ComponentCallbacks2

Kotlin |Java

interface ComponentCallbacks2 : ComponentCallbacks

android.content.ComponentCallbacks2

Known Direct Subclasses

Activity, Application, ContentProvider, Fragment, Service, VoiceInteractionSession

Activity	An activity is a single, focused thing that the user can do.
Application	Base class for maintaining global application state.
ContentProvider	Content providers are one of the primary building blocks of Android applications, providing content to applications.
Fragment	A Fragment is a piece of an application's user interface or behavior that can be placed in an `Activity`.
Service	A Service is an application component representing either an application's desire to perform a longer-running operation while not interacting with the user or to supply functionality for other applications to use.
VoiceInteractionSession	An active voice interaction session, providing a facility for the implementation to interact with the user in the voice interaction layer.

Known Indirect Subclasses

AbstractInputMethodService, AccessibilityService, AccountAuthenticatorActivity, ActivityGroup, AliasActivity, AutofillService, CallRedirectionService, CallScreeningService, CameraPrewarmService, CarrierMessagingClientService, CarrierMessagingService, CarrierService, and 54 others.

AbstractInputMethodService	AbstractInputMethodService provides a abstract base class for input methods.
AccessibilityService	Accessibility services should only be used to assist users with disabilities in using Android devices and apps.
AccountAuthenticatorActivity	Base class for implementing an Activity that is used to help implement an AbstractAccountAuthenticator.
ActivityGroup	A screen that contains and runs multiple embedded activities.
AliasActivity	Stub activity that launches another activity (and then finishes itself) based on information in its component's manifest meta-data.
AutofillService	An `AutofillService` is a service used to automatically fill the contents of the screen on behalf of a given user - for more information about autofill, read Autofill Framework.
CallRedirectionService	This service can be implemented to interact between Telecom and its implementor for making outgoing call with optional redirection/cancellation purposes.
CallScreeningService	This service can be implemented by the default dialer (see `TelecomManager#getDefaultDialerPackage()`) or a third party app to allow or disallow incoming calls before they are shown to a user.
CameraPrewarmService	Extend this class to implement a camera prewarm service.
CarrierMessagingClientService	If the default SMS app has a service that extends this class, the system always tries to bind it so that the process is always running, which allows the app to have a persistent connection to the server.
CarrierMessagingService	A service that receives calls from the system when new SMS and MMS are sent or received.
CarrierService	A service that exposes carrier-specific functionality to the system.
ChooserTargetService	A service that receives calls from the system when the user is asked to choose a target for an intent explicitly by another app.
CloudMediaProvider	Base class for a cloud media provider.
CompanionDeviceService	A service that receives calls from the system with device events.
ConditionProviderService	A service that provides conditions about boolean state.
ConnectionService	An abstract service that should be implemented by any apps which either: Can make phone calls (VoIP or otherwise) and want those calls to be integrated into the built-in phone app. Referred to as a system managed `ConnectionService`. Are a standalone calling app and don't want their calls to be integrated into the built-in phone app. Referred to as a self managed `ConnectionService`. Once implemented, the needs to take the following steps so that Telecom will bind to it:
ControlsProviderService	Service implementation allowing applications to contribute controls to the System UI.
CredentialProviderService	Service to be extended by credential providers, in order to return user credentials to the framework.
DeviceAdminService	Base class for a service that device owner/profile owners can optionally have.
DialogFragment	A fragment that displays a dialog window, floating on top of its activity's window.
DocumentsProvider	Base class for a document provider.
DreamService	Extend this class to implement a custom dream (available to the user as a "Daydream").
ExpandableListActivity	An activity that displays an expandable list of items by binding to a data source implementing the ExpandableListAdapter, and exposes event handlers when the user selects an item.
HostApduService	HostApduService is a convenience `Service` class that can be extended to emulate an NFC card inside an Android service component.
HostNfcFService	HostNfcFService is a convenience `Service` class that can be extended to emulate an NFC-F card inside an Android service component.
InCallService	This service is implemented by an app that wishes to provide functionality for managing phone calls.
InputMethodService	InputMethodService provides a standard implementation of an InputMethod, which final implementations can derive from and customize.
