BackgroundThreadStateHandler

Artifact: androidx.media3:media3-common

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Kotlin |Java

@UnstableApi
public final class BackgroundThreadStateHandler<T extends Object>

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Helper class to handle state updates on a background thread while maintaining a placeholder state on the foreground thread.

Parameters
<T extends Object>	An immutable object representing the entire state. Must implement equals.

Summary

Nested types
public interface BackgroundThreadStateHandler.StateChangeListener<T extends Object> An interface to handle changes to the state on the foreground thread.

Public constructors
BackgroundThreadStateHandler(     T initialState,     Looper backgroundLooper,     Looper foregroundLooper,     Clock clock,     BackgroundThreadStateHandler.StateChangeListener<T> onStateChanged ) Creates the helper for background thread state updates.

Public methods
T	get() Returns the current state.
void	runInBackground(Runnable runnable) Runs the provided Runnable on the background thread.
void	setStateInBackground(T newState) Updates the background state directly, independent to any operation started from the foreground thread.
void	updateStateAsync(     Function<T, T> placeholderState,     Function<T, T> backgroundStateUpdate ) Starts an asynchronous state update.

Public constructors

BackgroundThreadStateHandler

public BackgroundThreadStateHandler(
    T initialState,
    Looper backgroundLooper,
    Looper foregroundLooper,
    Clock clock,
    BackgroundThreadStateHandler.StateChangeListener<T> onStateChanged
)

Creates the helper for background thread state updates.

This constructor may be called on any thread.

Parameters
T initialState	The initial state value.
Looper backgroundLooper	The Looper to run background operations on.
Looper foregroundLooper	The Looper to run foreground operations on.
Clock clock	The Clock to control the handler messages.
BackgroundThreadStateHandler.StateChangeListener<T> onStateChanged	The StateChangeListener to listen to state changes.

Public methods

get

public T get()

Returns the current state.

Can be called on either the foreground or background thread, returning the respective current state of this thread.

runInBackground

public void runInBackground(Runnable runnable)

Runs the provided Runnable on the background thread.

Can be called from any thread.

Note: This method is useful to update the state on the background using setStateInBackground for events arriving from external sources. Use updateStateAsync if the intention is update the state in response the a foreground thread method call.

Parameters
Runnable runnable	The Runnable to be called on the background thread.

setStateInBackground

public void setStateInBackground(T newState)

Updates the background state directly, independent to any operation started from the foreground thread.

Must only be called on the background thread.

Parameters
T newState	The new state.

updateStateAsync

public void updateStateAsync(
    Function<T, T> placeholderState,
    Function<T, T> backgroundStateUpdate
)

Starts an asynchronous state update.

Must only be called on the foreground thread.

Parameters
Function<T, T> placeholderState	A function to create a placeholder state from the current state while the operation is pending. Will be called on the foreground thread.
Function<T, T> backgroundStateUpdate	A function to handle the background state update, taking in the current background state and returning the updated state. Will be called on the background thread.