此应用程序旨在从2个坐标点获得距离。方法是单击要计算距离的位置地图的地图。但是从一开始就存在问题,即应用程序无法改变位置。
这是我的代码:
public class MapsActivity extends FragmentActivity {
// the Google Map object
private GoogleMap mMap;
//ArrayList markerPoints;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// we set the layout for the Activity
setContentView(R.layout.activity_maps);
// the geocoder is instantiated for the first time
geocoder=new Geocoder(this);
// if there isn't a map, it will be created
setUpMapIfNeeded();
}
// LatLng objects store a pair of terrestrial coordinates (latitude and longitude)
private static LatLng STARTING_MARKER_POSITION =new LatLng(3.099465, 101.717111);
/* distanceFrom indicates the starting point to calculate the distance from.
It's initialized with STARTING_MARKER_POSITION
*/
private LatLng distanceFrom= STARTING_MARKER_POSITION;
// line will be drawn at the click event
private Polyline line=null;
// A Geocoder can transform a pair of latitude/longitude into a street address and viceversa.
// We'll use it in the listener
private static Geocoder geocoder=null;
private GoogleMap.OnMapClickListener clickListener=new GoogleMap.OnMapClickListener() {
@Override
public void onMapClick(final LatLng pos) {
// this method is called when the user taps the map
// if a line already appears, it's removed
if (line!=null)
line.remove();
// a new line is created
line = mMap.addPolyline(new PolylineOptions()
.add(distanceFrom, pos)
.width(9) // width of the line
.color(Color.BLUE)); // line color
// call the converter object for geocoding invocation and distance calculation
new AddressConverter().execute(distanceFrom, pos);
}
};
@Override
protected void onResume() {
super.onResume();
// the availability of the GoogleMap will be checked before the Activity starts interacting with the user
setUpMapIfNeeded();
}
private void setUpMapIfNeeded() {
// the map is created only it has not been initialized
if (mMap == null) {
// the map is located in the layout
mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map)).getMap();
// if a map exists, we proceed with initialization
if (mMap != null) {
setUpMap();
}
}
}
// Now it's time to configure the map. We can add markers, shapes, event handlers and so on
private void setUpMap() {
// the camera will be positioned according to the new coordinates
mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(STARTING_MARKER_POSITION, 14));
// we choose the type of the map: Satellite in this case
mMap.setMapType(GoogleMap.MAP_TYPE_NORMAL);
// markerOptions describes the marker we want to place
MarkerOptions markerOptions=new MarkerOptions()
.position(STARTING_MARKER_POSITION)
.draggable(true);
// the marker has to be draggable as we'll move it
// the marker is rendered on the map
mMap.addMarker(markerOptions);
// we define the object to invoke when the marker is dragged
mMap.setOnMarkerDragListener(new GoogleMap.OnMarkerDragListener()
{
@Override
public void onMarkerDragStart(Marker arg0)
{
// this method is called when the drag starts
// the operation we need is the cancellation of a preexisting line
if (line!=null)
line.remove();
}
@Override
public void onMarkerDragEnd(final Marker pos)
{
// we get the final position of the marker
distanceFrom=pos.getPosition();
}
@Override
public void onMarkerDrag(Marker arg0)
{
// operations performed during the movement. Nothing to do
}
});
// the callback to invoke is set
mMap.setOnMapClickListener(clickListener);
}
// we want to know which address corresponds to this location
// we use AsyncTask to perform slower operations on a separate thread
private class AddressConverter extends AsyncTask<LatLng,Void,String>
{
// The ProgressDialog window we'll show during the calculation
private ProgressDialog progress=null;
// this method is called before the background job starts. It works on the main thread
@Override
protected void onPreExecute() {
// ProgressDialog is shown
progress= ProgressDialog.show(MapsActivity.this,"Distance calculator","We are calcultating the distance...", true,false);
}
// this method works on a separate thread
// it performs geocoding operations to retrieve the address of the points and calculates the distance in meters between them
@Override
protected String doInBackground(LatLng... params) {
float[] distance=new float[1];
try {
// the Location class contains what we need to calculate distances
Location.distanceBetween(params[0].latitude,params[0].longitude,params[1].latitude,params[1].longitude,distance);
// geocoding operations
List<Address> fromResult=geocoder.getFromLocation(params[0].latitude,params[0].longitude,1);
List<Address> toResult=geocoder.getFromLocation(params[1].latitude,params[1].longitude,1);
// the message informs the user about the distance from the marker to the point selected with the click
// if we have got both the addresses, we use them to compose the message, otherwise we show only the distance
if (fromResult.size()>0 && toResult.size()>0)
{
// ((TextView) findViewById(R.id.tvDuration)).setText(route.duration.text);
return "The distance between " + getAddressDescription(fromResult.get(0)) + " and " + getAddressDescription(toResult.get(0)) + " is " + Math.round(distance[0]) + " meters";
}
else
return "The distance is " + Math.round(distance[0]) + " meters";
}
catch (IOException e) {
return "The distance is " + Math.round(distance[0]) + " meters";
}
}
@Override
protected void onPostExecute(String message)
{
if (progress!=null)
progress.dismiss();
// The builder of the window is instantiated
AlertDialog.Builder builder=new AlertDialog.Builder(MapsActivity.this);
builder.setTitle("Distance");
builder.setMessage(message);
// the Alert dialog appears
builder.show();
}
}
// this method only formats the message with addresses
private String getAddressDescription(Address a)
{
String city=a.getLocality();
String address=a.getAddressLine(0);
return "'"+address+"' ("+city+")";
}}
答案 0 :(得分:2)
使用 distanceBetween()方法,它会以米为单位给出精确的距离。
Location.distanceBetween(double startLatitude, double startLongitude,
double endLatitude, double endLongitude, float[] results);