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not able to differ the contains of the two different fragments

I'm developing android screen for showing 2 different dashboard using tablayout & viewpager but only one screen shown at two different tabs(i.e. on MyDashboard & TeamDashboard).Please check my code.I'm new to android development.
I tried to use viewpager with pageradapter for swipe the screen.
public class ViewPagerAdapter extends FragmentPagerAdapter {
private int position;
private String tabTitles[] = new String[]{"MyDashboard", "Team` `Dashboard"};
public ViewPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int i) {
// MyDashboard_Fragment dashboard_fragment=new `MyDashboard_Fragment();
// TeamDashboard_Fragment dashboard_fragment1=new `TeamDashboard_Fragment();
// position = position + 1;
// Bundle bundle=new Bundle();
// bundle.putString("message","Fragment :" +position);
// dashboard_fragment.setArguments(bundle);
// return dashboard_fragment;
Fragment fragment = null;
switch (position) {
case 0:
fragment = new MyDashboard_Fragment();
break;
case 1:
fragment = new TeamDashboard_Fragment();
break;
}
return fragment;
}
#Override
public int getCount() {
return 2;
}
#Nullable
#Override
public CharSequence getPageTitle(int position) {
return tabTitles[position];
}
}

Problem is because you are not assigning the new value to position variable before use it, please update your code like bellow
public class ViewPagerAdapter extends FragmentPagerAdapter {
private int position;
private String tabTitles[] = new String[]{"MyDashboard", "Team` `Dashboard"};
public ViewPagerAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int i) {
// MyDashboard_Fragment dashboard_fragment=new `MyDashboard_Fragment();
// TeamDashboard_Fragment dashboard_fragment1=new `TeamDashboard_Fragment();
// position = position + 1;
// Bundle bundle=new Bundle();
// bundle.putString("message","Fragment :" +position);
// dashboard_fragment.setArguments(bundle);
// return dashboard_fragment;
position=i;
Fragment fragment = null;
switch (position) {
case 0:
fragment = new MyDashboard_Fragment();
break;
case 1:
fragment = new TeamDashboard_Fragment();
break;
}
return fragment;
}
#Override
public int getCount() {
return 2;
}
#Nullable
#Override
public CharSequence getPageTitle(int position) {
return tabTitles[position];
}
}

add callback listener in each viewpager fragment

I've 2 fragments in viewpager and I want to add callback methods using interface in both. I add the interface listener while initiating fragments in viewpager adapter but only the last fragment's is being called. That's why when I click on the MainActivity's menu option, only the Toast in MyFragB is being called even if MyFragA is showing.
Both Fragments... Only Activity calling MyFragB Toast is showing when wither fragment is opened
public class MyFragA extends Fragment implements FragmentCaller {
private TextView myTxt;
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
return inflater.inflate(R.layout.myfraga, container, false);
}
#Override
public void CallFragment() {
if(getActivity()!=null)
Toast.makeText(getActivity(), "Activity calling MyFragA", Toast.LENGTH_SHORT).show();
}
}
public class MyFragB extends Fragment implements FragmentCaller{
private TextView myTxt;
#Nullable
#Override
public View onCreateView(LayoutInflater inflater, #Nullable ViewGroup container, #Nullable Bundle savedInstanceState) {
return inflater.inflate(R.layout.myfragb, container, false);
}
#Override
public void CallFragment() {
if(getActivity()!=null)
Toast.makeText(getActivity(), "Activity calling MyFragB", Toast.LENGTH_SHORT).show();
}
}
Main Activity
public class MainActivity extends AppCompatActivity {
TabLayout tabs;
ViewPager viewpager;
FragmentCaller fragListerner = null;
public interface FragmentCaller {
void CallFragment();
}
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tabs = (TabLayout)findViewById(R.id.tabs);
viewpager = (ViewPager)findViewById(R.id.viewpager);
SimpleFragmentPagerAdapter adapter = new SimpleFragmentPagerAdapter(this, getSupportFragmentManager());
viewpager.setAdapter(adapter);
tabs.setupWithViewPager(viewpager);
} // onCreate ends
public class SimpleFragmentPagerAdapter extends FragmentStatePagerAdapter {
private Context mContext;
public SimpleFragmentPagerAdapter(Context context, FragmentManager fm) {
super(fm);
mContext = context;
}
// This determines the fragment for each tab
#Override
public Fragment getItem(int position) {
Fragment fragment = null;
if (position == 0) {
fragment = new MyFragA();
fragListerner = (FragmentCaller) fragment;
return fragment;
} else if (position == 1){
fragment = new MyFragB();
fragListerner = (FragmentCaller)fragment;
return fragment;
}
return null;
}
// This determines the number of tabs
#Override
public int getCount() {
return 2;
}
// This determines the title for each tab
#Override
public CharSequence getPageTitle(int position) {
// Generate title based on item position
switch (position) {
case 0:
return mContext.getString(R.string.fraga);
case 1:
return mContext.getString(R.string.fragb);
default:
return null;
}
}
}
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.callback, menu);
return true;
}
public boolean onOptionsItemSelected(MenuItem item) {
super.onOptionsItemSelected(item);
switch (item.getItemId()){
case R.id.call:
if(fragListerner!=null){
if(fragListerner instanceof MyFragA){
fragListerner.CallFragment();
}else if(fragListerner instanceof MyFragB){
fragListerner.CallFragment();
}
}
break;
}
return true;
}
}

