Added in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels) Summary: [Nested Classes](https://developer.android.com/reference/android/os/MessageQueue#nestedclasses) \| [Methods](https://developer.android.com/reference/android/os/MessageQueue#pubmethods) \| [Protected Methods](https://developer.android.com/reference/android/os/MessageQueue#promethods) \| [Inherited Methods](https://developer.android.com/reference/android/os/MessageQueue#inhmethods)

# MessageQueue

*** ** * ** ***

` public final class MessageQueue `   
` extends https://developer.android.com/reference/java/lang/Object ` ` `

|---|---|
| [java.lang.Object](https://developer.android.com/reference/java/lang/Object) ||
| ↳ | android.os.MessageQueue |

<br />

*** ** * ** ***

Low-level class holding the list of messages to be dispatched by a `https://developer.android.com/reference/android/os/Looper`. Messages are not added directly to a MessageQueue, but rather through `https://developer.android.com/reference/android/os/Handler` objects associated with the Looper.

You can retrieve the MessageQueue for the current thread with `https://developer.android.com/reference/android/os/Looper#myQueue()`.

## Summary

| ### Nested classes ||
|---|---|
| ` interface` | `https://developer.android.com/reference/android/os/MessageQueue.IdleHandler` Callback interface for discovering when a thread is going to block waiting for more messages. |
| ` interface` | `https://developer.android.com/reference/android/os/MessageQueue.OnFileDescriptorEventListener` A listener which is invoked when file descriptor related events occur. |

| ### Public methods ||
|---|---|
| ` void` | ` https://developer.android.com/reference/android/os/MessageQueue#addIdleHandler(android.os.MessageQueue.IdleHandler)(https://developer.android.com/reference/android/os/MessageQueue.IdleHandler handler) ` Add a new `https://developer.android.com/reference/android/os/MessageQueue.IdleHandler` to this message queue. |
| ` void` | ` https://developer.android.com/reference/android/os/MessageQueue#addOnFileDescriptorEventListener(java.io.FileDescriptor,%20int,%20android.os.MessageQueue.OnFileDescriptorEventListener)(https://developer.android.com/reference/java/io/FileDescriptor fd, int events, https://developer.android.com/reference/android/os/MessageQueue.OnFileDescriptorEventListener listener) ` Adds a file descriptor listener to receive notification when file descriptor related events occur. |
| ` boolean` | ` https://developer.android.com/reference/android/os/MessageQueue#isIdle()() ` Returns true if the looper has no pending messages which are due to be processed and is not blocked on a sync barrier. |
| ` void` | ` https://developer.android.com/reference/android/os/MessageQueue#removeIdleHandler(android.os.MessageQueue.IdleHandler)(https://developer.android.com/reference/android/os/MessageQueue.IdleHandler handler) ` Remove an `https://developer.android.com/reference/android/os/MessageQueue.IdleHandler` from the queue that was previously added with `https://developer.android.com/reference/android/os/MessageQueue#addIdleHandler(android.os.MessageQueue.IdleHandler)`. |
| ` void` | ` https://developer.android.com/reference/android/os/MessageQueue#removeOnFileDescriptorEventListener(java.io.FileDescriptor)(https://developer.android.com/reference/java/io/FileDescriptor fd) ` Removes a file descriptor listener. |

| ### Protected methods ||
|---|---|
| ` void` | ` https://developer.android.com/reference/android/os/MessageQueue#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 ` https://developer.android.com/reference/java/lang/Object ` ` https://developer.android.com/reference/java/lang/Object` ` https://developer.android.com/reference/java/lang/Object#clone()() `

Creates and returns a copy of this object.
` boolean` ` https://developer.android.com/reference/java/lang/Object#equals(java.lang.Object)(https://developer.android.com/reference/java/lang/Object obj) `

Indicates whether some other object is "equal to" this one.
` void` ` https://developer.android.com/reference/java/lang/Object#finalize()() `

Called by the garbage collector on an object when garbage collection determines that there are no more references to the object.
` final https://developer.android.com/reference/java/lang/Class<?>` ` https://developer.android.com/reference/java/lang/Object#getClass()() `

Returns the runtime class of this `Object`.
` int` ` https://developer.android.com/reference/java/lang/Object#hashCode()() `

Returns a hash code value for the object.
` final void` ` https://developer.android.com/reference/java/lang/Object#notify()() `

Wakes up a single thread that is waiting on this object's monitor.
` final void` ` https://developer.android.com/reference/java/lang/Object#notifyAll()() `

Wakes up all threads that are waiting on this object's monitor.
` https://developer.android.com/reference/java/lang/String` ` https://developer.android.com/reference/java/lang/Object#toString()() `

Returns a string representation of the object.
` final void` ` https://developer.android.com/reference/java/lang/Object#wait(long,%20int)(long timeoutMillis, int nanos) `

Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*, or until a certain amount of real time has elapsed.
` final void` ` https://developer.android.com/reference/java/lang/Object#wait(long)(long timeoutMillis) `

Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*, or until a certain amount of real time has elapsed.
` final void` ` https://developer.android.com/reference/java/lang/Object#wait()() `

Causes the current thread to wait until it is awakened, typically by being *notified* or *interrupted*.

