Loader

Artifact: androidx.loader:loader

View Source

Added in 1.0.0

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Kotlin |Java

class Loader<D>

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.

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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 types
inner class Loader.ForceLoadContentObserver : ContentObserver 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.
interface Loader.OnLoadCanceledListener<D> Interface that is implemented to discover when a Loader has been canceled before it finished loading its data.
interface Loader.OnLoadCompleteListener<D> Interface that is implemented to discover when a Loader has finished loading its data.

Public constructors
Loader(context: Context) Stores away the application context associated with context.

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

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

Public constructors

Loader

Added in 1.0.0

Loader(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 functions

abandon

Added in 1.0.0

@MainThread
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

Added in 1.0.0

@MainThread
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.

Returns
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

Added in 1.0.0

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

Added in 1.0.0

fun dataToString(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

Added in 1.0.0

@MainThread
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

Added in 1.0.0

@MainThread
fun deliverResult(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

Added in 1.0.0

Deprecated in 1.0.0

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

This function is deprecated.

Consider using enableDebugLogging 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

Added in 1.0.0

@MainThread
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

Added in 1.0.0

fun getContext(): Context

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

getId

Added in 1.0.0

fun getId(): Int

Returns
Int	the ID of this loader

isAbandoned

Added in 1.0.0

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

Added in 1.0.0

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

Added in 1.0.0

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

Added in 1.0.0

@MainThread
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

Added in 1.0.0

@MainThread
fun registerListener(id: Int, 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

Added in 1.0.0

@MainThread
fun registerOnLoadCanceledListener(
    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

Added in 1.0.0

@MainThread
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

Added in 1.0.0

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

Added in 1.0.0

@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

Added in 1.0.0

@MainThread
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

Added in 1.0.0

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

fun toString(): String

unregisterListener

Added in 1.0.0

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

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

unregisterOnLoadCanceledListener

Added in 1.0.0

@MainThread
fun unregisterOnLoadCanceledListener(
    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 functions

onAbandon

Added in 1.0.0

@MainThread
protected 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

Added in 1.0.0

@MainThread
protected 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.

Returns
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

Added in 1.0.0

@MainThread
protected 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

Added in 1.0.0

@MainThread
protected 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

Added in 1.0.0

@MainThread
protected 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

Added in 1.0.0

@MainThread
protected 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.