IllegalStateException: Fragment already added in the tabhost fragment

You just have to check one condition in your fragment mentioned below:

if(!isAdded())
{
return;
}

isAdded = Return true if the fragment is currently added to its activity. Taken from the official document. This will not add that fragment if it is already added

Check below link for a reference:
http://developer.android.com/reference/android/app/Fragment.html#isAdded()

This happens when we try to add same fragment or DialogFragment twice before dismissing,

just call

if(mFragment.isAdded())
{
return; //or return false/true, based on where you are calling from
}

Having said that, I don't see any reason why to remove old fragment and add the same fragment again since we can update the UI/data by simply passing parameters to the method inside the fragment

Sometimes it happens for not finding proper id from the respective layout. I faced this problem. Then after many hours I found that I set wrong recyclerview id. I change it, and works fine for me.

So, double check your fragment layout.

You just have to check one condition before start fragment transaction

 if (!fragmentOne.isAdded()){
transaction = manager.beginTransaction();
transaction.add(R.id.group,fragmentOne,"Fragment_One");
transaction.commit();
}

this is working perfactly for me...

Remove the old fragment in case it is still added and then add the new fragment:

FragmentManager fm = getSupportFragmentManager();
Fragment oldFragment = fm.findFragmentByTag("fragment_tag");
if (oldFragment != null) {
fm.beginTransaction().remove(oldFragment).commit();
}
MyFragment newFragment = new MyFragment();
fm.beginTransaction().add(newFragment , "fragment_tag");

For me it works like:

Fragment oldFragment = manager.findFragmentByTag(READER_VIEW_POPUP);
if (oldFragment != null) {
manager.beginTransaction().remove(oldFragment).commit();
}


FragmentTransaction ft = manager.beginTransaction();
ft.add(this, tag);
ft.commit();

It even can occur if in FragmentStatePagerAdapter of your ViewPager you create an item that already exists:

override fun getItem(position: Int): Fragment {
return tabs[0] // Right variant: tabs[position]
}

(private val tabs: List<Fragment> is a list of fragments in tabs).

To my surprise, I made stupid mistake by calling the fragment transaction twice:

if (!FirebaseManager.isClientA && !FirebaseManager.isClientB) {
fragment = new FragmentA();
getFragmentManager().beginTransaction().add(R.id.fragment_frame, fragment, null).addToBackStack("").commit();
} else if (FirebaseManager.isClientB) {
fragment = new FragmentB();
} else {
fragment = new FragmentC();
}
getFragmentManager().beginTransaction().add(R.id.fragment_frame, fragment, null).addToBackStack("").commit();

Make sure you don't make the same mistake.

Add Fragment as below

FragmentTransaction t = getSupportFragmentManager().beginTransaction();
t.replace(R.id.realtabcontent, mFrag);
t.addToBackStack(null);
t.commitNowAllowingStateLoss();

You can try this:

 if (dialogFolderGallery.isAdded()) {
dialogFolderGallery.dismiss();
} else { //bla...bla..
}

I have this error when not wrapping my body XML inside a ViewGroup inside FrameLayout.

Error:

<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".screens.home.HomeEpoxyFragment">


<androidx.swiperefreshlayout.widget.SwipeRefreshLayout
android:id="@+id/swipe_refresh_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">


<androidx.recyclerview.widget.RecyclerView
android:id="@+id/rv"
android:overScrollMode="never"
android:layout_width="match_parent"
android:layout_height="match_parent" />


</androidx.swiperefreshlayout.widget.SwipeRefreshLayout>


</FrameLayout>

Solved:

<FrameLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context=".screens.home.HomeEpoxyFragment">


<androidx.constraintlayout.widget.ConstraintLayout
android:layout_width="match_parent"
android:layout_height="match_parent">


<androidx.swiperefreshlayout.widget.SwipeRefreshLayout
android:id="@+id/swipe_refresh_layout"
android:layout_width="match_parent"
android:layout_height="match_parent">


<androidx.recyclerview.widget.RecyclerView
android:id="@+id/rv"
android:overScrollMode="never"
android:layout_width="match_parent"
android:layout_height="match_parent" />


</androidx.swiperefreshlayout.widget.SwipeRefreshLayout>
</androidx.constraintlayout.widget.ConstraintLayout>


</FrameLayout>

Hope this may help someone.

I got this error when incorrectly used my ViewModel inside of Fragment like this:

//This is wrong!
MyViewModel viewModel = new MyViewModel(getActivity().getApplication());

Correct way:

viewModel = new ViewModelProvider(this, ViewModelProvider.AndroidViewModelFactory.getInstance(getActivity().getApplication())).get(MyViewModel.class);

Here my solution for Dialog Fragment (you can use this concept also for fragment class)

I have try to click show dialog fragment by tap button multiple time and quickly.

FragmentManager fm = getSupportFragmentManager();
Fragment oldFragment = fm.findFragmentByTag("wait_modal");


if(oldFragment != null && oldFragment.isAdded())
return;


if(oldFragment == null
&& !please_wait_modal.isAdded()
&& !please_wait_modal.isVisible()) {
fm.executePendingTransactions();
please_wait_modal.show(fm, "wait_modal");
}

not good solving, but it work)

if(!ConfirmDataSync.isVisible) show()