Skip to content

Most visited

Recently visited

navigation

MessageQueue

public final class MessageQueue
extends Object

java.lang.Object
   ↳ android.os.MessageQueue


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()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.

Inherited methods

From class java.lang.Object

Public methods

addIdleHandler

Added in API level 1
void addIdleHandler (MessageQueue.IdleHandler handler)

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 MessageQueue.IdleHandler: The IdleHandler to be added.

addOnFileDescriptorEventListener

Added in API level 23
void addOnFileDescriptorEventListener (FileDescriptor fd, 
                int events, 
                MessageQueue.OnFileDescriptorEventListener listener)

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 FileDescriptor: The file descriptor for which a listener will be registered.
events int: 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 MessageQueue.OnFileDescriptorEventListener: The listener to invoke when file descriptor events occur.

See also:

isIdle

Added in API level 23
boolean isIdle ()

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.

removeIdleHandler

Added in API level 1
void removeIdleHandler (MessageQueue.IdleHandler handler)

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 MessageQueue.IdleHandler: The IdleHandler to be removed.

removeOnFileDescriptorEventListener

Added in API level 23
void removeOnFileDescriptorEventListener (FileDescriptor fd)

Removes a file descriptor listener.

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

Parameters
fd FileDescriptor: The file descriptor whose listener will be unregistered.

See also:

Protected methods

finalize

Added in API level 1
void finalize ()

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object. A subclass overrides the finalize method to dispose of system resources or to perform other cleanup.

The general contract of finalize is that it is invoked if and when the JavaTM virtual machine has determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, except as a result of an action taken by the finalization of some other object or class which is ready to be finalized. The finalize method may take any action, including making this object available again to other threads; the usual purpose of finalize, however, is to perform cleanup actions before the object is irrevocably discarded. For example, the finalize method for an object that represents an input/output connection might perform explicit I/O transactions to break the connection before the object is permanently discarded.

The finalize method of class Object performs no special action; it simply returns normally. Subclasses of Object may override this definition.

The Java programming language does not guarantee which thread will invoke the finalize method for any given object. It is guaranteed, however, that the thread that invokes finalize will not be holding any user-visible synchronization locks when finalize is invoked. If an uncaught exception is thrown by the finalize method, the exception is ignored and finalization of that object terminates.

After the finalize method has been invoked for an object, no further action is taken until the Java virtual machine has again determined that there is no longer any means by which this object can be accessed by any thread that has not yet died, including possible actions by other objects or classes which are ready to be finalized, at which point the object may be discarded.

The finalize method is never invoked more than once by a Java virtual machine for any given object.

Any exception thrown by the finalize method causes the finalization of this object to be halted, but is otherwise ignored.

Throws
Throwable
This site uses cookies to store your preferences for site-specific language and display options.

Hooray!

This class requires API level or higher

This doc is hidden because your selected API level for the documentation is . You can change the documentation API level with the selector above the left navigation.

For more information about specifying the API level your app requires, read Supporting Different Platform Versions.