forked from mystiq/hydrogen-web
c6e2607f1f
This came up now because Timeline uses a MappedList to map PendingEvents to PendingEventEntries. In the map function, we setup links between entries to support local echo for relations. When opening a timeline that has unsent relations, the initial populating of the MappedList will try to emit an update for the target entry in remoteEntries. This all happens while the ListView of the timeline is calling subscribe and all collections in the chain are populating themselves based on their sources. This usually entails calling subscribe on the source, and now you are subscribed, iterate over the source (as you're not allowed to query an unsubscribed observable collection, as it might not be populated yet, and even if it did, it wouldn't be guaranteed to be up to date as events aren't flowing yet). So in this concrete example, TilesCollection hadn't populated its tiles yet and when the update to the target of the unsent relation reached TilesCollection, the tiles array was still null and it crashed. I thought what would be the best way to fix this and have a solid model for observable collections to ensure they are always compatible with each other. I considered splitting up the subscription process in two steps where you'd first populate the source and then explicitly start events flowing. I didn't go with this way because it's really only updates that make sense to be emitted during setup. A missed update wouldn't usually bring the collections out of sync like a missed add or remove would. It would just mean the UI isn't updated (or any subsequent filtered collections are not updated), but this should be fine to ignore during setup, as you can rely on the subscribing collections down the chain picking up the update while populating. If we ever want to support add or remove events during setup, we would have to explicitly support them, but for now they are correct to throw. So for now, just ignore update events that happen during setup where needed. |
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| .. | ||
| list | ||
| map | ||
| BaseObservable.js | ||
| index.js | ||
| ObservableValue.js | ||