IssueTracker

Only the `argType="reference"` accepts resource IDs (and returns an int that you'd pass to getContext().getString()), so it is working as intended that a "string" type is exactly what you put into your XML. It was important that the build time code gen and the runtime behavior always matches and that was not possible in the general cases - see edge cases such as https://issuetracker.google.com/issues/111736515 for some background.

Please star https://issuetracker.google.com/issues/36994900 to track progress towards allowing placeholders in XML files, which would be the recommended way of filling in placeholders at compile time.

Ok thanks, I understand now, I wasn't aware of argType="reference". Anyway I think it is a bit strange that behavior is different if we navigate using safe args gen code (navController.navigate(WebPageFragmentDirections.actionGlobalHomeFragment())) and code without safe args (navController.navigate(R.id.homeFragment)) if the navigation xml file is the same.

Yes, I think we can make it more explicit that only reference types can have references to other resources.

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

commit bb456e84a524d4e5cd241a6a839a1062297b9cf4
Author: Ian Lake <ilake@google.com>
Date:   Thu Jan 31 15:46:55 2019

    Enforce "reference" types for reference default values
   
    In order to ensure that inflation of a navigation
    graph results in the same arguments as Safe Args,
    we now enforce usage of the "reference" type for any
    argument that has a defaultValue that references
    another resource (i.e., @string/app_name, etc).
   
    This makes it much more obvious that the default value
    in Safe Args is in the form of R.string.app_name and
    any provided override for that should also be in the
    form of R.string.some_value.
   
    In these cases, it is expected that developers either
    1) Use the ids directly (for example, passing an
    R.string to a method that takes a resource id)
    2) Specifically call context.getString() with the
    resource id they retrieve from their NavArgs instance.
   
    Test: updated NavInflaterTest
    Change-Id: I06b8c9a0d1420821b8c0064c22f176788da43d7a
    Fixes: 123551990

M       navigation/runtime/src/androidTest/java/androidx/navigation/NavInflaterTest.kt
M       navigation/runtime/src/androidTest/res/navigation/nav_default_arguments.xml
A       navigation/runtime/src/androidTest/res/navigation/nav_invalid_argument_arg_type.xml
A       navigation/runtime/src/androidTest/res/navigation/nav_invalid_argument_default_value.xml
M       navigation/runtime/src/main/java/androidx/navigation/NavInflater.java

https://android-review.googlesource.com/891680
https://goto.google.com/android-sha1/bb456e84a524d4e5cd241a6a839a1062297b9cf4