ViewModelProvider
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class ViewModelProvider
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open class ViewModelProvider
A utility class that manages the lifecycle, caching, and instantiation of ViewModel instances.
A ViewModelProvider acts as the central orchestrator that coordinates:
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Caching / Retrieval: It checks a
ViewModelStoreto see if an instance of the requestedViewModelclass already exists under a given key. If found, it returns the cached instance. -
Extras Injection: It automatically populates a
MutableCreationExtraswith the unique registration key underVIEW_MODEL_KEY, combining it with defaultCreationExtrasprovided by the owner. -
Instantiation: If no cached instance exists, it invokes a
ViewModelProvider.Factoryto create a new instance using the prepared extras, caches it in theViewModelStore, and returns it.
To ensure that ViewModel instances survive configuration changes, the underlying ViewModelStore must be retained (for example, by using a ViewModelStoreOwner such as ComponentActivity or Fragment which automatically handles this retention).
The following diagram illustrates the retrieval and creation flow of a ViewModel instance:
ViewModelProvider.get(key)
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v
Is ViewModel cached
in ViewModelStore?
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Yes No
/ \
v v
Return cached Create via Factory & CreationExtras,
ViewModel cache in ViewModelStore, and return
Summary
Nested types |
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Factory that creates |
interface ViewModelProvider.FactoryImplementations of the |
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Factory that creates |
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Simple factory, which calls empty constructor on the give class. |
Public companion functions |
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ViewModelProvider |
create(Creates a |
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ViewModelProvider |
create(Creates a |
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Public companion properties |
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CreationExtras.Key<String> |
A |
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Public constructors |
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ViewModelProvider(owner: ViewModelStoreOwner)Creates |
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ViewModelProvider(Creates a |
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ViewModelProvider(Creates a |
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Public functions |
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open operator T |
Returns an existing |
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operator T |
@MainThreadReturns an existing |
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open operator T |
Returns an existing |
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operator T |
@MainThreadReturns an existing |
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Extension functions |
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inline VM |
@MainThreadReturns an existing ViewModel or creates a new one in the scope (usually, a fragment or an activity), associated with this |
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inline VM |
@MainThreadReturns an existing ViewModel or creates a new one in the scope (usually, a fragment or an activity), associated with this |
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Public companion functions
create
fun create(
owner: ViewModelStoreOwner,
factory: ViewModelProvider.Factory = owner.defaultViewModelProviderFactory,
extras: CreationExtras = owner.defaultViewModelCreationExtras
): ViewModelProvider
Creates a ViewModelProvider bound to the given ViewModelStoreOwner.
The provider generates ViewModel instances using the specified Factory and stores them within the ViewModelStore of the ViewModelStoreOwner.
| Parameters | |
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owner: ViewModelStoreOwner |
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factory: ViewModelProvider.Factory = owner.defaultViewModelProviderFactory |
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extras: CreationExtras = owner.defaultViewModelCreationExtras |
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create
fun create(
store: ViewModelStore,
factory: ViewModelProvider.Factory = DefaultViewModelProviderFactory,
extras: CreationExtras = CreationExtras.Empty
): ViewModelProvider
Creates a ViewModelProvider backed by the given ViewModelStore.
The provider generates ViewModel instances using the specified Factory and stores them within the provided ViewModelStore.
| Parameters | |
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store: ViewModelStore |
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factory: ViewModelProvider.Factory = DefaultViewModelProviderFactory |
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extras: CreationExtras = CreationExtras.Empty |
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Public companion properties
VIEW_MODEL_KEY
val VIEW_MODEL_KEY: CreationExtras.Key<String>
A CreationExtras.Key used to retrieve the key associated with a requested ViewModel.
The ViewModelProvider automatically includes the key in the CreationExtras passed to ViewModelProvider.Factory. This applies to keys generated by either of these usage patterns:
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ViewModelProvider.get(key, MyViewModel::class): providedkeyis used. -
ViewModelProvider.get(MyViewModel::class): generates akeyfrom givenclass.
Public constructors
ViewModelProvider
ViewModelProvider(owner: ViewModelStoreOwner)
Creates ViewModelProvider. This will create ViewModel instances and retain them in the ViewModelStore of the given ViewModelStoreOwner.
This method will use the default factory if the owner implements HasDefaultViewModelProviderFactory. Otherwise, a NewInstanceFactory will be used.
ViewModelProvider
ViewModelProvider(
owner: ViewModelStoreOwner,
factory: ViewModelProvider.Factory
)
Creates a ViewModelProvider. This provider generates ViewModel instances using the specified Factory and stores them within the ViewModelStore of the provided ViewModelStoreOwner.
| Parameters | |
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owner: ViewModelStoreOwner |
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factory: ViewModelProvider.Factory |
ViewModelProvider
ViewModelProvider(
store: ViewModelStore,
factory: ViewModelProvider.Factory,
defaultCreationExtras: CreationExtras = CreationExtras.Empty
)
Creates a ViewModelProvider. This provider generates ViewModel instances using the specified Factory and stores them within the ViewModelStore of the provided ViewModelStoreOwner.
| Parameters | |
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store: ViewModelStore |
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factory: ViewModelProvider.Factory |
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defaultCreationExtras: CreationExtras = CreationExtras.Empty |
additional data to be passed to the |
Public functions
get
open operator fun <T : ViewModel> get(modelClass: Class<T>): T
Returns an existing ViewModel or creates a new one in the scope (usually, a Fragment or an Activity) associated with this ViewModelProvider.
The created ViewModel is associated with the given scope and will be retained as long as the scope is alive (e.g., if it is an Activity, until it is finished or the process is killed).
| Throws | |
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IllegalArgumentException |
if the given |
get
@MainThread
operator fun <T : ViewModel> get(modelClass: KClass<T>): T
Returns an existing ViewModel or creates a new one in the scope (usually, a Fragment or an Activity) associated with this ViewModelProvider.
The created ViewModel is associated with the given scope and is retained as long as the scope is alive (e.g., until the Activity is finished or the process is killed).
| Throws | |
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IllegalArgumentException |
if the given |
get
open operator fun <T : ViewModel> get(key: String, modelClass: Class<T>): T
Returns an existing ViewModel or creates a new one in the scope (usually, a Fragment or an Activity) associated with this ViewModelProvider.
The created ViewModel is associated with the given scope and will be retained as long as the scope is alive (e.g., if it is an Activity, until it is finished or the process is killed).
get
@MainThread
operator fun <T : ViewModel> get(key: String, modelClass: KClass<T>): T
Returns an existing ViewModel or creates a new one in the scope (usually, a Fragment or an Activity) associated with this ViewModelProvider.
The created ViewModel is associated with the given scope and is retained as long as the scope is alive (e.g., until the Activity is finished or the process is killed).
Extension functions
ViewModelProvider.get
@MainThread
inline fun <VM : ViewModel> ViewModelProvider.get(): VM
Returns an existing ViewModel or creates a new one in the scope (usually, a fragment or an activity), associated with this ViewModelProvider.
| See also | |
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get |
(Class) |
ViewModelProvider.get
@MainThread
inline fun <VM : ViewModel> ViewModelProvider.get(key: String): VM
Returns an existing ViewModel or creates a new one in the scope (usually, a fragment or an activity), associated with this ViewModelProvider and the given key.
| Parameters | |
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key: String |
The key to use to identify the ViewModel. |
| See also | |
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get |
(String, Class) |