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since it is already marked as deprecated, we can probably do it by now.

My suggestion pointed you to the root of the problem, which is that you are popping all of the destinations of a graph off the back stack with the popUpTo set the graph id. So when your to_level_2 action attempts to popUpTo level_1_graph it no longer exist.

As part of the work that went into multiple back stacks which was introduced in Navigation 2.4, it was ensured that any graph that does not have an associated destination is not kept on a back stack as it does not actually represent a location that you can go back to since graphs cannot be displayed.

With that change in mind, the code here is doing exactly what you are telling it to do, which is to pop off all the graph's destinations off the back stack, at which point Navigation automatically also removes the graph. You then try to do another navigate call, telling it to popUpTo a graph that no longer exists on the back stack, hence the error.

My suggestion of changing the popUpTo to use the start destination was under the assumption that you actually intended for the graphs to remain in your back stack and you wanted a destination associated with them since having only a graph in the back stack is not very useful.

Hi, thank you for your answer. Unfortunately, I think there are still two things which contradicts some of your thoughts: 1. If the destination of to_level_2 is a Fragment, not some included graph, everything works fine. It means, that the problem is not a missing level_1_graph or an empty backstack. Even if the graph is empty and level_1_graph is removed the navigation is still possible to SOME kinds of destinations. Please read the following code: This will work:

<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/level_1_graph"
    app:startDestination="@id/level_1_fragment">

    <fragment
        android:id="@+id/level_1_fragment"
        android:name="com.example.nestedpopupto.Level1Fragment"
        tools:layout="@layout/fragment_level_1">

        <action
            android:id="@+id/to_level_2"
            app:popUpTo="@id/level_1_graph"
            app:destination="@id/level_2" />   <!-- <<< This action WILL work <<< -->
    </fragment>

    <navigation
        android:id="@+id/level_2"
        app:startDestination="@id/level_2_fragment"> <!-- <<<< The startDestination is a Fragment <<< -->

        <fragment
            android:id="@+id/level_2_fragment"
            android:name="com.example.nestedpopupto.Level2Fragment"
            tools:layout="@layout/fragment_level_2" />
    </navigation>

</navigation>

While this won't work:

<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/level_1_graph"
    app:startDestination="@id/level_1_fragment">

    <fragment
        android:id="@+id/level_1_fragment"
        android:name="com.example.nestedpopupto.Level1Fragment"
        tools:layout="@layout/fragment_level_1">

        <action
            android:id="@+id/to_level_2"
            app:popUpTo="@id/level_1_graph"
            app:destination="@id/level_2" />    <!-- <<< This action WON'T work, although it is the same as in the previous code snippet << -->
    </fragment>

    <navigation
        android:id="@+id/level_2"
        app:startDestination="@id/level_2_graph">    <!-- <<<< The startDestination is an included graph -->

        <include app:graph="@navigation/level_2_graph" />
    </navigation>

</navigation>

As you can see, the only difference is the content of "<navigation android:id="@+id/level_2".

2. Adding dead/empty code solves the issue. Again, this an indication that there is something really wrong. This will work:

<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/level_1_graph"
    app:startDestination="@id/level_1_fragment">

    <fragment
        android:id="@+id/level_1_fragment"
        android:name="com.example.nestedpopupto.Level1Fragment"
        tools:layout="@layout/fragment_level_1">

        <action
            android:id="@+id/to_level_2"
            app:popUpTo="@id/level_1_graph"
            app:destination="@id/level_2" />
    </fragment>

    <navigation
        android:id="@+id/level_2"
        app:startDestination="@id/level_2_graph">

        <include app:graph="@navigation/level_2_graph" />
    </navigation>
    <include app:graph="@navigation/level_2_graph" />

</navigation>

Even if we assume that we are trying to do something which you no longer support, theres is still a problem with the lib, because it behaves in inconsistent way:

* If the startDestination of level_2 graph is a Fragment everything works fine, while if the startDestination of level_2 is a graph, the app crashes. * Adding dead/unused the code magically "solves" the issue (I would not focus on this one too much)

I suggest to move the focus from what we are doing wrong (trying to use no longer supported feature) to why the lib can still navigate to SOME kind of destinations and not to the others when popUpTo is used. It clearly contradicts what you are trying to tell us (that the navigation is impossible because the backstack is empty and level_1_graph is no longer there).

I was able to find that is this particular case Navigation is indeed losing the proper back stack.

Again, this is not something we recommend doing when using Navigation as the startDestination is meant to be the entry and exit point of a particular graph. If this is something that the app needs, it might be a sign that the architecture needs to be re-evaluated.

This has been fixed and will be a part of the Navigation 2.5.2 and 2.6.0-alpha01 releases.

Thank you! Have a nice day :)

This bug was linked in a change in the following release(s):

• androidx.navigation:navigation-runtime:2.6.0-alpha01
• androidx.navigation:navigation-runtime:2.5.2