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kotlinlang

Good morning (for some at least i guess :sweat_smile: ) I'm starting to use flows and I wonder how can i specify the thread the function I pass onto `collect` is executed.
I'm trying:
```
launch(UI) {
  flow.collect {
    // i was hoping this was executed in UI
  }
```
should that be running in the UI Dispatcher?

You can use `kotlinx.coroutines.Dispatchers.Main` for the UI

You don’t need to launch { flow.collect { } }, because you would have callabacks and too many scopes
Instead, you can launch flow in some scope, for example:
```
flow
    .onEach { doSmth(it) }
    .launchOn(Dispatcher.Main)
```

<@UNKNBSP33> that doesn't consume the the value, does it?

it just creates new flow that does that on when there is a new item

Yes it does, `launchOn()` calls `collect()`

There is a nice simple example
<https://kotlin.github.io/kotlinx.coroutines/kotlinx-coroutines-core/kotlinx.coroutines.flow/launch-in.html>

Because other way we would have too many scopes
```
launch(UI) {
   flow.collect {
       too many scopes
   }
}
```

<https://github.com/Kotlin/kotlinx.coroutines/blob/8d8b6eb8a1186ae987610a31ac441d107d04b034/kotlinx-coroutines-core/common/src/flow/terminal/Collect.kt>
```
@ExperimentalCoroutinesApi // tentatively stable in 1.3.0
public fun &lt;T&gt; Flow&lt;T&gt;.launchIn(scope: CoroutineScope): Job = scope.launch {
    collect() // tail-call
}
```

<@U6LA7QTH9> When collecting a flow with `collect`, the passed block invoked for each collected item,  and * always in the context of the current coroutine*.
Note that `UI` is deprecated in favor of `Dispatchers.Main`.
If you want some flow operations to be executed on another Thread/Dispatcher, you could use the `flowOn` operator. Note that unlike Rx `subscribeOn`/`observeOn`, `flowOn` is only applied to upstream operations.