Fixed
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da...@google.com
I haven't looks on repro yet, but there is no such thing as AlwaysOnLifecycle in latest versions, LiveData has strong references on all observers (including that were added as observeForever). If nothings keeps a livedata, then it is gced.
ap...@google.com
ah I see: in observe with Lifecycle we add LiveData as observer to Lifecycle and it keeps it alive. However keeping observerforever + livedata, when nothing has reference on them, is a memory leak by definition: user can't clean this memory anyhow, because neither observer / livedata could be referenced.
da...@google.com
It is true, though from usage perspective, it is not obvious at all.
e.g. you are in a class, like a singleton repository where you want to observe the database for some query.
and you write:
MyRepository(dao : MyDao) {
dao.someLiveData().observeForever(....do something...);
}
And it suddenly stops working :/ which is very non-obvious from the developer's perspective.
If we kept the lifecycle in memory as long as it has observers, wouldn't it solve the problem since they can break the chain by calling stopObserving(observer) ?
When they use observeForever, they are already responsible to remove the observer so I think it is fine?
e.g. you are in a class, like a singleton repository where you want to observe the database for some query.
and you write:
MyRepository(dao : MyDao) {
dao.someLiveData().observeForever(....do something...);
}
And it suddenly stops working :/ which is very non-obvious from the developer's perspective.
If we kept the lifecycle in memory as long as it has observers, wouldn't it solve the problem since they can break the chain by calling stopObserving(observer) ?
When they use observeForever, they are already responsible to remove the observer so I think it is fine?
an...@google.com
well, the issue is: no reference on observer, you can't break the chain because you don't have a reference. If you have a reference, LiveData (unfortunately) wouldn't be gc-ed, because even AlwaysActiveObserver inrenally has strong reference on livedata.
Description
Version used: 2.2.0
Devices/Android versions reproduced on:
- device usb:336662528X product:xcover4ltexx model:SM_G390F device:xcover4lte transport_id:5
- device product:sdk_gphone_x86 model:Android_SDK_built_for_x86 device:generic_x86 transport_id:4
- device usb:336662528X product:zerofltexx model:SM_G920F device:zeroflte transport_id:15
In Version 2.1.0 annotation @Relation was only allowed for list types, if you used it on a non-list type the following runtime error occured:
error: Fields annotated with @Relation must be a List or Set.
Since Version 2.2.0 @Relation can be used on non-list types, in order to model relations with a single object reference.
This is handy if you have 1-to-1 relations and you don't have to explicitly get the first item from the result list, instead you get the object directly.
release notes:
One-to-One Relations: The restriction in POJO fields annotated with @Relation to be of type List or Set has been lifted, effectively allowing single-value relations to be represented.
It seems that this new feature is only supported up to a certain amount of table rows. In more details it means that if you run a query on tables with 100 rows, the returned POJOs have all valid non-null references to the object specified by the @Relation annotation. If you run the same query on tables with more than 999 rows (999 still works, 1000 will fail) the result will be that all returned POJOs have NULL as referenced object (see my example project).
If you use the list type with @Relation annotation you don't have this limitation.
Please refer to the attached example project unit test.
In the example project the same entities are used but with two different POJO types. One is using a List<> type annotated with @Relation, and the other is using the newly supported object type.
Android unit test show that the list type always works but the object type works up to 999 rows, after that it starts to fail.