I used rick's answer from here.
public class MainActivity extends AppCompatActivity {
TabLayout tabs;
ViewPager viewpager;
public static int currentFrag=0;
SimpleFragmentPagerAdapter adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
tabs = (TabLayout)findViewById(R.id.tabs);
viewpager = (ViewPager)findViewById(R.id.viewpager);
adapter = new SimpleFragmentPagerAdapter(this, getSupportFragmentManager());
viewpager.setAdapter(adapter);
tabs.setupWithViewPager(viewpager);
viewpager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
#Override
public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {
}
#Override
public void onPageSelected(int position) {
System.out.println("sammy_current_position: "+position);
currentFrag = position;
}
#Override
public void onPageScrollStateChanged(int state) {
}
});
} // onCreate ends
public class SimpleFragmentPagerAdapter extends FragmentStatePagerAdapter {
private Context mContext;
public SimpleFragmentPagerAdapter(Context context, FragmentManager fm) {
super(fm);
mContext = context;
}
#Override
public Fragment getItem(int position) {
if (position == 0) {
return new MyFragA();
} else if (position == 1){
return new MyFragB();
}
return null;
}
#Override
public int getCount() {
return 2;
}
// This determines the title for each tab
#Override
public CharSequence getPageTitle(int position) {
// Generate title based on item position
switch (position) {
case 0:
return mContext.getString(R.string.fraga);
case 1:
return mContext.getString(R.string.fragb);
default:
return null;
}
}
}
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflater = getMenuInflater();
inflater.inflate(R.menu.callback, menu);
return true;
}
public boolean onOptionsItemSelected(MenuItem item) {
super.onOptionsItemSelected(item);
switch (item.getItemId()){
case R.id.call:
if(currentFrag == 0) {
MyFragA frag1 = (MyFragA)viewpager.getAdapter().instantiateItem(viewpager, viewpager.getCurrentItem());
frag1.specialCase();
}
break;
}
return true;
}
}

but only the last fragment's is being called
Of Course ! because at pos == 0 you are setting fragListerner = (FragmentCaller) fragment then at again in pos == 1 you re-set fragListerner = (FragmentCaller)fragment;. So this condition, fragListerner instanceof MyFragB will always be true!
#Override
public Fragment getItem(int position) {
Fragment fragment = null;
if (position == 0) {
fragment = new MyFragA();
fragListerner = (FragmentCaller) fragment;
return fragment;
} else if (position == 1){
fragment = new MyFragB();
fragListerner = (FragmentCaller)fragment;
return fragment;
}
return null;
}
So, you are trying to communicate from activity to fragment
okay, if you still want to use interfaces, you can do it like that:
create an instance of your interface for each fragment! and in getItem assign them both,
#Override
public Fragment getItem(int position) {
Fragment fragment = null;
if (position == 0) {
fragment = new MyFragA();
fragAListerner = (FragmentCaller) fragment;
return fragment;
} else if (position == 1){
fragment = new MyFragB();
fragBListerner = (FragmentCaller)fragment;
return fragment;
}
return null;
}
But, there is an easier way to call fragment's methods from it's parent activity, which is like follows, for ex:
Fragment fragment = adapter.getItem(0); // MyFragA is at pos 0
fragment.<specific_function_name>();
Or, by using it's id!
MyFragA fragment = (MyFragA) getFragmentManager().findFragmentById(R.id.MyFragAId);
fragment.<specific_function_name>();
Or, by using it's tag!
MyFragA fragment = (MyFragA) getFragmentManager().findFragmentByTag("MyFragATag");
fragment.<specific_function_name>();

Reload fragments inside ViewPager which inside another fragment inViewPager

I have an activity, which includes ViewPager with three fragments. In the second fragment i have ViewPager with two different fragments too.
This my MainActivityPagerAdapter which connected with ViewPager in MainActivity:
public class MainActivityPagerAdapter extends FragmentStatePagerAdapter implements LoginView.LoginStateChangeListener {
private static final String TAG = MainActivityPagerAdapter.class.getName();
private MapFragment mapFragment = new MapFragment();
private UserProfileFragment userProfileFragment = new UserProfileFragment();
private CompanyProfileFragment CompanyProfileFragment = new DiveCenterProfileFragment();
private NotificationsFragment notificationsFragment = new notificationsFragment();
public MainActivityPagerAdapter(FragmentManager manager) {
super(manager);
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return mapFragment;
case 1:
return notificationsFragment;
case 2:
switch (MyApplication.getInstance().getSharedPreferenceHelper().getActiveUserType()) {
case DIVECENTER:
return companyProfileFragment;
case DIVER:
case INSTRUCTOR:
return userProfileFragment;
case NONE:
return userProfileFragment;
}
default:
return null;
}
}
#Override
public int getCount() {
return 3;
}
#Override
public int getItemPosition(Object object) {
Log.i(TAG, "getItemPosition");
return POSITION_NONE;
}
#Override
public CharSequence getPageTitle(int position) {
return null;
}
}
This my pager adapter for ViewPager at the second fragment:
public class NotificationsPagerAdapter extends FragmentStatePagerAdapter {
private PersonalNotificationsFragment personalNotificationsFragment = new PersonalNotificationsFragment();
private ActivityNotificationsFragment activityNotificationsFragment = new ActivityNotificationsFragment();
public NotificationsPagerAdapter(FragmentManager manager) {
super(manager);
}
#Override
public Fragment getItem(int position) {
switch (position) {
case 0:
return personalNotificationsFragment;
case 1:
return activityNotificationsFragment;
default:
return null;
}
}
#Override
public int getCount() {
return 2;
}
public void setPersonalNotificationsFragment(PersonalNotificationsFragment personalNotificationsFragment) {
this.personalNotificationsFragment = personalNotificationsFragment;
}
public void setActivityNotificationsFragment(ActivityNotificationsFragment activityNotificationsFragment) {
this.activityNotificationsFragment = activityNotificationsFragment;
}
#Override
public CharSequence getPageTitle(int position) {
return null;
}
#Override
public int getItemPosition(Object object) {
return POSITION_NONE;
}
}
So, there are two user types in app:
Simple user
Company
When user changing his type i need to refresh all fragments in MainActivity including fragments inside second fragment. For this I'm using notifyDataSetChanged() for MainActivityViewPager, it work correctly, but fragments inside second fragment don't update(onCreateView don't called, and i see only empty views).
In what may be a problem?

