我正在尝试创建一个跟踪用户步行路线的应用，并访问gps以获取其位置。然后，我将在这些点之间绘制折线以显示路线。我想知道我是如何循环以获得积分，然后如何将这些点放在地图上以显示路线。这就是我到目前为止所拥有的。这个循环是否可以将点放在列表中？如果不是，我将如何做我想做的事情？
一个小问题是它说变量mContext可能尚未初始化。这是在我添加
之后public GPSTracker(){
arrayPoints = new ArrayList<LatLng>();
}
GPSTracker类： 导入com.google.android.gms.maps.model.LatLng;
import java.util.ArrayList;
import android.app.AlertDialog;
import android.app.Service;
import android.content.Context;
import android.content.DialogInterface;
import android.content.Intent;
import android.location.Location;
import android.location.LocationListener;
import android.location.LocationManager;
import android.os.Bundle;
import android.os.IBinder;
import android.provider.Settings;
import android.util.Log;
import javax.crypto.spec.GCMParameterSpec;
public class GPSTracker extends Service implements LocationListener {
//array with latitude and longitude points for polylines
public static ArrayList<LatLng> arrayPoints;
// intent.putExtra("arrayPoints", arrayPoints);
private final Context mContext;
// flag for GPS status
boolean isGPSEnabled = false;
// flag for network status
boolean isNetworkEnabled = false;
// flag for GPS status
boolean canGetLocation = false;
Location location; // location
double latitude; // latitude
double longitude; // longitude
// The minimum distance to change Updates in meters
private static final long MIN_DISTANCE_CHANGE_FOR_UPDATES = 10; // 10 meters
// The minimum time between updates in milliseconds
private static final long MIN_TIME_BW_UPDATES = 1000 * 60 * 1; // 1 minute
// Declaring a Location Manager
protected LocationManager locationManager;
public GPSTracker(Context context) {
this.mContext = context;
getLocation();
}
public GPSTracker(){
arrayPoints = new ArrayList<LatLng>();
}
public ArrayList<LatLng> getLocation() {
try {
locationManager = (LocationManager) mContext
.getSystemService(LOCATION_SERVICE);
// getting GPS status
isGPSEnabled = locationManager
.isProviderEnabled(LocationManager.GPS_PROVIDER);
// getting network status
isNetworkEnabled = locationManager
.isProviderEnabled(LocationManager.NETWORK_PROVIDER);
if (!isGPSEnabled && !isNetworkEnabled) {
// no network provider is enabled
} else {
this.canGetLocation = true;
// First get location from Network Provider
if (isNetworkEnabled) {
locationManager.requestLocationUpdates(
LocationManager.NETWORK_PROVIDER,
MIN_TIME_BW_UPDATES,
MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
Log.d("Network", "Network");
if (locationManager != null) {
location = locationManager
.getLastKnownLocation(LocationManager.NETWORK_PROVIDER);
if (location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
}
}
}
// if GPS Enabled get lat/long using GPS Services
if (isGPSEnabled) {
if (location == null) {
locationManager.requestLocationUpdates(
LocationManager.GPS_PROVIDER,
MIN_TIME_BW_UPDATES,
MIN_DISTANCE_CHANGE_FOR_UPDATES, this);
Log.d("GPS Enabled", "GPS Enabled");
while(locationManager != null) {
location = locationManager
.getLastKnownLocation(LocationManager.GPS_PROVIDER);
if (location != null) {
latitude = location.getLatitude();
longitude = location.getLongitude();
arrayPoints.add(new LatLng(latitude, longitude));
}
}
}
}
}
} catch (Exception e) {
e.printStackTrace();
}
return arrayPoints;
}
public ArrayList<LatLng> getPoints(){
return arrayPoints;
}
/**
* Stop using GPS listener
* Calling this function will stop using GPS in your app
* */
public void stopUsingGPS(){
if(locationManager != null){
locationManager.removeUpdates(GPSTracker.this);
}
}
/**
* Function to get latitude
* */
public double getLatitude(){
if(location != null){
latitude = location.getLatitude();
}
// return latitude
return latitude;
}
/**
* Function to get longitude
* */
public double getLongitude(){
if(location != null){
longitude = location.getLongitude();
}
// return longitude
return longitude;
}
/**
* Function to check GPS/wifi enabled
* @return boolean
* */
public boolean canGetLocation() {
return this.canGetLocation;
}
/**
* Function to show settings alert dialog
* On pressing Settings button will lauch Settings Options
* */
public void showSettingsAlert(){
AlertDialog.Builder alertDialog = new AlertDialog.Builder(mContext);
// Setting Dialog Title
alertDialog.setTitle("GPS is disabled");
// Setting Dialog Message
alertDialog.setMessage("GPS is not enabled. Turn it on in settings.");
// On pressing Settings button
alertDialog.setPositiveButton("Settings", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog,int which) {
Intent intent = new Intent(Settings.ACTION_LOCATION_SOURCE_SETTINGS);
mContext.startActivity(intent);
}
});
// on pressing cancel button
alertDialog.setNegativeButton("Cancel", new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.cancel();
}
});
// Showing Alert Message
alertDialog.show();
}
@Override
public void onLocationChanged(Location location) {
}
@Override
public void onProviderDisabled(String provider) {
}
@Override
public void onProviderEnabled(String provider) {
}
@Override
public void onStatusChanged(String provider, int status, Bundle extras) {
}
@Override
public IBinder onBind(Intent arg0) {
return null;
}
MapsActivity类：
private GoogleMap mMap; // Might be null if Google Play services APK is not available.
