in the back handling section I would assume if my `BackCallb

Question

in the back handling section I would assume if my `BackCallback` didn t do anything then the back would do nothing the UI wouldn t go back is that correct ```private val backCallback = BackCallback do nothing ```

Adam Brown · Answer

also I see it is applied in `init` but I would expect to need to unregister it in a lifecycle callback is that not needed

Adam Brown · Answer

basically I m trying to prevent the back action in certain cases

Adam Brown · Answer

ah I think it s due to other back handlers being registered

Adam Brown · Answer

hhmmm so i was unregistering a backhandler in `onStop` for a component that was getting pushed on top of in a stack But that doesnt appear to be getting called Are components lower down in a stack not active to be considered started

Arkadii Ivanov · Answer

Unfortunately due to the way the predictive back gesture works on Android it s not possible to intercept the back button press This was the case a while ago when the back handler was returning a boolean But I had to align the API with the AndroidX `OnBackPressedDispatcher` So you have to update the callback s `isEnabled` property according to your state

Adam Brown · Answer

okay so updating that state as things change not when a back event is propagating

Adam Brown · Answer

way to make things more difficult google stuck out tongue but thats fine

Adam Brown · Answer

the next thing here is the started resumed state though this seems off to me

Arkadii Ivanov · Answer

Yeah Turned out there are technical limitations on Android There was an interesting conversation about it which explains everything <https twitter com ianhlake status 1553433732329009152|https twitter com ianhlake status 1553433732329009152>

Adam Brown · Answer

oh nvm

Adam Brown · Answer

I think i discovered my state issue here

Adam Brown · Answer

but last question do I really not need to worry about calling `unregister` ever

Arkadii Ivanov · Answer

Usually you don t It s the same as unsubscribing from Lifecycle

Adam Brown · Answer

ah okay

Adam Brown · Answer

what I ve been digging around the edges of here is that the backhandler in `Comp A` always fires but never the backhandler in `Comp B` Maybe the order of operations I m expecting is different I would expect a bottom up propagation so a child could steal the event first

Arkadii Ivanov · Answer

That s because the component s BackHandler has the same scope as the component itself

Adam Brown · Answer

if both handlers are enabled that is

Arkadii Ivanov · Answer

By default back callbacks are called in reverse order If you register a callback after creating your Child Stack it has higher priority Starting with Essenty 1 2 x alpha you can specify a priority for your callback

Adam Brown · Answer

oohhh

Adam Brown · Answer

up that was it my init block doing the registering was lower down in the file than my call to `componentContext childStack `

Adam Brown · Answer

thanks

Arkadii Ivanov · Answer

Perhaps it would be nice to have this documented I will add this

Arkadii Ivanov · Answer

Add this to the doc Thanks <https arkivanov github io Decompose component back button callback order>

Adam Brown · Answer

looks great thanks