Concurrency with Kotlin Flow
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In this demo, you’ll use what you learned in the previous lesson. Start Android Studio, and open the 03-leverage-flow-operators/Starter folder. Make sure you don’t continue on the project from the last lesson because the starter project has some new code for this lesson.
private val _categories: MutableStateFlow<List<MovieCategoryViewState>> = MutableStateFlow(emptyList())
val categories: Flow<List<MovieCategoryViewState>> = _categories
private val _moviesByCategories: MutableStateFlow<Map<String, List<MovieViewState>>> = MutableStateFlow(emptyMap())
val moviesByCategories: Flow<Map<String, List<MovieViewState>>> = _moviesByCategories
private fun fetchFavoriteCategories() {
viewModelScope.launch {
movieRepository.fetchFavoriteCategories()
.map { favoriteCategories ->
favoriteCategories.map { MovieCategoryViewState(it.id, it.name) }
}
.collect { _categories.emit(it) }
}
}
private fun fetchMoviesByCategories() {
viewModelScope.launch {
movieRepository.fetchMoviesByCategory()
.transform { moviesByCategories ->
val movieViewStates: Map<String, List<MovieViewState>> = moviesByCategories.mapValues { (category, movies) ->
movies.map { movie ->
val description = movieRepository.fetchMovieDescriptionsSuspending(movieId = movie.id)
val imageRes = movieRepository.fetchMovieImage(movieId = movie.id)
MovieViewState(
id = movie.id,
title = movie.title,
description = description,
imageRes = imageRes
)
}
}
emit(movieViewStates)
}
.collect {
_moviesByCategories.emit(it)
}
}
}
fun fetchMovieDescriptionsSuspending(movieId: String): String {
return movieDatabase.getMovieDescription(movieId = movieId)
}
RootContainer(
categories = categories, // here
moviesByCategories = moviesByCategories, // here
onRatingsClicked = onRatingsClicked,
onCategoryClicked = onCategoryClicked,
onMovieClicked = onMovieClicked
)