private GoogleApiClient mGoogleApiClient;
private LocationRequest mLocationRequest;
private GPSTracker gpsTracker;
public static final String TAG = MapsActivity.class.getSimpleName();
Location Location;
public MapsActivity(){
gpsTracker = new GPSTracker();
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_maps);
setUpMapIfNeeded();
mMap.moveCamera(CameraUpdateFactory.newLatLngZoom(
new LatLng(40.0139, -105.1507), 3));
try {
GPSTracker gps = new GPSTracker(MapsActivity.this);
// check if GPS enabled
if (gps.canGetLocation()) {
double latitude = gps.getLatitude();
double longitude = gps.getLongitude();
// \n is for new line
Toast.makeText(getApplicationContext(), "Your Location is - \nLat: " + latitude + "\nLong: " + longitude, Toast.LENGTH_LONG).show();
} else {
// can't get location
// GPS or Network is not enabled
// Ask user to enable GPS/network in settings
gps.showSettingsAlert();
}
// Loading map
initializeMap();
} catch (Exception e) {
e.printStackTrace();
}
}
private void initializeMap() {
if (mMap == null) {
mMap = ((MapFragment) getFragmentManager().findFragmentById(
R.id.map)).getMap();
// check if map is created successfully or not
if (mMap == null) {
Toast.makeText(getApplicationContext(),
"Error: Unable to create map", Toast.LENGTH_SHORT)
.show();
}
mMap.setMyLocationEnabled(true);
mMap.getUiSettings().setMyLocationButtonEnabled(true);
mMap.setMapType(GoogleMap.MAP_TYPE_HYBRID);
}
}
public void onMapReady(GoogleMap mMap) {
ArrayList<LatLng> arrayPoints = gpsTracker.getPoints();
if (arrayPoints.size() > 1) {
PolylineOptions polyline_options = new PolylineOptions()
.addAll(arrayPoints).color(Color.GREEN).width(2);
Polyline polyline = mMap.addPolyline(polyline_options);
}
}
/* @Override
protected void onResume() {
super.onResume();
setUpMapIfNeeded();
}*/
/**
* 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
* call {@link #setUpMap()} once when {@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.
* <p/>
* c * A an return to this FragmentActivity after following the prompt and correctly
* installing/updating/enabling the Google Play services. Since the FragmentActivity may not
* have been completely destroyed during this process (it is likely that it would only be
* stopped or paused), {@link #onCreate(Bundle)} may not be called again so we should call this
* method in {@link #onResume()} to guarantee that it will be called.
*/
private void setUpMapIfNeeded() {
// Do a null check to confirm that we have not already instantiated the map.
if (mMap == null) {
// Try to obtain the map from the SupportMapFragment.
mMap = ((SupportMapFragment) getSupportFragmentManager().findFragmentById(R.id.map))
.getMap();
// Check if we were successful in obtaining the map.
if (mMap != null) {
setUpMap();
}
}
}
private void setUpMap() {
mMap.addMarker(new MarkerOptions().position(new LatLng(0, 0)).title("Marker"));
}
}
感谢您的帮助，请告诉我是否需要澄清更多信息或显示更少的代码。
答案 0 :(得分：0)
试着给你一个想法：你可以跟踪最新添加的标记并每隔一段时间返回用户当前位置，如果用户当前latLong和前一个latLong标记的距离大于某个值，添加新标记。迭代更新前一个标记和用户当前latLong的过程。只是一个想法，请试一试。