Android APIs
public final class

MessageQueue

extends Object
java.lang.Object
   ↳ android.os.MessageQueue

Class Overview

Low-level class holding the list of messages to be dispatched by a Looper. Messages are not added directly to a MessageQueue, but rather through Handler objects associated with the Looper.

You can retrieve the MessageQueue for the current thread with Looper.myQueue().

Summary

Nested Classes
interface MessageQueue.IdleHandler Callback interface for discovering when a thread is going to block waiting for more messages. 
interface MessageQueue.OnFileDescriptorEventListener A listener which is invoked when file descriptor related events occur. 
Public Methods
void addIdleHandler(MessageQueue.IdleHandler handler)
Add a new MessageQueue.IdleHandler to this message queue.
void addOnFileDescriptorEventListener(FileDescriptor fd, int events, MessageQueue.OnFileDescriptorEventListener listener)
Adds a file descriptor listener to receive notification when file descriptor related events occur.
boolean isIdle()
Returns true if the looper has no pending messages which are due to be processed.
void removeIdleHandler(MessageQueue.IdleHandler handler)
Remove an MessageQueue.IdleHandler from the queue that was previously added with addIdleHandler(MessageQueue.IdleHandler).
void removeOnFileDescriptorEventListener(FileDescriptor fd)
Removes a file descriptor listener.
Protected Methods
void finalize()
Invoked when the garbage collector has detected that this instance is no longer reachable.
[Expand]
Inherited Methods
From class java.lang.Object

Public Methods

public void addIdleHandler (MessageQueue.IdleHandler handler)

Added in API level 1

Add a new MessageQueue.IdleHandler to this message queue. This may be removed automatically for you by returning false from IdleHandler.queueIdle() when it is invoked, or explicitly removing it with removeIdleHandler(MessageQueue.IdleHandler).

This method is safe to call from any thread.

Parameters
handler The IdleHandler to be added.

public void addOnFileDescriptorEventListener (FileDescriptor fd, int events, MessageQueue.OnFileDescriptorEventListener listener)

Added in API level 23

Adds a file descriptor listener to receive notification when file descriptor related events occur.

If the file descriptor has already been registered, the specified events and listener will replace any that were previously associated with it. It is not possible to set more than one listener per file descriptor.

It is important to always unregister the listener when the file descriptor is no longer of use.

Parameters
fd The file descriptor for which a listener will be registered.
events The set of events to receive: a combination of the EVENT_INPUT, EVENT_OUTPUT, and EVENT_ERROR event masks. If the requested set of events is zero, then the listener is unregistered.
listener The listener to invoke when file descriptor events occur.

public boolean isIdle ()

Added in API level 23

Returns true if the looper has no pending messages which are due to be processed.

This method is safe to call from any thread.

Returns
boolean True if the looper is idle.

public void removeIdleHandler (MessageQueue.IdleHandler handler)

Added in API level 1

Remove an MessageQueue.IdleHandler from the queue that was previously added with addIdleHandler(MessageQueue.IdleHandler). If the given object is not currently in the idle list, nothing is done.

This method is safe to call from any thread.

Parameters
handler The IdleHandler to be removed.

public void removeOnFileDescriptorEventListener (FileDescriptor fd)

Added in API level 23

Removes a file descriptor listener.

This method does nothing if no listener has been registered for the specified file descriptor.

Parameters
fd The file descriptor whose listener will be unregistered.

Protected Methods

protected void finalize ()

Added in API level 1

Invoked when the garbage collector has detected that this instance is no longer reachable. The default implementation does nothing, but this method can be overridden to free resources.

Note that objects that override finalize are significantly more expensive than objects that don't. Finalizers may be run a long time after the object is no longer reachable, depending on memory pressure, so it's a bad idea to rely on them for cleanup. Note also that finalizers are run on a single VM-wide finalizer thread, so doing blocking work in a finalizer is a bad idea. A finalizer is usually only necessary for a class that has a native peer and needs to call a native method to destroy that peer. Even then, it's better to provide an explicit close method (and implement Closeable), and insist that callers manually dispose of instances. This works well for something like files, but less well for something like a BigInteger where typical calling code would have to deal with lots of temporaries. Unfortunately, code that creates lots of temporaries is the worst kind of code from the point of view of the single finalizer thread.

If you must use finalizers, consider at least providing your own ReferenceQueue and having your own thread process that queue.

Unlike constructors, finalizers are not automatically chained. You are responsible for calling super.finalize() yourself.

Uncaught exceptions thrown by finalizers are ignored and do not terminate the finalizer thread. See Effective Java Item 7, "Avoid finalizers" for more.

Throws
Throwable