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@rharter
Last active August 9, 2022 14:58
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A kotlin property delegate to scope any object to an android lifecycle. Blog post at https://ryanharter.com/blog/easy-android-scopes/
import androidx.lifecycle.get
import androidx.lifecycle.ViewModel
import androidx.lifecycle.ViewModelProvider
import androidx.lifecycle.ViewModelStore
import androidx.lifecycle.ViewModelStoreOwner
/**
* Returns a property delegate to access the wrapped value, which will be retained for the
* duration of the lifecycle of this [ViewModelStoreOwner].
*
* ```
* class MyFragment : Fragment() {
* private val presenter by scoped { MyPresenter() }
*
* override fun onCreate(savedInstanceState: Bundle?) {
* super.onCreate(savedInstanceState)
* presenter.models.collect {
* // ...
* }
* }
* }
* ```
*/
inline fun <reified T> ViewModelStoreOwner.scoped(noinline creator: () -> T): Lazy<T> {
return LazyScopedValue({ viewModelStore }, { ScopeViewModel.Factory(creator) })
}
class ScopeViewModel<V>(
val value: V
) : ViewModel() {
class Factory<V>(val valueFactory: () -> V) : ViewModelProvider.Factory {
@Suppress("UNCHECKED_CAST")
override fun <T : ViewModel?> create(modelClass: Class<T>): T =
ScopeViewModel(valueFactory()) as? T
?: throw java.lang.IllegalArgumentException("Unknown type")
}
}
class LazyScopedValue<T>(
private val storeProducer: () -> ViewModelStore,
private val factoryProducer: () -> ViewModelProvider.Factory
) : Lazy<T> {
private var cached: Any = NotSet
@Suppress("UNCHECKED_CAST")
override val value: T
get() {
val value = cached
return if (value == NotSet) {
val factory = factoryProducer()
val store = storeProducer()
val viewModel = ViewModelProvider(store, factory).get<ScopeViewModel<T>>()
viewModel.value.also {
cached = it as Any
}
} else {
value as T
}
}
override fun isInitialized() = cached != NotSet
companion object {
private val NotSet = Any()
}
}
@mochadwi
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Awesome! Thanks for explaining @rharter

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