Package android.os

Class Looper

  • public final class Looper
extends Object
    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() {
              public void handleMessage(Message msg) {
                  // process incoming messages here
              }
          };

          Looper.loop();
      }
  }

    • Method Detail

      • prepare

        public static void prepare()
        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

        public static void prepareMainLooper()
        Initialize the current thread as a looper, marking it as an application's main looper. The main looper for your application is created by the Android environment, so you should never need to call this function yourself. See also: prepare()

      • getMainLooper

        public static Looper getMainLooper()
        Returns the application's main looper, which lives in the main thread of the application.

      • loop

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

      • myLooper

        public static Looper myLooper()
        Return the Looper object associated with the current thread. Returns null if the calling thread is not associated with a Looper.

      • myQueue

        public static MessageQueue myQueue()
        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.

      • isCurrentThread

        public boolean isCurrentThread()
        Returns true if the current thread is this looper's thread.

      • setMessageLogging

        public void setMessageLogging​(Printer printer)
        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 - A Printer object that will receive log messages, or null to disable message logging.

      • quit

        public void quit()
        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

        public void quitSafely()
        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.

      • getThread

        public Thread getThread()
        Gets the Thread associated with this Looper.
        Returns:
        The looper's thread.

      • getQueue

        public MessageQueue getQueue()
        Gets this looper's message queue.
        Returns:
        The looper's message queue.

      • dump

        public void dump​(Printer pw,
                 String prefix)
        Dumps the state of the looper for debugging purposes.
        Parameters:
        pw - A printer to receive the contents of the dump.
        prefix - A prefix to prepend to each line which is printed.

      • toString

        public String toString()
        Description copied from class: Object
        Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression: 
           getClass().getName() + '@' + Integer.toHexString(hashCode())

        See Writing a useful toString method if you intend implementing your own toString method.

        Overrides:
        toString in class Object
        Returns:
        a printable representation of this object.