Use getChildFragmentManager() for inner viewPager

Use getChildFragmentManager() instead of getFragmentManager() for changing fragments inside the viewPager

NullPointerException when using fragment in Activity

There are some fragments in my activity.
private MainFragment mMainFragment;
... //other fragments
Here's my PagerAdapter.
private class MainPagerAdapter extends FragmentPagerAdapter {
...
#Override
public Fragment getItem(int position) {
if (DEBUG) {
Log.w(TAG, "position: " + position);
}
if (position == 0) {
mMainFragment = MainFragment.newInstance(PAGE_MAIN_INDEX);
return mMainFragment;
}
}
#Override
public int getCount() {
return FRAGMENT_COUNT;
}
}
Sometimes, when my app goes to background, the system kills the activity, then if my app return to foreground and system try restore my page. It looks everything is fine, every view shows correctly. But when I try to refresh my fragment, my app is crash. Log shows the fragment is null. I don't why. Any ideas?
Here's my Fragment.onCreate(Bundle savedInstanceState)
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
mActivity = (SubmitTenderActivity) getActivity();
mInflater = (LayoutInflater) mActivity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
mResources = getResources();
}

getItem() does not get called again when a Fragment is being restored by the framework, so your mMainFragment is null after restoring. instantiateItem() method is called for every Fragment that is being restored by the framework so you must reassign mMainFragment again in this method. Change your code as following should solve your problem:
private class MainPagerAdapter extends FragmentPagerAdapter {
...
#Override
public Fragment getItem(int position) {
if (DEBUG) {
Log.w(TAG, "position: " + position);
}
if (position == 0) {
mMainFragment = MainFragment.newInstance(PAGE_MAIN_INDEX);
return mMainFragment;
}
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
Object obj = super.instantiateItem(container, position);
if (position == 0) {
mMainFragment = (MainFragment)obj;
}
return obj;
}
#Override
public int getCount() {
return FRAGMENT_COUNT;
}
}

Try something like this
#Override
public Fragment getItem(int position) {
switch(position){
case 0:
return new Fragment1();
case 1:
return new Fragment2();
default:
break;
}
return null;
}

Its better to use below method in fragment:
#Override
public void onAttach(Activity activity) {
super.onAttach(activity);
mActivity = activity;
}

I would think you should move the return mMainFragment out of the if statement in method getItem.

Why don't you try this? Its working fine for me.
public class UpdateTabsAdapter extends FragmentPagerAdapter {
public UpdateTabsAdapter(FragmentManager fm) {
super(fm);
}
#Override
public Fragment getItem(int index) {
switch (index) {
case 0:
return new AcademicDocumentsFragment();
case 1:
return new EmployementDocumentsFragment();
case 2:
return new UploadPhotoDetailsFragment();
}
return null;
}
#Override
public int getCount() {
return 3;
}
}

