Loader

Kotlin |Java

open class Loader<D : Any!>

kotlin.Any
↳	androidx.loader.content.Loader

Known Direct Subclasses AsyncTaskLoader AsyncTaskLoader Static library support version of the framework's android.content.AsyncTaskLoader.

Known Indirect Subclasses CursorLoader CursorLoader Static library support version of the framework's android.content.CursorLoader.

Static library support version of the framework's android.content.Loader. Used to write apps that run on platforms prior to Android 3.0. When running on Android 3.0 or above, this implementation is still used; it does not try to switch to the framework's implementation. See the framework SDK documentation for a class overview.

Summary

Nested classes
	ForceLoadContentObserver An implementation of a ContentObserver that takes care of connecting it to the Loader to have the loader re-load its data when the observer is told it has changed.
abstract	OnLoadCanceledListener Interface that is implemented to discover when a Loader has been canceled before it finished loading its data.
abstract	OnLoadCompleteListener Interface that is implemented to discover when a Loader has finished loading its data.

Public constructors
<init>(@NonNull context: Context) Stores away the application context associated with context.

Public methods
open Unit	abandon() This function will normally be called for you automatically by LoaderManager when restarting a Loader.
open Boolean	cancelLoad() Attempt to cancel the current load task.
open Unit	commitContentChanged() Commit that you have actually fully processed a content change that was returned by takeContentChanged.
open String	dataToString(@Nullable data: D?) For debugging, converts an instance of the Loader's data class to a string that can be printed.
open Unit	deliverCancellation() Informs the registered OnLoadCanceledListener that the load has been canceled.
open Unit	deliverResult(@Nullable data: D?) Sends the result of the load to the registered listener.
open Unit	dump(prefix: String!, fd: FileDescriptor!, writer: PrintWriter!, args: Array<String!>!) Print the Loader's state into the given stream.
open Unit	forceLoad() Force an asynchronous load.
open Context	getContext()
open Int	getId()
open Boolean	isAbandoned() Return whether this loader has been abandoned.
open Boolean	isReset() Return whether this load has been reset.
open Boolean	isStarted() Return whether this load has been started.
open Unit	onContentChanged() Called when ForceLoadContentObserver detects a change.
open Unit	registerListener(id: Int, @NonNull listener: Loader.OnLoadCompleteListener<D>) Registers a class that will receive callbacks when a load is complete.
open Unit	registerOnLoadCanceledListener(@NonNull listener: Loader.OnLoadCanceledListener<D>) Registers a listener that will receive callbacks when a load is canceled.
open Unit	reset() This function will normally be called for you automatically by LoaderManager when destroying a Loader.
open Unit	rollbackContentChanged() Report that you have abandoned the processing of a content change that was returned by takeContentChanged() and would like to rollback to the state where there is again a pending content change.
Unit	startLoading() This function will normally be called for you automatically by LoaderManager when the associated fragment/activity is being started.
open Unit	stopLoading() This function will normally be called for you automatically by LoaderManager when the associated fragment/activity is being stopped.
open Boolean	takeContentChanged() Take the current flag indicating whether the loader's content had changed while it was stopped.
open String	toString()
open Unit	unregisterListener(@NonNull listener: Loader.OnLoadCompleteListener<D>) Remove a listener that was previously added with registerListener.
open Unit	unregisterOnLoadCanceledListener(@NonNull listener: Loader.OnLoadCanceledListener<D>) Unregisters a listener that was previously added with registerOnLoadCanceledListener.

Protected methods
open Unit	onAbandon() Subclasses implement this to take care of being abandoned.
open Boolean	onCancelLoad() Subclasses must implement this to take care of requests to cancelLoad().
open Unit	onForceLoad() Subclasses must implement this to take care of requests to forceLoad().
open Unit	onReset() Subclasses must implement this to take care of resetting their loader, as per reset().
open Unit	onStartLoading() Subclasses must implement this to take care of loading their data, as per startLoading().
open Unit	onStopLoading() Subclasses must implement this to take care of stopping their loader, as per stopLoading().

Public constructors

<init>

Loader(@NonNull context: Context)

Stores away the application context associated with context. Since Loaders can be used across multiple activities it's dangerous to store the context directly; always use getContext() to retrieve the Loader's Context, don't use the constructor argument directly. The Context returned by getContext is safe to use across Activity instances.

Parameters
context	Context: used to retrieve the application context.

