Looper

Kotlin |Java

class Looper

kotlin.Any
↳	android.os.Looper

Class used to run a message loop for a thread. Threads by default do not have a message loop associated with them; to create one, call prepare in the thread that is to run the loop, and then loop to have it process messages until the loop is stopped.

Most interaction with a message loop is through the Handler class.

This is a typical example of the implementation of a Looper thread, using the separation of prepare and loop to create an initial Handler to communicate with the Looper.

class LooperThread extends Thread {
       public Handler mHandler;
 
       public void run() {
           Looper.prepare();
 
           mHandler = new Handler(Looper.myLooper()) {
               public void handleMessage(Message msg) {
                   // process incoming messages here
               }
           };
 
           Looper.loop();
       }
   }

Summary

Public methods
Unit	`dump(pw: Printer, prefix: String)` Dumps the state of the looper for debugging purposes.
static Looper!	`getMainLooper()` Returns the application's main looper, which lives in the main thread of the application.
MessageQueue	`getQueue()` Gets this looper's message queue.
Thread	`getThread()` Gets the Thread associated with this Looper.
Boolean	`isCurrentThread()` Returns true if the current thread is this looper's thread.
static Unit	`loop()` Run the message queue in this thread.
static Looper?	`myLooper()` Return the Looper object associated with the current thread.
static MessageQueue	`myQueue()` Return the `MessageQueue` object associated with the current thread.
static Unit	`prepare()` Initialize the current thread as a looper.
static Unit	`prepareMainLooper()` Initialize the current thread as a looper, marking it as an application's main looper.
Unit	`quit()` Quits the looper.
Unit	`quitSafely()` Quits the looper safely.
Unit	`setMessageLogging(printer: Printer?)` Control logging of messages as they are processed by this Looper.
String	`toString()`

Public methods

dump

Added in API level 1

fun dump(
    pw: Printer, 
    prefix: String
): Unit

Dumps the state of the looper for debugging purposes.

Parameters
`pw`	Printer: A printer to receive the contents of the dump. This value cannot be `null`.
`prefix`	String: A prefix to prepend to each line which is printed. This value cannot be `null`.

getMainLooper

Added in API level 1

static fun getMainLooper(): Looper!

Returns the application's main looper, which lives in the main thread of the application.

getQueue

Added in API level 23

fun getQueue(): MessageQueue

Gets this looper's message queue.

Return
`MessageQueue`	The looper's message queue. This value cannot be `null`.

getThread

Added in API level 3

fun getThread(): Thread

Gets the Thread associated with this Looper.

Return
`Thread`	The looper's thread. This value cannot be `null`.

isCurrentThread

Added in API level 23

fun isCurrentThread(): Boolean

Returns true if the current thread is this looper's thread.

loop

Added in API level 1

static fun loop(): Unit

Run the message queue in this thread. Be sure to call quit() to end the loop.

myLooper

Added in API level 1

static fun myLooper(): Looper?

Return the Looper object associated with the current thread. Returns null if the calling thread is not associated with a Looper.

myQueue

Added in API level 1

static fun myQueue(): MessageQueue

Return the MessageQueue object associated with the current thread. This must be called from a thread running a Looper, or a NullPointerException will be thrown.

Return
`MessageQueue`	This value cannot be `null`.

prepare

Added in API level 1

static fun prepare(): Unit

Initialize the current thread as a looper. This gives you a chance to create handlers that then reference this looper, before actually starting the loop. Be sure to call loop() after calling this method, and end it by calling quit().

prepareMainLooper

Added in API level 1
Deprecated in API level 30

static fun prepareMainLooper(): Unit

Deprecated: The main looper for your application is created by the Android environment, so you should never need to call this function yourself.

Initialize the current thread as a looper, marking it as an application's main looper. See also: prepare()

quit

Added in API level 1

fun quit(): Unit

Quits the looper.

Causes the loop method to terminate without processing any more messages in the message queue.

Any attempt to post messages to the queue after the looper is asked to quit will fail. For example, the Handler.sendMessage(Message) method will return false.

Using this method may be unsafe because some messages may not be delivered before the looper terminates. Consider using quitSafely instead to ensure that all pending work is completed in an orderly manner.

See Also

#quitSafely

quitSafely

Added in API level 18

fun quitSafely(): Unit

Quits the looper safely.

Causes the loop method to terminate as soon as all remaining messages in the message queue that are already due to be delivered have been handled. However pending delayed messages with due times in the future will not be delivered before the loop terminates.

Any attempt to post messages to the queue after the looper is asked to quit will fail. For example, the Handler.sendMessage(Message) method will return false.

setMessageLogging

Added in API level 1

fun setMessageLogging(printer: Printer?): Unit

Control logging of messages as they are processed by this Looper. If enabled, a log message will be written to printer at the beginning and ending of each message dispatch, identifying the target Handler and message contents.

Parameters
`printer`	Printer?: A Printer object that will receive log messages, or null to disable message logging.

toString

Added in API level 1

fun toString(): String

Return
`String`	a string representation of the object.