Single viewmodel for multiple activities Jan 2, 2024 · If we need a shared Scope to share dependencies between ViewModels then the obvious choice is the Activity Scope. ViewModel class acts as an interface between Fragments to sharing data. Keeping everything in one view model would make testing harder and also you have to keep viewmodel for all 20 fragments may be scoping to activity. , the main Mar 27, 2020 · By requiring the ViewModel to only implement an interface, the Fragment can be used from multiple Activities, each with their own ViewModel, as long as the ViewModels implement said interface. Aug 12, 2024 · In Android development, ViewModel serves as a means to facilitate data sharing among different fragments or activities. Of course this third, common object can also have LiveData as a member, which one of the ViewModel can update and the other - observe. View first simply means the view is what drives the creation or discovery of the view model. ViewModels are a part of Android’s May 4, 2020 · private val viewModel: MainViewModel by viewModels() The regular way would involve using ViewModelProvider which we can skip thanks to that extension. However, I still find it hard to have one View per Model. This becomes particularly important with shared ViewModels. ViewModelsProvider. You can get activity level view model in onCreate() callback of fragments: Feb 3, 2019 · my View Model which is Singleton class and liveData is singleton so I can share the live data between activities. Feb 5, 2025 · What is Single Activity Architecture (SAA)? In a typical Android app, you might have multiple Activities, each representing a different screen or feature. If that is the case, you may take a look at Dependency Injection which will allow you to create a ViewModel as a singleton and use in multiple fragments/activities. You can create a ViewModel extending AndroidViewModel. ViewModel objects store and Feb 10, 2025 · ViewModel is the right place to handle business logic in the UI layer. For instance, one activity could handle Dec 27, 2024 · Navigation Complexity: Sharing a single ViewModel across multiple Activities or deep navigation graphs is complicated. Consolidate related UI data into a single ViewModel to simplify the architecture and reduce complexity. In this blog Nov 19, 2023 · Single Responsibility: Each ViewModel should have a clear and single Activities, or Fragments. You are welcome to have multiple activities, but they should be very loosely coupled with other activities in the app, in cases where there would be no need for a shared ViewModel (e. After you've refactored your code to use the Navigation library, you can pass the previous back stack entry in order to get the same instance of the View Model. – Mar 20, 2018 · When getting the view model using the ViewModelProviders you are passing as lifecycle owner the MainActivity, this will give the view model for the that activity. How do I make a singleton ViewModel? 5 Answers Feb 10, 2025 · The following sections show you how to use ViewModel and the Fragment Result API to communicate between your fragments and activities. While a view should only have one viewmodel, a single viewmodel might be used by multiple views (imagine a wizard, for example, that has three views but all bind to the same viewmodel that drives the process). But what do we do when we only have one Activity for our whole Application? May 25, 2017 · @luis, An activity can share its ViewModel to all child fragments of that activity. Jul 10, 2022 · Let's start with shared viewModel which is the simplest way of sharing the data between fragments/activities. Two Views can share the same View Model of their state had to be synchronized. This means a single ViewModel, minimal coupling, high code-readability, and easy data-flow. If you've got data that has to be represented by multiple views then that should be in your model layer, with multiple view model instances exposing that data to their associated views. This is particularly useful in scenarios where you have a parent activity with multiple child fragments that need to access the same data. and get the value from live Data in another Activity. Oct 3, 2023 · Since a single Activity can have multiple fragments, so by default there is a relation between them. Note that ViewModels can be easily used with both Fragments and Activities, which I’ll call UI controllers. of(activity) scopes your ViewModel to the activity, so when you attempt to ask for your ViewModel, you will receive it in the Fragment. To keep the example simple, you can implement the LiveData class as a singleton as follows: You can create a singleton for your view model like I did here: Jan 23, 2025 · Navigation Complexity: Sharing a single ViewModel across multiple Activities or deep navigation graphs is complicated. In the activity : val viewModel: SharedViewModel by viewModels() And in fragments: val viewModel: SharedViewModel by Mar 6, 2021 · This has multiple benefits but