Public methods

abandon

@MainThread open fun abandon(): Unit

This function will normally be called for you automatically by LoaderManager when restarting a Loader. When using a Loader with LoaderManager, you must not call this method yourself, or you will conflict with its management of the Loader. Tell the Loader that it is being abandoned. This is called prior to reset to have it retain its current data but not report any new data.

Must be called from the process's main thread.

cancelLoad

@MainThread open fun cancelLoad(): Boolean

Attempt to cancel the current load task. Must be called on the main thread of the process.

Cancellation is not an immediate operation, since the load is performed in a background thread. If there is currently a load in progress, this method requests that the load be canceled, and notes this is the case; once the background thread has completed its work its remaining state will be cleared. If another load request comes in during this time, it will be held until the canceled load is complete.

Return
Boolean	Returns false if the task could not be canceled, typically because it has already completed normally, or because startLoading() hasn't been called; returns true otherwise. When true is returned, the task is still running and the OnLoadCanceledListener will be called when the task completes.

commitContentChanged

open fun commitContentChanged(): Unit

Commit that you have actually fully processed a content change that was returned by takeContentChanged. This is for use with rollbackContentChanged() to handle situations where a load is cancelled. Call this when you have completely processed a load without it being cancelled.

dataToString

@NonNull open fun dataToString(@Nullable data: D?): String

For debugging, converts an instance of the Loader's data class to a string that can be printed. Must handle a null data.

deliverCancellation

@MainThread open fun deliverCancellation(): Unit

Informs the registered OnLoadCanceledListener that the load has been canceled. Should only be called by subclasses. Must be called from the process's main thread.

deliverResult

@MainThread open fun deliverResult(@Nullable data: D?): Unit

Sends the result of the load to the registered listener. Should only be called by subclasses. Must be called from the process's main thread.

Parameters
data	D?: the result of the load

dump

open fun dump(
    prefix: String!, 
    fd: FileDescriptor!, 
    writer: PrintWriter!, 
    args: Array<String!>!
): Unit

Deprecated: Consider using LoaderManager#enableDebugLogging(boolean) to understand the series of operations performed by LoaderManager.

Print the Loader's state into the given stream.

Parameters
prefix	String!: Text to print at the front of each line.
fd	FileDescriptor!: The raw file descriptor that the dump is being sent to.
writer	PrintWriter!: A PrintWriter to which the dump is to be set.
args	Array<String!>!: Additional arguments to the dump request.

forceLoad

@MainThread open fun forceLoad(): Unit

Force an asynchronous load. Unlike startLoading() this will ignore a previously loaded data set and load a new one. This simply calls through to the implementation's onForceLoad(). You generally should only call this when the loader is started -- that is, isStarted() returns true.

Must be called from the process's main thread.

getContext

@NonNull open fun getContext(): Context

Return
Context	an application context retrieved from the Context passed to the constructor.

getId

open fun getId(): Int

Return
Int	the ID of this loader

isAbandoned

open fun isAbandoned(): Boolean

Return whether this loader has been abandoned. In this state, the loader must not report any new data, and must keep its last reported data valid until it is finally reset.

isReset

open fun isReset(): Boolean

Return whether this load has been reset. That is, either the loader has not yet been started for the first time, or its reset() has been called.

isStarted

open fun isStarted(): Boolean

Return whether this load has been started. That is, its startLoading() has been called and no calls to stopLoading() or reset() have yet been made.

onContentChanged

@MainThread open fun onContentChanged(): Unit

Called when ForceLoadContentObserver detects a change. The default implementation checks to see if the loader is currently started; if so, it simply calls forceLoad(); otherwise, it sets a flag so that takeContentChanged() returns true.

Must be called from the process's main thread.

registerListener

@MainThread open fun registerListener(
    id: Int, 
    @NonNull listener: Loader.OnLoadCompleteListener<D>
): Unit

Registers a class that will receive callbacks when a load is complete. The callback will be called on the process's main thread so it's safe to pass the results to widgets.

Must be called from the process's main thread.

registerOnLoadCanceledListener

@MainThread open fun registerOnLoadCanceledListener(@NonNull listener: Loader.OnLoadCanceledListener<D>): Unit

Registers a listener that will receive callbacks when a load is canceled. The callback will be called on the process's main thread so it's safe to pass the results to widgets. Must be called from the process's main thread.