Remove Fragment Page from ViewPager in Android

I'm trying to dynamically add and remove Fragments from a ViewPager, adding works without any problems, but removing doesn't work as expected.
Everytime I want to remove the current item, the last one gets removed.
I also tried to use an FragmentStatePagerAdapter or return POSITION_NONE in the adapter's getItemPosition method.
What am I doing wrong?
Here's a basic example:
MainActivity.java
public class MainActivity extends FragmentActivity implements TextProvider {
private Button mAdd;
private Button mRemove;
private ViewPager mPager;
private MyPagerAdapter mAdapter;
private ArrayList<String> mEntries = new ArrayList<String>();
#Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mEntries.add("pos 1");
mEntries.add("pos 2");
mEntries.add("pos 3");
mEntries.add("pos 4");
mEntries.add("pos 5");
mAdd = (Button) findViewById(R.id.add);
mRemove = (Button) findViewById(R.id.remove);
mPager = (ViewPager) findViewById(R.id.pager);
mAdd.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View view) {
addNewItem();
}
});
mRemove.setOnClickListener(new OnClickListener() {
#Override
public void onClick(View view) {
removeCurrentItem();
}
});
mAdapter = new MyPagerAdapter(this.getSupportFragmentManager(), this);
mPager.setAdapter(mAdapter);
}
private void addNewItem() {
mEntries.add("new item");
mAdapter.notifyDataSetChanged();
}
private void removeCurrentItem() {
int position = mPager.getCurrentItem();
mEntries.remove(position);
mAdapter.notifyDataSetChanged();
}
#Override
public String getTextForPosition(int position) {
return mEntries.get(position);
}
#Override
public int getCount() {
return mEntries.size();
}
private class MyPagerAdapter extends FragmentPagerAdapter {
private TextProvider mProvider;
public MyPagerAdapter(FragmentManager fm, TextProvider provider) {
super(fm);
this.mProvider = provider;
}
#Override
public Fragment getItem(int position) {
return MyFragment.newInstance(mProvider.getTextForPosition(position));
}
#Override
public int getCount() {
return mProvider.getCount();
}
}
}
TextProvider.java
public interface TextProvider {
public String getTextForPosition(int position);
public int getCount();
}
MyFragment.java
public class MyFragment extends Fragment {
private String mText;
public static MyFragment newInstance(String text) {
MyFragment f = new MyFragment(text);
return f;
}
public MyFragment() {
}
public MyFragment(String text) {
this.mText = text;
}
#Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View root = inflater.inflate(R.layout.fragment, container, false);
((TextView) root.findViewById(R.id.position)).setText(mText);
return root;
}
}
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<Button
android:id="#+id/add"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="add new item" />
<Button
android:id="#+id/remove"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:text="remove current item" />
<android.support.v4.view.ViewPager
android:id="#+id/pager"
android:layout_width="match_parent"
android:layout_height="0dip"
android:layout_weight="1" />
</LinearLayout>
fragment.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="#+id/position"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="center"
android:textSize="35sp" />
</LinearLayout>

The ViewPager doesn't remove your fragments with the code above because it loads several views (or fragments in your case) into memory. In addition to the visible view, it also loads the view to either side of the visible one. This provides the smooth scrolling from view to view that makes the ViewPager so cool.
To achieve the effect you want, you need to do a couple of things.
Change the FragmentPagerAdapter to a FragmentStatePagerAdapter. The reason for this is that the FragmentPagerAdapter will keep all the views that it loads into memory forever. Where the FragmentStatePagerAdapter disposes of views that fall outside the current and traversable views.
Override the adapter method getItemPosition (shown below). When we call mAdapter.notifyDataSetChanged(); the ViewPager interrogates the adapter to determine what has changed in terms of positioning. We use this method to say that everything has changed so reprocess all your view positioning.
And here's the code...
private class MyPagerAdapter extends FragmentStatePagerAdapter {
//... your existing code
#Override
public int getItemPosition(Object object){
return PagerAdapter.POSITION_NONE;
}
}

The solution by Louth was not enough to get things working for me, as the existing fragments were not getting destroyed. Motivated by this answer, I found that the solution is to override the getItemId(int position) method of FragmentPagerAdapter to give a new unique ID whenever there has been a change in the expected position of a Fragment.
Source Code:
private class MyPagerAdapter extends FragmentPagerAdapter {
private TextProvider mProvider;
private long baseId = 0;
public MyPagerAdapter(FragmentManager fm, TextProvider provider) {
super(fm);
this.mProvider = provider;
}
#Override
public Fragment getItem(int position) {
return MyFragment.newInstance(mProvider.getTextForPosition(position));
}
#Override
public int getCount() {
return mProvider.getCount();
}
//this is called when notifyDataSetChanged() is called
#Override
public int getItemPosition(Object object) {
// refresh all fragments when data set changed
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;
}
}
Now, for example if you delete a single tab or make some change to the order, you should call notifyChangeInPosition(1) before calling notifyDataSetChanged(), which will ensure that all the Fragments will be recreated.
Why this solution works
Overriding getItemPosition():
When notifyDataSetChanged() is called, the adapter calls the notifyChanged() method of the ViewPager which it is attached to. The ViewPager then checks the value returned by the adapter's getItemPosition() for each item, removing those items which return POSITION_NONE (see the source code) and then repopulating.
Overriding getItemId():
This is necessary to prevent the adapter from reloading the old fragment when the ViewPager is repopulating. You can easily understand why this works by looking at the source code for instantiateItem() in FragmentPagerAdapter.
final long itemId = getItemId(position);
// Do we already have this fragment?
String name = makeFragmentName(container.getId(), itemId);
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,
makeFragmentName(container.getId(), itemId));
}
As you can see, the getItem() method is only called if the fragment manager finds no existing fragments with the same Id. To me it seems like a bug that the old fragments are still attached even after notifyDataSetChanged() is called, but the documentation for ViewPager does clearly state that:
Note this class is currently under early design and development. The API will likely change in later updates of the compatibility library, requiring changes to the source code of apps when they are compiled against the newer version.
So hopefully the workaround given here will not be necessary in a future version of the support library.

my working solution to remove fragment page from view pager
public class MyFragmentAdapter extends FragmentStatePagerAdapter {
private ArrayList<ItemFragment> pages;
public MyFragmentAdapter(FragmentManager fragmentManager, ArrayList<ItemFragment> pages) {
super(fragmentManager);
this.pages = pages;
}
#Override
public Fragment getItem(int index) {
return pages.get(index);
}
#Override
public int getCount() {
return pages.size();
}
#Override
public int getItemPosition(Object object) {
int index = pages.indexOf (object);
if (index == -1)
return POSITION_NONE;
else
return index;
}
}
And when i need to remove some page by index i do this
pages.remove(position); // ArrayList<ItemFragment>
adapter.notifyDataSetChanged(); // MyFragmentAdapter
Here it is my adapter initialization
MyFragmentAdapter adapter = new MyFragmentAdapter(getSupportFragmentManager(), pages);
viewPager.setAdapter(adapter);

The fragment must be already removed but the issue was viewpager save state
Try
myViewPager.setSaveFromParentEnabled(false);
Nothing worked but this solved the issue !
Cheers !