IntentService	IntentService is an extension of the `Service` component class that handles asynchronous requests (expressed as `Intent`s) on demand.
IsolatedService	Base class for services that are started by ODP on a call to `OnDevicePersonalizationManager#execute(ComponentName, PersistableBundle, java.util.concurrent.Executor, OutcomeReceiver)` and run in an isolated process.
JobService	Entry point for the callback from the `android.app.job.JobScheduler`.
LauncherActivity	Displays a list of all activities which can be performed for a given intent.
ListActivity	An activity that displays a list of items by binding to a data source such as an array or Cursor, and exposes event handlers when the user selects an item.
ListFragment	A fragment that displays a list of items by binding to a data source such as an array or Cursor, and exposes event handlers when the user selects an item.
MediaBrowserService	Base class for media browser services.
MediaRoute2ProviderService	Base class for media route provider services.
MediaSession2Service	This API is not generally intended for third party application developers.
MidiDeviceService	A service that implements a virtual MIDI device.
MidiUmpDeviceService	A service that implements a virtual MIDI device for Universal MIDI Packets (UMP).
MockApplication	A mock `android.app.Application` class.
MockContentProvider	Mock implementation of ContentProvider.
NativeActivity	Convenience for implementing an activity that will be implemented purely in native code.
NotificationListenerService	A service that receives calls from the system when new notifications are posted or removed, or their ranking changed.
OffHostApduService	OffHostApduService is a convenience `Service` class that can be extended to describe one or more NFC applications that are residing off-host, for example on an embedded secure element or a UICC.
PreferenceActivity	This is the base class for an activity to show a hierarchy of preferences to the user.
PreferenceFragment	Shows a hierarchy of `Preference` objects as lists.
PrintService	This is the base class for implementing print services.
QuickAccessWalletService	A `QuickAccessWalletService` provides a list of `WalletCard`s shown in the Quick Access Wallet.
RecognitionService	This class provides a base class for recognition service implementations.
RemoteViewsService	The service to be connected to for a remote adapter to request RemoteViews.
SearchRecentSuggestionsProvider	This superclass can be used to create a simple search suggestions provider for your application.
SettingInjectorService	Dynamically specifies the summary (subtitle) and enabled status of a preference injected into the list of app settings displayed by the system settings app
SliceProvider	A SliceProvider allows an app to provide content to be displayed in system spaces.
SpellCheckerService	SpellCheckerService provides an abstract base class for a spell checker.
TabActivity	For apps developing against `android.os.Build.VERSION_CODES#HONEYCOMB` or later, tabs are typically presented in the UI using the new `ActionBar.newTab()` and related APIs for placing tabs within their action bar area.
TextToSpeechService	Abstract base class for TTS engine implementations.
TileService	A TileService provides the user a tile that can be added to Quick Settings.
TvInputService	The TvInputService class represents a TV input or source such as HDMI or built-in tuner which provides pass-through video or broadcast TV programs.
TvInteractiveAppService	A TV interactive application service is a service that provides runtime environment and runs TV interactive applications.
VisualVoicemailService	This service is implemented by dialer apps that wishes to handle OMTP or similar visual voicemails.
VoiceInteractionService	Top-level service of the current global voice interactor, which is providing support for hotwording, the back-end of a `android.app.VoiceInteractor`, etc.
VoiceInteractionSessionService	An active voice interaction session, initiated by a `VoiceInteractionService`.
VpnService	VpnService is a base class for applications to extend and build their own VPN solutions.
VrListenerService	A service that is bound from the system while running in virtual reality (VR) mode.
WallpaperService	A wallpaper service is responsible for showing a live wallpaper behind applications that would like to sit on top of it.
WebViewFragment	A fragment that displays a WebView.

Extended ComponentCallbacks interface with a new callback for finer-grained memory management. This interface is available in all application components (android.app.Activity, android.app.Service, ContentProvider, and android.app.Application).

You should implement onTrimMemory to incrementally release memory based on current system constraints. Using this callback to release your resources helps provide a more responsive system overall, but also directly benefits the user experience for your app by allowing the system to keep your process alive longer. That is, if you don't trim your resources based on memory levels defined by this callback, the system is more likely to kill your process while it is cached in the least-recently used (LRU) list, thus requiring your app to restart and restore all state when the user returns to it.

