当用户停止移动相机时，Android google maps v2会执行asynctask

Question

I am making an app which is using google maps api v2. My problem is that when I register camera change listener, it executes each time the camera moves not when the moving stops. I want to achieve the latter. How can I modify my code to register only when moving stops ?

Here is my code:

mMap.setOnCameraChangeListener(new GoogleMap.OnCameraChangeListener() {
            @Override
            public void onCameraChange(CameraPosition position) {
                LatLngBounds bounds = mMap.getProjection().getVisibleRegion().latLngBounds;
                ne = bounds.northeast;
                sw = bounds.southwest;
                ne1 = ne.latitude;
                ne2 = ne.longitude;
                sw1 = sw.latitude;
                sw2 = sw.longitude;
                new DownloadJSON().execute();
            }
        });

Answer 1

I implemented custom timer to execute after certain time only when conditions are met. Here is my code:

mMap.setOnCameraChangeListener(new GoogleMap.OnCameraChangeListener() {
                @Override
                public void onCameraChange(CameraPosition position) {
                    LatLngBounds bounds = mMap.getProjection().getVisibleRegion().latLngBounds;
                    ne = bounds.northeast;
                    sw = bounds.southwest;
                    if(t!=null){
                        t.purge();
                        t.cancel();
                    }
                    t = new Timer();
                    t.schedule(new TimerTask() {
                        public void run() {
                            if(ne1 != ne.latitude && ne2 != ne.longitude && sw1 != sw.latitude && sw2 != sw.longitude){
                                ne1 = ne.latitude;
                                ne2 = ne.longitude;
                                sw1 = sw.latitude;
                                sw2 = sw.longitude;
                                Log.d("Tag","Refreshing data");
                                new DownloadJSON().execute();
                                t.cancel();
                            }
                            else{
                            ne1 = ne.latitude;
                            ne2 = ne.longitude;
                            sw1 = sw.latitude;
                            sw2 = sw.longitude;}
                            t.cancel(); // also just top the timer thread, otherwise, you may receive a crash report
                        }
                    }, 1000);
                    //new DownloadJSON().execute();
                }
            });

Answer 2

I think you can not do this "oncamerachange" triggers an event at the end of the movement, but may trigger, or not, others during the movement.

Google docs : " Called after the camera position has changed . During an animation , listener May not be Notified of intermediate camera positions . It is always called for the end position in the animation . "

And there are no listeners for start or end camera movement.

One way to do something similar, is to save the last point ( latlang ) where you loaded the json for the last time and every time there is a " oncamerachange " event, compare the current point to the previous point and decide if you want to reload the json again or not.

Edited to post workaround from google gmaps-api-issues.

Maybe this is what are you loocking for. From the discusion on google issues.

https://code.google.com/p/gmaps-api-issues/issues/attachmentText?id=4636&aid=46360026000&name=sample_inner_listener.java&token=ABZ6GAdaQesCaWQ_IU8t9J222IBYzPceUA%3A1431366784956

new GoogleMap.OnCameraChangeListener() {
    private static int CAMERA_MOVE_REACT_THRESHOLD_MS = 500;
    private long lastCallMs = Long.MIN_VALUE;

    @Override
    public void onCameraChange(CameraPosition cameraPosition) {
     final long snap = System.currentTimeMillis();
     if (lastCallMs + CAMERA_MOVE_REACT_THRESHOLD_MS > snap) {
       lastCallMs = snap;
       return;
     }

     ;; // here the actual call whatever you want to do on camera change

     lastCallMs = snap;
    }

};

Comment from the author:

hi, I've attached a sample of anon listener wrapper implementation, you can play with CAMERA_MOVE_REACT_THRESHOLD_MS to evaluate best value for you, if its not enough, you could also add kinda autosensing though, which would adapt that threshold value to the onCameraChange() call frequency