在asynctask中每x次更新标记位置

Question

I wanted to mock location of a marker on map. I have list of LatLng values store in ArrayList. I use this value to update on map every second. I need this function to works in AsyncTask so that my UI thread will still responsive.

Initially, I tried using Thread.sleep() but made application not responsive.

protected String doInBackground(Void... voids) {
    new Handler(Looper.getMainLooper()).postDelayed(new Runnable() {
        @Override
        public void run() {
            for (int i = 0; i < waypoint.size(); i++) {
                marker = googleMap.addMarker(new MarkerOptions().position(waypoint.get(0)));
                marker.setPosition(waypoint.get(i));
                try {
                    Thread.sleep(1000); // Thread sleep made application not responsive.
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        }
    }, 500);
    return null;
}

I also tried using .postDelayed but the integer i needs to get declared final which is a problem because I need the integer to change value.

protected String doInBackground(Void... voids) {
    for (int i = 0; i < waypoint.size(); i++) {
        new Handler(Looper.getMainLooper()).postDelayed(new Runnable() {
            @Override
            public void run() {
                marker = googleMap.addMarker(new MarkerOptions().position(waypoint.get(0)));
                marker.setPosition(waypoint.get(i)); // Integer i needs to declare final.
            }
        }, 1000);
    }
    return null;
}

Is there any way to do this? Thank you.

Answer 1

The Thread.sleep() approach is OK if you can spare a worker thread. The problem in your code is that the thread you are pausing is the UI Thread, that's why your application freezes. You have to understand that what your doing there is just publishing a runnable to the UI Thread using the Handler construct, nothing more.

In your second approach, you can dump the Handler part and use publishProgress (called from the background) after you override onProgressUpdate (delivered in UI thread) in your AsyncTask based class. It does effectively the same but with less boilerplate. Take a look at https://developer.android.com/reference/android/os/AsyncTask for details.

Finally, to circumvent the final requirement in anonymous classes, you can declare a final array of one element and use position 0 to read/write the value. Hopefully, you won't need to do this too often.

Answer 2

The fastest (but not the most correct when working with MultiThreading) way is:

protected String doInBackground(Void... voids) {
for (final TYPE_OF_WAYPOINT cWaypoint : waypoint) {
    new Handler(Looper.getMainLooper()).postDelayed(new Runnable() {
        @Override
        public void run() {
            marker = googleMap.addMarker(new MarkerOptions().position(waypoint.get(0)));
            marker.setPosition(cWaypoint);
        }
    }, 1000);
}
return null;

}

I don't know what was the Type of "waypoint" List, so I wrote "TYPE_OF_WAYPOINTS" as placeholder.

Answer 3

@emandt answer does not work but the idea he gave could work. So I tried and it is working flawlessly with some modified from his answer:

protected String doInBackground(Void... voids) {
for (final TYPE_OF_WAYPOINT cWaypoint : waypoint) {
    new Handler(Looper.getMainLooper()).post(new Runnable() {
        @Override
        public void run() {
            marker = googleMap.addMarker(new MarkerOptions().position(waypoint.get(0)));
            marker.setPosition(cWaypoint);
        }
    });
    try {
        Thread.sleep(1000);
    } catch (Exception e) {
        // catch exception here
    }
}
return null;
}

Firstly, I have change the .postDelayed to .post . Then, to delay the operation by one second, I have added Thread.sleep(1000) inside for (...) but outside new Handler(Looper.getMainLooper()).post(...)); .

Now, the application could do the process in the background with user still be able to interact with the UI. Thanks.