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I am using `avedInstanceState`in dev14 but getting this error
`cannot be saved using the current UiSavedInstanceStateRegistry. The default implementation only supports types which can be stored inside the Bundle. Please consider implementing a custom Saver for this class and pass it to savedInstanceState() or rememberSavedInstanceState()`

That error message is pretty clear imo, what part doesn’t make sense?

Do I need to add `saver` in custom object part ?

You pass the saver to `rememberSavedInstanceState`

```val navigationSaver = Saver&lt;NavigationStack&lt;MainScreen&gt;, NavigationStack&lt;MainScreen&gt;&gt;(
    save = { it },
    restore = {  NavigationStack(init = MainScreen.Watchlist) }
)

this.navigation = rememberSavedInstanceState&lt;NavigationStack&lt;MainScreen&gt;&gt;(saver = navigationSaver) {
    NavigationStack(init = MainScreen.Watchlist)
}```
Above code is giving me `java.lang.IllegalStateException: Check  failed.` error

`Check failed.`
        `at androidx.ui.savedinstancestate.ValueProvider$updateAndReturnValue$1.invoke(RememberSavedInstanceState.kt:106)`
        `at androidx.ui.savedinstancestate.UiSavedStateRegistryImpl.performSave(UiSavedStateRegistry.kt:116)`
        `at androidx.ui.core.SavedStateDelegate.dispatchSaveInstanceState(SavedStateDelegate.kt:106)`
        `at androidx.ui.core.AndroidComposeView.dispatchSaveInstanceState(AndroidComposeView.kt:690)``

Is `NavigationStack` `Serializable` or `Parcelable`? The error message you posted initially says “The default implementation only supports types which can be stored inside the Bundle”

<https://cs.android.com/androidx/platform/frameworks/support/+/androidx-master-dev:compose/runtime/runtime-saved-instance-state/samples/src/main/java/androidx/compose/runtime/savedinstancestate/samples/Samples.kt;l=45?q=CustomSaverSample&amp;ss=androidx%2Fplatform%2Fframeworks%2Fsupport>

Right, so you need to return something from the `save` lambda that can be stored in a `Bundle`.

The example you posted does it. It returns/restores `Holder.value`, which is an `Int`, i.e. something that can be stored in a `Bundle`.

The saver is basically your serialization/deserialization logic, but instead of serializing to a byte array, you’re serializing to any of the types supported by `Bundle`.