折线未在地图上绘制答案

【问题标题】：Polyline is not being drawn on the Map折线未在地图上绘制
【发布时间】：2013-05-23 16:07:53
【问题描述】：

我正在尝试在地图上绘制一条折线来跟踪我的位置。出于某种原因，我不确定为什么我的方法 onMyLocationChanged(location) 没有被调用并且没有在地图上绘制折线。这是与 lcoationToLatLng(loc) 方法一起使用的方法，该方法旨在帮助在地图上绘制多段线来跟踪我的去向。为什么不绘制这条折线？这是我的代码：

public class RouteTracking extends FragmentActivity implements View.OnClickListener, OnMyLocationChangeListener{
    private GoogleMap mMap = null;
    private Context context = this;
    private Location lastLocationloc = null;

    @Override
protected void onCreate(Bundle load) { 
    super.onCreate(load);

    setContentView(R.layout.fragment_ride_tracking);

    mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.myMapView)).getMap();
    int result = GooglePlayServicesUtil.isGooglePlayServicesAvailable(context);
    mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);

     //Get the current location
    LocationManager locationManager = (LocationManager) getSystemService(LOCATION_SERVICE);
    Criteria criteria = new Criteria();
    String provider = locationManager.getBestProvider(criteria, true);
    Location location = locationManager.getLastKnownLocation(provider);

    //Zooms into the current location when the activity is started
    double latitude = location.getLatitude();
    double longitude = location.getLongitude();
    float zoom = (float) 10.0;
    mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(new LatLng(latitude, longitude), zoom));      


    if (mMap != null) { 
        mMap.setMyLocationEnabled(true);
    }
   }

   @Override
   public void onMyLocationChange(Location location) { 
       if (lastLocationloc == null) { 
           lastLocationloc = location;
       }
       LatLng lastLatLng = locationToLatLng(lastLocationloc);
       LatLng thisLatLng = locationToLatLng(location);
       mMap.addPolyline(new PolylineOptions().add(lastLatLng).add(thisLatLng).width(3).color(Color.RED));
       lastLocationloc = location;
   }

   public static LatLng locationToLatLng(Location loc) { 
       if (loc != null) 
           return new LatLng(loc.getLatitude(), loc.getLongitude());
       return null;
   }
}

【问题讨论】：

标签： java android google-maps-android-api-2 android-location android-maps-v2

【解决方案1】：

我觉得你应该实现LocationListener(implements LocationListener)，然后把代码修改成：

   @Override
   public void onLocationChanged(Location location) { 
       if (lastLocationloc == null) { 
           lastLocationloc = location;
       }
       LatLng lastLatLng = locationToLatLng(lastLocationloc);
       LatLng thisLatLng = locationToLatLng(location);
       mMap.addPolyline(new PolylineOptions().add(lastLatLng).add(thisLatLng).width(3).color(Color.RED));
       lastLocationloc = location;
   }

试试看，希望能解决你的问题，祝你好运^^

【讨论】：

【解决方案2】：

您需要向位置经理请求（注册）更新（或者至少我没有看到您在哪里这样做）。

    public void init(Context context)
    {
         this.context = context;

         locationManager = (LocationManager) this.context
            .getSystemService(Context.LOCATION_SERVICE);

         // exceptions will be thrown if gps provider is not permitted.
        try
        {
             gpsEnabled = locationManager
                .isProviderEnabled(LocationManager.GPS_PROVIDER);

        } catch (Exception e)
        {
             Log.d("Fail", e.getMessage());
        }

                // ask for gps updates from the device if gps is enabled
        if (gpsEnabled)
        {
           locationManager.requestLocationUpdates(LocationManager.GPS_PROVIDER, 0, 0,this);
        }
    }

【讨论】：