Come to think of it, how would one create a Handler for another
thread? You'd have to dispatch the thread and have it create the
Handler and pass the pointer back to you (we won't worry about how),
but then that thread needs to go into a message receive loop.
Apparently this is done via Looper. I'm guessing the code would be
like this:
class LooperThread extends Thread {
public Handler mHandler;
public void run() {
Looper.prepare();
mHandler = new Handler();
Looper.loop();
}
}
You'd start this thread and then use your pointer to it to access
mHandler (though you'd have to guard somehow against getting a null
before the reference was set). Then dispatch Runnables or Messages
via that handler.
(Gotta wonder where Looper stashes the instance it creates of itself
to attach to the Thread. I suppose it uses ThreadLocal.)
On Oct 7, 4:38 pm, DanH <[email protected]> wrote:
> But I don't see anywhere in the Handler spec where it says the thread
> will be dispatched. It appears to me that when the thread is posted,
> Handler will just run its "run" method, without starting the thread.
> If you wanted to run on a separate thread it appears to me that you'd
> have to start the thread, have that thread create a Handler and pass
> it back to you somehow, and then post via THAT Handler.
>
> At least that's how I'd interpret this: "Each Handler instance is
> associated with a single thread and that thread's message queue. When
> you create a new Handler, it is bound to the thread / message queue of
> the thread that is creating it -- from that point on, it will deliver
> messages and runnables to that message queue and execute them as they
> come out of the message queue."
>
> On Oct 7, 4:25 pm, Jeremy Wadsack <[email protected]> wrote:
>
> > Fair point. The "// Do some tasks" is doing long-running (Internet-
> > connected) stuff, so I want it to run in a separate thread. As I
> > understand, posting the Runnable without a thread would run it on the
> > main thread.
>
> > I assume the gc will clean up the Threads as they expire, but I could
> > also redesign this to have a single active thread that posts Runnables
> > (or even just messages) to it's own MessageQueue at specified
> > intervals. Then I'd be managing the looper myself (that is, calling
> > Looper.loop), which would probably resolve this issue.
>
> > That doesn't answer the original question but it may be the right
> > approach if it's more "android-y".
>
> > --
> > Jeremy Wadsack
>
> > On Oct 7, 1:20 pm, DanH <[email protected]> wrote:
>
> > > Kind of off-topic, but why are you creating a new Thread with each
> > > post, vs simply posting the Runnable?
>
> > > On Oct 5, 5:47 pm, Jeremy Wadsack <[email protected]> wrote:
>
> > > > I have a class that uses a Handler for a timed, asynchronous activity.
> > > > Something like this:
>
> > > > public class SampleClass {
> > > > private static final long DELAY = 30000;
> > > > private boolean isRunning = false;
> > > > private Handler handler = new Handler();
>
> > > > public start() {
> > > > if (!isRunning) {
> > > > isRunning = true;
> > > > handler.post(new Thread(task));
> > > > }
> > > > }
>
> > > > public stop() {
> > > > isRunning = false;
> > > > }
>
> > > > private Runnable task = new Runnable() {
> > > > public void run() {
> > > > if (!isRunning) {
> > > > return;
> > > > }
>
> > > > // Do some tasks
> > > > handler.postDelayed(new Thread(this), DELAY);
> > > > }
> > > > }
>
> > > > }
>
> > > > I am trying to write a unit test (without having to implement an
> > > > activity that instantiates the class) but I can't seem to get the
> > > > items that are posted to the MessageQueue to ever be fired. Inheriting
> > > > from junit.framework.TestCase doesn't work, but then there wouldn't be
> > > > a MessageQueue for the handler, I'd expect (although, there's no
> > > > error, but the Runnable never gets called). I tried inheriting the
> > > > test class from AndroidTestCase and ApplicationTestCase<Application>
> > > > but neither of those works, even though the former is supposed to
> > > > provide a Context and the latter "all the life cycle of an
> > > > application."
>
> > > > Anyone have any pointers?
>
> > > > --
> > > > Jeremy Wadsack
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