IssueTracker

You don't need to do step 1 or 2 - ensuring you've called addNavigator() before setGraph() is enough.

Specifically, see https://issuetracker.google.com/issues/110763345#comment2

Also mentioned is the fact that you can override createFragmentNavigator(), call navController.navigatorProvider.addNavigator() there, then return super.createFragmentNavigator().

It's may also be of interest that I am making use of a custom navigator to implement conditional routing.  My custom destination/nodes simply implement an interface like this:  
interface DynamicNode {
    @IdRes
    fun getDestination(context: Context, @IdRes destinationIn: Int, argsIn: Bundle?) : Int
}

The Navigator then implements a navigate method that simply calls NavController.navigate using the ID returned by the DynamicNode and returns null, essentially performing a redirect.  It would be cool to see something like this baked-in with a later version of the Navigation component.

>> You don't need to do step 1 or 2 - ensuring you've called addNavigator() before setGraph() is enough.

Ah gotcha.  Okay that's a nicer then.  Thanks!

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

commit 238c09170a34e1c94af42bc3c6e9fce551883aef
Author: Ian Lake <ilake@google.com>
Date:   Mon Apr 22 12:54:51 2019

    Rename createFragmentNavigator()
   
    Fix confusion around what method should
    be overriden to add custom Navigators to
    a NavHostFragment.
   
    Test: tested in testapp
    Fixes: 122802849
    Change-Id: I969dca429a62e0533cb4ca93c77e68e062278a6f

M       navigation/fragment/api/2.1.0-alpha03.txt
M       navigation/fragment/api/current.txt
M       navigation/fragment/src/main/java/androidx/navigation/fragment/NavHostFragment.java

https://android-review.googlesource.com/947645
https://goto.google.com/android-sha1/238c09170a34e1c94af42bc3c6e9fce551883aef

We've decided to rename createFragmentNavigator() to onCreateNavController(NavController) to make it more clear that this is something you can override to get a callback for when the NavController is created.

This will be available in Navigation 2.1.0-alpha03

Can you include a sample that reproduces your issue?

Ok. I'm confused. I'll write here, at least for my own investigation.

What I described in #4, that really happens. But that is solved by simply adding defaultValue="@null" in the XML, like people said somewhere else on the webs. By doing that, null is added to the corresponding field in the constructor of the Args class. This thus invalidates #6.

But, the deep link part doesn't like defaultValue="@null" when I try to navigate (through navigation component) with an URI that does not have that argument/parameter. As described in #1, the string parameter defined with defaultValue="@null" gets the string "@null". In short: navigating directly gives that argument with the default value null (from the Args class), but navigating with deepLink gives "@null".

I've also found that optional parameter in deepLinks has been introduced in the change linked here https://issuetracker.google.com/issues/133273839#comment3, which includes the code I referenced in #1.

I can workaround all this by adjusting my code to use empty string as the marker for not present field, and setting defaultValue to "". The editor doesn't like it ("missing value"), but that's another issue.

We would like to investigate as well. Do you have a sample project that reproduces the issues that you can upload as a part of this bug?

Here it goes:

- in order to avoid dealing with initial boilerplate, cloned https://github.com/googlecodelabs/android-navigation;
- uncomented TODO from the codelab steps;
- updated deps, plugins versions, fixed some compiling issue;
- removed code, left Home and DeepLinkFragment only;
- changed app:uri to

  "www.example.com/query?param1={param1}&param2={param2}";

- added arguments in deepLinkFrangment in mobile_navigation.xml:

        <argument
            android:name="param1"
            android:defaultValue="@null"
            app:nullable="true"/>

        <argument
            android:name="param2"
            android:defaultValue="@null"
            app:nullable="true"/>


- added action in homeFragment targeting deepLinkFragment

        <action
            android:id="@+id/deeplink_action"
            app:destination="@+id/deeplink_dest" />


- added a button and the following code to HomeFragment, using action generated code (notice that no argument is passed because they default to null):
        view.findViewById<Button>(R.id.navigate_direct_button)?.setOnClickListener {
            findNavController().navigate(HomeFragmentDirections.deeplinkAction(param1 = "HELLO"))
        }

- added a button and the following code to HomeFragment, using Uri (notice that param2 is absent):
        view.findViewById<Button>(R.id.navigate_deeplink_button)?.setOnClickListener {
            findNavController().navigate(
                Uri.parse("example://www.example.com/query?param1=HELLO"))
        }

(had to change app:uri from "www.example.com" to "example://www.example.com/..." because the first wasn't matching (another issue i guess))

- adjusted DeepLinkFragment to show param1 and param2, from the arguments bundle (could have used by navArgs with same result)

        textView.text = arguments?.getString("param1", "") + arguments?.getString("param2", "")

Running the app, when the "navigate with direct action" button is clicked, "HELLO" is shown in the next fragment, as expected. When "navigate with deeplink" is clicked, "HELLO@null" is shown, which is the issue.

I'm facing this issue as well, default null seems never be null.
The root cause seems in the androidx.navigation.NavDeepLink.java:

// Missing parameter so see if it has a default value or is Nullable
if (argument != null
    && (value == null || value.replaceAll("[{}]", "").equals(argName))) {
    if (argument.getDefaultValue() != null) {
        value = argument.getDefaultValue().toString();
    } else if (argument.isNullable()) {
        value = "@null";
    }
}

+1
arguments?.run {
            val args by navArgs<BFragmentArgs>()
            //Should be null instead "@null"?
            Log.d("ARGS", "Token ${args.token}")
        }

It would be helpful if defaultValue is really null, instead "@null" on deeplink cases like com.sample://fragmentB?token= (that we could receive by mistake from backend/external service)

<argument
            android:name="token"
            android:defaultValue="@null"
            app:argType="string"
            app:nullable="true" />
        <deepLink
            android:id="@+id/cta"
            app:uri="com.sample://fragmentB?token={token}" />

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

commit 6e93d1d7ee8ac63451e8822422fb3b1da90fa321
Author: Jeremy Woods <jbwoods@google.com>
Date:   Mon Nov 25 15:29:59 2019

    Make nullable deep link params default to null
   
    Currently a deep link param that cannot be matched but is marked as
    nullable will be stored in the argument bundle with a value of "@null".
    This causes the behavior for a missing param to be inconsistent between
    a normal navigation and navigation from a deep link.
   
    This change stores null an instance of null in the bundle for the value
    instead to ensure we mimic the behavior of non-deep link nullable
    params.
   
    Test: adjusted NavDeepLinkTest
    BUG: 141613546
    Change-Id: I14625699fc9365088e07df9456a05257974a375b

M       navigation/navigation-common/src/androidTest/java/androidx/navigation/NavDeepLinkTest.kt
M       navigation/navigation-common/src/main/java/androidx/navigation/NavDeepLink.java

https://android-review.googlesource.com/1174705

This has been fixed internally and will be available in the Navigation 2.2.0-rc03 release.

  The following changes were cherrypicked through Coastguard (https://android-build.googleplex.com/coastguard/)
  Release Track: (https://android-build.googleplex.com/coastguard/dashboard/6205454677704704/#/history/all)
  Created: 2019-11-26 03:40:40.026747+00:00
  Changes: aosp/1174705