/**   * 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   * {@link #prepare} in the thread that is to run the loop, and then   * {@link #loop} to have it process messages until the loop is stopped.   *   * 
Most interaction with a message loop is through the   * {@link Handler} class.   *   * 
This is a typical example of the implementation of a Looper thread,   * using the separation of {@link #prepare} and {@link #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();   *      }   *  }
   */

/** 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   * {@link #loop()} after calling this method, and end it by calling   * {@link #quit()}.   */ public static void prepare() {
      prepare(true); } private static void prepare(boolean quitAllowed) {
      if (sThreadLocal.get() != null) {
          throw new RuntimeException("Only one Looper may be created per thread");     }     sThreadLocal.set(new Looper(quitAllowed)); }

/**  * Run the message queue in this thread. Be sure to call  * {@link #quit()} to end the loop.  */ public static void loop() {
      final Looper me = myLooper();     if (me == null) {
          throw new RuntimeException("No Looper; Looper.prepare() wasn't called on this thread.");     }     final MessageQueue queue = me.mQueue;     // Make sure the identity of this thread is that of the local process,     // and keep track of what that identity token actually is.     Binder.clearCallingIdentity();     final long ident = Binder.clearCallingIdentity();     for (;;) {
          Message msg = queue.next(); // might block         if (msg == null) {
              // No message indicates that the message queue is quitting.             return;         }         // This must be in a local variable, in case a UI event sets the logger         Printer logging = me.mLogging;         if (logging != null) {
              logging.println(">>>>> Dispatching to " + msg.target + " " +                     msg.callback + ": " + msg.what);         }         msg.target.dispatchMessage(msg);         if (logging != null) {
              logging.println("<<<<< Finished to " + msg.target + " " + msg.callback);         }         // Make sure that during the course of dispatching the         // identity of the thread wasn't corrupted.         final long newIdent = Binder.clearCallingIdentity();         if (ident != newIdent) {
              Log.wtf(TAG, "Thread identity changed from 0x"                     + Long.toHexString(ident) + " to 0x"                     + Long.toHexString(newIdent) + " while dispatching to "                     + msg.target.getClass().getName() + " "                     + msg.callback + " what=" + msg.what);         }         msg.recycleUnchecked();     } }