I had the idea of simply copy the source code from android.support.v4.app.FragmentPagerAdpater into a custom class named
CustumFragmentPagerAdapter. This gave me the chance to modify the instantiateItem(...) so that every time it is called, it removes / destroys the currently attached fragment before it adds the new fragment received from getItem() method.
Simply modify the instantiateItem(...) in the following way:
#Override
public Object instantiateItem(ViewGroup container, int position) {
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
final long itemId = getItemId(position);
// Do we already have this fragment?
String name = makeFragmentName(container.getId(), itemId);
Fragment fragment = mFragmentManager.findFragmentByTag(name);
// remove / destroy current fragment
if (fragment != null) {
mCurTransaction.remove(fragment);
}
// get new fragment and add it
fragment = getItem(position);
mCurTransaction.add(container.getId(), fragment, makeFragmentName(container.getId(), itemId));
if (fragment != mCurrentPrimaryItem) {
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
}
return fragment;
}

You can combine both for better :
private class MyPagerAdapter extends FragmentStatePagerAdapter {
//... your existing code
#Override
public int getItemPosition(Object object){
if(Any_Reason_You_WantTo_Update_Positions) //this includes deleting or adding pages
return PagerAdapter.POSITION_NONE;
}
else
return PagerAdapter.POSITION_UNCHANGED; //this ensures high performance in other operations such as editing list items.
}

I had some problems with FragmentStatePagerAdapter.
After removing an item:
there was another item used for a position (an item which did not belong to the position but to a position next to it)
or some fragment was not loaded (there was only blank background visible on that page)
After lots of experiments, I came up with the following solution.
public class SomeAdapter extends FragmentStatePagerAdapter {
private List<Item> items = new ArrayList<Item>();
private boolean removing;
#Override
public Fragment getItem(int position) {
ItemFragment fragment = new ItemFragment();
Bundle args = new Bundle();
// use items.get(position) to configure fragment
fragment.setArguments(args);
return fragment;
}
#Override
public int getCount() {
return items.size();
}
#Override
public int getItemPosition(Object object) {
if (removing) {
return PagerAdapter.POSITION_NONE;
}
Item item = getItemOfFragment(object);
int index = items.indexOf(item);
if (index == -1) {
return POSITION_NONE;
} else {
return index;
}
}
public void addItem(Item item) {
items.add(item);
notifyDataSetChanged();
}
public void removeItem(int position) {
items.remove(position);
removing = true;
notifyDataSetChanged();
removing = false;
}
}
This solution only uses a hack in case of removing an item. Otherwise (e.g. when adding an item) it retains the cleanliness and performance of an original code.
Of course, from the outside of the adapter, you call only addItem/removeItem, no need to call notifyDataSetChanged().

For future readers!
Now you can use ViewPager2 for dynamically adding, removing fragment from the viewpager.
Quoting form API reference
ViewPager2 replaces ViewPager, addressing most of its predecessor’s
pain-points, including right-to-left layout support, vertical
orientation, modifiable Fragment collections, etc.
Take look at MutableCollectionFragmentActivity.kt in googlesample/android-viewpager2 for an example of adding, removing fragments dynamically from the viewpager.
For your information:
Articles:
Exploring the ViewPager2
Look deep into ViewPager2
API reference
Release notes
Samples Repo: https://github.com/googlesamples/android-viewpager2

Louth's answer works fine. But I don't think always return POSITION_NONE is a good idea. Because POSITION_NONE means that fragment should be destroyed and a new fragment will be created.
You can check that in dataSetChanged function in the source code of ViewPager.
if (newPos == PagerAdapter.POSITION_NONE) {
mItems.remove(i);
i--;
... not related code
mAdapter.destroyItem(this, ii.position, ii.object);
So I think you'd better use an arraylist of weakReference to save all the fragments you have created. And when you add or remove some page, you can get the right position from your own arraylist.
public int getItemPosition(Object object) {
for (int i = 0; i < mFragmentsReferences.size(); i ++) {
WeakReference<Fragment> reference = mFragmentsReferences.get(i);
if (reference != null && reference.get() != null) {
Fragment fragment = reference.get();
if (fragment == object) {
return i;
}
}
}
return POSITION_NONE;
}
According to the comments, getItemPosition is Called when the host view is attempting to determine if an item's position has changed. And the return value means its new position.
But this is not enought. We still have an important step to take.
In the source code of FragmentStatePagerAdapter, there is an array named "mFragments" caches the fragments which are not destroyed. And in instantiateItem function.
if (mFragments.size() > position) {
Fragment f = mFragments.get(position);
if (f != null) {
return f;
}
}
It returned the cached fragment directly when it find that cached fragment is not null. So there is a problem. From example, let's delete one page at position 2, Firstly, We remove that fragment from our own reference arraylist. so in getItemPosition it will return POSITION_NONE for that fragment, and then that fragment will be destroyed and removed from "mFragments".
mFragments.set(position, null);
Now the fragment at position 3 will be at position 2. And instantiatedItem with param position 3 will be called. At this time, the third item in "mFramgents" is not null, so it will return directly. But actually what it returned is the fragment at position 2. So when we turn into page 3, we will find an empty page there.
To work around this problem. My advise is that you can copy the source code of FragmentStatePagerAdapter into your own project, and when you do add or remove operations, you should add and remove elements in the "mFragments" arraylist.
Things will be simpler if you just use PagerAdapter instead of FragmentStatePagerAdapter. Good Luck.

