keeping viewpager2 item position when navigatiing to other fragment

Question

I'm using viewpager2 with navigation component. When I click on one item in viewpager, it goes to another fragment, but when I go back to previous fragment with viewpager, the position of viewpager resets to the first one. How can I keep the viewpager position when navigating to other fragment?

Answer 1

The best way to accomplish what you want is to have a viewmodel that will save your viewpager position.

In your fragment:

private lateinit var viewModel : TestViewModel

override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?
    ): View? {

viewModel = ViewModelProvider(this).get(TestViewModel::class.java)

#### all other regular fragment stuff still aplies

}

fun setViewPager(){

        ### regular VP2 code here (adapter, etc)

viewModel.viewPagerSelected.observe(viewLifecycleOwner, Observer { page ->
                viewPager.currentItem = page
            })

viewPager.registerOnPageChangeCallback(object : ViewPager2.OnPageChangeCallback() {

            override fun onPageSelected(page: Int) {
                viewModel.updatePageSelected(page)
            }
}

ViewModel

class TestViewModel() : ViewModel() {

    private val _viewPagerSelected = MutableLiveData<Int>()
    val viewPagerSelected: LiveData<Int> = _viewPagerSelected

    fun updatePageSelected(newSelection: Int) {
        _viewPagerSelected.postValue(newSelection)
    }

}

I hope it helps!