## Public methods

### addIdleHandler

Added in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public void addIdleHandler (MessageQueue.IdleHandler handler)
```

Add a new `https://developer.android.com/reference/android/os/MessageQueue.IdleHandler` to this message queue. This may be removed automatically for you by returning false from `https://developer.android.com/reference/android/os/MessageQueue.IdleHandler#queueIdle()` when it is invoked, or explicitly removing it with `https://developer.android.com/reference/android/os/MessageQueue#removeIdleHandler(android.os.MessageQueue.IdleHandler)`.

This method is safe to call from any thread.

<br />

| Parameters ||
|---|---|
| `handler` | `MessageQueue.IdleHandler`: The IdleHandler to be added. This value cannot be `null`. <br /> |

### addOnFileDescriptorEventListener

Added in [API level 23](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public 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.

<br />

<br />

| Parameters ||
|---|---|
| `fd` | `FileDescriptor`: The file descriptor for which a listener will be registered. This value cannot be `null`. <br /> |
| `events` | `int`: The set of events to receive: a combination of the `https://developer.android.com/reference/android/os/MessageQueue.OnFileDescriptorEventListener#EVENT_INPUT`, `https://developer.android.com/reference/android/os/MessageQueue.OnFileDescriptorEventListener#EVENT_OUTPUT`, and `https://developer.android.com/reference/android/os/MessageQueue.OnFileDescriptorEventListener#EVENT_ERROR` event masks. If the requested set of events is zero, then the listener is unregistered. Value is either `0` or a combination of the following: - `https://developer.android.com/reference/android/os/MessageQueue.OnFileDescriptorEventListener#EVENT_INPUT` - `https://developer.android.com/reference/android/os/MessageQueue.OnFileDescriptorEventListener#EVENT_OUTPUT` - `https://developer.android.com/reference/android/os/MessageQueue.OnFileDescriptorEventListener#EVENT_ERROR` |
| `listener` | `MessageQueue.OnFileDescriptorEventListener`: The listener to invoke when file descriptor events occur. This value cannot be `null`. <br /> |

**See also:**

- `https://developer.android.com/reference/android/os/MessageQueue.OnFileDescriptorEventListener`
- `https://developer.android.com/reference/android/os/MessageQueue#removeOnFileDescriptorEventListener(java.io.FileDescriptor)`

### isIdle

Added in [API level 23](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public boolean isIdle ()
```

Returns true if the looper has no pending messages which are due to be processed and is not blocked on a sync barrier.

This method is safe to call from any thread.

<br />

| Returns ||
|---|---|
| `boolean` | True if the looper is idle. <br /> |

### removeIdleHandler

Added in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public void removeIdleHandler (MessageQueue.IdleHandler handler)
```

Remove an `https://developer.android.com/reference/android/os/MessageQueue.IdleHandler` from the queue that was previously added with `https://developer.android.com/reference/android/os/MessageQueue#addIdleHandler(android.os.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.

<br />

| Parameters ||
|---|---|
| `handler` | `MessageQueue.IdleHandler`: The IdleHandler to be removed. This value cannot be `null`. <br /> |

### removeOnFileDescriptorEventListener

Added in [API level 23](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
public void removeOnFileDescriptorEventListener (FileDescriptor fd)
```

Removes a file descriptor listener.

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

<br />

<br />

| Parameters ||
|---|---|
| `fd` | `FileDescriptor`: The file descriptor whose listener will be unregistered. This value cannot be `null`. <br /> |

**See also:**

- `https://developer.android.com/reference/android/os/MessageQueue.OnFileDescriptorEventListener`
- `https://developer.android.com/reference/android/os/MessageQueue#addOnFileDescriptorEventListener(java.io.FileDescriptor,%20int,%20android.os.MessageQueue.OnFileDescriptorEventListener)`

## Protected methods

### finalize

Added in [API level 1](https://developer.android.com/guide/topics/manifest/uses-sdk-element#ApiLevels)

```
protected 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 Java 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.

<br />

| Throws ||
|---|---|
| `https://developer.android.com/reference/java/lang/Throwable` |   |