IssueTracker

Component used: Navigation
Version used: 2.3.5.
Devices/Android versions reproduced on: all

I'm facing an inconsistent behaviour when using the generated safe args as opposed to the deeplink strategy.

Say I have following navigation graph:

<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"
    app:startDestination="@+id/home_dest">

    <fragment
        android:id="@+id/home_dest"
        android:name="com.example.android.codelabs.navigation.HomeFragment"
        android:label="@string/home"
        tools:layout="@layout/home_fragment" >
        <action
            android:id="@+id/action_home_dest_to_deeplink_dest"
            app:destination="@id/deeplink_dest" />
    </fragment>

    <fragment
        android:id="@+id/deeplink_dest"
        android:name="com.example.android.codelabs.navigation.DeepLinkFragment"
        android:label="@string/deeplink"
        tools:layout="@layout/deeplink_fragment">

        <argument
            android:name="myarg"
            app:argType="string" />

        <deepLink app:uri="example://my-deelink-frag?myArg={myarg}" />
    </fragment>
</navigation>

I have defined 2 ways to navigate to the DeepLinkFragment:

• Navigation action with id action_home_dest_to_deeplink_dest
• A deeplink example://my-deelink-frag?myArg={myarg}

In the DeepLinkFragment I'm using the navArgs() function to de-serialize the incoming Bundle and show a simple Toast message.

class DeepLinkFragment : Fragment() {

    private val args : DeepLinkFragmentArgs by navArgs()
    
    override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
        super.onViewCreated(view, savedInstanceState)
        Toast.makeText(requireContext(), args.myarg, Toast.LENGTH_SHORT).show()
    }
}

When navigating with the generated safe args I can sent an empty string as the value for myArg. No problem.

findNavController().navigate(HomeFragmentDirections.actionHomeDestToDeeplinkDest(""))

However, when navigating with an empty string as argument via the deeplink way:

val arg = ""
findNavController().navigate("example://my-deelink-frag?myArg=${arg}".toUri())

I get following stacktrace:

 Caused by: java.lang.IllegalArgumentException: Required argument "myarg" is missing and does not have an android:defaultValue
    at com.example.android.codelabs.navigation.DeepLinkFragmentArgs$Companion.fromBundle(DeepLinkFragmentArgs.kt:29)
    at com.example.android.codelabs.navigation.DeepLinkFragmentArgs.fromBundle(Unknown Source:2)
    at java.lang.reflect.Method.invoke(Native Method) 
    at androidx.navigation.NavArgsLazy.getValue(NavArgsLazy.kt:52) 
    at androidx.navigation.NavArgsLazy.getValue(NavArgsLazy.kt:34) 
    at com.example.android.codelabs.navigation.DeepLinkFragment.getArgs(DeepLinkFragment.kt:30) 
    at com.example.android.codelabs.navigation.DeepLinkFragment.onViewCreated(DeepLinkFragment.kt:34) 
    at androidx.fragment.app.Fragment.performViewCreated(Fragment.java:2987) 
    at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:546) 
    at androidx.fragment.app.FragmentStateManager.moveToExpectedState(FragmentStateManager.java:282) 
    at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:2189) 
    at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:2106) 
    at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:2002) 
    at androidx.fragment.app.FragmentManager$5.run(FragmentManager.java:524) 
    at android.os.Handler.handleCallback(Handler.java:938) 
    at android.os.Handler.dispatchMessage(Handler.java:99) 
    at android.os.Looper.loop(Looper.java:233) 
    at android.app.ActivityThread.main(ActivityThread.java:8068) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:631) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:978) 

Which is coming from the generated DeeplinkFragmentArgs code

public data class DeepLinkFragmentArgs(
  public val myarg: String = ""
) : NavArgs {
  public fun toBundle(): Bundle {
    val result = Bundle()
    result.putString("myarg", this.myarg)
    return result
  }

  public companion object {
    @JvmStatic
    public fun fromBundle(bundle: Bundle): DeepLinkFragmentArgs {
      bundle.setClassLoader(DeepLinkFragmentArgs::class.java.classLoader)
      val __myarg : String?
      if (bundle.containsKey("myarg")) {
        __myarg = bundle.getString("myarg")
        if (__myarg == null) {
          throw IllegalArgumentException("Argument \"myarg\" is marked as non-null but was passed a null value.")
        }
      } else {
        __myarg = ""
      }
      return DeepLinkFragmentArgs(__myarg)
    }
  }
}

Looking at the code it seems as if an empty string is making the bundle.getString("myarg") return null instead of the empty string?!

As a fix I could add the android:defaultValue.
However I feel like this is a bug since it is possible with the safe args.

<argument
    android:name="myarg"
    android:defaultValue=""
    app:argType="string" />