add or remove fragment in viewpager dynamically.
Call setupViewPager(viewPager) on activity start.
To load different fragment call setupViewPagerCustom(viewPager).
e.g. on button click call: setupViewPagerCustom(viewPager);
private void setupViewPager(ViewPager viewPager)
{
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFrag(new fragmnet1(), "HOME");
adapter.addFrag(new fragmnet2(), "SERVICES");
viewPager.setAdapter(adapter);
}
private void setupViewPagerCustom(ViewPager viewPager)
{
ViewPagerAdapter adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFrag(new fragmnet3(), "Contact us");
adapter.addFrag(new fragmnet4(), "ABOUT US");
viewPager.setAdapter(adapter);
}
//Viewpageradapter, handles the views
static class ViewPagerAdapter extends FragmentStatePagerAdapter
{
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public ViewPagerAdapter(FragmentManager manager){
super(manager);
}
#Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}
#Override
public int getCount() {
return mFragmentList.size();
}
#Override
public int getItemPosition(Object object){
return PagerAdapter.POSITION_NONE;
}
public void addFrag(Fragment fragment, String title){
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
}
#Override
public CharSequence getPageTitle(int position){
return mFragmentTitleList.get(position);
}
}

Try this solution. I have used databinding for binding view. You can use common "findViewById()" function.
public class ActCPExpense extends BaseActivity implements View.OnClickListener, {
private static final String TAG = ActCPExpense.class.getSimpleName();
private Context mContext;
private ActCpLossBinding mBinding;
private ViewPagerAdapter adapter;
#Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
try {
setContentView(R.layout.act_cp_loss);
mBinding = DataBindingUtil.setContentView(this, R.layout.act_cp_loss);
mContext = ActCPExpense.this;
initViewsAct();
} catch (Exception e) {
LogUtils.LOGE(TAG, e);
}
}
private void initViewsAct() {
adapter = new ViewPagerAdapter(getSupportFragmentManager());
adapter.addFragment(FragmentCPPayee.newInstance(), "Title");
mBinding.viewpager.setAdapter(adapter);
mBinding.tab.setViewPager(mBinding.viewpager);
}
#Override
public boolean onOptionsItemSelected(MenuItem itemActUtility) {
int i = itemActUtility.getItemId();
if (i == android.R.id.home) {
onBackPressed();
}
return super.onOptionsItemSelected(itemActUtility);
}
#Override
public void onClick(View view) {
super.onClick(view);
int id = view.getId();
if (id == R.id.btnAdd) {
addFragment();
} else if (id == R.id.btnDelete) {
removeFragment();
}
}
private void addFragment(){
adapter.addFragment(FragmentCPPayee.newInstance("Title");
adapter.notifyDataSetChanged();
mBinding.tab.setViewPager(mBinding.viewpager);
}
private void removeFragment(){
adapter.removeItem(mBinding.viewpager.getCurrentItem());
mBinding.tab.setViewPager(mBinding.viewpager);
}
class ViewPagerAdapter extends FragmentStatePagerAdapter {
private final List<Fragment> mFragmentList = new ArrayList<>();
private final List<String> mFragmentTitleList = new ArrayList<>();
public ViewPagerAdapter(FragmentManager manager) {
super(manager);
}
#Override
public int getItemPosition(#NonNull Object object) {
return PagerAdapter.POSITION_NONE;
}
#Override
public Fragment getItem(int position) {
return mFragmentList.get(position);
}
#Override
public int getCount() {
return mFragmentList.size();
}
public void addFragment(Fragment fragment, String title) {
mFragmentList.add(fragment);
mFragmentTitleList.add(title);
}
public void removeItem(int pos) {
destroyItem(null, pos, mFragmentList.get(pos));
mFragmentList.remove(pos);
mFragmentTitleList.remove(pos);
adapter.notifyDataSetChanged();
mBinding.viewpager.setCurrentItem(pos - 1, false);
}
#Override
public CharSequence getPageTitle(int position) {
return "Title " + String.valueOf(position + 1);
}
}
}

