FragmentTransaction hide/show doesn't work sometimes

Question

I have an activity with bottom navigation tabs that are changing the fragments in it. When I click back and forth on those tabs, at some point it stops working. Code executes just fine as I put some logs in it. But the fragments aren't being switched.

Code is in kotlin but it's rather straight forward

fun showTabFragment(tag: String) {
        val currentFragment: Fragment? = supportFragmentManager.fragments?.lastOrNull()
        var fragment = supportFragmentManager.findFragmentByTag(tag)
        val fragmentExists = fragment != null
        if (fragment == null) {
            when (tag) {
                TAG_LOGBOOK -> fragment = LogbookFragment()
                TAG_RECIPES -> fragment = RecipesFragment()
                TAG_PROFILE -> fragment = ProfileFragment()
                else -> fragment = MeetingPlacesFragment()
            }
        }

        val transaction = supportFragmentManager.beginTransaction()

        if (currentFragment != null) {
            Log.i("jacek", "hiding " + currentFragment.javaClass.simpleName)
            transaction.hide(currentFragment)
        }

        if (fragmentExists) {
            Log.i("jacek", "showing " + fragment.javaClass.simpleName)
            transaction.show(fragment)
        } else {
            Log.i("jacek", "adding " + fragment.javaClass.simpleName)
            transaction.add(R.id.container, fragment, tag)
        }

        transaction.commit()
    }

The fragments are quite heavy. I will try with some lightweight ones, but still that shouldn't be a problem in my opinion. Is there anything else I could try?

I'm using the latest support library - 25.2.0 Also I'm not interested in replacing the fragments as the point is to add crossfade animation without recreating them

Answer 1

You need to reuse the same instance of a fragment that you wanted to hide or show.

private fun replaceFragment(fragment: Fragment) {
    supportFragmentManager.beginTransaction().apply {
        if (fragment.isAdded) {
            show(fragment)
        } else {
            add(R.id.fmFragmentContainer, fragment)
        }

        supportFragmentManager.fragments.forEach {
            if (it != fragment && it.isAdded) {
                hide(it)
            }
        }
    }.commit()
}

Answer 2

@Ali's answer is good, yet imagine if you have 5 fragments. This is another way to show/hide your fragments:

    // in BaseFragment
    public abstract String getTAG();

    //in FragmentA, FragmentB and FragmentC
    public String getTAG(){
        return TAG;
    }

    //Activity containing the fragments
    //android.support.v4.app.Fragment;    
    private FragmentA fragmentA; //inherited BaseFragment
    private FragmentB fragmentB; //inherited BaseFragment
    private FragmentC fragmentC; //inherited BaseFragment
    private ConcurrentHashMap<String,BaseFragment> mapOfAddedFragments = new ConcurrentHashMap<>();


    /**
     * Displays fragment A
     */
    private void displayFragmentA() {
        displayFragment(fragmentA)
    }

    /**
     * Displays  fragment B
     */
    private void displayFragmentB() {
       displayFragment(fragmentB)
    }

    /**
     * Displays  fragment C
     */
    private void displayFragmentC() {
        displayFragment(fragmentC)
    }


     /**
     * Loads a fragment using show a fragment
     * @param fragment
     */
    private void displayFragment(BaseFragment fragment){
        if(!mapOfAddedFragments.containsKey(fragment.getTAG()))
            mapOfAddedFragments.put(fragment.getTAG(), fragment);

        showFragment(fragment.getTAG(), R.id.containerBody);
    }

    /**
     * Displays a fragment and hides all the other ones
     * @param fragmentTag is the tag of the fragment we want to display
     */
    private void showFragment(String fragmentTag, @IdRes int containerViewId){
        FragmentTransaction ft = this.getSupportFragmentManager().beginTransaction();
        BaseFragment fragment = null;

        fragment = mapOfAddedFragments.get(fragmentTag);
        if(fragment != null) {
            if (fragment.isAdded())
                ft.show(fragment);
            else { //fragment needs to be added to the frame container
                ft.add(containerViewId, fragment, fragment.getTAG());
            }
        }
        else //the chosen fragment doesn't exist
            return;

        //we hide the other fragments
        for (ConcurrentHashMap.Entry<String, BaseFragment> entry : mapOfAddedFragments.entrySet()){
            if(!entry.getKey().equals(fragmentTag)){
                BaseFragment fragmentTemp = entry.getValue();
                // Hide the other fragments
                if(fragmentTemp != null)
                    if(fragmentTemp.isAdded())
                        ft.hide(fragmentTemp);
            }
        }

        //commit changes
        ft.commit();
    }

And to instantiate them you can do this in the onCreate() method of your activity:

//don't forget to get the .TAG elsewhere before using them here
    //never call them directly
    private void instantiateFragments(Bundle inState) {
        if (inState != null) {
            fragmentA = inState.containsKey(FragmentA.TAG) ?
                    (FragmentA) getSupportFragmentManager().getFragment(inState, FragmentA.TAG):
                    FragmentA.newInstance(FragmentA.TAG,"0");

            fragmentB = inState.containsKey(FragmentB.TAG) ?
                    (FragmentB) getSupportFragmentManager().getFragment(inState, FragmentB.TAG):
                    FragmentB.newInstance(FragmentB.TAG,"1");        

            fragmentc = inState.containsKey(FragmentC.TAG) ?
                    (FragmentC) getSupportFragmentManager().getFragment(inState, FragmentC.TAG):
                    FragmentC.newInstance(FragmentC.TAG,"2");         
        }
        else{
            fragmentA = FragmentA.newInstance(FragmentA.TAG,"0");
            fragmentB = FragmentB.newInstance(FragmentB.TAG,"1");
            fragmentc = FragmentC.newInstance(FragmentC.TAG,"2");
        }
    }

Edit according to Shujaat Ali Khan's question:

The BaseFragment extends support4 fragment:

public abstract class BaseFragment extends Fragment {
    public abstract String getTAG();
    //whatever we can add to be inherited
}

FragmentA for example:

public class FragmentA extends BaseFragment {
    // Store instance variables
    private static final String ARG_PARAM1 = "param1";
    private static final String ARG_PARAM2 = "param2";

    private String mParam1;
    private String mParam2;

    public static final String TAG = "FragmentA";

    // newInstance constructor for creating fragment with arguments
    public static FragmentA newInstance(String param1, String param2) {
        FragmentA fragment = new FragmentA();
        Bundle args = new Bundle();
        args.putString(ARG_PARAM1, param1);
        args.putString(ARG_PARAM2, param2);
        fragment.setArguments(args);
        return fragment;
    }

    // Store instance variables based on arguments passed
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        if (getArguments() != null) {
            mParam1 = getArguments().getString(ARG_PARAM1);
            mParam2 = getArguments().getString(ARG_PARAM2);
        }
    }

    // Inflate the view for the fragment based on layout XML
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container,
                             Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragmentA, container, false);
        return view;
    }

    //other lifecycle methods

    @Override
    public String getTAG() {
        return TAG;
    }
}

Finally the R.id.containerBody is the id of a FrameLayout containing the fragments in the activity containing these fragments.