Change markers position base on Realtime Firebase lat and lang values

问题

I seek to change the position of markers in google maps with the value of the real-time database

I try to mMap.clear to but it's not the right solution because if I have 100 markers and change position of 1 marker the 100 is clear and reposition for make 1 marker change

    myRef.addValueEventListener(new ValueEventListener() {
    @Override
    public void onDataChange(DataSnapshot dataSnapshot) {
      mMap.clear();           
 for (DataSnapshot ds : dataSnapshot.getChildren()) {

            Double lang = ds.child("lang").getValue(Double.class);
            Double lat = ds.child("lat").getValue(Double.class);
            save = new model(lat, lang);
            ll = new LatLng(save.getLat(), save.getLang());

            mCurrLocationMarker = mMap.addMarker(options
                    .position(ll));

        }

    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

I try to change position for the marker but actual results add a new one if I not write mMap.clear and clear all markers and added them for change one marker if I write mMap.clear

回答1:

Without removing marker update new position in google map()

1.initially created marker:

        Double lang = ds.child("lang").getValue(Double.class);
        Double lat = ds.child("lat").getValue(Double.class);
          LatLng latLng=new latLng(lang ,lat )
     // Creating a marker

      Marker marker= mMap.addMarker(new MarkerOptions()
                      .position(latLng)
                      .draggable(true));

2.while getting updateedlocation

   LatLng oldLocation, newLocaation;

float bearing = (float) bearingBetweenLocations(oldLocation, newLocaation);
rotateMarker(marker, bearing);

private double bearingBetweenLocations(LatLng perviousPos,LatLng newPos) {

    double PI = 3.14159;
    double lat1 = perviousPos.latitude * PI / 180;
    double long1 = perviousPos.longitude * PI / 180;
    double lat2 = newPos.latitude * PI / 180;
    double long2 = newPos.longitude * PI / 180;

    double dLon = (long2 - long1);

    double y = Math.sin(dLon) * Math.cos(lat2);
    double x = Math.cos(lat1) * Math.sin(lat2) - Math.sin(lat1)
            * Math.cos(lat2) * Math.cos(dLon);

    double brng = Math.atan2(y, x);

    brng = Math.toDegrees(brng);
    brng = (brng + 360) % 360;

    return brng;
}


   .To rotate marker using above bearing angle i have used this code

 Here isMarkerRotating is a boolean value. Add isMarkerRotating = false in OnCreate 
method

private void rotateMarker(final Marker marker, final float toRotation) {
    if(!isMarkerRotating) {
        final Handler handler = new Handler();
        final long start = SystemClock.uptimeMillis();
        final float startRotation = marker.getRotation();
        final long duration = 2000;

        final Interpolator interpolator = new LinearInterpolator();

        handler.post(new Runnable() {
            @Override
            public void run() {
                isMarkerRotating = true;

                long elapsed = SystemClock.uptimeMillis() - start;
                float t = interpolator.getInterpolation((float) elapsed / duration);

                float rot = t * toRotation + (1 - t) * startRotation;

                float bearing =  -rot > 180 ? rot / 2 : rot;

                marker.setRotation(bearing);

                if (t < 1.0) {
                    // Post again 16ms later.
                    handler.postDelayed(this, 16);
                } else {
                    isMarkerRotating = false;
                }
            }
        });
    }
}

回答2:

I suggest store marker in an array or Hashmap throw which you can update whenever you want like bellow.

//            code for ploat and store marker
            HashMap<String, Marker> mPlotedMarker = new HashMap<>();
            if (mMap != null) {
                mMap.clear();
                ArrayList<MarkerDataModel> mDataList = new ArrayList<>();
                //With Hash map

                for (int positon = 0; positon < mDataList.size(); positon++) {
                    LatLng markerPosition = new LatLng(mDataList.get(positon).getMarkerLat(), mDataList.get(positon).getMarkerLong());
                    Marker marker = mMap.addMarker(new MarkerOptions().position(markerPosition)
                            .title(mDataList.get(positon).getMarkerTitle()));
                    mPlotedMarker.put(mDataList.get(positon).getMarkerId(), marker);
                }
            }

            //Now whenever you want to update
            String markerId="1"; // replace which you want to update
            if(mPlotedMarker.containsKey(markerId)){
                Marker marker=mPlotedMarker.get(markerId);
                if(marker!=null){
                    marker.setPosition(newPostion); //Specifie new position
                }
            }

回答3:

You can store marker object as a global variable and just change selected markers position on location change.

Like,

if (mCurrLocationMarker == null)
    mCurrLocationMarker = mGoogleMap.addMarker(new MarkerOptions().icon(BitmapDescriptorFactory.fromResource(R.drawable.ic_pin_red)).position(location));
else
    mCurrLocationMarker.setPosition(location);

As you have more then one markers, you can try the same logic by using ArrayList or LinkedHashMap.

Please check this file: https://filebin.net/m2vgvcms6g73kef2/TestFragment.java?t=e9g0tdki

Hope it helps.. :)

来源：https://stackoverflow.com/questions/55570188/change-markers-position-base-on-realtime-firebase-lat-and-lang-values