The values provided by onTrimMemory do not represent a single linear progression of memory limits, but provide you different types of clues about memory availability:

When your app is running:
1. TRIM_MEMORY_RUNNING_MODERATE
  The device is beginning to run low on memory. Your app is running and not killable.
2. TRIM_MEMORY_RUNNING_LOW
  The device is running much lower on memory. Your app is running and not killable, but please release unused resources to improve system performance (which directly impacts your app's performance).
3. TRIM_MEMORY_RUNNING_CRITICAL
  The device is running extremely low on memory. Your app is not yet considered a killable process, but the system will begin killing background processes if apps do not release resources, so you should release non-critical resources now to prevent performance degradation.
When your app's visibility changes:
1. TRIM_MEMORY_UI_HIDDEN
  Your app's UI is no longer visible, so this is a good time to release large resources that are used only by your UI.
When your app's process resides in the background LRU list:
1. TRIM_MEMORY_BACKGROUND
  The system is running low on memory and your process is near the beginning of the LRU list. Although your app process is not at a high risk of being killed, the system may already be killing processes in the LRU list, so you should release resources that are easy to recover so your process will remain in the list and resume quickly when the user returns to your app.
2. TRIM_MEMORY_MODERATE
  The system is running low on memory and your process is near the middle of the LRU list. If the system becomes further constrained for memory, there's a chance your process will be killed.
3. TRIM_MEMORY_COMPLETE
  The system is running low on memory and your process is one of the first to be killed if the system does not recover memory now. You should release absolutely everything that's not critical to resuming your app state.
  To support API levels lower than 14, you can use the onLowMemory method as a fallback that's roughly equivalent to the ComponentCallbacks2#TRIM_MEMORY_COMPLETE level.
Note: When the system begins killing processes in the LRU list, although it primarily works bottom-up, it does give some consideration to which processes are consuming more memory and will thus provide more gains in memory if killed. So the less memory you consume while in the LRU list overall, the better your chances are to remain in the list and be able to quickly resume.

More information about the different stages of a process lifecycle (such as what it means to be placed in the background LRU list) is provided in the Processes and Threads document.

Summary

Constants
static Int	`TRIM_MEMORY_BACKGROUND` Level for `onTrimMemory(int)`: the process has gone on to the LRU list.
static Int	`TRIM_MEMORY_COMPLETE` Level for `onTrimMemory(int)`: the process is nearing the end of the background LRU list, and if more memory isn't found soon it will be killed.
static Int	`TRIM_MEMORY_MODERATE` Level for `onTrimMemory(int)`: the process is around the middle of the background LRU list; freeing memory can help the system keep other processes running later in the list for better overall performance.
static Int	`TRIM_MEMORY_RUNNING_CRITICAL` Level for `onTrimMemory(int)`: the process is not an expendable background process, but the device is running extremely low on memory and is about to not be able to keep any background processes running.
static Int	`TRIM_MEMORY_RUNNING_LOW` Level for `onTrimMemory(int)`: the process is not an expendable background process, but the device is running low on memory.
static Int	`TRIM_MEMORY_RUNNING_MODERATE` Level for `onTrimMemory(int)`: the process is not an expendable background process, but the device is running moderately low on memory.
static Int	`TRIM_MEMORY_UI_HIDDEN` Level for `onTrimMemory(int)`: the process had been showing a user interface, and is no longer doing so.

Public methods
abstract Unit	`onTrimMemory(level: Int)` Called when the operating system has determined that it is a good time for a process to trim unneeded memory from its process.

Inherited functions

From class ComponentCallbacks

Unit

onConfigurationChanged(newConfig: Configuration)

Called by the system when the device configuration changes while your component is running. Note that, unlike activities, other components are never restarted when a configuration changes: they must always deal with the results of the change, such as by re-retrieving resources.

At the time that this function has been called, your Resources object will have been updated to return resource values matching the new configuration.

For more information, read Handling Runtime Changes.

Unit

onLowMemory()

This is called when the overall system is running low on memory, and actively running processes should trim their memory usage. While the exact point at which this will be called is not defined, generally it will happen when all background process have been killed. That is, before reaching the point of killing processes hosting service and foreground UI that we would like to avoid killing.

Constants

TRIM_MEMORY_BACKGROUND

Added in API level 14

static val TRIM_MEMORY_BACKGROUND: Int

Level for onTrimMemory(int): the process has gone on to the LRU list. This is a good opportunity to clean up resources that can efficiently and quickly be re-built if the user returns to the app.

Value: 40