it all depends on how the app is organized: It is not about a “single” Activity, but rather how “screens” are organized — that is, a complete workflow Nov 30, 2019 · A view is the declarative element of your GUI while the view model is the abstraction of that views state; data-binding is what holds them together. This May 27, 2019 · In Android Jetpack development, closely-coupled UI screens are supposed to be implemented as fragments, and they might share a common ViewModel. The question is related to how to properly architect the MVVM based Compose app. The order details get displayed on an order summary screen and can be shared to another app to send the order. xml with the following. Jul 17, 2019 · After some research or discussion on architecture level and also report and issue github Koin,i found solution for this In this scenario,We should save that state/data into Repository which we need to share between multiple activities not in the viewModel and two or more different ViewModels can access same state/data that are saved in single instance of repository Oct 20, 2023 · The decision between a single activity and multiple activities is akin to selecting the blueprint for a house; it profoundly influences the flow, complexity, and scalability of the application Jul 22, 2019 · is there any way to pass custom ViewModel Factory class or any way to share same view model instance between multiple activities ? i need to share same ViewModel instance between 2 activities and i Jul 12, 2022 · Would it be good to have the necessary View Models for each screen so that each one has a single responsibility? This multiple View Model approach I believe would improve reusability, encapsulation, and fragmentation; since if two screens need to do the same action, there is no need to duplicate the code of the corresponding View Models or pass Sep 21, 2017 · I don't know what is your use case but in general I'd avoid connecting one ViewModel to the another. , Fragment or Activity). Can I share ViewModel between activities? You can’t share a ViewModel across Activities. Dec 11, 2021 · In fact you can have multiple view models for a single fragments doing different things for you. Although it is a good approach, but easy to be misused if not taken care of. One would be related to the rootActivity and second + third related directly to particular components like RecyclerView or UI stuff from particular ViewModel. Conclusion Single activity with multiple fragments, ViewModel, data binding, LiveaData and Jetpack Navigation This app contains an order flow for cupcakes with options for quantity, flavor, and pickup date. The second model will have a second live data. A Better Solution: The StateHolder Pattern Sep 1, 2015 · "A clean implementation of MVVM would seem to dictate that I'd have one model for every view model;" - I honestly don't think so. Share data using a ViewModel. 3. Both solutions rely on ViewModel, so it’s worth emphasizing a critical best practice: avoid references from the ViewModel to UI widgets or the Activity. xml will be the Oct 9, 2024 · 1. It helps separate the business logic and UI presentation concerns in your code for better organization. ️ Easier Data Sharing — Uses ViewModel Oct 9, 2018 · If you want to relay on ViewModel architecture, is better to have everything regarding requests, network and data things in view models. In the case of simply sharing the ViewModel rather than the ViewModel observing some source (whether that is the other ViewModels, or a shared object/repo), it seems to me that either: Each fragment must notify both its ViewModel and the shared ViewModel of changes, such that some data is duplicated. I recently saw a Koin Documentation h Jun 28, 2017 · The lifetime of the ViewModel is shown next to the associated Activity lifecycle. First thing is to have a navigation layout file for setting up the fragments and navigation actions, create a xml file at navigation/nav_graph. Then you start splitting apart functions into their viewmodel/ui counterparts with the strictly UI functions inside of the activity and the viewmodel related functions to the viewModel. We probably have to wait for Google to make it more mature Feb 9, 2024 · I want to use share same viewmodel instance in koin in jetpack compose navigation. g. Finally, create the new Fragment class Apr 30, 2022 · HENCE, the entire idea and need of multiple activities gets destroyed. ViewModel is an ideal choice when you need to share data between multiple fragments or between fragments and their host activity. In MVVM, the ViewModel acts as an intermediary between the View (UI) and the Model (data), allowing for enhanced testability and maintainability. This is the same reason Model-View-ViewModel (MVVM) is a software architectural pattern that has become very popular for building Android apps. Can two activities have same ViewModel?. I know there is a function in koinViewModel() to get instance of viewModel. Just like there can be