How to get Current Fragment in ViewPager2

Question

i used this ViewPager2 dependency:

implementation 'androidx.viewpager2:viewpager2:1.0.0'

then i wrote code and make Adapter for FragmentStateAdapter like below:

private inner class ViewPagerAdapter(fragmentManager: FragmentManager,
                                         lifecycle: Lifecycle, config: TribunConfig?)
        : FragmentStateAdapter(fragmentManager, lifecycle) {
        private val config: TribunConfig?
        override fun createFragment(position: Int): Fragment {
            return TribunNewsFragment.newInstance(if (menuTribun!!.get(position) == "News") "home"
            else menuTribun!!.get(position)!!.replace(" ", "").toLowerCase(), config)!!
        }

        override fun getItemCount(): Int {
            return menuTribun!!.size
        }

        init {
            this.config = config
        }
    }

an in method onCreate i implement some code related viewpager2 and its adapter like below:

        viewPager2!!.offscreenPageLimit = 1
        viewPager2!!.adapter = ViewPagerAdapter(supportFragmentManager, lifecycle, config)
        TabLayoutMediator(tabLayout!!, viewPager2!!, TabLayoutMediator.TabConfigurationStrategy { tab: TabLayout.Tab?, position: Int -> tab!!.text = menuTribun!!.get(position) }).attach()

But i have problem when i want to make swipeRefresh. My swipeRefresh needs current fragment to access the method inside fragment. But there is NO METHOD getItem in FragmentStateAdapter. Anyone can help me?

1. Create property in your adapter to save all your fragments 2. Save current position 3. Get fragment from frgament list (property) by position when you need it — Oleg Skidan, Apr 08 '20 at 08:32
can you show in code please. so i can vote your answer, if it's correct — Nanda Z, Apr 08 '20 at 08:34
@NandaZ : Please show your code how you add fragment in viewpager — Shweta Chauhan, Apr 08 '20 at 08:38
@ShwetaChauhan did you mean that you want to see `TribunNewsFragment` class? if you want to know how i added fragment, i have wrote it in method `createFragment` — Nanda Z, Apr 08 '20 at 08:49

score 3 · Accepted Answer · answered Apr 08 '20 at 08:44

3

Create property in your adapter to save all your fragments
Save current position
Get fragment from fragment list (property) by position when you need it

Something like this:

    val fragments: MutableList<Fragment> = mutableListOf()

    private val config: TribunConfig?
    override fun createFragment(position: Int): Fragment {
        val fragment = TribunNewsFragment.newInstance(if (menuTribun!!.get(position) == "News") "home"
        else menuTribun!!.get(position)!!.replace(" ", "").toLowerCase(), config)!!

        fragments.add(fragment)
        return fragment
    }

Parent:

 yourTabLayout.addOnTabSelectedListener(object : TabLayout.OnTabSelectedListener {
        override fun onTabSelected(tab: TabLayout.Tab?) {
            val fragment = adapter.fragments[tab!!.position]
            // cast fragment to your fragment class and do what you want
        }

        override fun onTabUnselected(tab: TabLayout.Tab?) {
        }

        override fun onTabReselected(tab: TabLayout.Tab?) {
        }
    })

Also you can use when or if-else for your fragments position or create base class with methods you need and cast getting fragment to it.

answered Apr 08 '20 at 08:44

Oleg Skidan

617
6
24

1

As a note ViewPager2 has a page changed callback https://developer.android.com/reference/androidx/viewpager2/widget/ViewPager2.OnPageChangeCallback so this could be done without Tabs – Andrew Apr 08 '20 at 09:40
But, i had counter problem. When i try to click tab which the index is more than size of mutableList and it cause crash – Nanda Z Apr 08 '20 at 10:00
How is it possible? Do you have more tabs than fragments? – Oleg Skidan Apr 08 '20 at 10:02
1

it's because of `viewPager2!!.offscreenPageLimit = 1`, so i don't create all fragment just two fragment for first opening – Nanda Z Apr 08 '20 at 13:03
So it's easy. CurrentTab.position+1 is maximum for you, except lastPosition. – Oleg Skidan Apr 08 '20 at 13:09
I think i can accept your answer, because i add delay time for event in `onTabSelected`. It's works now – Nanda Z Apr 08 '20 at 13:20
8

This doesn't handle configuration changes (i.e. app running out of memory in the background) - `createFragment` is not called when that happens, it is restored without calling that and your list becomes empty. – lawonga May 13 '20 at 23:36
@Iawonga is right. You need to store the fragments in a `FragmentManager` and retrieve them after the config change using `putFragment` and `getFragment` respectively. This is obviously a lot of boilerplate and I think the more formal answer is to avoid relying on fragment references in your activity if possible. I've yet to see a good example by google on how to handle this. – rosghub Aug 29 '20 at 03:17
An alternative would be [this answer](https://stackoverflow.com/a/61178226/4322363) that relies on the internal logic of `ViewPager2` storing fragments by tag. – rosghub Aug 29 '20 at 03:28
This causes memory leak issues for the fragments maintained in mutablelist. – Sagar Pujari Apr 12 '22 at 12:06

Rafael Guimarães · Answer 2 · 2020-08-06T10:46:12.003

1

Following @Oleg's answer, you can access the Fragments like this in your Adapter instead of creating a local list and adding each fragment on createFragment method:

private val fragmentList: List<TribunNewsFragment>
        get() {
            return fragment.childFragmentManager.fragments.filterIsInstance<TribunNewsFragment>()
        }

It's important to use childFragmentManager instead of fragmentManager if you are creating the ViewPager inside another fragment.

And it survives configuration changes, regarding @lawonga's comment on the answer's topic.

edited Aug 06 '20 at 10:46

answered Aug 06 '20 at 10:41

Rafael Guimarães

19
3

1

It looks like you already have a `fragment` reference here. How are you referencing it from your adapter? – rosghub Aug 22 '20 at 22:01

How to get Current Fragment in ViewPager2

2 Answers2