跟随用户的地图视图 - Android Maps API v2 的 MyLocationOverlay 类型功能 [英] Map view following user - MyLocationOverlay type functionality for Android Maps API v2

问题描述

我切换到 Android 版地图 v2，并尝试移植以下功能:

I switched to v2 of Maps for Android, and I am trying to port over the following functionality:

使用 MyLocationOverlay，我可以显示设备的当前位置(蓝点).当用户的位置发生变化并且点到达可见区域的边缘时，地图会实时显示动画，使点成为视图的中心.

With MyLocationOverlay I can show the devices current location (Blue Dot). When the user's location changes and the dot reaches the edge of the visible area, the map animates out so the dot becomes the center of the view, in real time.

在 v2 中，我使用 SupportMapFragment 和 getMap().setMyLocationEnabled(true).当前位置显示为蓝点(箭头)，但当设备更改位置时，地图视图不会移动，并且该点最终会离开视图.

In v2, I am using SupportMapFragment with getMap().setMyLocationEnabled(true). The current location appears as a blue dot(arrow), but when the device changes location, the map view does not shift and the dot eventually leaves the view.

有什么想法吗?

推荐答案

UPDATE:Google 推出了新的 LocationClient 和相关的 LocationListener(OnMyLocationChangeListener 接口现已弃用).所以现在相机的自动居中是一项微不足道的任务.

UPDATE: Google introduced the new LocationClient and associated LocationListener (the OnMyLocationChangeListener interface is now deprecated). So now automatic centering of the camera is a trivial task.

虽然spotdog 已经回答了这个问题，但我想分享我自己的例子，我希望这能帮助 Android 初学者更好地理解为 my-location 层制作自定义 LocationSource 需要什么.希望您会发现代码得到了很好的记录/注释.

Although spotdog already answered the question I wanted to share my own example, which I hope will help fellow Android beginners better understand what it takes to make a custom LocationSource for the my-location layer. Hopefully you will find that the code is well documented/commented.

public class PlaceMapFragment extends SupportMapFragment {

    // Note that this may be null if the Google Play services APK is not available.
    private GoogleMap mMap;

    protected PlaceActivity activity;
    private FollowMeLocationSource followMeLocationSource;
    private Context mContext;

    /* We need the Context in order to get a reference to the Location Manager
     * (when instantiating this fragment from your activity use:
     *  PlaceMapFragment mapFragment = new PlaceMapFragment(this); ) */
    public PlaceMapFragment(Context context) {
        this.mContext = context;
    }

    @Override
    public void onActivityCreated(Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);

        activity = (PlaceActivity)getActivity();
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        // creates our custom LocationSource and initializes some of its members
        followMeLocationSource = new FollowMeLocationSource();

        /* We can't be guaranteed that the map is available because Google Play services might not be available.
         * (un-comment the following line when using this code in a FragmentActivity / Activity 
         *  to try get a reference to the map here !) */
        //setUpMapIfNeeded();
    }

    @Override
    public void onResume() {
        super.onResume();

        /* We query for the best Location Provider everytime this fragment is displayed
         * just in case a better provider might have become available since we last displayed it */
        followMeLocationSource.getBestAvailableProvider();

        // Get a reference to the map/GoogleMap object
        setUpMapIfNeeded();

        /* Enable the my-location layer (this causes our LocationSource to be automatically activated.)
         * While enabled, the my-location layer continuously draws an indication of a user's
         * current location and bearing, and displays UI controls that allow a user to interact
         * with their location (for example, to enable or disable camera tracking of their location and bearing).*/
        mMap.setMyLocationEnabled(true);
    }

