上一个任务完成后，定期运行AsyncTask

Question

I have an AsyncTask which currently runs only once and takes about between 5 - 30 secs to finish.

What I want to do is:

1. Start the App
2. Run the Task
3. Wait for it to Finish.
4. Wait for a Fixed amount of time eg 5 seconds
5. Repeat Step 2.

I looked around several posts which suggest using Handlers and that's how I have tried to do it:

 @Override
    protected void onCreate(Bundle savedInstanceState) {

        super.onCreate(savedInstanceState);

        setContentView(R.layout.activity_main);

        final Activity activity = this;

        final Handler handler = new Handler();
        handler.postDelayed(new Runnable() {
            public void run() {

                // Start AsyncTask
                new MyTask(activity).execute();
            }
        }, 5000); //Every 5 seconds
    }

MyTask is a sub-class of AsyncTask in some another .java file.

This only runs the task once on start-up after a delay of 5 seconds. It doesn't re-execute itself as it should.

Note that I want to run the next task only if its not already running and run it 5 seconds after it.

So, why doesn't it work as excepted?

Answer 1

Try putting your handler code again into the onPostExecute method of the AsyncTask. That way once it finishes it will wait 5 seconds to launch itself again.

hope it helps ;)

Answer 2

Here is how I use my code to run a method call ListDevices every DELAY time.

private ScheduledFuture<?> scheduledFutureListDevices

private void startListDevicesTaskAtRate(int rate) {

Runnable runnable = this::requestListDeviceService;

scheduledFutureListDevices = scheduledThreadPoolExecutor.scheduleWithFixedDelay(runnable, DELAY, rate, TimeUnit.SECONDS);

Log.d(TAG, "STARTING LIST DEVICES TASK AT " + (rate == Constants.FAST_RATE ? " FAST " : " NORMAL ") + " RATE");

if (scheduledFutureListDevices != null) {
   scheduledFutureListDevices.cancel(false);
}

Runnable runnable = this::requestListDeviceService;

scheduledFutureListDevices = scheduledThreadPoolExecutor.scheduleWithFixedDelay(runnable, DELAY, rate, 
       TimeUnit.SECONDS);
}

I am assigning the result of scheduledThreadPoolExecutor.scheduleWithFixedDelay to scheduledFutureListDevices so you can cancel it or resumen wherever you need