The recommended substitute for clearTask of popUpTo with popUpToInclusive only works from start destination actions [116831650]

Fixed

Bug

Status Update

No update yet.

Description

[Deleted User]

created issue #1

Sep 28, 2018 10:32AM

I was previously using clearTask in my navigation actions to make sure that the user could not navigate back to the previous destination (useful for splash screens and login screens). After it was deprecated I decided to try the recommended approach of instead setting popUpTo pointing to the root of the graph together with setting popUpToInclusive="true", but this didn't have the effect I wanted.

This approach only seem to work on actions originating from the graph's start destination, and fails on actions between any other destinations. I created a sample project which reproduces the issue:

https://github.com/hsson/android-navigation-component-alpha06-bug

Here is the project's README detailing the issue:

# Bug in Android Navigation Component (alpha06)
(Note: I have only verified this in alpha06, I don't know if it exists in
previous versions)

## The problem
Basically the problem is that the NavOption "clearTask" was removed in
alpha02, and the recommended substitute was to use app:popUpTo pointing to
the root of the graph/the graph ID, together with app:popUpToInclusive="true".
However, this method does not work. It only seems to work for actions
going from the graph's start destination. If we have the following graph:

x y
A ---> B ---> C

Where A, B, and C are fragments, A is the start destination of the grapg,
and x, y are actions going from A to B and B to C respectively. Let's say
the graph's ID is "@+id/graph"

Then, if both actions x and y have
app:popUpTo="@+id/graph"
app:popUpToInclusive="true"

Then when navigating from A to B through x, and then hitting the back button
will exit the app (as expected). But if navigating from A to B to C through
x and y, and then hitting the back button we will navigate back to B — this
is not what was expected. The expected behavior with this graph is to always
exit the app when clicking the back button

## Environment
This was verified using:
Android Studio 3.2 RC 3
Build #AI-181.5540.7.32.4987877, built on August 31, 2018
JRE: 1.8.0_152-release-1136-b06 x86_64
JVM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
macOS 10.13.6

Comments

[Deleted User] <[Deleted User]> #2Oct 1, 2018 08:14AM

Verified library version is `1.0.0-beta02`

il...@google.com <il...@google.com> Oct 1, 2018 10:56PM

Assigned to il...@google.com.

[Deleted User] <[Deleted User]> #3Oct 10, 2018 09:20AM

More information on this in:

http://issuetracker.google.com/124042228#comment3

http://issuetracker.google.com/124042228#comment7

il...@google.com <il...@google.com> #4Oct 18, 2018 06:05PM

> More information on this in:
>

http://issuetracker.google.com/124042228#comment3
>

http://issuetracker.google.com/124042228#comment7

I think that is probably the same problem.

[Deleted User] <[Deleted User]> #5Oct 19, 2018 11:44AM

I investigated the sample:

https://github.com/marbat87/ScrollingViewPager2.git

See attached video:
1) no scrolling issues as long as angle is kept very close to x or y axis (0 -- 13s)
2) when scroll angle changes during a scroll, that is respected; if you remove NestedScrollView from the layout hierarchy (in fragment_main.xml) and have RecyclerView there directly, scroll orientation locking happens and makes for a better user experience
3) threshold / angle exploration (29s -- end) -- clearly the threshold angle is too narrow (touch slop not respected); it's worse with AppBarLayout collapsed than when it's expanded -- it confirms the issue; we'll investigate further

mi...@gmail.com <mi...@gmail.com> #6Oct 19, 2018 12:22PM

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

commit fb1c82582399043b149eb2630f524c75de9c88dc
Author: Jelle Fresen <jellefresen@google.com>
Date: Thu Aug 15 11:34:36 2019

Disallow intercept, touch slop and canScroll in nestedPreScroll

* Disallow intercept (requestDisallowInterceptTouchEvent(true))
When scroll delta is consumed by dispatchNestedPreScroll, the parent
should be requested not to intercept subsequent touch events, just as
when scroll is consumed by the widget itself or dispatchNestedScroll.

* Touch slop
NestedScrollingChild implementations should only call
dispatchNestedPreScroll after the delta x/y has exceeded the touch slop.