Parameters
listener	Loader.OnLoadCanceledListener<D>: The listener to register.

reset

@MainThread open fun reset(): Unit

This function will normally be called for you automatically by LoaderManager when destroying a Loader. When using a Loader with LoaderManager, you must not call this method yourself, or you will conflict with its management of the Loader. Resets the state of the Loader. The Loader should at this point free all of its resources, since it may never be called again; however, its startLoading() may later be called at which point it must be able to start running again.

This updates the Loader's internal state so that isStarted() and isReset() will return the correct values, and then calls the implementation's onReset().

Must be called from the process's main thread.

rollbackContentChanged

open fun rollbackContentChanged(): Unit

Report that you have abandoned the processing of a content change that was returned by takeContentChanged() and would like to rollback to the state where there is again a pending content change. This is to handle the case where a data load due to a content change has been canceled before its data was delivered back to the loader.

startLoading

@MainThread fun startLoading(): Unit

This function will normally be called for you automatically by LoaderManager when the associated fragment/activity is being started. When using a Loader with LoaderManager, you must not call this method yourself, or you will conflict with its management of the Loader. Starts an asynchronous load of the Loader's data. When the result is ready the callbacks will be called on the process's main thread. If a previous load has been completed and is still valid the result may be passed to the callbacks immediately. The loader will monitor the source of the data set and may deliver future callbacks if the source changes. Calling stopLoading will stop the delivery of callbacks.

This updates the Loader's internal state so that isStarted() and isReset() will return the correct values, and then calls the implementation's onStartLoading().

Must be called from the process's main thread.

stopLoading

@MainThread open fun stopLoading(): Unit

This function will normally be called for you automatically by LoaderManager when the associated fragment/activity is being stopped. When using a Loader with LoaderManager, you must not call this method yourself, or you will conflict with its management of the Loader.

Stops delivery of updates until the next time startLoading() is called. Implementations should not invalidate their data at this point -- clients are still free to use the last data the loader reported. They will, however, typically stop reporting new data if the data changes; they can still monitor for changes, but must not report them to the client until and if startLoading() is later called.

This updates the Loader's internal state so that isStarted() will return the correct value, and then calls the implementation's onStopLoading().

Must be called from the process's main thread.

takeContentChanged

open fun takeContentChanged(): Boolean

Take the current flag indicating whether the loader's content had changed while it was stopped. If it had, true is returned and the flag is cleared.

toString

@NonNull open fun toString(): String

unregisterListener

@MainThread open fun unregisterListener(@NonNull listener: Loader.OnLoadCompleteListener<D>): Unit

Remove a listener that was previously added with registerListener. Must be called from the process's main thread.

unregisterOnLoadCanceledListener

@MainThread open fun unregisterOnLoadCanceledListener(@NonNull listener: Loader.OnLoadCanceledListener<D>): Unit

Unregisters a listener that was previously added with registerOnLoadCanceledListener. Must be called from the process's main thread.

Parameters
listener	Loader.OnLoadCanceledListener<D>: The listener to unregister.

Protected methods

onAbandon

@MainThread protected open fun onAbandon(): Unit

Subclasses implement this to take care of being abandoned. This is an optional intermediate state prior to onReset() -- it means that the client is no longer interested in any new data from the loader, so the loader must not report any further updates. However, the loader must keep its last reported data valid until the final onReset() happens. You can retrieve the current abandoned state with isAbandoned. This will always be called from the process's main thread.

onCancelLoad

@MainThread protected open fun onCancelLoad(): Boolean

Subclasses must implement this to take care of requests to cancelLoad(). This will always be called from the process's main thread.

Return
Boolean	Returns false if the task could not be canceled, typically because it has already completed normally, or because startLoading() hasn't been called; returns true otherwise. When true is returned, the task is still running and the OnLoadCanceledListener will be called when the task completes.

onForceLoad

@MainThread protected open fun onForceLoad(): Unit

Subclasses must implement this to take care of requests to forceLoad(). This will always be called from the process's main thread.

onReset

@MainThread protected open fun onReset(): Unit

Subclasses must implement this to take care of resetting their loader, as per reset(). This is not called by clients directly, but as a result of a call to reset(). This will always be called from the process's main thread.

onStartLoading

@MainThread protected open fun onStartLoading(): Unit

Subclasses must implement this to take care of loading their data, as per startLoading(). This is not called by clients directly, but as a result of a call to startLoading(). This will always be called from the process's main thread.

onStopLoading

@MainThread protected open fun onStopLoading(): Unit

Subclasses must implement this to take care of stopping their loader, as per stopLoading(). This is not called by clients directly, but as a result of a call to stopLoading(). This will always be called from the process's main thread.