android MapView + ViewPager2 + DataBinding issue

Question

I've recently came upon a really strange issue. I had a mapview in my layout which was inflated using databinding. After I added ViewPager2 to my layout I got this issue:

java.lang.IllegalArgumentException: Wrong state class, expecting View State but received class androidx.recyclerview.widget.RecyclerView$SavedState instead. This usually happens when two views of different type have the same id in the same hierarchy. This view's id is id/0x1. Make sure other views do not use the same id.

But it happens only when you first open first fragment and go to next one, then press back.

If I remove mapview from my layout everything works.
If I remove viewpager2 from my layout everything works.
If I remove databinding everything works.

It seems it has something to do with view state, but is there anything I could do to address this issue?

Here's a sample fragment code:

class TestFragment(override val layoutRes: Int = R.layout.fragment_test) : BaseFragment() {

lateinit var binding: FragmentTestBinding

override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
    binding = FragmentTestBinding.inflate(inflater, container, false)
    setupMap(savedInstanceState)
    return binding.root
}

override fun onResume() {
    super.onResume()
    binding.mapView.onResume()
}

override fun onPause() {
    super.onPause()
    binding.mapView.onPause()
}

private fun setupMap(savedInstanceState: Bundle?) {
    binding.mapView.onCreate(savedInstanceState)
    binding.mapView.onResume()
    binding.mapView.getMapAsync { }
}
}

Sample layout:

<?xml version="1.0" encoding="utf-8"?>
<layout>
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">

    <com.google.android.gms.maps.MapView
        android:id="@+id/mapView"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

    <androidx.viewpager2.widget.ViewPager2
        android:id="@+id/viewPager"
        android:layout_width="match_parent"
        android:layout_height="match_parent" />

</FrameLayout>
</layout>

To reproduce I have to open another fragment and then press back

**EDIT: ** Seems like moving viewpager in front of mapview also helps, so databinding can still be used.

Hi, did you find the cause of the issue? This problem is driving me nuts :S — lelloman, Jan 30 '20 at 14:50
@lelloman, I think I ended up using older viewpager. Glad to see you found a different solution :) — SMGhost, Feb 01 '20 at 15:19
Have exactly the same issue, have you find the solution maybe? Currently only solution i see is to go with ViewPager instead of ViewPager2... — RadoVidjen, Apr 05 '20 at 15:50
Strange when i place viewPager2 behind the map, it works, however in cant be seen since mapView is covering VP2... — RadoVidjen, Apr 05 '20 at 16:17

lelloman · Answer 1 · 2020-02-03T11:22:35.200

The problem seems to be that MapView and ViewPager2 both inflate views and assign dynamically-generated ids to them.

ViewPager2 (version 1.0.0 atm) does that by calling ViewCompat.generateViewId(), I have no idea what MapView is doing, it's not using LayoutInflater to inflate its children views and I suspect it is not calling ViewCompat.generateViewId() either.

The cause of the issue is that the view hierarchy ends up containing 2 View with the same id (with value 1 for me), one is the RecyclerView inside the ViewPager2 (TIL that ViewPager2 is a wrapper of a RecyclerView, amazing), the other is a LinearLayout containing 2 ImageView inside the MapView.

I'm currently hacking this unfortunate situation by calling:

for(i in 0 until 1000) ViewCompat.generateViewId()

before setContentView(Int) in the Activity.

score 2 · Answer 2 · answered May 17 '22 at 12:19

The issue seems to be that the viewpager wraps a recyclerview to which it assigns an ID of 1, and the mapview assigns the same ID of 1. I resolved this with:

viewPager = binding.viewPager
    for (view in viewPager.children) {
        if (view is RecyclerView) {
            view.id = 99999999
            break
        }
    }

android MapView + ViewPager2 + DataBinding issue

2 Answers2