How can I switch between two fragments, without recreating the fragments each time?

Question

I\'m working on an android application, that uses a navigation drawer to switch between two fragments. However, each time I switch, the fragment is completely recreated.

Answer 1

Just find the current fragment calling getFragmentById("id of your container") and then hide it and show needed fragment.

private void openFragment(Fragment fragment, String tag) {
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        Fragment existingFragment = fragmentManager.findFragmentByTag(tag);
        if (existingFragment != null) {
            Fragment currentFragment = fragmentManager.findFragmentById(R.id.container);
            fragmentTransaction.hide(currentFragment);
            fragmentTransaction.show(existingFragment);
        }
        else {
            fragmentTransaction.add(R.id.container, fragment, tag);
        }
        fragmentTransaction.commit();
    }

Answer 2

How about playing with the Visible attribute?

Answer 3

After @meredrica pointed out that replace() destroys the fragments, I went back through the FragmentManager documentation. This is the solution I've come up with, that seems to be working.

/* The click listener for ListView in the navigation drawer */
private class DrawerItemClickListener implements ListView.OnItemClickListener {
    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
        selectItem(position);
    }
}

private void selectItem(int position) {
    android.support.v4.app.FragmentManager; fragmentManager = getSupportFragmentManager();

    switch(position) {
        case 0:
            if(fragmentManager.findFragmentByTag("one") != null) {
                //if the fragment exists, show it.
                fragmentManager.beginTransaction().show(fragmentManager.findFragmentByTag("one")).commit();
            } else {
                //if the fragment does not exist, add it to fragment manager.
                fragmentManager.beginTransaction().add(R.id.container, new OneFragment(), "one").commit();
            }
            if(fragmentManager.findFragmentByTag("two") != null){
                //if the other fragment is visible, hide it.
                fragmentManager.beginTransaction().hide(fragmentManager.findFragmentByTag("two")).commit();
            }
            break;
        case 1:
            if(fragmentManager.findFragmentByTag("two") != null) {
                //if the fragment exists, show it.
                fragmentManager.beginTransaction().show(fragmentManager.findFragmentByTag("two")).commit();
            } else {
                //if the fragment does not exist, add it to fragment manager.
                fragmentManager.beginTransaction().add(R.id.container, new TwoFragment(), "two").commit();
            }
            if(fragmentManager.findFragmentByTag("one") != null){
                //if the other fragment is visible, hide it.
                fragmentManager.beginTransaction().hide(fragmentManager.findFragmentByTag("one")).commit();
            }
            break;
    }

    // update selected item and title, then close the drawer
    mDrawerList.setItemChecked(position, true);
    setTitle(mNavTitles[position]);
    mDrawerLayout.closeDrawer(mDrawerList);
}

I also added this bit, but I'm not sure if it's necessary or not.

@Override
public void onDestroy() {
    super.onDestroy();
    FragmentManager fragmentManager = getSupportFragmentManager();
    if(fragmentManager.findFragmentByTag("one") != null){
        fragmentManager.beginTransaction().remove(fragmentManager.findFragmentByTag("one")).commit();
    }
    if(fragmentManager.findFragmentByTag("two") != null){
        fragmentManager.beginTransaction().remove(fragmentManager.findFragmentByTag("two")).commit();
    }
}

Answer 4

The replace method destroys your fragments. One workaround is to set them to Visibility.GONE, another (less easy) method is to hold them in a variable. If you do that, make sure you don't leak memory left and right.

Answer 5

Same idea as Tester101 but this is what I ended up using.

    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();

    Fragment oldFragment = fragmentManager.findFragmentByTag( "" + m_lastDrawerSelectPosition );
    if ( oldFragment != null )
        fragmentTransaction.hide( oldFragment );

    Fragment newFragment = fragmentManager.findFragmentByTag( "" + position );
    if ( newFragment == null )
    {
        newFragment = getFragment( position );
        fragmentTransaction.add( R.id.home_content_frame, newFragment, "" + position );
    }

    fragmentTransaction.show( newFragment );
    fragmentTransaction.commit();

Answer 6

Hide easily in kotlin using extensions:

fun FragmentManager.present(newFragment: Fragment, lastFragment: Fragment? = null, containerId: Int) {
    if (lastFragment == newFragment) return

    val transaction = beginTransaction()
    if (lastFragment != null && findFragmentByTag(lastFragment.getTagg()) != null) {
        transaction.hide(lastFragment)
    }

    val existingFragment = findFragmentByTag(newFragment.getTagg())
    if (existingFragment != null) {
        transaction.show(existingFragment).commit()
    } else {
        transaction.add(containerId, newFragment, newFragment.getTagg()).commit()
    }
}

fun Fragment.getTagg(): String = this::class.java.simpleName

Usage

supportFragmentManager.present(fragment, lastFragment, R.id.fragmentPlaceHolder)
lastFragment = fragment