I added a function "clearFragments" and I used that function to clear adapter before setting the new fragments. This calls the proper remove actions of Fragments. My pagerAdapter class:
private class ChartPagerAdapter extends FragmentPagerAdapter{
private ArrayList<Fragment> fragmentList;
ChartPagerAdapter(FragmentManager fm){
super(fm);
fragmentList = new ArrayList<>();
}
void setFragments(ArrayList<? extends Fragment> fragments){
fragmentList.addAll(fragments);
}
void clearFragments(){
for(Fragment fragment:fragmentList)
getChildFragmentManager().beginTransaction().remove(fragment).commit();
fragmentList.clear();
}
#Override
public Fragment getItem(int i) {
return fragmentList.get(i);
}
#Override
public int getCount() {
return fragmentList.size();
}
}

i solved this problem by these steps
1- use FragmentPagerAdapter
2- in each fragment create a random id
fragment.id = new Random().nextInt();
3- override getItemPosition in adapter
#Override
public int getItemPosition(#NonNull Object object) {
return PagerAdapter.POSITION_NONE;
}
4-override getItemId in adapter
#Override
public long getItemId(int position) {
return mDatasetFragments.get(position).id;
}
5- now delete code is
adapter.mDatasetFragments.remove(< item to delete position >);
adapter.notifyDataSetChanged();
this worked for me i hope help