several Views using the same view model, for example different layouts for different devices for the same interaction with data there can be several different view models for a single model, providing different interactions with the said data. Another approach is using a shared ViewModel instance across multiple fragments within the Aug 1, 2023 · Do you want to say when I scope my ViewModel to a Fragment, I get two instances per each Fragment, but when I scope ViewModel to a common activity, I get a single ViewModel across fragments? Another question is in case I have two instances of ViewModel, then why onCleared() call on the first fragment affects viewModelScope on the second fragment? Sep 15, 2020 · TL;DR: We can pass parameters to our ViewModel, use it as a data holder, also to share data between Fragments, and to persist its state across process recreation. 2. The activity_main. In this comprehensive guide, I‘ll teach you how to implement MVVM properly in your Android projects. Jun 4, 2021 · Anyone having any sample or any knowledge about how to architect multi screen app (say 30-35) in pure jetpack Compose with MVVM? Do you guys use single activity and single viewmodel and handle it there only? Or you prefer creating multiple activities or fragments?. When a ViewModel is shared across multiple screens, it may outlive the UI widgets or the Dec 22, 2022 · The other way is to have 1 ViewModel per composable, that can separate the logic, but it depends if you need to communicate data between them, if you need to communicate, you will need to send arguments between the navigation of each screen and live the ViewModels in the respective composable A View Model represents the state of the View. Dec 1, 2022 · View Models are encouraged by Google to share data between fragments in an activity. Do you use a single ViewModel for the whole app or multiple ? In the Single Activity (and navigation component) world of Google how do you choose to do multiple ViewModels ? Is it a much more practical approach to use a single ViewModel and multiple LiveData (per fragment) ? Jun 27, 2021 · If I understand your concern correctly, you want to have a single ViewModel that is used in multiple activities/fragments. If their state is different, then they should have separate View Models. By utilizing the same ViewModel across multiple fragments, each fragment gains access to the shared data and functionality encapsulated within the ViewModel. I have list of my To share the same ViewModel across different activities, you can use a shared ViewModel with a `ViewModelProvider` that is scoped to the application's lifecycle or an activity group like fragments within a single activity. However, in some cases Mar 3, 2025 · Let’s compare Single Activity vs Multiple Activities ️ Seamless Navigation — Jetpack Navigation Component handles transitions smoothly. Sharing a single ViewModel across multiple Views using @StateObject and @EnvironmentObject not only maintained consistent state but also streamlined my codebase, making it more organized and After some research or discussion on architecture level and also report and issue github Koin,i found solution for this In this scenario,We should save that state/data into Repository which we need to share between multiple activities not in the viewModel and two or more different ViewModels can access same state/data that are saved in single instance of repository Aug 7, 2021 · Also the compose navigation does NOT properly call onCleared() on view models which go out of screen. May 3, 2024 · Conclusion: By leveraging the shared ViewModel approach in Jetpack Compose, we can optimize the usage of ViewModel instances and avoid unnecessary recreation. The android developement is moving towards one activity with compsables as screens. The activity may want to present parts of multiple models and we could have a single view connected with multiple ViewModels. That’s specifically one of the downsides of using multiple activities as per the Single Activity talk. Hypothetically it would make sense for the fragment's viewmodel to get the "parent viewmodel" as a constructor argument, however due to the way ViewModels are initialized (lazily on first access) this is impossible, therefore yes, it's totally ok to have 2 VMs. The ViewModel is also in charge of handling events and delegating them to other layers of the hierarchy when business logic needs to be applied to modify application data. Single activity apps are more efficient too, since there's only one activity so you do not have to explicitly handle the data-flow between various activities. One way to achieve this using AndroidViewModel. When designing my apps, should I be using multiple ViewModels for different activities/fragments or should I be using a single ViewModel for all activities/fragments? The Model-View-ViewModel (MVVM) architecture is a powerful design pattern that facilitates clean separation of concerns in your Android applications, especially