Type-safe access to SavedStateHandle

• The kmp-viewmodel-savedstate artifact provides the type-safe API that allows you to access SavedStateHandle in a type-safe way.

• All API are available on all platforms and are located in the com.hoc081098.kmp.viewmodel.safe package.

• There are 2 types of keys:

  • NonNullSavedStateHandleKey<T>: key for values stored in SavedStateHandle. The type of the value associated with this key is T (non-null).
  • NullableSavedStateHandleKey<T>: key for values stored in SavedStateHandle. The type of the value associated with this key is T? (nullable, null is valid).

• Using SavedStateHandle.safe extension function to access SavedStateHandle in a type-safe way. It accepts a lambda with a single parameter of type SafeSavedStateHandle. SafeSavedStateHandle provides methods:
  • public inline operator fun <T : Any> get(key: NonNullSavedStateHandleKey<T>): T.
  • public inline operator fun <T : Any> get(key: NullableSavedStateHandleKey<T>): T?.
  • public inline operator fun <T : Any> set(key: NonNullSavedStateHandleKey<T>, value: T): Unit.
  • public inline operator fun <T : Any> set(key: NullableSavedStateHandleKey<T>, value: T?): Unit.
  • public inline fun <T : Any> getStateFlow(key: NonNullSavedStateHandleKey<T>): StateFlow<T>.
  • public inline fun <T : Any> getStateFlow(key: NullableSavedStateHandleKey<T>): StateFlow<T?>.
  • public inline fun <T : Any> remove(key: NullableSavedStateHandleKey<T>).

1. Define your SavedStateHandle keys

import com.hoc081098.kmp.viewmodel.safe.NonNullSavedStateHandleKey
import com.hoc081098.kmp.viewmodel.safe.string

private val searchTermKey: NonNullSavedStateHandleKey<String> = NonNullSavedStateHandleKey.string(
  key = "search_term",
  defaultValue = ""
)
private val userIdKey: NullableSavedStateHandleKey<String> = NullableSavedStateHandleKey.string("user_id")

2. Use SavedStateHandle.safe extension function

import com.hoc081098.kmp.viewmodel.SavedStateHandle
import com.hoc081098.kmp.viewmodel.ViewModel
import com.hoc081098.kmp.viewmodel.safe.NonNullSavedStateHandleKey
import com.hoc081098.kmp.viewmodel.safe.NullableSavedStateHandleKey
import com.hoc081098.kmp.viewmodel.safe.safe
import com.hoc081098.kmp.viewmodel.safe.string
import com.hoc081098.kmp.viewmodel.wrapper.NonNullStateFlowWrapper
import com.hoc081098.kmp.viewmodel.wrapper.NullableStateFlowWrapper
import com.hoc081098.kmp.viewmodel.wrapper.wrap

class SearchViewModel(
  private val savedStateHandle: SavedStateHandle,
) : ViewModel() {
  internal val searchTermStateFlow: NonNullStateFlowWrapper<String> = savedStateHandle
    .safe { it.getStateFlow(searchTermKey) }
    .wrap()

  internal val userIdStateFlow: NullableStateFlowWrapper<String?> = savedStateHandle
    .safe { it.getStateFlow(userIdKey) }
    .wrap()

  internal fun changeSearchTerm(searchTerm: String) {
    savedStateHandle.safe { it[searchTermKey] = searchTerm }
  }

  private fun setUserId(userId: String?) = savedStateHandle.safe { it[userIdKey] = userId }

  companion object {
    private val searchTermKey: NonNullSavedStateHandleKey<String> = NonNullSavedStateHandleKey.string(
      key = "search_term",
      defaultValue = "",
    )
    private val userIdKey: NullableSavedStateHandleKey<String> = NullableSavedStateHandleKey.string("user_id")
  }
}