Question

我正在创建瑞典一些城市的地图，并希望添加一些功能。我想显示城市名称和距离地图中心最近的城市距离，我在布局XML文件中通过ImageView放置了一个十字准线。有没有正确的方法来实现这个目标？

这是我目前用于创建地图并放置城市标记的代码：

public class MyMap extends Activity implements OnMapReadyCallback
{
    public final Context context = this;
    private String fileString = "";
    private String coordsFileName = "coords";
    private GoogleMap myMap = null;
    private LatLngBounds bounds = null;

@Override
protected void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_my_map);

    // Gets the map fragment from the xml file
    MapFragment mapFragment = (MapFragment) getFragmentManager().findFragmentById(R.id.map);
    mapFragment.getMapAsync(this);

    // Load strings from file
    fileString = ReadFromFile(coordsFileName);
}

@Override
public void onMapReady(GoogleMap map)
{
    myMap = map;
    List<Marker> markers = new ArrayList<Marker>();

    String[] locations = fileString.split(";");
    for (String location : locations)
    {   
        try
        {
            String[] cityLatLng = location.split(":|,");
            String cityName = cityLatLng[0];
            Double lat = Double.parseDouble(cityLatLng[1]);
            Double lng = Double.parseDouble(cityLatLng[2]);
            LatLng cityPos = new LatLng(lat, lng);

            // Create marker
            Marker marker = myMap.addMarker(new MarkerOptions()
            .position(cityPos)
            .title(cityName));

            // Add new marker to array of markers
            markers.add(marker);
        }
        catch(Exception e)
        {
            System.out.println("Error 3: " + e.getMessage());
        }
    }

    // Move the camera to show all markers
    LatLngBounds.Builder builder = new LatLngBounds.Builder();
    for (Marker marker : markers)
    {
        builder.include(marker.getPosition());
    }
    bounds = builder.build();

    myMap.setOnMapLoadedCallback(new GoogleMap.OnMapLoadedCallback()
    { 
        @Override 
        public void onMapLoaded()
        {
            // Pixel offset from edge of map
            int padding = 30;

            // Move the camera
            myMap.moveCamera(CameraUpdateFactory.newLatLngBounds(bounds, padding));
        } 
    });
 }

}

这是我的布局xml文件：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout 
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<fragment
    android:id="@+id/map"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:name="com.google.android.gms.maps.MapFragment"/>
<ImageView
    android:id="@+id/imageView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:src="@drawable/ic_action_locate"
    android:layout_gravity="center_vertical"
    android:layout_centerInParent="true"
    android:contentDescription="@string/crosshairs"/>
</RelativeLayout>

Answer 1

可能的解决方案之一是首先使用

找到地图的中心坐标

map.getCenter();

这将返回latlang对象。然后你可以使用Google Distance Matrix API比较中心与每个位置标记（代表城市）的距离，使用minDist（）方法找出min并返回最小距离的标记坐标（是城市的名称）

希望这会有所帮助!!!

Answer 2

我实际上设法使用Location对象和GoogleMap.setOnCameraChangeListener（）来解决它，以便每次用户导航地图时重新计算。下面是我为实现这一目标而设法编写的代码。

        myMap.setOnCameraChangeListener(new OnCameraChangeListener()
        {
            @SuppressLint("DefaultLocale") @Override
            public void onCameraChange(CameraPosition position)
            {
                // Get the latlng of the map center
                LatLng mapCenter = myMap.getCameraPosition().target;

                // Create a centerlocation based on the map's latlng
                Location centerLocation = new Location("CenterLocation");
                centerLocation.setLatitude(mapCenter.latitude);
                centerLocation.setLongitude(mapCenter.longitude);

                // Location for storage of the city closest to the map
                Location closestCity = new Location("ClosestCity");
                float distance = 0;

                for (City city : cities)
                {
                    Location cityLocation = new Location(city.getCityName());
                    cityLocation.setLatitude(city.getLatitude());
                    cityLocation.setLongitude(city.getLongitude());

                    float currentCityDistance = cityLocation.distanceTo(centerLocation);

                    if(distance == 0)
                    {
                        distance = currentCityDistance;
                        closestCity = cityLocation;
                    }

                    if(currentCityDistance < distance)
                    {
                        distance = currentCityDistance;
                        closestCity = cityLocation;
                    }
                }

                // Convert from meters to kilometers
                float distanceKm = distance / 1000;
                String kilometersString = String.format("%.2f", distanceKm);

                // Present a toast with information
                Toast.makeText(getBaseContext(), "Distance to " + closestCity.getProvider() + ": " + kilometersString + " km", Toast.LENGTH_SHORT).show();
            }
        });

敬酒名称和最接近地图中心的城市的距离

2 个答案: