Allow apps to provide custom Bundle equality logic

[derat]

I'm having trouble with PlayerInterface.Listener.onTimelineChanged() not being consistently called when my SimpleBasePlayer-derived class updates an item's MediaMetadata.extra bundle and calls invalidateState().

I can see that this behavior is documented in various places:

• https://developer.android.com/reference/androidx/media3/common/MediaMetadata#extras()

  Given the complexities of checking the equality of two Bundle instances, the contents of these extras are not considered in the equals and hashCode implementation.

• https://developer.android.com/reference/androidx/media3/common/MediaMetadata#equals(java.lang.Object)

  Note: Equality checking does not consider extras.

• #470

I'm using the extras bundle to store information that changes at runtime (e.g. user-controlled tags), so I need some way to notify clients about changes. In order to force a playlist change when I modify the extras bundle, is my best bet changing the value of some arbitrary field in MediaMetadata, MediaItem, or SimpleBasePlayer.MediaItemData that I'm not currently using?

[icbaker]

As you've pointed out, the equality of Bundle extras fields has come up a few times. We have no plans to implement general-purpose equality comparisons for these fields - but we have recently discussed the idea of allowing apps to provide a custom equality comparison, which I think would solve your issue (since you know the key values you want to inspect/compare).

We would likely try and do this in a way that's consistent for all the various extras fields in the library, which will require a bit of design thought (especially how we can keep the comparison consistent across both sides of the session/controller IPC for some of the extras fields) - so I'm afraid we don't have capacity to work on this soon - but it would be helpful if you could let us know if you agree whether this sort of approach would solve your problem.

In the meantime, I suspect what you've proposed is the best approach - or you could wire up your own direct side-channel from your SimpleBasePlayer to notify your clients of changes directly (assuming they are invoking your type directly, rather than via MediaSession/Controller).

[derat]

@icbaker, thanks for the reply! I think that being able to supply a custom comparison as you suggested would work for my case.

In the meantime, here's what I went with in case it helps anyone else:

if (itemData.equals(old)) {
    itemData = itemData.buildUpon().setManifest(object {}).build()
}

(I wasn't using the manifest field for anything.)

[icbaker]

Updating title and labels to use this to track the idea of allowing apps to provide a custom equality for bundles.