Android Navigation: shared element transitions not working between fragments - android-fragments

Question

I followed the instructions here.
Here's my code:
val navDirections = PostsListFragmentDirections.actionPostsListFragmentToPostDetailFragment(post)
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
val animationExtras = FragmentNavigatorExtras(
title to title.transitionName,
body to body.transitionName
)
navigateWithAnimations(navDirections, animationExtras)
} else {
navigateTo(navDirections)
}
navigateTo and navigateWithAnimations are extensions functions:
fun Fragment.navigateTo(navDirections: NavDirections) {
NavHostFragment.findNavController(this).navigate(navDirections)
}
fun Fragment.navigateWithAnimations(navDirections: NavDirections, extras: Navigator.Extras) {
NavHostFragment.findNavController(this).navigate(navDirections, extras)
}
The code is being executed but the animations are not working.
Here's the nav_graph.xml
<fragment
android:id="#+id/postsListFragment"
android:name="PostsListFragment"
android:label="PostsListFragment">
<action
android:id="#+id/action_postsListFragment_to_postDetailFragment"
app:destination="#id/postDetailFragment">
<argument
android:name="post"
app:argType="Post"
app:nullable="true"
android:defaultValue="#null" />
</action>
</fragment>
<fragment
android:id="#+id/postDetailFragment"
android:name="PostDetailsFragment"
android:label="PostDetailFragment">
<argument
android:name="post"
app:argType="Post"
app:nullable="true"
android:defaultValue="#null" />
</fragment>
And here's how I'm setting the view into the second (destination fragment):
private val args: PostDetailsFragmentArgs by navArgs()
override fun onViewCreated(view: View, savedInstanceState: Bundle?) {
super.onViewCreated(view, savedInstanceState)
args.post?.let { post ->
tv_title.text = post.title
tv_body.text = post.title
}
}
In both XML files I have defined:
android:transitionName="transition_title"
android:transitionName="transition_body"

Answer 1

Did you establish the sharedElementEnterTransition property in your second fragment? You would have to do something like this in the onCreate method:
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
main = requireActivity() as MainActivity
sharedElementEnterTransition = ChangeBounds().apply {
duration = 750
interpolator = AccelerateDecelerateInterpolator()
}
sharedElementReturnTransition = ChangeBounds().apply {
duration = 750
interpolator = AccelerateDecelerateInterpolator()
}
}
In other words, the receiving fragment needs to know how to deal with shared elements.