IssueTracker

I think it makes a lot of sense for NavigationUI to ignore onDestinationChanged callbacks when the destination is a floating window like for <dialog> destinations. We'll look into what the best way of doing this is.

As a workaround, you can add any dialog destinations you open from your start destination to your AppBarConfiguration as an additional top level destination: https://developer.android.com/guide/navigation/navigation-ui#appbarconfiguration - the title will still change (if you have an android:label set on your dialog destination, something you could remove as well), but the Up button won't appear on top level destinations.

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

commit b17330acca92cd173e0535ac83cbec50fc95a24c
Author: jbwoods <jbwoods@google.com>
Date:   Fri May 31 16:16:44 2019

    Ensure ActionBar is not updated when destination is floating window
   
    When showing a dialog destination, the actionbar updates to show an up
    arrow. This behavior is unexpected and it is not possible to use the
    back button. The action bar should remain the same when interacting with
    any floating window.
   
    This change adds a marker inferface, FloatingWindow, that should be
    implemented by classes considered to be floating windows.
    AbstractAppBarOnDestinationChangeListener checks if the destination is an
    instance of FloatingWindow to determine if the AppBar should be
    updated.
   
    Added label for dialog destination in integration app for testing.
   
    Test: Tested in integration app. ./gradlew checkApi
    BUG: 133600763
    Change-Id: Ie4efab6c265eca13583bd21615f8d571c2236443

M       navigation/common/api/2.1.0-alpha06.txt
M       navigation/common/api/current.txt
A       navigation/common/src/main/java/androidx/navigation/FloatingWindow.java
M       navigation/fragment/api/2.1.0-alpha06.txt
M       navigation/fragment/api/current.txt
M       navigation/fragment/src/main/java/androidx/navigation/fragment/DialogFragmentNavigator.java
M       navigation/integration-tests/testapp/src/main/res/navigation/nav_main.xml
M       navigation/ui/src/main/java/androidx/navigation/ui/AbstractAppBarOnDestinationChangedListener.java
M       navigation/ui/src/main/java/androidx/navigation/ui/NavigationUI.java

https://android-review.googlesource.com/973528
https://goto.google.com/android-sha1/b17330acca92cd173e0535ac83cbec50fc95a24c

We have fixed the underlying issue internally and it will be available in the Navigation 2.1.0-alpha06 release.