLoss();
mCurTransaction = null;
mFragmentManager.executePendingTransactions();
}
}
#Override
public boolean isViewFromObject(View view, Object object) {
return ((Fragment) object).getView() == view;
}
#Override
public Parcelable saveState() {
return null;
}
#Override
public void restoreState(Parcelable state, ClassLoader loader) {
}
public long getItemId(int position) {
return position;
}
private static String makeFragmentName(int viewId, long id) {
return "android:switcher:" + viewId + ":" + id;
}
protected abstract String getTag(int position);
}
then extend it, override these abstract method,don't need to be afraid of Android Group change
FragmentPageAdapter source code in the future
class TimeLinePagerAdapter extends AppFragmentPagerAdapter {
List<Fragment> list = new ArrayList<Fragment>();
public TimeLinePagerAdapter(FragmentManager fm) {
super(fm);
list.add(new FriendsTimeLineFragment());
list.add(new MentionsTimeLineFragment());
list.add(new CommentsTimeLineFragment());
}
public Fragment getItem(int position) {
return list.get(position);
}
#Override
protected String getTag(int position) {
List<String> tagList = new ArrayList<String>();
tagList.add(FriendsTimeLineFragment.class.getName());
tagList.add(MentionsTimeLineFragment.class.getName());
tagList.add(CommentsTimeLineFragment.class.getName());
return tagList.get(position);
}
#Override
public int getCount() {
return list.size();
}
}
Also works without problems:
somewhere in page fragment's layout:
<FrameLayout android:layout_width="0dp" android:layout_height="0dp" android:visibility="gone" android:id="#+id/fragment_reference">
<View android:layout_width="0dp" android:layout_height="0dp" android:visibility="gone"/>
</FrameLayout>
in fragment's onCreateView():
...
View root = inflater.inflate(R.layout.fragment_page, container, false);
ViewGroup ref = (ViewGroup)root.findViewById(R.id.fragment_reference);
ref.setTag(this);
ref.getChildAt(0).setTag("fragment:" + pageIndex);
return root;
and method to return Fragment from ViewPager, if exists:
public Fragment getFragment(int pageIndex) {
View w = mViewPager.findViewWithTag("fragment:" + pageIndex);
if (w == null) return null;
View r = (View) w.getParent();
return (Fragment) r.getTag();
}
Alternatively you can override setPrimaryItem method from FragmentPagerAdapter like so:
public void setPrimaryItem(ViewGroup container, int position, Object object) {
if (mCurrentFragment != object) {
mCurrentFragment = (Fragment) object; //Keep reference to object
((MyInterface)mCurrentFragment).viewDidAppear();//Or call a method on the fragment
}
super.setPrimaryItem(container, position, object);
}
public Fragment getCurrentFragment(){
return mCurrentFragment;
}
I want to give my approach in case it can help anyone else:
This is my pager adapter:
public class CustomPagerAdapter extends FragmentStatePagerAdapter{
private Fragment[] fragments;
public CustomPagerAdapter(FragmentManager fm) {
super(fm);
fragments = new Fragment[]{
new FragmentA(),
new FragmentB()
};
}
#Override
public Fragment getItem(int arg0) {
return fragments[arg0];
}
#Override
public int getCount() {
return fragments.length;
}
}
In my activity I have:
public class MainActivity {
private ViewPager view_pager;
private CustomPagerAdapter adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
adapter = new CustomPagerAdapter(getSupportFragmentManager());
view_pager = (ViewPager) findViewById(R.id.pager);
view_pager.setAdapter(adapter);
view_pager.setOnPageChangeListener(this);
...
}
}
Then to get the current fragment what I do is:
int index = view_pager.getCurrentItem();
Fragment currentFragment = adapter.getItem(index);
This is my solution since I don't need to keep track of my tabs and need to refresh them all anyway.
Bundle b = new Bundle();
b.putInt(Constants.SharedPreferenceKeys.NUM_QUERY_DAYS,numQueryDays);
for(android.support.v4.app.Fragment f:getSupportFragmentManager().getFragments()){
if(f instanceof HomeTermFragment){
((HomeTermFragment) f).restartLoader(b);
}
}
I'm working with a FragmentStatePagerAdapter using this example.
The MyAdapter class is implemented as follows:
public static class MyAdapter extends FragmentStatePagerAdapter {
public MyAdapter(FragmentManager fm) {
super(fm);
}
#Override
public int getCount() {
return NUM_ITEMS;
}
#Override
public Fragment getItem(int position) {
return ArrayListFragment.newInstance(position);
}
}
The ListFragment class includes the following method to create a new instance:
/**
* Create a new instance of CountingFragment, providing "num"
* as an argument.
*/
static ArrayListFragment newInstance(int num) {
ArrayListFragment f = new ArrayListFragment();
// Supply num input as an argument.
Bundle args = new Bundle();
args.putInt("num", num);
f.setArguments(args);
return f;
}
When I create a new fragment state pager adapter in my activity, getItem is called, which in turn calls the newInstance method in the ListFragment class. This is great when I want to create a new fragment.
But it's not clear to me how to modify getItem (if even needed) to get the fragment object when it already exists and the user pages from, for example, page 2 to page 1. I'd like my Activity to retrieve that existing, previously created fragment so that it can run an inner class AsyncMethod, which resides in the fragment class.
