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satyan
12/08/2020, 7:55 PMHey 👋
I just published my first article on migrating from LiveData to StateFlow
https://fabernovel.github.io/2020-12-07/android-from-livedata-to-flows
Feel free if you have feedbacks to hit me on my Twitter 😉
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Daniel
12/09/2020, 10:18 PMThank you for the article!
How does StateFlow behave when the screen is recrated (rotation)?
Also if the answer is: The value is observed again, how would it be possible to make a SingleLiveDataEvent with StateFlow? With other words: A value wich is really only observed one time and then consumed
a
allan.conda
12/10/2020, 9:55 AMOh, just in time, I’m literally doing this right now.
Seems there’s no info about savedStateHandle? That’s kinda the blocker for me right now.
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satyan
12/10/2020, 3:41 PM@Daniel
How does StateFlow behave when the screen is recrated (rotation)?
Also if the answer is: The value is observed again, how would it be possible to make a SingleLiveDataEvent with StateFlow? With other words: A value wich is really only observed one time and then consumedI had a part about SingleLiveEvent initially, but it was going to be too long. You can use a SharedFlow instead of a StateFlow On collect, a SharedFlow will emits its replay cache then emit the next values, so you can use a SharedFlow with a replay cache of 0
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class MyViewModel {
private val _toast = MutableSharedFlow<String>() // by default replay cache is 0
val toast: SharedFlow<String> = _toast
fun foo() {
viewModelScope.launch {
// suspend until collected
_toast.emit("Hello")
}
}
}On configuration changes. the Stateflow value will be collected again yes
@allan.conda
Oh, just in time, I’m literally doing this right now.
Seems there’s no info about savedStateHandle? That’s kinda the blocker for me right now.What do you mean ? I used savedStateHandle to save data but it’s only going to be use initially to restore the state.
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class MyViewModel (savedStateHandle: SavedStateHandle) {
val _state = MutableStateFlow(restoreState())
val state: StateFlow<State> = _state
private fun restoreState(): State {
return savedStateHandle.get(KEY) ?: INITIAL_STATE
}
}a
allan.conda
12/10/2020, 4:10 PMHow do you save it? restoring is easy
I’m aware about the gotcha about large lists
s
satyan
12/10/2020, 4:21 PMWhen you’re updating the state, you can save the relevant part to the savedStateHandle:
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fun foo() {
viewmodelScope.launch {
val user = userRepository.getUser(id)
_state.value = mapper.mapState(user) savedStateHandle[KEY] = user
}
}⚠️ You can only save types that can be save to a bundle inside the savedStateHandle.
So you could create a UserSavedState parcelable type
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allan.conda
12/10/2020, 4:56 PMI see, so you simply update the savedStateHandle as well whenever you assigned a new value
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satyan
12/10/2020, 5:44 PMYep’ I’m only relying on savedStateHandle to save/restore a state not to hold the entire screen state.
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allan.conda
12/10/2020, 5:56 PMSavedStateHandle.getLiveData returns a MutableLiveData which you could update directly.
I’m currently trying to come up with a similar api with MutableStateFlow.
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Daniel
12/10/2020, 8:44 PMThank you! @satyan
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