* canScroll (canScrollHorizontally/canScrollVertically)
The dx/dy values passed to dispatchNestedPreScroll should be zero if the
child can't scroll in that direction.

Fixed in:
- RecyclerView
- NestedScrollView

Bug: 138668210
Bug: 139530818
Test: ./gradlew connectedCheck
Change-Id: I85b327ad096fbbd204adb92f630770ec7fad5990

M core/core/src/androidTest/java/androidx/core/widget/NestedScrollViewNestedScrollingChildTest.java
M core/core/src/main/java/androidx/core/widget/NestedScrollView.java
M recyclerview/recyclerview/src/androidTest/java/androidx/recyclerview/widget/RecyclerViewNestedScrolling3RequestDisallowInterceptTouchTest.java
M recyclerview/recyclerview/src/androidTest/java/androidx/recyclerview/widget/RecyclerViewNestedScrollingChildTest.java
M recyclerview/recyclerview/src/main/java/androidx/recyclerview/widget/RecyclerView.java

https://android-review.googlesource.com/1105373

https://goto.google.com/android-sha1/fb1c82582399043b149eb2630f524c75de9c88dc

[Deleted User] <[Deleted User]> #7Oct 19, 2018 12:24PM

1) N/A
2) Remove NestedScrollView
3) Was due to a bug in RecyclerView with pre-scroll, fix is on it's way

il...@google.com <il...@google.com> #8Oct 19, 2018 03:36PM

Correction, the fix is in. Will be released in the coming release of recyclerview (1.1.0-beta04)

mi...@gmail.com <mi...@gmail.com> #9Oct 19, 2018 03:50PM

So if I understand this correctly, D is a Fragment and it should call its Activity (the one and only one in the app) finish(), in case there's something wrong, like going back from the login screen?

I find this complicated and can lead to issues that resemble "callback hell", having multiple checks and flags everywhere, to know if we already navigates to some destination and if we are back and without a proper value... Can't we come up with a more streamlined solution?

il...@google.com <il...@google.com> #10Oct 19, 2018 04:13PM

D can do whatever it needs to if the user chooses not to log in, be it finishing the activity (if you know it is the root of your whole graph), calling navController.popBackStack(), or showing an inline prompt for the user to sign in. This is core business logic for your app.

One thing that you need to keep in mind is that the user can hit the home button at any point then come back to *exactly that same destination in your app* an arbitrary amount of time later. If your logins expire or if users can delete their accounts (just to offer two examples), then *every* login required destination needs to handle this exact case - punting users to your login flow then handling whether they log in or not before showing their protected content. By making that the *only* flow for handling invalid login cases in your app, you can do things the right way just once.

mi...@gmail.com <mi...@gmail.com> #11Oct 19, 2018 04:16PM

Good point.

dc...@gmail.com <dc...@gmail.com> #12Oct 23, 2018 05:19PM

About your comment on #8 (mentioned bellow):

>>> - B+C should be handled as conditional navigation from D - D starts B and if you return to D without logging in, D calls finish().

Basically D needs to know the outcome of a task that was accomplished in B, meaning D needs to know if it was reached through opening the app (since it's a startDestination) or through pressing back in B (meaning the user canceled the login process).

Wouldn't this be a break in abstraction? My understanding was that a destination should receive it's arguments and this should be enough for it to work but in this example D needs to detect it was reached through a BACK press in B.

I don't even know how I would implement such a thing unless I start passing arguments between destinations to know about my navigation history.

da...@gmail.com <da...@gmail.com> #13Oct 26, 2018 10:58PM

I made this work, kind of: splash to main activity; starting destination D. It inflates a layout only to save state and go to the back stack as I bounce to B. If I press back, I go through the steps of restoring D--which briefly makes an appearance on screen--only to finish the activity.

I actually like the thought of an incorrect graph if it lets me handle this stuff precisely without some of the overhead needed to make a generic solution.

il...@google.com <il...@google.com> #14Nov 30, 2018 11:21PM

Marked as fixed.

I've confirmed that this is fixed in alpha08 as a result of

https://android-review.googlesource.com/833717 and a number of other internal changes.

app:popUpTo="@+id/graph" should always work now.