those involving multiple activities. the main point is to ease the communtication between screens and reduce overhead of activties. This is probably the usual case. This viewmodel will be binded to application lifecycle and same instance will be available through out the lifecycle of the application. A Better Solution: The StateHolder Pattern This post will demonstrate multiple fragments in an activity, a shared ViewModel across fragments, data binding, LiveData, and the Jetpack Navigation component. May 14, 2020 · I've recently started working on Android architecture components. Sep 16, 2022 · Shared viewmodel between multiple activities is not supported. Sep 1, 2024 · Using ViewModelProviders allows you to create a single instance of a ViewModel that can be shared across different fragments and activities. AFAIK ViewModels survive across activities via fragments You mean the way ViewModels survive configuration changes from one Activity instance to another (but still within the same Activity ofc)? It used to live in a retained fragment before the VM support merged into appcompat, afterwards it was added to the activity non-config just like the I would recommend that you move all the data model variables into a view model to start and change your references to the values in the view model. The Shared ViewModel approach uses a single ViewModel shared across multiple composable destinations to hold and pass data. Based on the missbehavior I experience, I would say that Google is working towards that (to bind the view model lifecycle to the compose navigation properly) but still not there. So all this logic from your example should be in viewModel. Jan 2, 2024 · We cannot share dependencies installed in ViewModelComponent between ViewModels, but we can nest the instance lifecycle of ViewModels so that a ViewModel associated with a parent navigation node Jun 28, 2023 · In Android’s MVVM (Model-View-ViewModel) architecture, it is common to break complex screens into multiple fragments, each with its own ViewModel and Contract class. I found MVVM architecture to be extremely handy, and I would like to master it. Create multiple ViewModels for the same UI component: Avoid creating multiple ViewModels for the same UI component (e. You just scope the ViewModel to the activity. Can a fragment reuse in multiple activities? Dec 22, 2020 · Iam trying to create shared view model between activity and the fragments. Jetpack Compose Sep 26, 2024 · Transitioning to SwiftUI brought its own set of challenges, but understanding and effectively utilizing ViewModels has been a significant milestone. This requires application instance. After 10+ years of professional Android development […] Feb 17, 2025 · Traditionally, Android apps were built using multiple activities, but with the introduction of Jetpack components, Single Activity Architecture has become the recommended approach. This is part of a multi-part Jan 10, 2025 · A Note on ViewModel Best Practices. 1. This leads to a more efficient and Apr 17, 2022 · The recommendation is use a single activity and navigate through screens using Navigation library. As you can see that the same ViewModel will be shared between multiple fragments, that’s hi guys, I'm trying to think through the best practices here. while indeed using a shared view model ease the communication between composables but this will happen only on small projects, large projects will require you to create multi viewmodels and back again to tiersome of After more consideration I agree that each model should get its own ViewModel. ViewModel in Single Activity Apr 9, 2024 · 5. Apr 9, 2019 · You can use shared view model of activity for fragments. . However, while building several ViewModels and Fragments, which reference those views it would make sense to reference few ViewModels in a single Fragment. Which item is selected, which panels are expanded, etc. For example, you have ItemActivity and it hosts ItemFragment for item preview and ItemEditFragment for editing. In the second activity you will get a different instance of that ViewModel, this time for your second Activity. I'd rather create another object and inject the same instance of it to the both ViewModels. Testing: A large shared ViewModel can become cumbersome to mock or verify. If you need more Oct 29, 2018 · The fact that LiveData objects are lifecycle-aware means that you can share them between multiple activities, fragments, and services. You should just observe final result, except if you want to show on UI also partial results. Can a ViewModel have multiple views? While a view should only have one viewmodel, a single viewmodel might be used by multiple views (imagine a wizard, for example, that has three views but all bind to the same viewmodel that drives the process). Shared ViewModel Approach. The ViewModel class is designed to store and manage UI-related data in a lifecycle-conscious way. gwwhg ezpa jzzybf izzx oxrgc ntiefb yzogw kxfeq jrjsrcp nthl