Fix a bug where simultaneously listening to a reused Preference would not propagate changes to other listeners #1
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As it turns out, the "initial stable release" was not bug-free.
The bug
If you did this:
Only
value1
would now contain9
as expected, whilevalue2
andvalue3
would be0
.However, if you did:
Everything was fine. The bug only appeared when reusing a
Preference
and when all the listeners were listening to it at the same time.To show the thing in action, see this screencast sharing a
Preference
between multiplePreferenceBuilders
in a same screen:The reason
This bug was introduced by this commit. It happened because the cached
T lastValue
field should've existed in theonListen()
callback, not as a field in theEmitValueChanges
transformer.The purpose was to optimize the
Preference
stream so that the last emitted value wouldn't be unnecessarily added to the Stream again. Unfortunately, this "optimization" was too effective: it only allowed the first listener to receive the change but the other ones would always miss it.The fix
The solution was to move the cached value inside the
onListen()
callback. This way each individual listener would enjoy the caching benefits while actually being able to receive updates.There is now a test case in place to prevent this from happening again.