EpubNavigator blank/empty after unmount/remount until navigator.go

[smoores-dev]

Hey folks, me again 😁

When I migrated Storyteller to the v3 toolkit, we ran into an issue that, at the time, I just worked around, but now it seems that maybe my workaround is causing issues, sooo I'm back to ask for some more help. Here's the issue:

I have an EpubFragment that's responsible for creating/managing the EpubNavigatorFactory.

This gets mounted and unmounted in an EpubView.

Mounting the EpubView -> EpubFragment -> EpubNavigator works correctly the first time the EpubView is mounted. After unmounting and remounting, however, the resourcePager doesn't seem to mount any child views:

If I then trigger a navigator.go() manually, this immediately resolves. Buuuut I'm triggering navigator.go() when first mounting the EpubView, and that call doesn't seem to help. I need to wait for the initial mount to finish, and then trigger a navigator.go()? Not sure what's going on, exactly.

Any thoughts about what I could be doing wrong here?

[qnga]

Hi,

After unmounting and remounting

I assume you wouldn't get any issue if you'd start with a fresh navigator every time. Why do you "unmount" the EpubView without destroying the EpubNavigatorFragment? If you need to temporarily show something else, you should be able to do it on top of the EpubNavigatorFragment` without any lifecycle issue as it is the way we use it in the testapp.

Besides, embedding a fragment in a view looks very weird to me. You don't have a FragmentManager except the one of the activity, which is supposed to manage by itself its own view. Do you have a good reason to do so?

[smoores-dev]

Why do you "unmount" the EpubView without destroying the EpubNavigatorFragment?

I'm pretty sure that I just used the wrong lifecycle terminology there; when I add an onDestroy lifecycle method with a breakpoint to EpubFragment, it does get called. Is there something that I would need to do in that method to destroy the EpubNavigator? Or is there some way to add an onDestroy callback to the EpubNavigator so I can confirm whether it is actually being destroyed?

I want to actually destroy the EpubView any time it's not being viewed, because this is a Media Overlay-enabled reader/player, and having decoration and location updates to the WebView occur while the WebView is in the background seems to sometimes cause issues. It's both expensive and can cause the WebView to get stuck, I think, and sometimes even recycled by the OS, if I remember correctly from before I started destroying the view when it was unfocused.

Besides, embedding a fragment in a view looks very weird to me. You don't have a FragmentManager except the one of the activity, which is supposed to manage by itself its own view. Do you have a good reason to do so

Agreed, this is extremely awkward. As best I can tell, this is the only way to expose a Fragment in an Expo Module in React Native, which only has support for exposing plain functions, events, and views. If you have other ideas I'm all ears, though I suspect this is just the cost of doing business with React Native in this case. FWIW this worked with the Readium v2 toolkits without issue!

[qnga]

Ok, it sounds like:

• Either the EpubNavigatorFragment is not properly destroyed. I can't see anything you would do wrong about that though.
• Or more likely, creating a fresh EpubNavigatorFragment in some particular context doesn't work. Unfortunately, it's hard for me to tell what this context is, especially as you're messing up the already messy Android lifecycles. You're not supposed to have to call navigator.go at all for the resourcePager to add children.

For your information, we've got a brand new navigator, not fully ready, written in Compose. I hope the React Native integration will be cleaner!