IllegalStateException: Fragment already added in the tabhost fragment

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");

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()

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...

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");
}

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.

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();

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);

not good solving, but it work)

if(!ConfirmDataSync.isVisible) show()

Fragment transactions are asynchronous.

It is possible that you have two or more calls to this code before the fragment transactions are executed. !selectPlan04Dialog.isVisible() & !selectPlan04Dialog.isAdded() condition is true and show() schedules another fragment transaction to execute later.

Some options for fixing this:

• Create a new dialog every time and don't try to reuse an old one
• Change asynchronous fragment transactions to synchronous with a call to fragment manager executePendingTransactions()
• Сall like this

  videoOptionDialog.show(supportFragmentManager.beginTransaction().remove(videoOptionDialog),TrainingVideoMoreOptionDialog.TAG)
  

Better to use commitNow() for the transaction. See the docs.

/**
     * After a {@link FragmentTransaction} is committed with
     * {@link FragmentTransaction#commit FragmentTransaction.commit()}, it
     * is scheduled to be executed asynchronously on the process's main thread.
     * If you want to immediately executing any such pending operations, you
     * can call this function (only from the main thread) to do so.  Note that
     * all callbacks and other related behavior will be done from within this
     * call, so be careful about where this is called from.
     *
     * <p>If you are committing a single transaction that does not modify the
     * fragment back stack, strongly consider using
     * {@link FragmentTransaction#commitNow()} instead. This can help avoid
     * unwanted side effects when other code in your app has pending committed
     * transactions that expect different timing.</p>
     * <p>
     * This also forces the start of any postponed Transactions where
     * {@link Fragment#postponeEnterTransition()} has been called.
     *
     * @return Returns true if there were any pending transactions to be
     * executed.
     */