I think the solution is much simpler than the answers provided.
If you take a look at the source of FragmentStatePagerAdapter.instantiateItem(), you'll notice that instantiateItem() handles this logic for you, and thus your implementation of getItem() should always return a new instance.
So in order to return an existing Fragment, simply do (assuming you're calling from ViewPager):
Fragment f = (Fragment) getAdapter().instantiateItem(this, getCurrentItem());
While #imiric's solution is very concise, it still bothers me that it requires knowledge of the implementation of the class. My solution involves adding the following to your adapter, which should behave nicely with a FragmentStatePagerAdapter possibly destroying fragments:
private SparseArray<WeakReference<Fragment>> mFragments = new SparseArray<>();
#Override
public Object instantiateItem(ViewGroup container, int position) {
Fragment f = (Fragment) super.instantiateItem(container, position);
mFragments.put(position, new WeakReference<>(f)); // Remember what fragment was in position
return f;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
super.destroyItem(container, position, object);
mFragments.remove(position);
}
public Fragment getFragment(int position) {
WeakReference<Fragment> ref = mFragments.get(position);
Fragment f = ref != null ? ref.get() : null;
if (f == null) {
Log.d(TAG, "fragment for " + position + " is null!");
}
return f;
}
I have implemented something similar to what you have. I extended the FragmentPagerAdapter class like so:
public class ContactsFragmentPagerAdapter extends FragmentPagerAdapter {
ActionBar mActionBar;
private List<Fragment> mFragments;
public ContactsFragmentPagerAdapter(FragmentManager fm, List<Fragment> fragments) {
super(fm);
mFragments = fragments;
}
#Override
public int getCount() {
return mFragments.size();
}
#Override
public Fragment getItem(int position) {
return mFragments.get(position);
}
public void setActionBar(ActionBar bar) {
mActionBar = bar;
}
}
Notice I have added an argument to the constructor to pass in the List of Fragment objects. This way the getItem() method of this class can return any class that extends Fragment or any of its subclasses and not just one specific class ArrayListFragment like you have done.
In the Activity where I instantiate my subclass of FragmentPagerAdapter I have passed in the list of Fragment objects:
Class the instantiates the FragmentPagerAdapter
public final class ContactManager extends Activity {
private ContactsFragmentPagerAdapter mAdapter;
private ViewPager mPager;
public ActionBar mActionBar;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.contact_manager);
List<Fragment> fragments = new Vector<Fragment>();
fragments.add(Fragment.instantiate(this, ContactsListFragment.class.getName()));
fragments.add(Fragment.instantiate(this, GroupsListFragment.class.getName()));
mAdapter = new ContactsFragmentPagerAdapter(this.getFragmentManager(), fragments);
mPager = (ViewPager) findViewById(R.id.pager);
mPager.setAdapter(mAdapter);
mPager.setOnPageChangeListener(new OnPageChangeListener() {
#Override
public void onPageScrollStateChanged(int arg0) {}
#Override
public void onPageScrolled(int arg0, float arg1, int arg2) {}
#Override
public void onPageSelected(int arg0) {
mActionBar.getTabAt(arg0).select();
}
});
}
}
By accessing the variable "fragments", you can access a previously created Fragment so that you can run methods of that Fragment.
public class MyPagerAdapter extends FragmentStatePagerAdapter {
final Context m_context;
final WeakReference<Fragment>[] m_fragments;
public DetailPagerAdapter(FragmentManager fm) {
super(fm);
m_context = ...
m_fragments = new WeakReference[enter size here];
}
#Override
public Fragment getItem(int position) {
final Fragment fragment = instantiate your fragment;
m_fragments[position] = new WeakReference<Fragment>(fragment);
return fragment;
}
#Override
public int getCount() {
return ...
}
public Fragment getFragment(final int position) {
return m_fragments[position] == null ? null :
m_fragments[position].get();
}
}
Do not need modify the FragmentPagerAdapter, because fragments are cached by the FragmentManager. So you must need find inside it. Use this function to find the fragment by pager adapter position.
public Fragment findFragmentByPosition(int position) {
FragmentPagerAdapter fragmentPagerAdapter = getFragmentPagerAdapter();
return getSupportFragmentManager().findFragmentByTag(
"android:switcher:" + getViewPager().getId() + ":"
+ fragmentPagerAdapter.getItemId(position));
}
Sample code for v4 support api.
I think this could help:
class HomePagerAdapter(fragmentManager: FragmentManager) : FragmentStatePagerAdapter(fragmentManager, BEHAVIOR_RESUME_ONLY_CURRENT_FRAGMENT) {
private val fragmentConstructors: List<() -> Fragment> by lazy {
listOf(
::AuctionLotsFragment,
::ChatListFragment,
::MarketHomeFragment,
::WalletSectionsFragment,
::SettingsFragment
)
}
private val fragments: HashMap<Int, WeakReference<Fragment>> by lazy {
HashMap()
}
override fun getCount(): Int = fragmentConstructors.size
override fun getItem(position: Int): Fragment {
return fragments[position]?.get() ?: this.createFragmentForPosition(position)
}
private fun createFragmentForPosition(position: Int): Fragment {
val fragment = fragmentConstructors[position].invoke()
fragments[position] = WeakReference(fragment)
return fragment
}
}