Android: Quitting the Looper?

Question

I have a thread I use to periodically update the data in my Activity. I create the thread and start a looper for using a handler with postDelay(). In onDestroy() for my activity, I call removeCallbacks() on my handler.

Should I then call handler.getLooper().quit()? Or not worry about it and let the OS deal with it? Or would it just run forever then, consuming CPU cycles?

Answer 1

According to the Android Documentation you should call quit().

When you call Looper.loop() a while loop is started. Calling Looper.quit() causes the loop to terminate. The garbage collector cannot collect your object while the loop is executing.

Here are the relevant section from Looper.java:

public static final void loop() {
    Looper me = myLooper();
    MessageQueue queue = me.mQueue;
    while (true) {
        Message msg = queue.next(); // might block
        //if (!me.mRun) {
        //    break;
        //}
        if (msg != null) {
            if (msg.target == null) {
                // No target is a magic identifier for the quit message.
                return;
            }
            if (me.mLogging!= null) me.mLogging.println(
                    ">>>>> Dispatching to " + msg.target + " "
                    + msg.callback + ": " + msg.what
                    );
            msg.target.dispatchMessage(msg);
            if (me.mLogging!= null) me.mLogging.println(
                    "<<<<< Finished to    " + msg.target + " "
                    + msg.callback);
            msg.recycle();
        }
    }
}

public void quit() {
    Message msg = Message.obtain();
    // NOTE: By enqueueing directly into the message queue, the
    // message is left with a null target.  This is how we know it is
    // a quit message.
    mQueue.enqueueMessage(msg, 0);
}