[Feature Request] Preserve initial value of StateFlow / SharedFlow in FlowLiveData::asLiveData [157380488]

Fixed

Feature Request

androidx-ui-starter-projects

Status Update

No update yet.

Description

zi...@gmail.com

created issue #1

May 25, 2020 09:23PM

Component used: lifecycle-livedata-ktx
Version used: 2.3.0-alpha03

StateFlow and (as of now, not yet released) SharedFlow contain initial values. Those are not set on the LiveData created by the asLiveData extension methods on Flow in FlowLiveData.kt. It would be nice if the initial value was available as value on the created LiveData to help reduce unnecessary UI updates that happen when the values arrive on the Flow after the lifecycle method responsible for creating the initial view has already finished.

Here is a failing test for StateFlow that should work, IMHO:

@Test
fun asLiveData_should_preserve_initial_value_of_StateFlow() {
    val result = MutableStateFlow("init")
        .asLiveData()
        .value
    Truth.assertThat(result).isNotNull()
}

Comments

il...@google.com <il...@google.com> Nov 18, 2021 10:12PM

Status: New

sa...@google.com <sa...@google.com> Aug 18, 2022 11:21PM

Assigned to sa...@google.com.

ap...@google.com <ap...@google.com> #2Aug 23, 2022 12:44AM

Marked as fixed.

Project: platform/frameworks/support
Branch: androidx-main

commit 9f854289a3f2199754cb5d1fe5fba72f1a46a222
Author: Sanura N'Jaka <sanura@google.com>
Date: Fri Aug 19 21:29:02 2022

Preserve initial value of StateFlow in FlowLiveData's asLiveData

Currently, when FlowLiveData creates a LiveData object
from a given Flow using its asLiveData function, it does
not contain any initial value. Meaning that if the Flow
is a StateFlow, which always contains an initial value,
that initial value will not be initially accessible in
the LiveData. We will now preserve this initial value.

RelNote: "`FlowLiveData`'s `asLiveData` function will now
preserve the initial value of a `StateFlow` when creating
the new `LiveData` object."
Test: asLiveData_preserveStateFlowInitialValue
Fixes: 157380488

Change-Id: I3f53068b1a071e2f334f2cbab2819e7f7a4c60b2

M lifecycle/lifecycle-livedata-ktx/src/androidTest/java/androidx.lifecycle/FlowAsLiveDataIntegrationTest.kt
M lifecycle/lifecycle-livedata-ktx/build.gradle
M lifecycle/lifecycle-livedata-ktx/src/main/java/androidx/lifecycle/FlowLiveData.kt

https://android-review.googlesource.com/2190406

il...@google.com <il...@google.com> #3Aug 23, 2022 05:42PM

This has been fixed internally and will be available in Lifecycle 2.6.0-alpha02.

na...@google.com <na...@google.com> #4Sep 12, 2022 05:52PM

This bug was linked in a change in the following release(s):

androidx.lifecycle:lifecycle-livedata-ktx:2.6.0-alpha02

Issue 157380488