This lesson shows you how to implement a Runnable
class, which runs the code
in its Runnable.run()
method on a separate thread. You can also
pass a Runnable
to another object that can then attach it to a thread and
run it. One or more Runnable
objects that perform a particular operation are
sometimes called a task.
Thread
and Runnable
are basic classes that, on their own,
have only limited power. Instead, they're the basis of powerful Android classes such as
HandlerThread
, AsyncTask
, and
IntentService
. Thread
and Runnable
are
also the basis of the class ThreadPoolExecutor
. This class
automatically manages threads and task queues, and can even run multiple threads in parallel.
Implementing a class that implements Runnable
is straightforward. For example:
public class PhotoDecodeRunnable implements Runnable { ... @Override public void run() { /* * Code you want to run on the thread goes here */ ... } ... }
In the class, the Runnable.run()
method contains the
code that's executed. Usually, anything is allowable in a Runnable
. Remember,
though, that the Runnable
won't be running on the UI thread, so it can't
directly modify UI objects such as View
objects. To communicate with
the UI thread, you have to use the techniques described in the lesson
Communicate with the UI Thread.
At the beginning of the run()
method, set the thread to use
background priority by calling
Process.setThreadPriority()
with
THREAD_PRIORITY_BACKGROUND
. This approach reduces
resource competition between the Runnable
object's thread and the UI
thread.
You should also store a reference to the Runnable
object's
Thread
in the Runnable
itself, by calling
Thread.currentThread()
.
The following snippet shows how to set up the run()
method:
class PhotoDecodeRunnable implements Runnable { ... /* * Defines the code to run for this task. */ @Override public void run() { // Moves the current Thread into the background android.os.Process.setThreadPriority(android.os.Process.THREAD_PRIORITY_BACKGROUND); ... /* * Stores the current Thread in the PhotoTask instance, * so that the instance * can interrupt the Thread. */ mPhotoTask.setImageDecodeThread(Thread.currentThread()); ... } ... }