My final version code, fixed ALL bugs. It took me 3 days
Updated 2020/07/18:
I had changed a lot of the source code and fix so many bugs, but I don't promise it still work today.
https://github.com/lin1987www/FragmentBuilder/blob/master/commonLibrary/src/main/java/android/support/v4/app/FragmentStatePagerAdapterFix.java
public class FragmentStatePagerAdapterFix extends PagerAdapter {
private static final String TAG = FragmentStatePagerAdapterFix.class.getSimpleName();
private static final boolean DEBUG = false;
private WeakReference<FragmentActivity> wrFragmentActivity;
private WeakReference<Fragment> wrParentFragment;
private final FragmentManager mFragmentManager;
private FragmentTransaction mCurTransaction = null;
protected ArrayList<Fragment> mFragments = new ArrayList<>();
protected ArrayList<FragmentState> mFragmentStates = new ArrayList<>();
protected ArrayList<String> mFragmentTags = new ArrayList<>();
protected ArrayList<String> mFragmentClassNames = new ArrayList<>();
protected ArrayList<Bundle> mFragmentArgs = new ArrayList<>();
private Fragment mCurrentPrimaryItem = null;
private boolean[] mTempPositionChange;
#Override
public int getCount() {
return mFragmentClassNames.size();
}
public FragmentActivity getFragmentActivity() {
return wrFragmentActivity.get();
}
public Fragment getParentFragment() {
return wrParentFragment.get();
}
public FragmentStatePagerAdapterFix(FragmentActivity activity) {
mFragmentManager = activity.getSupportFragmentManager();
wrFragmentActivity = new WeakReference<>(activity);
wrParentFragment = new WeakReference<>(null);
}
public FragmentStatePagerAdapterFix(Fragment fragment) {
mFragmentManager = fragment.getChildFragmentManager();
wrFragmentActivity = new WeakReference<>(fragment.getActivity());
wrParentFragment = new WeakReference<>(fragment);
}
public void add(Class<? extends android.support.v4.app.Fragment> fragClass) {
add(fragClass, null, null);
}
public void add(Class<? extends android.support.v4.app.Fragment> fragClass, Bundle args) {
add(fragClass, args, null);
}
public void add(Class<? extends android.support.v4.app.Fragment> fragClass, String tag) {
add(fragClass, null, tag);
}
public void add(Class<? extends android.support.v4.app.Fragment> fragClass, Bundle args, String tag) {
add(fragClass, args, tag, getCount());
}
public void add(Class<? extends android.support.v4.app.Fragment> fragClass, Bundle args, String tag, int position) {
mFragments.add(position, null);
mFragmentStates.add(position, null);
mFragmentTags.add(position, tag);
mFragmentClassNames.add(position, fragClass.getName());
mFragmentArgs.add(position, args);
mTempPositionChange = new boolean[getCount()];
}
public void remove(int position) {
if (position < getCount()) {
mTempPositionChange = new boolean[getCount()];
for (int i = position; i < mTempPositionChange.length; i++) {
mTempPositionChange[i] = true;
}
mFragments.remove(position);
mFragmentStates.remove(position);
mFragmentTags.remove(position);
mFragmentClassNames.remove(position);
mFragmentArgs.remove(position);
}
}
public void clear(){
mFragments.clear();
mFragmentStates.clear();
mFragmentTags.clear();
mFragmentClassNames.clear();
mFragmentArgs.clear();
}
#Override
public void startUpdate(ViewGroup container) {
}
#Override
public Object instantiateItem(ViewGroup container, int position) {
Fragment fragment;
// If we already have this item instantiated, there is nothing
// to do. This can happen when we are restoring the entire pager
// from its saved state, where the fragment manager has already
// taken care of restoring the fragments we previously had instantiated.
fragment = mFragments.get(position);
if (fragment != null) {
return fragment;
}
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
FragmentState fs = mFragmentStates.get(position);
if (fs != null) {
fragment = fs.instantiate(getFragmentActivity(), getParentFragment());
// Fix bug
// http://stackoverflow.com/questions/11381470/classnotfoundexception-when-unmarshalling-android-support-v4-view-viewpagersav
if (fragment.mSavedFragmentState != null) {
fragment.mSavedFragmentState.setClassLoader(fragment.getClass().getClassLoader());
}
}
if (fragment == null) {
fragment = Fragment.instantiate(getFragmentActivity(), mFragmentClassNames.get(position), mFragmentArgs.get(position));
}
if (DEBUG) {
Log.v(TAG, "Adding item #" + position + ": f=" + fragment);
}
fragment.setMenuVisibility(false);
fragment.setUserVisibleHint(false);
mFragments.set(position, fragment);
mFragmentStates.set(position, null);
mCurTransaction.add(container.getId(), fragment, mFragmentTags.get(position));
return fragment;
}
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
Fragment fragment = (Fragment) object;
if (mCurTransaction == null) {
mCurTransaction = mFragmentManager.beginTransaction();
}
if (DEBUG) {
Log.v(TAG, "Removing item #" + position + ": f=" + object
+ " v=" + ((Fragment) object).getView());
}
if (position < getCount()) {
FragmentState fragmentState = new FragmentState(fragment);
Fragment.SavedState savedState = mFragmentManager.saveFragmentInstanceState(fragment);
if (savedState != null) {
fragmentState.mSavedFragmentState = savedState.mState;
}
mFragmentStates.set(position, fragmentState);
mFragments.set(position, null);
}
mCurTransaction.remove(fragment);
}
#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();
// Fix: Fragment is added by transaction. BUT didn't add to FragmentManager's mActive.
for (Fragment fragment : mFragments) {
if (fragment != null) {
fixActiveFragment(mFragmentManager, fragment);
}
}
}
}
#Override
public boolean isViewFromObject(View view, Object object) {
return ((Fragment) object).getView() == view;
}
#Override
public Parcelable saveState() {
Bundle state = null;
// 目前顯示的 Fragments
for (int i = 0; i < mFragments.size(); i++) {
Fragment f = mFragments.get(i);
if (f != null && f.isAdded()) {
if (state == null) {
state = new Bundle();
}
String key = "f" + i;
mFragmentManager.putFragment(state, key, f);
}
}
if (mFragmentStates.size() > 0) {
if (state == null) {
state = new Bundle();
}
FragmentState[] fs = new FragmentState[mFragmentStates.size()];
mFragmentStates.toArray(fs);
state.putParcelableArray("states_fragment", fs);
}
return state;
}
#Override
public void restoreState(Parcelable state, ClassLoader loader) {
if (state != null) {
Bundle bundle = (Bundle) state;
bundle.setClassLoader(loader);
Parcelable[] fs = bundle.getParcelableArray("states_fragment");
mFragments.clear();
mFragmentStates.clear();
mFragmentTags.clear();
mFragmentClassNames.clear();
mFragmentArgs.clear();
if (fs != null) {
for (int i = 0; i < fs.length; i++) {
FragmentState fragmentState = (FragmentState) fs[i];
mFragmentStates.add(fragmentState);
if (fragmentState != null) {
mFragmentArgs.add(fragmentState.mArguments);
mFragmentTags.add(fragmentState.mTag);
mFragmentClassNames.add(fragmentState.mClassName);
} else {
mFragmentArgs.add(null);
mFragmentTags.add(null);
mFragmentClassNames.add(null);
}
mFragments.add(null);
}
}
Iterable<String> keys = bundle.keySet();
for (String key : keys) {
if (key.startsWith("f")) {
int index = Integer.parseInt(key.substring(1));
Fragment f = mFragmentManager.getFragment(bundle, key);
if (f != null) {
f.setMenuVisibility(false);
mFragments.set(index, f);
mFragmentArgs.set(index, f.mArguments);
mFragmentTags.set(index, f.mTag);
mFragmentClassNames.set(index, f.getClass().getName());
} else {
Log.w(TAG, "Bad fragment at key " + key);
}
}
}
// If restore will change
notifyDataSetChanged();
}
}
public static void fixActiveFragment(FragmentManager fragmentManager, Fragment fragment) {
FragmentManagerImpl fm = (FragmentManagerImpl) fragmentManager;
if (fm.mActive != null) {
int index = fragment.mIndex;
Fragment origin = fm.mActive.get(index);
if (origin != null) {
if ((origin.mIndex != fragment.mIndex) || !(origin.equals(fragment))) {
Log.e(TAG,
String.format("fixActiveFragment: Not Equal! Origin: %s %s, Fragment: %s $s",
origin.getClass().getName(), origin.mIndex,
fragment.getClass().getName(), fragment.mIndex
));
}
}
fm.mActive.set(index, fragment);
}
}
// Fix
// http://stackoverflow.com/questions/10396321/remove-fragment-page-from-viewpager-in-android
#Override
public int getItemPosition(Object object) {
int index = mFragments.indexOf(object);
if (index < 0) {
return PagerAdapter.POSITION_NONE;
}
boolean isPositionChange = mTempPositionChange[index];
int result = PagerAdapter.POSITION_UNCHANGED;
if (isPositionChange) {
result = PagerAdapter.POSITION_NONE;
}
return result;
}
}

2020 now.
Simple add this to PageAdapter:
override fun getItemPosition(`object`: Any): Int {
return PagerAdapter.POSITION_NONE
}

You could just override the destroyItem method
#Override
public void destroyItem(ViewGroup container, int position, Object object) {
fragmentManager.beginTransaction().remove((Fragment) object).commitNowAllowingStateLoss();
}

I hope this can help what you want.
private class MyPagerAdapter extends FragmentStatePagerAdapter {
//... your existing code
#Override
public int getItemPosition(Object object){
return PagerAdapter.POSITION_UNCHANGED;
}
}