It s good way Dao Room ``` Query SELECT FROM ModelRepo WHERE id = id fun getModel id Long Flow lt ModelRepo gt ``` ViewModel ```val findByIdRepo Long gt Flow lt ModelRepo gt = id gt dataRepo getModel id distinctUntilChanged ``` Composable ```val model ModelRepo by viewModel findByIdRepo repoId collectAsState initial = null ```

You can solve this by remembering the flow you use unless the viewModel or the repoId change ```val model by remember viewModel repoId viewModel findByIdRepo repo collectAsState null ```

gt little silly Why Isn t it the same thing

Check `View Kotlin bytecode` on each approach in the IDE slightly smiling face

It s good way Dao Room ``` Query SELECT FROM ModelRepo WHERE kotlinlang #compose

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Title

# compose

Vitaliy Zarubin

05/28/2021, 2:35 PM

It's good way? Dao Room

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@Query("SELECT * FROM ModelRepo WHERE id = :id")
fun getModel(id: Long): Flow<ModelRepo>

ViewModel

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val findByIdRepo: (Long) -> Flow<ModelRepo?> = { id -> dataRepo.getModel(id).distinctUntilChanged() }

@Composable

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val model: ModelRepo? by viewModel.findByIdRepo(repoId).collectAsState(initial = null)

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🚫 1

nitrog42

05/28/2021, 2:59 PM

I will just say that

Copy code

val findByIdRepo: (Long) -> Flow<ModelRepo?> = { id -> dataRepo.getModel(id).distinctUntilChanged() }

should probably just be a method :

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fun findByIdRepo(id: Long): Flow<ModelRepo?> = dataRepo.getModel(id).distinctUntilChanged()

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🙏 1

Vitaliy Zarubin

05/28/2021, 3:02 PM

👍 1

Adam Powell

05/28/2021, 3:24 PM

The

@Composable

code has a bug here:

viewModel.findByIdRepo

is returning a new

Flow

instance on each call. If

.collectAsState

has a new

Flow

instance to collect on a recomposition, it will cancel the old collection and start a new one fresh. This would cancel and re-start a lot of data loads if this function recomposes frequently.

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🙏 2

You can solve this by remembering the flow you use unless the viewModel or the repoId change:

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val model by remember(viewModel, repoId) {
  viewModel.findByIdRepo(repo)
}.collectAsState(null)

🙏 1

additionally it seems a little silly to use a function val for

findByIdRepo

instead of a normal function there, but that won't affect correctness, just add a little overhead

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Vitaliy Zarubin

05/28/2021, 3:28 PM

little silly

Why? Isn't it the same thing?

Adam Powell

05/28/2021, 3:29 PM

Check

View Kotlin bytecode

on each approach in the IDE 🙂

➕ 1

🙂 1

for most situations on android (combinations of kotlin compiler, d8 desugaring of openjdk8 language features, the specific device OS version) the val + lambda version ends up creating a separate object with an

invoke()

method as opposed to a plain final function call

🙏 1

Vitaliy Zarubin

05/28/2021, 3:48 PM

I think this is it. But how is this to be understood? How to learn to understand bytecode? 🙂

Adam Powell

05/28/2021, 3:58 PM

If you hit that "Decompile" button at the top it'll show something more java-like. Note that it's created a getter for a function object

you'll also want to look at the difference between the code that calls this function

Vitaliy Zarubin

05/28/2021, 4:02 PM

Got it. Thank you.

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