IssueTracker

I attach a project to reproduce the issue.

There are 2 buttons: one add a named fragment transaction (which you can remove with back) and the other navigate to another fragment using nav graph.

You should be using childFragmentManager, not requireFragmentManager(). As of Alpha 04 and https://issuetracker.google.com/issues/111345778, back button presses are automatically passed to the child FragmentManager of the active Fragment, allowing you to do whatever FragmentTransactions you want in that child FragmentManager (using Navigation or not).

We can improve the error message though.

Ah, of course I should....
shame on me.

Improving the error message will surely help fools like me :) thanks

We've added a better error message in https://android-review.googlesource.com/861401 and this will be available in 1.0.0-alpha10.

I've tried your solution:

Tried to set left and right padding of the underlying recyclerView, like so:
(pager.getChildAt(0) as RecyclerView).apply {
            //hijacking padding from pager
            setPadding(
                    pager.paddingLeft, //resolves to 53
                    pager.paddingTop,
                    pager.paddingRight, //resolves to 53
                    pager.paddingBottom
            )
            //reseting padding on pager
            pager.setPadding(0, pager.paddingTop, 0, pager.paddingBottom)
            clipToPadding = false
        }

 got this exception:

E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.easecentral.ease.debug, PID: 23890
    java.lang.IllegalStateException: Page can only be offset by a positive amount, not by -53
        at androidx.viewpager2.widget.ScrollEventAdapter.updateScrollEventValues(ScrollEventAdapter.java:260)
        at androidx.viewpager2.widget.ScrollEventAdapter.onScrolled(ScrollEventAdapter.java:168)
        at androidx.recyclerview.widget.RecyclerView.dispatchOnScrolled(RecyclerView.java:5152)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayoutStep3(RecyclerView.java:4212)
        at androidx.recyclerview.widget.RecyclerView.dispatchLayout(RecyclerView.java:3843)
        at androidx.recyclerview.widget.RecyclerView.onLayout(RecyclerView.java:4385)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at androidx.viewpager2.widget.ViewPager2.onLayout(ViewPager2.java:511)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at androidx.constraintlayout.widget.ConstraintLayout.onLayout(ConstraintLayout.java:1915)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.widget.ScrollView.onLayout(ScrollView.java:1552)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at com.android.internal.policy.DecorView.onLayout(DecorView.java:753)
        at android.view.View.layout(View.java:20672)
        at android.view.ViewGroup.layout(ViewGroup.java:6194)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:2792)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2319)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1460)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:7183)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
        at android.view.Choreographer.doCallbacks(Choreographer.java:761)
        at android.view.Choreographer.doFrame(Choreographer.java:696)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
        at android.os.Handler.handleCallback(Handler.java:873)
E/AndroidRuntime:     at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6669)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)


I'll try to provide some minimum sample app, but can't promise anything right now, as I'm swarmed with other projects

That's our internal checks kicking-in. For now I can only offer a workaround of disabling overscroll, which I recognise is not ideal.

We'll have a look at some point - sample app will help.

Thanks again for reporting!

Project: platform/frameworks/support
Branch: androidx-master-dev

commit 450e0c3c50cb320b0f6222626034455a48aca54b
Author: Jelle Fresen <jellefresen@google.com>
Date:   Tue Aug 13 10:18:41 2019

    Take RV padding and item decorations into account
   
    RecyclerView's padding and item decorations shift the position of the
    current page when idle. The padding also shrinks the page size.
   
    Bug: 139012032
    Test: ./gradlew viewpager2:cC
   
    Change-Id: Ia03646db95bb8d392408bce4d22430981c3f9171

M       viewpager2/src/androidTest/java/androidx/viewpager2/widget/BaseTest.kt
A       viewpager2/src/androidTest/java/androidx/viewpager2/widget/PaddingMarginDecorationTest.kt
M       viewpager2/src/androidTest/java/androidx/viewpager2/widget/PageChangeCallbackTest.kt
M       viewpager2/src/main/java/androidx/viewpager2/widget/ScrollEventAdapter.java
M       viewpager2/src/main/java/androidx/viewpager2/widget/ViewPager2.java

https://android-review.googlesource.com/1101299
https://goto.google.com/android-sha1/450e0c3c50cb320b0f6222626034455a48aca54b

Project: platform/frameworks/support
Branch: androidx-master-dev

commit 6faf0d9fbabf6b59465ed135b4b44100bb2b3806
Author: Jelle Fresen <jellefresen@google.com>
Date:   Wed Aug 14 16:33:05 2019

    Always snap to center between padding
   
    Even when clipToPadding is false, the center of RecyclerView is still
    the middle of the rectangle described on the inside of the padding, not
    the middle of the rectangle described on the outside of the padding.
   
    Bug: 139452422
    Bug: 139012032
    Test: ./gradlew recyclerview:recyclerview:cC \
            -Pandroid.testInstrumentationRunnerArguments.class=\
            androidx.recyclerview.widget.PagerSnapHelperTest
   
    Change-Id: I8869f13fdd6a45b49ee3b288ff83e224faffa3c9

M       recyclerview/recyclerview/src/main/java/androidx/recyclerview/widget/PagerSnapHelper.java
M       viewpager2/src/androidTest/java/androidx/viewpager2/widget/PaddingMarginDecorationTest.kt
M       viewpager2/src/androidTest/java/androidx/viewpager2/widget/swipe/PageSwiperEspresso.java
M       viewpager2/src/androidTest/java/androidx/viewpager2/widget/swipe/PageSwiperManual.java

https://android-review.googlesource.com/1103182
https://goto.google.com/android-sha1/6faf0d9fbabf6b59465ed135b4b44100bb2b3806

Hi, in the upcoming release of viewpager2, you will be able to set padding on RecyclerView. Note that if you have asymmetric padding, you will also need the upcoming release of recyclerview.

Closing the bug for now, but please feel free to re-open this if the suggested releases don't fix your problem, so we can continue the investigation.

beta04 will allow for a workaround (set padding in the inner RecyclerView), but we will keep this open for a long-term fix

Who this

Looping under a more general overscroll buganizer item.