    @Override
    public void onPause() {
        /* Disable the my-location layer (this causes our LocationSource to be automatically deactivated.) */
        mMap.setMyLocationEnabled(false);

        super.onPause();
    }

    /**
     * Sets up the map if it is possible to do so (i.e., the Google Play services APK is correctly
     * installed) and the map has not already been instantiated. This will ensure that we only ever
     * manipulate the map once when it {@link #mMap} is not null.
     * <p>
     * If it isn't installed {@link SupportMapFragment} (and {@link com.google.android.gms.maps.MapView
     * MapView}) will show a prompt for the user to install/update the Google Play services APK on their device.
     */
    private void setUpMapIfNeeded() {
        // Do a null check to confirm that we have not already instantiated the map.
        if (mMap == null) {
            mMap = getMap();
            // Check if we were successful in obtaining the map.
            if (mMap != null) {
                // The Map is verified. It is now safe to manipulate the map:

                // Replace the (default) location source of the my-location layer with our custom LocationSource
                mMap.setLocationSource(followMeLocationSource);

                // Set default zoom
                mMap.moveCamera(CameraUpdateFactory.zoomTo(15f));
            }
        }
    }

    /* Our custom LocationSource. 
     * We register this class to receive location updates from the Location Manager
     * and for that reason we need to also implement the LocationListener interface. */
    private class FollowMeLocationSource implements LocationSource, LocationListener {

        private OnLocationChangedListener mListener;
        private LocationManager locationManager;
        private final Criteria criteria = new Criteria();
        private String bestAvailableProvider;
        /* Updates are restricted to one every 10 seconds, and only when
         * movement of more than 10 meters has been detected.*/
        private final int minTime = 10000;     // minimum time interval between location updates, in milliseconds
        private final int minDistance = 10;    // minimum distance between location updates, in meters

        private FollowMeLocationSource() {
            // Get reference to Location Manager
            locationManager = (LocationManager) mContext.getSystemService(Context.LOCATION_SERVICE);

            // Specify Location Provider criteria
            criteria.setAccuracy(Criteria.ACCURACY_FINE);
            criteria.setPowerRequirement(Criteria.POWER_LOW);
            criteria.setAltitudeRequired(true);
            criteria.setBearingRequired(true);
            criteria.setSpeedRequired(true);
            criteria.setCostAllowed(true);
        }

        private void getBestAvailableProvider() {
            /* The preffered way of specifying the location provider (e.g. GPS, NETWORK) to use 
             * is to ask the Location Manager for the one that best satisfies our criteria.
             * By passing the 'true' boolean we ask for the best available (enabled) provider. */
            bestAvailableProvider = locationManager.getBestProvider(criteria, true);
        }

        /* Activates this provider. This provider will notify the supplied listener
         * periodically, until you call deactivate().
         * This method is automatically invoked by enabling my-location layer. */
        @Override
        public void activate(OnLocationChangedListener listener) {
            // We need to keep a reference to my-location layer's listener so we can push forward
            // location updates to it when we receive them from Location Manager.
            mListener = listener;

            // Request location updates from Location Manager
            if (bestAvailableProvider != null) {
                locationManager.requestLocationUpdates(bestAvailableProvider, minTime, minDistance, this);
            } else {
                // (Display a message/dialog) No Location Providers currently available.
            }
        }

        /* Deactivates this provider.
         * This method is automatically invoked by disabling my-location layer. */
        @Override
        public void deactivate() {
            // Remove location updates from Location Manager
            locationManager.removeUpdates(this);

            mListener = null;
        }

        @Override
        public void onLocationChanged(Location location) {
            /* Push location updates to the registered listener..
             * (this ensures that my-location layer will set the blue dot at the new/received location) */
            if (mListener != null) {
                mListener.onLocationChanged(location);
            }

            /* ..and Animate camera to center on that location !
             * (the reason for we created this custom Location Source !) */
            mMap.animateCamera(CameraUpdateFactory.newLatLng(new LatLng(location.getLatitude(), location.getLongitude())));
        }

        @Override
        public void onStatusChanged(String s, int i, Bundle bundle) {

        }

        @Override
        public void onProviderEnabled(String s) {

        }

        @Override
        public void onProviderDisabled(String s) {

        }
    }

}

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