Is there already a way to scope view models by composable

Question

Adam Powell · Answer

short answer yes longer answer what specific scoping behavior do you want what code do you want to be able to write

Tgo1014 · Answer

Let s say I ve a pager with the same composable and each needs their own instance of the same viewmodel How would I do that

Adam Powell · Answer

have each of your pages provide `LocalViewModelStoreOwner` and multiplex them into a host viewmodel this is how androidx navigation compose does it

Adam Powell · Answer

you ll have some decisions to make around the intended lifecycle of those viewmodels how long to keep them alive and when to clear them if you don t keep all of the pager s pages composed at the same time

Tgo1014 · Answer

so it requires some work I see I ll have to create some custom implementation of `LocalViewModelStoreOwner` right I need to check how the navigation does it then

Adam Powell · Answer

a little work but not too much the usual way to think about this is to have the composable function that provides the `LocalViewModelStoreOwner` fetch a container ViewModel that you write for this purpose Then use a `RememberObserver` to remove+clear the `ViewModelStore` when a page leaves the composition if the host activity `isChangingConfiguration` isn t `true`

Adam Powell · Answer

since if you re tearing down the composition for a config change you want to leave them alone

Adam Powell · Answer

the reason to use `RememberObserver` directly instead of `DisposableEffect` is because you need to hook `onAbandoned` too ViewModels are created during composition and need to be cleaned up if the composition they were created in doesn t commit

Adam Powell · Answer

shouldn t be more than ~70 100 lines of utility code that you write once and don t have to look at again slightly smiling face

Tgo1014 · Answer

Very detailed reply thanks for the help Adam smile

Adam Powell · Answer

you re welcome I was just doing this recently for a personal project a couple weeks ago so it was fresh smile

Tgo1014 · Answer

Do you think in the future it could be included directly on `hilt` Like specifying some key would get another view model and all calls for the same key would return the same Is this even possible haha

Adam Powell · Answer

I m not quite sure I understand the question or the relation to hilt this is lower level than hilt and you don t need hilt to do it

julioromano · Answer

gt have each of your pages provide `LocalViewModelStoreOwner` and multiplex them into a host viewmodel this is how androidx navigation compose does it < Adam Powell> I think I have an English problem here can you explain with different words what do you mean by multiplex them into a host viewmodel Thanks

Adam Powell · Answer

my apologies you have a point where you need to create one `ViewModelStore` per page each one establishes a namespace and scope for viewmodels obtained beneath it You need a place to store those `ViewModelStore`s and make sure they re retained Using another `ViewModel` is the most straightforward way to do this since it already provides all of the facilities and guarantees you want You ll create your own `ViewModel` that stores a map of some key that is unique for each page to a `ViewModelStore` and you ll need to manage the addition and removal of these `ViewModelStore`s from that map Then you ll need to provide the correct `ViewModelStore` via `LocalViewModelStoreOwner` to the content of each page