I have an activity that has many fragments in it, and I want to share things using a shared view model between fragments, but when I initialize it the way I do in fragments it doesn't work, it shows an error, what is the correct way to access it if it is possible?
val model : sharedViewModel by activityViewModels()
i have tried to do ViewModelProvider but didn't know how to do it properly cause I am coding using kotlin
To have multiple fragments in a common activity instance share a viewmodel, the fragments can use by activityViewModels() property delegate. This returns a viewmodel scoped to the activity.
If you also want the activity to work with this viewmodel, the activity would declare it using the simpler by viewModels() property delegate. They did not bother creating activityViewModels() for an activity, as it would just be the same as the simpler viewModels().
I suggest you read Share data between fragments documentation
Activity use viewModels<T>()
Fragments use activityViewModels<T>()
Related
In this link it is instructed to use viewModel() in any composable and in an activity, we will get the same object while calling viewModel(). Although it is instructed to use viewModel() inside a composable, I was able to use it in setContent{} (outside of any composable) also.
In this link it is instructed to use viewModels() in an activity or a fragment to get the object of a class that extends ViewModel.
In both of the cases, we are getting an object of a class that extends ViewModel. So, why do we need to use two different approaches (viewModel() and viewModels())?
If you ask if you can use only viewModel without viewModels in Compose, the answer is yes. But in some cases it is more convenient to use both of them.
viewModels belongs to the androidx.activity package, is an extension to ComponentActivity, and has nothing to do with Compose. It was used in view-based Android and can still be used with Compose when you need to initialize or update your view model with some activity-specific callbacks.
In turn, viewModel is part of Compose and allows you to easily create/access a view model from any Composable.
You can call it directly inside setContent since it already belongs to the composable scope, but you would not be as comfortable calling it anywhere else in the activity, such as in onActivityResult(I know it's deprecated, it's just an example). You can still do it as shown in this answer, but in some cases viewModels may be easier to use.
currently, my Kotlin based application consists of a single activity, 3 fragments and a navigation (with navigation drawer) between them.
How do I add a variable, which will be initialized in the start of the application, will be visible in all fragments, and can be updated in one of them?
a simple int or string for that matter so it should be with little overhead as possible, yet i'd like to follow correct coding conventions. Please elaborate on the correct function to perform the initial variable value, how to bind each fragment textview to it, and the correct way to set the new value.
Thanks!
Create ViewModel and fragments use viewmodel like this
val viewModel: YourViewModel by activityViewModels()
in that case your viewmodel's scope is the same as activity scope.
For more information please refer to this link
I use Single Activity Architecture in my application and I need to create a ViewModel common for two fragments using Dagger2. If I create ViewModel for Activity Scope, it will live longer than necessary. How can i implement this smartly? Or its ok to use Activity Scope?
From Android developers documentation, the approach to use Activity scope for sharing ViewModel between fragment is fine.
You can refer the document here Share data between fragments
I have a lot of fragment base architect component.
Is this true that I create ViewModel for per fragment? or I should create one ViewModel for all fragment?
Saw many project that uses ViewModel for each Activity, and they pass them to their fragments if needed.
Same goes for me, but figure out what functions that Activity will do, and then build a ViewModel based on that functions:
Activity/Fragments that create an object.
Activity/Fragment that fetch a list.
Activity/Fragment that deal with Objects, like delete, update.
You can pass ViewModel to fragments. Also you can use inheritance with your ViewModels.
I would like to ask if it's correct to share the same ViewModel between Fragment and its Activity.I have UserDetailActivity and UserDetailFragment. Can I use the same ViewModel to display detail data of a user in the UserDetailActivity and UserDetailFragment or is there better approach.
Yes you can pass ViewModal object from a Activity to Fragment or vice-versa by implementing Parcelable into ViewModal class and can share object with fragment setArguments() method.
I am not using MVVM but I think its the same with MVP, I use the same Presenter(ViewModel in your case) with my Activity and its child Fragment. It make since because a Fragment is literally a fragment of an Activity. There might be some special cases where you really want to separate viewModel of Fragment and Activity, but most of the time, they share. About the initialization, dont pass your viewmodel directly, you can use dagger and inject it.