BottomNavigationView - Multiple start destinations on back stack [253256629]

Fixed

Bug

Status Update

No update yet.

Description

po...@gmail.com

created issue #1

Oct 12, 2022 05:54PM

Component used: Navigation / NavigationUI Version used: 2.5.2 Devices/Android versions reproduced on: OnePlus 8T / Android 12

I'm using a menu resource file which is bound to a BottomNavigationView. Also I'm setting up the navigation like so NavigationUI.setupWithNavController(bottomNavigationView, navController, false) which means I'm using the experimental version of this API.

I don't want the state of each menu item to be saved since I want to come back to the respective start destination if a BottomNavigationView item gets reselected. So regardless of how deep I got in a navigation graph a reselection of the same item takes you back to the start destination.

I'm using a navGraph which consists of several nested navGraphs like so:

<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    android:id="@+id/navigation"
    app:startDestination="@id/destination_one">

    <include app:graph="@navigation/one_navigation" />

    <include app:graph="@navigation/two_navigation" />

    <include app:graph="@navigation/three_navigation" />

    <include app:graph="@navigation/four_navigation" />
</navigation>

The one_navigation could look like this:

<navigation xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/destination_one"
    app:startDestination="@id/destination_fragment_one">

    <fragment
        android:id="@+id/destination_fragment_one"
        android:name="com.example.OneFragment"
        android:label="@string/bottom_navigation_one"
        tools:layout="@layout/fragment_one">
    </fragment>
</navigation>

It works pretty good so far, the point is when I click the first BottomNavigationView's menu item N times I got the destination N+1 times on my back stack. If I wanted to leave the app by triggering the system's back navigation I'd have to do it N+1 times.

So I actually expect the startDestination to only exist once on the back stack regardless of how often I click the respective menu item setup with the above mentioned API.

Comments

il...@google.com <il...@google.com> #2Oct 12, 2022 06:07PM

Nested scrolling works partially (as per

http://b/122818889). Let's discuss if we need full support and if so make sure it works.

po...@gmail.com <po...@gmail.com> #3Oct 12, 2022 06:35PM

Hi!

What is 'partially' exactly?
How do I see it?
Thanks!

il...@google.com <il...@google.com> #4Oct 12, 2022 06:57PM

As of now:
- Nesting scroll views with a scroll direction perpendicular to the ViewPager2's orientation inside ViewPager2 works
- Nesting scroll views with a scroll direction parallel to the ViewPager2's orientation inside ViewPager2 does not work

po...@gmail.com <po...@gmail.com> #5Oct 13, 2022 05:32PM

Horizontal ViewPager2 not correctly working into a vertical RecyclerView
Set a setNestedScrollingEnabled to the RecyclerView into the ViewPager2 (across reflection) resolves the problem

il...@google.com <il...@google.com> Oct 18, 2022 08:52PM

Assigned to jb...@google.com.

jb...@google.com <jb...@google.com> #6Oct 21, 2022 12:14AM

Reassigned to cl...@google.com.

ageevvalentin@gmail.com, could you provide a sample app? I'd like to learn more about the circumstances that cause the problem; putting a clean ViewPager2 inside a clean RecyclerView seems to work fine, so there must be other factors involved.

po...@gmail.com <po...@gmail.com> #7Oct 21, 2022 08:02AM

Added a patch for androidx-master-dev that demos a horizontal ViewPager2 inside a vertical RecyclerView.

Verified that it works correctly on a:
- Nexus 4 emulator with API 17
- Nexus 5X emulator with API 28
- Pixel 2 device with API 29

To reproduce:
- Check out the Android Jetpack source (at commit 256899f482ff85cddfb050f37550be7b5ec927ef) (see steps in [1])
- Apply the patch (`git apply 0001-Add-sample-where-a-horizontal-ViewPager2-is-nested-i.patch`)
- Build and install viewpager2's integration-tests app: `./gradlew viewpager2:integration-tests:testapp:installDebug`
- Run it

Closing the issue for now, but please reopen if you have a minimal reproduction app

[1]

https://android.googlesource.com/platform/frameworks/support/+/256899f482ff85cddfb050f37550be7b5ec927ef

cl...@google.com <cl...@google.com> Nov 8, 2022 01:25AM

Accepted by cl...@google.com.

ap...@google.com <ap...@google.com> #8Dec 1, 2022 09:33PM

Re-opening as requested by a few users. Narrowed down the focus to nested scrolling elements with the same scroll direction.

ap...@google.com <ap...@google.com> #9Dec 14, 2022 07:34PM

Any progress on this? (only talking about the "same scroll direction" issue)

I searched a lot for workarounds on Google and SO, but it seems no one really found a suitable solution yet.
The thing is that all other VerticalViewPagers out there have other problems that are similarly annoying. Most of them revolve around touch issues like "What's a click and what's a swipe" or "what's the fling threshold to snap to the next page".

So if someone knows of a working sample of VerticalViewPagers, I'd be happy to see a link :)

cl...@google.com <cl...@google.com> #10Dec 14, 2022 07:39PM

Marked as fixed.

Hi, we're unlikely to address the "same scroll direction" issue before 1.0-Stable as it's likely going to require API changes (so v1.1+).

One possible option for VerticalViewPager with nested scrolling in the same scroll direction is using a RecyclerView implementing NestedScrollingParent + PagerSnapHelper to get snapping.
You'd then have to implement the NestedScrollingParent/Child contract between parent/child RecyclerView instances.

pr...@google.com <pr...@google.com> #11Feb 8, 2023 06:22PM

Cool, thanks for this quick answer - Both pieces of information are highly appreciated (rough estimate of tackling this as well as giving hint on how to do it).
I will try implementing what you suggested and in case it is readable code, I will post it here as sample project or somthing similar.