Given a `val isLoggedIn Flow lt Boolean gt ` that can emit ` kotlinlang #coroutines

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Title

z

zak.taccardi

07/27/2020, 10:18 PM

Given a

val isLoggedIn: Flow<Boolean>

that can emit

true

or

false

in any order and multiple times each - what would be the best way to observe when it switches from

true

to

false

? I would like to run a function when the user logs out - meaning the

Flow<Boolean>

emits

true

then

false

?

val isLoggedIn: Flow<Boolean>

isLoggedIn
  // <-- what operators do I need here?
  .onEach { 
    onLogout()
  }
  .launchIn(scope)

t

Tim Malseed

07/27/2020, 10:21 PM

Could you use

distinct

, and then just check if your value is

false

in you

onEach

block?

👍 2

z

Zach Klippenstein (he/him) [MOD]

07/27/2020, 10:21 PM

.distinctUntilChanged()
.filter { it }

👍 2

z

zak.taccardi

07/27/2020, 10:23 PM

oh that was easy

lol

wait I think I want the inverse

t

Tim Malseed

07/27/2020, 10:26 PM

Yeah,

filterNot { it }

👍 1

z

zak.taccardi

07/27/2020, 10:26 PM

but if the first value is

false

- won’t it emit and incorrectly call

onLogout()

I specifically want to run a function only when the stream switches from

true

to

false

so a single

flow { emit(false) }

should not trigger the

onLogout()

t

Tim Malseed

07/27/2020, 10:29 PM

I'm not sure what this would look like. Some kind of buffer? Maybe have a look at what distinct does under the hood?

z

zak.taccardi

07/27/2020, 10:35 PM

I think the following may work

.distinctUntilChanged()
.drop(1)
.filterNot { it }

☝️ 1

so

false

would not pass through the filter, but

false, true, false

would and

true, false

would as well

t

Tim Malseed

07/27/2020, 10:39 PM

Hah that was also easy

👍 1

s

satyan

07/28/2020, 2:04 PM

You could also use the

areEquivalent(old,new)

parameter of distinctUntilChanged to only match old = true and new = false

👏 4

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